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1 | //! Note: most of the tests relevant to this file can be found (at the time of writing) in |
2 | //! src/tests/ui/pattern/usefulness. | |
3 | //! | |
4 | //! This file includes the logic for exhaustiveness and usefulness checking for | |
5 | //! pattern-matching. Specifically, given a list of patterns for a type, we can | |
6 | //! tell whether: | |
7 | //! (a) the patterns cover every possible constructor for the type (exhaustiveness) | |
8 | //! (b) each pattern is necessary (usefulness) | |
9 | //! | |
10 | //! The algorithm implemented here is a modified version of the one described in: | |
11 | //! http://moscova.inria.fr/~maranget/papers/warn/index.html | |
12 | //! However, to save future implementors from reading the original paper, we | |
13 | //! summarise the algorithm here to hopefully save time and be a little clearer | |
14 | //! (without being so rigorous). | |
15 | //! | |
16 | //! # Premise | |
17 | //! | |
18 | //! The core of the algorithm revolves about a "usefulness" check. In particular, we | |
19 | //! are trying to compute a predicate `U(P, p)` where `P` is a list of patterns (we refer to this as | |
20 | //! a matrix). `U(P, p)` represents whether, given an existing list of patterns | |
21 | //! `P_1 ..= P_m`, adding a new pattern `p` will be "useful" (that is, cover previously- | |
22 | //! uncovered values of the type). | |
23 | //! | |
24 | //! If we have this predicate, then we can easily compute both exhaustiveness of an | |
25 | //! entire set of patterns and the individual usefulness of each one. | |
26 | //! (a) the set of patterns is exhaustive iff `U(P, _)` is false (i.e., adding a wildcard | |
27 | //! match doesn't increase the number of values we're matching) | |
28 | //! (b) a pattern `P_i` is not useful if `U(P[0..=(i-1), P_i)` is false (i.e., adding a | |
29 | //! pattern to those that have come before it doesn't increase the number of values | |
30 | //! we're matching). | |
31 | //! | |
32 | //! # Core concept | |
33 | //! | |
34 | //! The idea that powers everything that is done in this file is the following: a value is made | |
35 | //! from a constructor applied to some fields. Examples of constructors are `Some`, `None`, `(,)` | |
36 | //! (the 2-tuple constructor), `Foo {..}` (the constructor for a struct `Foo`), and `2` (the | |
37 | //! constructor for the number `2`). Fields are just a (possibly empty) list of values. | |
38 | //! | |
39 | //! Some of the constructors listed above might feel weird: `None` and `2` don't take any | |
40 | //! arguments. This is part of what makes constructors so general: we will consider plain values | |
41 | //! like numbers and string literals to be constructors that take no arguments, also called "0-ary | |
42 | //! constructors"; they are the simplest case of constructors. This allows us to see any value as | |
43 | //! made up from a tree of constructors, each having a given number of children. For example: | |
44 | //! `(None, Ok(0))` is made from 4 different constructors. | |
45 | //! | |
46 | //! This idea can be extended to patterns: a pattern captures a set of possible values, and we can | |
47 | //! describe this set using constructors. For example, `Err(_)` captures all values of the type | |
48 | //! `Result<T, E>` that start with the `Err` constructor (for some choice of `T` and `E`). The | |
49 | //! wildcard `_` captures all values of the given type starting with any of the constructors for | |
50 | //! that type. | |
51 | //! | |
52 | //! We use this to compute whether different patterns might capture a same value. Do the patterns | |
53 | //! `Ok("foo")` and `Err(_)` capture a common value? The answer is no, because the first pattern | |
54 | //! captures only values starting with the `Ok` constructor and the second only values starting | |
55 | //! with the `Err` constructor. Do the patterns `Some(42)` and `Some(1..10)` intersect? They might, | |
56 | //! since they both capture values starting with `Some`. To be certain, we need to dig under the | |
57 | //! `Some` constructor and continue asking the question. This is the main idea behind the | |
58 | //! exhaustiveness algorithm: by looking at patterns constructor-by-constructor, we can efficiently | |
59 | //! figure out if some new pattern might capture a value that hadn't been captured by previous | |
60 | //! patterns. | |
61 | //! | |
62 | //! Constructors are represented by the `Constructor` enum, and its fields by the `Fields` enum. | |
63 | //! Most of the complexity of this file resides in transforming between patterns and | |
64 | //! (`Constructor`, `Fields`) pairs, handling all the special cases correctly. | |
65 | //! | |
66 | //! Caveat: this constructors/fields distinction doesn't quite cover every Rust value. For example | |
67 | //! a value of type `Rc<u64>` doesn't fit this idea very well, nor do various other things. | |
68 | //! However, this idea covers most of the cases that are relevant to exhaustiveness checking. | |
69 | //! | |
70 | //! | |
71 | //! # Algorithm | |
72 | //! | |
73 | //! Recall that `U(P, p)` represents whether, given an existing list of patterns (aka matrix) `P`, | |
74 | //! adding a new pattern `p` will cover previously-uncovered values of the type. | |
75 | //! During the course of the algorithm, the rows of the matrix won't just be individual patterns, | |
76 | //! but rather partially-deconstructed patterns in the form of a list of fields. The paper | |
77 | //! calls those pattern-vectors, and we will call them pattern-stacks. The same holds for the | |
78 | //! new pattern `p`. | |
79 | //! | |
80 | //! For example, say we have the following: | |
81 | //! ``` | |
82 | //! // x: (Option<bool>, Result<()>) | |
83 | //! match x { | |
84 | //! (Some(true), _) => {} | |
85 | //! (None, Err(())) => {} | |
86 | //! (None, Err(_)) => {} | |
87 | //! } | |
88 | //! ``` | |
89 | //! Here, the matrix `P` starts as: | |
90 | //! [ | |
91 | //! [(Some(true), _)], | |
92 | //! [(None, Err(()))], | |
93 | //! [(None, Err(_))], | |
94 | //! ] | |
95 | //! We can tell it's not exhaustive, because `U(P, _)` is true (we're not covering | |
96 | //! `[(Some(false), _)]`, for instance). In addition, row 3 is not useful, because | |
97 | //! all the values it covers are already covered by row 2. | |
98 | //! | |
99 | //! A list of patterns can be thought of as a stack, because we are mainly interested in the top of | |
100 | //! the stack at any given point, and we can pop or apply constructors to get new pattern-stacks. | |
101 | //! To match the paper, the top of the stack is at the beginning / on the left. | |
102 | //! | |
103 | //! There are two important operations on pattern-stacks necessary to understand the algorithm: | |
104 | //! | |
105 | //! 1. We can pop a given constructor off the top of a stack. This operation is called | |
106 | //! `specialize`, and is denoted `S(c, p)` where `c` is a constructor (like `Some` or | |
107 | //! `None`) and `p` a pattern-stack. | |
108 | //! If the pattern on top of the stack can cover `c`, this removes the constructor and | |
109 | //! pushes its arguments onto the stack. It also expands OR-patterns into distinct patterns. | |
110 | //! Otherwise the pattern-stack is discarded. | |
111 | //! This essentially filters those pattern-stacks whose top covers the constructor `c` and | |
112 | //! discards the others. | |
113 | //! | |
114 | //! For example, the first pattern above initially gives a stack `[(Some(true), _)]`. If we | |
115 | //! pop the tuple constructor, we are left with `[Some(true), _]`, and if we then pop the | |
116 | //! `Some` constructor we get `[true, _]`. If we had popped `None` instead, we would get | |
117 | //! nothing back. | |
118 | //! | |
119 | //! This returns zero or more new pattern-stacks, as follows. We look at the pattern `p_1` | |
120 | //! on top of the stack, and we have four cases: | |
121 | //! 1.1. `p_1 = c(r_1, .., r_a)`, i.e. the top of the stack has constructor `c`. We | |
122 | //! push onto the stack the arguments of this constructor, and return the result: | |
123 | //! r_1, .., r_a, p_2, .., p_n | |
124 | //! 1.2. `p_1 = c'(r_1, .., r_a')` where `c ≠ c'`. We discard the current stack and | |
125 | //! return nothing. | |
126 | //! 1.3. `p_1 = _`. We push onto the stack as many wildcards as the constructor `c` has | |
127 | //! arguments (its arity), and return the resulting stack: | |
128 | //! _, .., _, p_2, .., p_n | |
129 | //! 1.4. `p_1 = r_1 | r_2`. We expand the OR-pattern and then recurse on each resulting | |
130 | //! stack: | |
131 | //! S(c, (r_1, p_2, .., p_n)) | |
132 | //! S(c, (r_2, p_2, .., p_n)) | |
133 | //! | |
134 | //! 2. We can pop a wildcard off the top of the stack. This is called `D(p)`, where `p` is | |
135 | //! a pattern-stack. | |
136 | //! This is used when we know there are missing constructor cases, but there might be | |
137 | //! existing wildcard patterns, so to check the usefulness of the matrix, we have to check | |
138 | //! all its *other* components. | |
139 | //! | |
140 | //! It is computed as follows. We look at the pattern `p_1` on top of the stack, | |
141 | //! and we have three cases: | |
142 | //! 1.1. `p_1 = c(r_1, .., r_a)`. We discard the current stack and return nothing. | |
143 | //! 1.2. `p_1 = _`. We return the rest of the stack: | |
144 | //! p_2, .., p_n | |
145 | //! 1.3. `p_1 = r_1 | r_2`. We expand the OR-pattern and then recurse on each resulting | |
146 | //! stack. | |
147 | //! D((r_1, p_2, .., p_n)) | |
148 | //! D((r_2, p_2, .., p_n)) | |
149 | //! | |
150 | //! Note that the OR-patterns are not always used directly in Rust, but are used to derive the | |
151 | //! exhaustive integer matching rules, so they're written here for posterity. | |
152 | //! | |
153 | //! Both those operations extend straightforwardly to a list or pattern-stacks, i.e. a matrix, by | |
154 | //! working row-by-row. Popping a constructor ends up keeping only the matrix rows that start with | |
155 | //! the given constructor, and popping a wildcard keeps those rows that start with a wildcard. | |
156 | //! | |
157 | //! | |
158 | //! The algorithm for computing `U` | |
159 | //! ------------------------------- | |
160 | //! The algorithm is inductive (on the number of columns: i.e., components of tuple patterns). | |
161 | //! That means we're going to check the components from left-to-right, so the algorithm | |
162 | //! operates principally on the first component of the matrix and new pattern-stack `p`. | |
163 | //! This algorithm is realised in the `is_useful` function. | |
164 | //! | |
165 | //! Base case. (`n = 0`, i.e., an empty tuple pattern) | |
166 | //! - If `P` already contains an empty pattern (i.e., if the number of patterns `m > 0`), | |
167 | //! then `U(P, p)` is false. | |
168 | //! - Otherwise, `P` must be empty, so `U(P, p)` is true. | |
169 | //! | |
170 | //! Inductive step. (`n > 0`, i.e., whether there's at least one column | |
171 | //! [which may then be expanded into further columns later]) | |
172 | //! We're going to match on the top of the new pattern-stack, `p_1`. | |
173 | //! - If `p_1 == c(r_1, .., r_a)`, i.e. we have a constructor pattern. | |
174 | //! Then, the usefulness of `p_1` can be reduced to whether it is useful when | |
175 | //! we ignore all the patterns in the first column of `P` that involve other constructors. | |
176 | //! This is where `S(c, P)` comes in: | |
177 | //! `U(P, p) := U(S(c, P), S(c, p))` | |
178 | //! This special case is handled in `is_useful_specialized`. | |
179 | //! | |
180 | //! For example, if `P` is: | |
181 | //! [ | |
182 | //! [Some(true), _], | |
183 | //! [None, 0], | |
184 | //! ] | |
185 | //! and `p` is [Some(false), 0], then we don't care about row 2 since we know `p` only | |
186 | //! matches values that row 2 doesn't. For row 1 however, we need to dig into the | |
187 | //! arguments of `Some` to know whether some new value is covered. So we compute | |
188 | //! `U([[true, _]], [false, 0])`. | |
189 | //! | |
190 | //! - If `p_1 == _`, then we look at the list of constructors that appear in the first | |
191 | //! component of the rows of `P`: | |
192 | //! + If there are some constructors that aren't present, then we might think that the | |
193 | //! wildcard `_` is useful, since it covers those constructors that weren't covered | |
194 | //! before. | |
195 | //! That's almost correct, but only works if there were no wildcards in those first | |
196 | //! components. So we need to check that `p` is useful with respect to the rows that | |
197 | //! start with a wildcard, if there are any. This is where `D` comes in: | |
198 | //! `U(P, p) := U(D(P), D(p))` | |
199 | //! | |
200 | //! For example, if `P` is: | |
201 | //! [ | |
202 | //! [_, true, _], | |
203 | //! [None, false, 1], | |
204 | //! ] | |
205 | //! and `p` is [_, false, _], the `Some` constructor doesn't appear in `P`. So if we | |
206 | //! only had row 2, we'd know that `p` is useful. However row 1 starts with a | |
207 | //! wildcard, so we need to check whether `U([[true, _]], [false, 1])`. | |
208 | //! | |
209 | //! + Otherwise, all possible constructors (for the relevant type) are present. In this | |
210 | //! case we must check whether the wildcard pattern covers any unmatched value. For | |
211 | //! that, we can think of the `_` pattern as a big OR-pattern that covers all | |
212 | //! possible constructors. For `Option`, that would mean `_ = None | Some(_)` for | |
213 | //! example. The wildcard pattern is useful in this case if it is useful when | |
214 | //! specialized to one of the possible constructors. So we compute: | |
215 | //! `U(P, p) := ∃(k ϵ constructors) U(S(k, P), S(k, p))` | |
216 | //! | |
217 | //! For example, if `P` is: | |
218 | //! [ | |
219 | //! [Some(true), _], | |
220 | //! [None, false], | |
221 | //! ] | |
222 | //! and `p` is [_, false], both `None` and `Some` constructors appear in the first | |
223 | //! components of `P`. We will therefore try popping both constructors in turn: we | |
224 | //! compute `U([[true, _]], [_, false])` for the `Some` constructor, and `U([[false]], | |
225 | //! [false])` for the `None` constructor. The first case returns true, so we know that | |
226 | //! `p` is useful for `P`. Indeed, it matches `[Some(false), _]` that wasn't matched | |
227 | //! before. | |
228 | //! | |
229 | //! - If `p_1 == r_1 | r_2`, then the usefulness depends on each `r_i` separately: | |
230 | //! `U(P, p) := U(P, (r_1, p_2, .., p_n)) | |
231 | //! || U(P, (r_2, p_2, .., p_n))` | |
232 | //! | |
233 | //! Modifications to the algorithm | |
234 | //! ------------------------------ | |
235 | //! The algorithm in the paper doesn't cover some of the special cases that arise in Rust, for | |
236 | //! example uninhabited types and variable-length slice patterns. These are drawn attention to | |
237 | //! throughout the code below. I'll make a quick note here about how exhaustive integer matching is | |
238 | //! accounted for, though. | |
239 | //! | |
240 | //! Exhaustive integer matching | |
241 | //! --------------------------- | |
242 | //! An integer type can be thought of as a (huge) sum type: 1 | 2 | 3 | ... | |
243 | //! So to support exhaustive integer matching, we can make use of the logic in the paper for | |
244 | //! OR-patterns. However, we obviously can't just treat ranges x..=y as individual sums, because | |
245 | //! they are likely gigantic. So we instead treat ranges as constructors of the integers. This means | |
246 | //! that we have a constructor *of* constructors (the integers themselves). We then need to work | |
247 | //! through all the inductive step rules above, deriving how the ranges would be treated as | |
248 | //! OR-patterns, and making sure that they're treated in the same way even when they're ranges. | |
249 | //! There are really only four special cases here: | |
250 | //! - When we match on a constructor that's actually a range, we have to treat it as if we would | |
251 | //! an OR-pattern. | |
252 | //! + It turns out that we can simply extend the case for single-value patterns in | |
253 | //! `specialize` to either be *equal* to a value constructor, or *contained within* a range | |
254 | //! constructor. | |
255 | //! + When the pattern itself is a range, you just want to tell whether any of the values in | |
256 | //! the pattern range coincide with values in the constructor range, which is precisely | |
257 | //! intersection. | |
258 | //! Since when encountering a range pattern for a value constructor, we also use inclusion, it | |
259 | //! means that whenever the constructor is a value/range and the pattern is also a value/range, | |
260 | //! we can simply use intersection to test usefulness. | |
261 | //! - When we're testing for usefulness of a pattern and the pattern's first component is a | |
262 | //! wildcard. | |
263 | //! + If all the constructors appear in the matrix, we have a slight complication. By default, | |
264 | //! the behaviour (i.e., a disjunction over specialised matrices for each constructor) is | |
265 | //! invalid, because we want a disjunction over every *integer* in each range, not just a | |
266 | //! disjunction over every range. This is a bit more tricky to deal with: essentially we need | |
267 | //! to form equivalence classes of subranges of the constructor range for which the behaviour | |
268 | //! of the matrix `P` and new pattern `p` are the same. This is described in more | |
269 | //! detail in `split_grouped_constructors`. | |
270 | //! + If some constructors are missing from the matrix, it turns out we don't need to do | |
271 | //! anything special (because we know none of the integers are actually wildcards: i.e., we | |
272 | //! can't span wildcards using ranges). | |
c30ab7b3 | 273 | use self::Constructor::*; |
60c5eb7d | 274 | use self::SliceKind::*; |
c30ab7b3 SL |
275 | use self::Usefulness::*; |
276 | use self::WitnessPreference::*; | |
277 | ||
dfeec247 | 278 | use rustc_data_structures::captures::Captures; |
f035d41b | 279 | use rustc_data_structures::fx::FxHashSet; |
e74abb32 | 280 | use rustc_index::vec::Idx; |
c30ab7b3 | 281 | |
e74abb32 XL |
282 | use super::{compare_const_vals, PatternFoldable, PatternFolder}; |
283 | use super::{FieldPat, Pat, PatKind, PatRange}; | |
c30ab7b3 | 284 | |
f035d41b | 285 | use rustc_arena::TypedArena; |
ba9703b0 XL |
286 | use rustc_attr::{SignedInt, UnsignedInt}; |
287 | use rustc_errors::ErrorReported; | |
dfeec247 XL |
288 | use rustc_hir::def_id::DefId; |
289 | use rustc_hir::{HirId, RangeEnd}; | |
ba9703b0 XL |
290 | use rustc_middle::mir::interpret::{truncate, AllocId, ConstValue, Pointer, Scalar}; |
291 | use rustc_middle::mir::Field; | |
292 | use rustc_middle::ty::layout::IntegerExt; | |
f9f354fc | 293 | use rustc_middle::ty::{self, Const, Ty, TyCtxt}; |
ba9703b0 | 294 | use rustc_session::lint; |
dfeec247 | 295 | use rustc_span::{Span, DUMMY_SP}; |
ba9703b0 | 296 | use rustc_target::abi::{Integer, Size, VariantIdx}; |
c30ab7b3 | 297 | |
e74abb32 | 298 | use smallvec::{smallvec, SmallVec}; |
dfeec247 | 299 | use std::borrow::Cow; |
e74abb32 XL |
300 | use std::cmp::{self, max, min, Ordering}; |
301 | use std::convert::TryInto; | |
c30ab7b3 | 302 | use std::fmt; |
8faf50e0 | 303 | use std::iter::{FromIterator, IntoIterator}; |
b7449926 | 304 | use std::ops::RangeInclusive; |
c30ab7b3 | 305 | |
dfeec247 XL |
306 | crate fn expand_pattern<'a, 'tcx>(cx: &MatchCheckCtxt<'a, 'tcx>, pat: Pat<'tcx>) -> Pat<'tcx> { |
307 | LiteralExpander { tcx: cx.tcx, param_env: cx.param_env }.fold_pattern(&pat) | |
0731742a XL |
308 | } |
309 | ||
dc9dc135 XL |
310 | struct LiteralExpander<'tcx> { |
311 | tcx: TyCtxt<'tcx>, | |
dfeec247 | 312 | param_env: ty::ParamEnv<'tcx>, |
c30ab7b3 SL |
313 | } |
314 | ||
dfeec247 | 315 | impl<'tcx> LiteralExpander<'tcx> { |
0731742a XL |
316 | /// Derefs `val` and potentially unsizes the value if `crty` is an array and `rty` a slice. |
317 | /// | |
318 | /// `crty` and `rty` can differ because you can use array constants in the presence of slice | |
319 | /// patterns. So the pattern may end up being a slice, but the constant is an array. We convert | |
320 | /// the array to a slice in that case. | |
321 | fn fold_const_value_deref( | |
322 | &mut self, | |
323 | val: ConstValue<'tcx>, | |
324 | // the pattern's pointee type | |
325 | rty: Ty<'tcx>, | |
326 | // the constant's pointee type | |
327 | crty: Ty<'tcx>, | |
328 | ) -> ConstValue<'tcx> { | |
48663c56 | 329 | debug!("fold_const_value_deref {:?} {:?} {:?}", val, rty, crty); |
e74abb32 | 330 | match (val, &crty.kind, &rty.kind) { |
0731742a | 331 | // the easy case, deref a reference |
dfeec247 XL |
332 | (ConstValue::Scalar(p), x, y) if x == y => { |
333 | match p { | |
334 | Scalar::Ptr(p) => { | |
f9f354fc | 335 | let alloc = self.tcx.global_alloc(p.alloc_id).unwrap_memory(); |
dfeec247 XL |
336 | ConstValue::ByRef { alloc, offset: p.offset } |
337 | } | |
338 | Scalar::Raw { .. } => { | |
339 | let layout = self.tcx.layout_of(self.param_env.and(rty)).unwrap(); | |
340 | if layout.is_zst() { | |
341 | // Deref of a reference to a ZST is a nop. | |
342 | ConstValue::Scalar(Scalar::zst()) | |
343 | } else { | |
344 | // FIXME(oli-obk): this is reachable for `const FOO: &&&u32 = &&&42;` | |
345 | bug!("cannot deref {:#?}, {} -> {}", val, crty, rty); | |
346 | } | |
347 | } | |
348 | } | |
e74abb32 | 349 | } |
0731742a XL |
350 | // unsize array to slice if pattern is array but match value or other patterns are slice |
351 | (ConstValue::Scalar(Scalar::Ptr(p)), ty::Array(t, n), ty::Slice(u)) => { | |
352 | assert_eq!(t, u); | |
dc9dc135 | 353 | ConstValue::Slice { |
f9f354fc | 354 | data: self.tcx.global_alloc(p.alloc_id).unwrap_memory(), |
dc9dc135 | 355 | start: p.offset.bytes().try_into().unwrap(), |
416331ca | 356 | end: n.eval_usize(self.tcx, ty::ParamEnv::empty()).try_into().unwrap(), |
dc9dc135 | 357 | } |
e74abb32 | 358 | } |
0731742a | 359 | // fat pointers stay the same |
e74abb32 | 360 | (ConstValue::Slice { .. }, _, _) |
dc9dc135 | 361 | | (_, ty::Slice(_), ty::Slice(_)) |
e74abb32 | 362 | | (_, ty::Str, ty::Str) => val, |
0731742a XL |
363 | // FIXME(oli-obk): this is reachable for `const FOO: &&&u32 = &&&42;` being used |
364 | _ => bug!("cannot deref {:#?}, {} -> {}", val, crty, rty), | |
365 | } | |
366 | } | |
367 | } | |
368 | ||
dfeec247 | 369 | impl<'tcx> PatternFolder<'tcx> for LiteralExpander<'tcx> { |
e74abb32 XL |
370 | fn fold_pattern(&mut self, pat: &Pat<'tcx>) -> Pat<'tcx> { |
371 | debug!("fold_pattern {:?} {:?} {:?}", pat, pat.ty.kind, pat.kind); | |
372 | match (&pat.ty.kind, &*pat.kind) { | |
0731742a XL |
373 | ( |
374 | &ty::Ref(_, rty, _), | |
e74abb32 | 375 | &PatKind::Constant { |
60c5eb7d XL |
376 | value: |
377 | Const { | |
378 | val: ty::ConstKind::Value(val), | |
379 | ty: ty::TyS { kind: ty::Ref(_, crty, _), .. }, | |
380 | }, | |
e74abb32 XL |
381 | }, |
382 | ) => Pat { | |
383 | ty: pat.ty, | |
384 | span: pat.span, | |
385 | kind: box PatKind::Deref { | |
386 | subpattern: Pat { | |
387 | ty: rty, | |
388 | span: pat.span, | |
389 | kind: box PatKind::Constant { | |
74b04a01 XL |
390 | value: Const::from_value( |
391 | self.tcx, | |
392 | self.fold_const_value_deref(*val, rty, crty), | |
393 | rty, | |
394 | ), | |
e74abb32 XL |
395 | }, |
396 | }, | |
397 | }, | |
398 | }, | |
60c5eb7d XL |
399 | |
400 | ( | |
401 | &ty::Ref(_, rty, _), | |
402 | &PatKind::Constant { | |
403 | value: Const { val, ty: ty::TyS { kind: ty::Ref(_, crty, _), .. } }, | |
404 | }, | |
405 | ) => bug!("cannot deref {:#?}, {} -> {}", val, crty, rty), | |
406 | ||
e74abb32 | 407 | (_, &PatKind::Binding { subpattern: Some(ref s), .. }) => s.fold_with(self), |
60c5eb7d | 408 | (_, &PatKind::AscribeUserType { subpattern: ref s, .. }) => s.fold_with(self), |
e74abb32 | 409 | _ => pat.super_fold_with(self), |
c30ab7b3 SL |
410 | } |
411 | } | |
412 | } | |
413 | ||
e74abb32 | 414 | impl<'tcx> Pat<'tcx> { |
60c5eb7d | 415 | pub(super) fn is_wildcard(&self) -> bool { |
c30ab7b3 | 416 | match *self.kind { |
e74abb32 XL |
417 | PatKind::Binding { subpattern: None, .. } | PatKind::Wild => true, |
418 | _ => false, | |
c30ab7b3 SL |
419 | } |
420 | } | |
421 | } | |
422 | ||
e74abb32 XL |
423 | /// A row of a matrix. Rows of len 1 are very common, which is why `SmallVec[_; 2]` |
424 | /// works well. | |
425 | #[derive(Debug, Clone)] | |
dfeec247 | 426 | crate struct PatStack<'p, 'tcx>(SmallVec<[&'p Pat<'tcx>; 2]>); |
e74abb32 XL |
427 | |
428 | impl<'p, 'tcx> PatStack<'p, 'tcx> { | |
dfeec247 | 429 | crate fn from_pattern(pat: &'p Pat<'tcx>) -> Self { |
e74abb32 XL |
430 | PatStack(smallvec![pat]) |
431 | } | |
432 | ||
433 | fn from_vec(vec: SmallVec<[&'p Pat<'tcx>; 2]>) -> Self { | |
434 | PatStack(vec) | |
435 | } | |
436 | ||
437 | fn from_slice(s: &[&'p Pat<'tcx>]) -> Self { | |
438 | PatStack(SmallVec::from_slice(s)) | |
439 | } | |
440 | ||
441 | fn is_empty(&self) -> bool { | |
442 | self.0.is_empty() | |
443 | } | |
444 | ||
445 | fn len(&self) -> usize { | |
446 | self.0.len() | |
447 | } | |
448 | ||
449 | fn head(&self) -> &'p Pat<'tcx> { | |
450 | self.0[0] | |
451 | } | |
452 | ||
453 | fn to_tail(&self) -> Self { | |
454 | PatStack::from_slice(&self.0[1..]) | |
455 | } | |
456 | ||
457 | fn iter(&self) -> impl Iterator<Item = &Pat<'tcx>> { | |
74b04a01 | 458 | self.0.iter().copied() |
e74abb32 XL |
459 | } |
460 | ||
60c5eb7d XL |
461 | // If the first pattern is an or-pattern, expand this pattern. Otherwise, return `None`. |
462 | fn expand_or_pat(&self) -> Option<Vec<Self>> { | |
463 | if self.is_empty() { | |
464 | None | |
465 | } else if let PatKind::Or { pats } = &*self.head().kind { | |
466 | Some( | |
467 | pats.iter() | |
468 | .map(|pat| { | |
469 | let mut new_patstack = PatStack::from_pattern(pat); | |
470 | new_patstack.0.extend_from_slice(&self.0[1..]); | |
471 | new_patstack | |
472 | }) | |
473 | .collect(), | |
474 | ) | |
475 | } else { | |
476 | None | |
477 | } | |
478 | } | |
479 | ||
e74abb32 XL |
480 | /// This computes `D(self)`. See top of the file for explanations. |
481 | fn specialize_wildcard(&self) -> Option<Self> { | |
482 | if self.head().is_wildcard() { Some(self.to_tail()) } else { None } | |
483 | } | |
484 | ||
485 | /// This computes `S(constructor, self)`. See top of the file for explanations. | |
60c5eb7d | 486 | fn specialize_constructor( |
e74abb32 | 487 | &self, |
60c5eb7d | 488 | cx: &mut MatchCheckCtxt<'p, 'tcx>, |
e74abb32 | 489 | constructor: &Constructor<'tcx>, |
f9f354fc | 490 | ctor_wild_subpatterns: &Fields<'p, 'tcx>, |
60c5eb7d | 491 | ) -> Option<PatStack<'p, 'tcx>> { |
f9f354fc XL |
492 | let new_fields = |
493 | specialize_one_pattern(cx, self.head(), constructor, ctor_wild_subpatterns)?; | |
494 | Some(new_fields.push_on_patstack(&self.0[1..])) | |
e74abb32 XL |
495 | } |
496 | } | |
497 | ||
498 | impl<'p, 'tcx> Default for PatStack<'p, 'tcx> { | |
499 | fn default() -> Self { | |
500 | PatStack(smallvec![]) | |
501 | } | |
502 | } | |
503 | ||
504 | impl<'p, 'tcx> FromIterator<&'p Pat<'tcx>> for PatStack<'p, 'tcx> { | |
505 | fn from_iter<T>(iter: T) -> Self | |
506 | where | |
507 | T: IntoIterator<Item = &'p Pat<'tcx>>, | |
508 | { | |
509 | PatStack(iter.into_iter().collect()) | |
510 | } | |
511 | } | |
512 | ||
513 | /// A 2D matrix. | |
60c5eb7d | 514 | #[derive(Clone)] |
dfeec247 | 515 | crate struct Matrix<'p, 'tcx>(Vec<PatStack<'p, 'tcx>>); |
c30ab7b3 | 516 | |
0731742a | 517 | impl<'p, 'tcx> Matrix<'p, 'tcx> { |
dfeec247 | 518 | crate fn empty() -> Self { |
c30ab7b3 SL |
519 | Matrix(vec![]) |
520 | } | |
521 | ||
60c5eb7d | 522 | /// Pushes a new row to the matrix. If the row starts with an or-pattern, this expands it. |
dfeec247 | 523 | crate fn push(&mut self, row: PatStack<'p, 'tcx>) { |
60c5eb7d | 524 | if let Some(rows) = row.expand_or_pat() { |
ba9703b0 XL |
525 | for row in rows { |
526 | // We recursively expand the or-patterns of the new rows. | |
527 | // This is necessary as we might have `0 | (1 | 2)` or e.g., `x @ 0 | x @ (1 | 2)`. | |
528 | self.push(row) | |
529 | } | |
60c5eb7d XL |
530 | } else { |
531 | self.0.push(row); | |
532 | } | |
c30ab7b3 | 533 | } |
e74abb32 XL |
534 | |
535 | /// Iterate over the first component of each row | |
536 | fn heads<'a>(&'a self) -> impl Iterator<Item = &'a Pat<'tcx>> + Captures<'p> { | |
537 | self.0.iter().map(|r| r.head()) | |
538 | } | |
539 | ||
540 | /// This computes `D(self)`. See top of the file for explanations. | |
541 | fn specialize_wildcard(&self) -> Self { | |
542 | self.0.iter().filter_map(|r| r.specialize_wildcard()).collect() | |
543 | } | |
544 | ||
545 | /// This computes `S(constructor, self)`. See top of the file for explanations. | |
60c5eb7d | 546 | fn specialize_constructor( |
e74abb32 | 547 | &self, |
60c5eb7d | 548 | cx: &mut MatchCheckCtxt<'p, 'tcx>, |
e74abb32 | 549 | constructor: &Constructor<'tcx>, |
f9f354fc | 550 | ctor_wild_subpatterns: &Fields<'p, 'tcx>, |
60c5eb7d XL |
551 | ) -> Matrix<'p, 'tcx> { |
552 | self.0 | |
553 | .iter() | |
554 | .filter_map(|r| r.specialize_constructor(cx, constructor, ctor_wild_subpatterns)) | |
555 | .collect() | |
e74abb32 | 556 | } |
c30ab7b3 SL |
557 | } |
558 | ||
559 | /// Pretty-printer for matrices of patterns, example: | |
f9f354fc XL |
560 | /// |
561 | /// ```text | |
e74abb32 XL |
562 | /// +++++++++++++++++++++++++++++ |
563 | /// + _ + [] + | |
564 | /// +++++++++++++++++++++++++++++ | |
565 | /// + true + [First] + | |
566 | /// +++++++++++++++++++++++++++++ | |
567 | /// + true + [Second(true)] + | |
568 | /// +++++++++++++++++++++++++++++ | |
569 | /// + false + [_] + | |
570 | /// +++++++++++++++++++++++++++++ | |
571 | /// + _ + [_, _, tail @ ..] + | |
572 | /// +++++++++++++++++++++++++++++ | |
0731742a | 573 | impl<'p, 'tcx> fmt::Debug for Matrix<'p, 'tcx> { |
9fa01778 | 574 | fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
c30ab7b3 SL |
575 | write!(f, "\n")?; |
576 | ||
577 | let &Matrix(ref m) = self; | |
e74abb32 XL |
578 | let pretty_printed_matrix: Vec<Vec<String>> = |
579 | m.iter().map(|row| row.iter().map(|pat| format!("{:?}", pat)).collect()).collect(); | |
c30ab7b3 SL |
580 | |
581 | let column_count = m.iter().map(|row| row.len()).max().unwrap_or(0); | |
582 | assert!(m.iter().all(|row| row.len() == column_count)); | |
e74abb32 XL |
583 | let column_widths: Vec<usize> = (0..column_count) |
584 | .map(|col| pretty_printed_matrix.iter().map(|row| row[col].len()).max().unwrap_or(0)) | |
585 | .collect(); | |
c30ab7b3 SL |
586 | |
587 | let total_width = column_widths.iter().cloned().sum::<usize>() + column_count * 3 + 1; | |
8faf50e0 | 588 | let br = "+".repeat(total_width); |
c30ab7b3 SL |
589 | write!(f, "{}\n", br)?; |
590 | for row in pretty_printed_matrix { | |
591 | write!(f, "+")?; | |
592 | for (column, pat_str) in row.into_iter().enumerate() { | |
593 | write!(f, " ")?; | |
594 | write!(f, "{:1$}", pat_str, column_widths[column])?; | |
595 | write!(f, " +")?; | |
596 | } | |
597 | write!(f, "\n")?; | |
598 | write!(f, "{}\n", br)?; | |
599 | } | |
600 | Ok(()) | |
601 | } | |
602 | } | |
603 | ||
e74abb32 | 604 | impl<'p, 'tcx> FromIterator<PatStack<'p, 'tcx>> for Matrix<'p, 'tcx> { |
0731742a | 605 | fn from_iter<T>(iter: T) -> Self |
e74abb32 XL |
606 | where |
607 | T: IntoIterator<Item = PatStack<'p, 'tcx>>, | |
c30ab7b3 | 608 | { |
60c5eb7d XL |
609 | let mut matrix = Matrix::empty(); |
610 | for x in iter { | |
611 | // Using `push` ensures we correctly expand or-patterns. | |
612 | matrix.push(x); | |
613 | } | |
614 | matrix | |
c30ab7b3 SL |
615 | } |
616 | } | |
617 | ||
dfeec247 XL |
618 | crate struct MatchCheckCtxt<'a, 'tcx> { |
619 | crate tcx: TyCtxt<'tcx>, | |
32a655c1 SL |
620 | /// The module in which the match occurs. This is necessary for |
621 | /// checking inhabited-ness of types because whether a type is (visibly) | |
622 | /// inhabited can depend on whether it was defined in the current module or | |
9fa01778 | 623 | /// not. E.g., `struct Foo { _private: ! }` cannot be seen to be empty |
32a655c1 SL |
624 | /// outside it's module and should not be matchable with an empty match |
625 | /// statement. | |
dfeec247 | 626 | crate module: DefId, |
f9f354fc | 627 | crate param_env: ty::ParamEnv<'tcx>, |
dfeec247 | 628 | crate pattern_arena: &'a TypedArena<Pat<'tcx>>, |
c30ab7b3 SL |
629 | } |
630 | ||
631 | impl<'a, 'tcx> MatchCheckCtxt<'a, 'tcx> { | |
32a655c1 | 632 | fn is_uninhabited(&self, ty: Ty<'tcx>) -> bool { |
0531ce1d | 633 | if self.tcx.features().exhaustive_patterns { |
ba9703b0 | 634 | self.tcx.is_ty_uninhabited_from(self.module, ty, self.param_env) |
32a655c1 SL |
635 | } else { |
636 | false | |
637 | } | |
638 | } | |
639 | ||
f9f354fc | 640 | /// Returns whether the given type is an enum from another crate declared `#[non_exhaustive]`. |
dfeec247 | 641 | crate fn is_foreign_non_exhaustive_enum(&self, ty: Ty<'tcx>) -> bool { |
e74abb32 | 642 | match ty.kind { |
60c5eb7d XL |
643 | ty::Adt(def, ..) => { |
644 | def.is_enum() && def.is_variant_list_non_exhaustive() && !def.did.is_local() | |
645 | } | |
abe05a73 XL |
646 | _ => false, |
647 | } | |
648 | } | |
c30ab7b3 SL |
649 | } |
650 | ||
60c5eb7d XL |
651 | #[derive(Copy, Clone, Debug, PartialEq, Eq)] |
652 | enum SliceKind { | |
653 | /// Patterns of length `n` (`[x, y]`). | |
654 | FixedLen(u64), | |
dfeec247 XL |
655 | /// Patterns using the `..` notation (`[x, .., y]`). |
656 | /// Captures any array constructor of `length >= i + j`. | |
657 | /// In the case where `array_len` is `Some(_)`, | |
658 | /// this indicates that we only care about the first `i` and the last `j` values of the array, | |
659 | /// and everything in between is a wildcard `_`. | |
60c5eb7d XL |
660 | VarLen(u64, u64), |
661 | } | |
662 | ||
663 | impl SliceKind { | |
664 | fn arity(self) -> u64 { | |
665 | match self { | |
666 | FixedLen(length) => length, | |
667 | VarLen(prefix, suffix) => prefix + suffix, | |
668 | } | |
669 | } | |
670 | ||
671 | /// Whether this pattern includes patterns of length `other_len`. | |
672 | fn covers_length(self, other_len: u64) -> bool { | |
673 | match self { | |
674 | FixedLen(len) => len == other_len, | |
675 | VarLen(prefix, suffix) => prefix + suffix <= other_len, | |
676 | } | |
677 | } | |
678 | ||
679 | /// Returns a collection of slices that spans the values covered by `self`, subtracted by the | |
680 | /// values covered by `other`: i.e., `self \ other` (in set notation). | |
681 | fn subtract(self, other: Self) -> SmallVec<[Self; 1]> { | |
682 | // Remember, `VarLen(i, j)` covers the union of `FixedLen` from `i + j` to infinity. | |
683 | // Naming: we remove the "neg" constructors from the "pos" ones. | |
684 | match self { | |
685 | FixedLen(pos_len) => { | |
686 | if other.covers_length(pos_len) { | |
687 | smallvec![] | |
688 | } else { | |
689 | smallvec![self] | |
690 | } | |
691 | } | |
692 | VarLen(pos_prefix, pos_suffix) => { | |
693 | let pos_len = pos_prefix + pos_suffix; | |
694 | match other { | |
695 | FixedLen(neg_len) => { | |
696 | if neg_len < pos_len { | |
697 | smallvec![self] | |
698 | } else { | |
699 | (pos_len..neg_len) | |
700 | .map(FixedLen) | |
701 | // We know that `neg_len + 1 >= pos_len >= pos_suffix`. | |
702 | .chain(Some(VarLen(neg_len + 1 - pos_suffix, pos_suffix))) | |
703 | .collect() | |
704 | } | |
705 | } | |
706 | VarLen(neg_prefix, neg_suffix) => { | |
707 | let neg_len = neg_prefix + neg_suffix; | |
708 | if neg_len <= pos_len { | |
709 | smallvec![] | |
710 | } else { | |
711 | (pos_len..neg_len).map(FixedLen).collect() | |
712 | } | |
713 | } | |
714 | } | |
715 | } | |
716 | } | |
717 | } | |
718 | } | |
719 | ||
720 | /// A constructor for array and slice patterns. | |
721 | #[derive(Copy, Clone, Debug, PartialEq, Eq)] | |
722 | struct Slice { | |
723 | /// `None` if the matched value is a slice, `Some(n)` if it is an array of size `n`. | |
724 | array_len: Option<u64>, | |
725 | /// The kind of pattern it is: fixed-length `[x, y]` or variable length `[x, .., y]`. | |
726 | kind: SliceKind, | |
727 | } | |
728 | ||
729 | impl Slice { | |
730 | /// Returns what patterns this constructor covers: either fixed-length patterns or | |
731 | /// variable-length patterns. | |
732 | fn pattern_kind(self) -> SliceKind { | |
733 | match self { | |
734 | Slice { array_len: Some(len), kind: VarLen(prefix, suffix) } | |
735 | if prefix + suffix == len => | |
736 | { | |
737 | FixedLen(len) | |
738 | } | |
739 | _ => self.kind, | |
740 | } | |
741 | } | |
742 | ||
743 | /// Returns what values this constructor covers: either values of only one given length, or | |
744 | /// values of length above a given length. | |
745 | /// This is different from `pattern_kind()` because in some cases the pattern only takes into | |
746 | /// account a subset of the entries of the array, but still only captures values of a given | |
747 | /// length. | |
748 | fn value_kind(self) -> SliceKind { | |
749 | match self { | |
750 | Slice { array_len: Some(len), kind: VarLen(_, _) } => FixedLen(len), | |
751 | _ => self.kind, | |
752 | } | |
753 | } | |
754 | ||
755 | fn arity(self) -> u64 { | |
756 | self.pattern_kind().arity() | |
757 | } | |
758 | } | |
759 | ||
f9f354fc XL |
760 | /// A value can be decomposed into a constructor applied to some fields. This struct represents |
761 | /// the constructor. See also `Fields`. | |
762 | /// | |
763 | /// `pat_constructor` retrieves the constructor corresponding to a pattern. | |
764 | /// `specialize_one_pattern` returns the list of fields corresponding to a pattern, given a | |
765 | /// constructor. `Constructor::apply` reconstructs the pattern from a pair of `Constructor` and | |
766 | /// `Fields`. | |
60c5eb7d | 767 | #[derive(Clone, Debug, PartialEq)] |
532ac7d7 | 768 | enum Constructor<'tcx> { |
f9f354fc XL |
769 | /// The constructor for patterns that have a single constructor, like tuples, struct patterns |
770 | /// and fixed-length arrays. | |
c30ab7b3 SL |
771 | Single, |
772 | /// Enum variants. | |
773 | Variant(DefId), | |
774 | /// Literal values. | |
60c5eb7d XL |
775 | ConstantValue(&'tcx ty::Const<'tcx>), |
776 | /// Ranges of integer literal values (`2`, `2..=5` or `2..5`). | |
777 | IntRange(IntRange<'tcx>), | |
778 | /// Ranges of floating-point literal values (`2.0..=5.2`). | |
779 | FloatRange(&'tcx ty::Const<'tcx>, &'tcx ty::Const<'tcx>, RangeEnd), | |
780 | /// Array and slice patterns. | |
781 | Slice(Slice), | |
782 | /// Fake extra constructor for enums that aren't allowed to be matched exhaustively. | |
783 | NonExhaustive, | |
e74abb32 XL |
784 | } |
785 | ||
8bb4bdeb | 786 | impl<'tcx> Constructor<'tcx> { |
e74abb32 XL |
787 | fn is_slice(&self) -> bool { |
788 | match self { | |
60c5eb7d | 789 | Slice(_) => true, |
e74abb32 XL |
790 | _ => false, |
791 | } | |
792 | } | |
793 | ||
9fa01778 XL |
794 | fn variant_index_for_adt<'a>( |
795 | &self, | |
796 | cx: &MatchCheckCtxt<'a, 'tcx>, | |
797 | adt: &'tcx ty::AdtDef, | |
798 | ) -> VariantIdx { | |
dfeec247 XL |
799 | match *self { |
800 | Variant(id) => adt.variant_index_with_id(id), | |
e74abb32 | 801 | Single => { |
ff7c6d11 | 802 | assert!(!adt.is_enum()); |
a1dfa0c6 | 803 | VariantIdx::new(0) |
c30ab7b3 | 804 | } |
f035d41b XL |
805 | ConstantValue(c) => cx |
806 | .tcx | |
807 | .destructure_const(cx.param_env.and(c)) | |
808 | .variant | |
809 | .expect("destructed const of adt without variant id"), | |
e74abb32 XL |
810 | _ => bug!("bad constructor {:?} for adt {:?}", self, adt), |
811 | } | |
812 | } | |
813 | ||
60c5eb7d XL |
814 | // Returns the set of constructors covered by `self` but not by |
815 | // anything in `other_ctors`. | |
816 | fn subtract_ctors(&self, other_ctors: &Vec<Constructor<'tcx>>) -> Vec<Constructor<'tcx>> { | |
817 | if other_ctors.is_empty() { | |
818 | return vec![self.clone()]; | |
819 | } | |
820 | ||
e74abb32 | 821 | match self { |
60c5eb7d XL |
822 | // Those constructors can only match themselves. |
823 | Single | Variant(_) | ConstantValue(..) | FloatRange(..) => { | |
824 | if other_ctors.iter().any(|c| c == self) { vec![] } else { vec![self.clone()] } | |
e74abb32 | 825 | } |
60c5eb7d XL |
826 | &Slice(slice) => { |
827 | let mut other_slices = other_ctors | |
828 | .iter() | |
829 | .filter_map(|c: &Constructor<'_>| match c { | |
830 | Slice(slice) => Some(*slice), | |
831 | // FIXME(oli-obk): implement `deref` for `ConstValue` | |
832 | ConstantValue(..) => None, | |
833 | _ => bug!("bad slice pattern constructor {:?}", c), | |
834 | }) | |
835 | .map(Slice::value_kind); | |
836 | ||
837 | match slice.value_kind() { | |
838 | FixedLen(self_len) => { | |
839 | if other_slices.any(|other_slice| other_slice.covers_length(self_len)) { | |
840 | vec![] | |
841 | } else { | |
842 | vec![Slice(slice)] | |
843 | } | |
844 | } | |
845 | kind @ VarLen(..) => { | |
846 | let mut remaining_slices = vec![kind]; | |
847 | ||
848 | // For each used slice, subtract from the current set of slices. | |
849 | for other_slice in other_slices { | |
850 | remaining_slices = remaining_slices | |
851 | .into_iter() | |
852 | .flat_map(|remaining_slice| remaining_slice.subtract(other_slice)) | |
853 | .collect(); | |
854 | ||
855 | // If the constructors that have been considered so far already cover | |
856 | // the entire range of `self`, no need to look at more constructors. | |
857 | if remaining_slices.is_empty() { | |
858 | break; | |
859 | } | |
860 | } | |
e74abb32 | 861 | |
60c5eb7d XL |
862 | remaining_slices |
863 | .into_iter() | |
864 | .map(|kind| Slice { array_len: slice.array_len, kind }) | |
865 | .map(Slice) | |
866 | .collect() | |
867 | } | |
868 | } | |
e74abb32 | 869 | } |
60c5eb7d XL |
870 | IntRange(self_range) => { |
871 | let mut remaining_ranges = vec![self_range.clone()]; | |
872 | for other_ctor in other_ctors { | |
873 | if let IntRange(other_range) = other_ctor { | |
874 | if other_range == self_range { | |
875 | // If the `self` range appears directly in a `match` arm, we can | |
876 | // eliminate it straight away. | |
877 | remaining_ranges = vec![]; | |
878 | } else { | |
74b04a01 | 879 | // Otherwise explicitly compute the remaining ranges. |
60c5eb7d XL |
880 | remaining_ranges = other_range.subtract_from(remaining_ranges); |
881 | } | |
882 | ||
883 | // If the ranges that have been considered so far already cover the entire | |
884 | // range of values, we can return early. | |
885 | if remaining_ranges.is_empty() { | |
886 | break; | |
887 | } | |
888 | } | |
889 | } | |
e74abb32 | 890 | |
60c5eb7d XL |
891 | // Convert the ranges back into constructors. |
892 | remaining_ranges.into_iter().map(IntRange).collect() | |
e74abb32 | 893 | } |
60c5eb7d XL |
894 | // This constructor is never covered by anything else |
895 | NonExhaustive => vec![NonExhaustive], | |
c30ab7b3 | 896 | } |
e74abb32 XL |
897 | } |
898 | ||
e74abb32 XL |
899 | /// Apply a constructor to a list of patterns, yielding a new pattern. `pats` |
900 | /// must have as many elements as this constructor's arity. | |
901 | /// | |
f9f354fc | 902 | /// This is roughly the inverse of `specialize_one_pattern`. |
60c5eb7d | 903 | /// |
e74abb32 XL |
904 | /// Examples: |
905 | /// `self`: `Constructor::Single` | |
906 | /// `ty`: `(u32, u32, u32)` | |
907 | /// `pats`: `[10, 20, _]` | |
908 | /// returns `(10, 20, _)` | |
909 | /// | |
910 | /// `self`: `Constructor::Variant(Option::Some)` | |
911 | /// `ty`: `Option<bool>` | |
912 | /// `pats`: `[false]` | |
913 | /// returns `Some(false)` | |
f9f354fc | 914 | fn apply<'p>( |
e74abb32 | 915 | &self, |
f9f354fc | 916 | cx: &MatchCheckCtxt<'p, 'tcx>, |
e74abb32 | 917 | ty: Ty<'tcx>, |
f9f354fc | 918 | fields: Fields<'p, 'tcx>, |
e74abb32 | 919 | ) -> Pat<'tcx> { |
f9f354fc | 920 | let mut subpatterns = fields.all_patterns(); |
60c5eb7d XL |
921 | |
922 | let pat = match self { | |
923 | Single | Variant(_) => match ty.kind { | |
924 | ty::Adt(..) | ty::Tuple(..) => { | |
925 | let subpatterns = subpatterns | |
926 | .enumerate() | |
927 | .map(|(i, p)| FieldPat { field: Field::new(i), pattern: p }) | |
928 | .collect(); | |
929 | ||
930 | if let ty::Adt(adt, substs) = ty.kind { | |
931 | if adt.is_enum() { | |
932 | PatKind::Variant { | |
933 | adt_def: adt, | |
934 | substs, | |
935 | variant_index: self.variant_index_for_adt(cx, adt), | |
936 | subpatterns, | |
937 | } | |
938 | } else { | |
939 | PatKind::Leaf { subpatterns } | |
e74abb32 XL |
940 | } |
941 | } else { | |
942 | PatKind::Leaf { subpatterns } | |
943 | } | |
e74abb32 | 944 | } |
74b04a01 | 945 | ty::Ref(..) => PatKind::Deref { subpattern: subpatterns.next().unwrap() }, |
60c5eb7d | 946 | ty::Slice(_) | ty::Array(..) => bug!("bad slice pattern {:?} {:?}", self, ty), |
e74abb32 XL |
947 | _ => PatKind::Wild, |
948 | }, | |
60c5eb7d XL |
949 | Slice(slice) => match slice.pattern_kind() { |
950 | FixedLen(_) => { | |
951 | PatKind::Slice { prefix: subpatterns.collect(), slice: None, suffix: vec![] } | |
952 | } | |
953 | VarLen(prefix, _) => { | |
954 | let mut prefix: Vec<_> = subpatterns.by_ref().take(prefix as usize).collect(); | |
955 | if slice.array_len.is_some() { | |
956 | // Improves diagnostics a bit: if the type is a known-size array, instead | |
957 | // of reporting `[x, _, .., _, y]`, we prefer to report `[x, .., y]`. | |
958 | // This is incorrect if the size is not known, since `[_, ..]` captures | |
959 | // arrays of lengths `>= 1` whereas `[..]` captures any length. | |
960 | while !prefix.is_empty() && prefix.last().unwrap().is_wildcard() { | |
961 | prefix.pop(); | |
962 | } | |
963 | } | |
964 | let suffix: Vec<_> = if slice.array_len.is_some() { | |
965 | // Same as above. | |
966 | subpatterns.skip_while(Pat::is_wildcard).collect() | |
967 | } else { | |
968 | subpatterns.collect() | |
969 | }; | |
970 | let wild = Pat::wildcard_from_ty(ty); | |
971 | PatKind::Slice { prefix, slice: Some(wild), suffix } | |
972 | } | |
973 | }, | |
974 | &ConstantValue(value) => PatKind::Constant { value }, | |
975 | &FloatRange(lo, hi, end) => PatKind::Range(PatRange { lo, hi, end }), | |
976 | IntRange(range) => return range.to_pat(cx.tcx), | |
977 | NonExhaustive => PatKind::Wild, | |
e74abb32 XL |
978 | }; |
979 | ||
980 | Pat { ty, span: DUMMY_SP, kind: Box::new(pat) } | |
981 | } | |
982 | ||
983 | /// Like `apply`, but where all the subpatterns are wildcards `_`. | |
984 | fn apply_wildcards<'a>(&self, cx: &MatchCheckCtxt<'a, 'tcx>, ty: Ty<'tcx>) -> Pat<'tcx> { | |
f9f354fc XL |
985 | self.apply(cx, ty, Fields::wildcards(cx, self, ty)) |
986 | } | |
987 | } | |
988 | ||
989 | /// Some fields need to be explicitly hidden away in certain cases; see the comment above the | |
990 | /// `Fields` struct. This struct represents such a potentially-hidden field. When a field is hidden | |
991 | /// we still keep its type around. | |
992 | #[derive(Debug, Copy, Clone)] | |
993 | enum FilteredField<'p, 'tcx> { | |
994 | Kept(&'p Pat<'tcx>), | |
995 | Hidden(Ty<'tcx>), | |
996 | } | |
997 | ||
998 | impl<'p, 'tcx> FilteredField<'p, 'tcx> { | |
999 | fn kept(self) -> Option<&'p Pat<'tcx>> { | |
1000 | match self { | |
1001 | FilteredField::Kept(p) => Some(p), | |
1002 | FilteredField::Hidden(_) => None, | |
1003 | } | |
1004 | } | |
1005 | ||
1006 | fn to_pattern(self) -> Pat<'tcx> { | |
1007 | match self { | |
1008 | FilteredField::Kept(p) => p.clone(), | |
1009 | FilteredField::Hidden(ty) => Pat::wildcard_from_ty(ty), | |
1010 | } | |
1011 | } | |
1012 | } | |
1013 | ||
1014 | /// A value can be decomposed into a constructor applied to some fields. This struct represents | |
1015 | /// those fields, generalized to allow patterns in each field. See also `Constructor`. | |
1016 | /// | |
1017 | /// If a private or `non_exhaustive` field is uninhabited, the code mustn't observe that it is | |
1018 | /// uninhabited. For that, we filter these fields out of the matrix. This is subtle because we | |
1019 | /// still need to have those fields back when going to/from a `Pat`. Most of this is handled | |
1020 | /// automatically in `Fields`, but when constructing or deconstructing `Fields` you need to be | |
1021 | /// careful. As a rule, when going to/from the matrix, use the filtered field list; when going | |
1022 | /// to/from `Pat`, use the full field list. | |
1023 | /// This filtering is uncommon in practice, because uninhabited fields are rarely used, so we avoid | |
1024 | /// it when possible to preserve performance. | |
1025 | #[derive(Debug, Clone)] | |
1026 | enum Fields<'p, 'tcx> { | |
1027 | /// Lists of patterns that don't contain any filtered fields. | |
1028 | /// `Slice` and `Vec` behave the same; the difference is only to avoid allocating and | |
1029 | /// triple-dereferences when possible. Frankly this is premature optimization, I (Nadrieril) | |
1030 | /// have not measured if it really made a difference. | |
1031 | Slice(&'p [Pat<'tcx>]), | |
1032 | Vec(SmallVec<[&'p Pat<'tcx>; 2]>), | |
1033 | /// Patterns where some of the fields need to be hidden. `kept_count` caches the number of | |
1034 | /// non-hidden fields. | |
1035 | Filtered { | |
1036 | fields: SmallVec<[FilteredField<'p, 'tcx>; 2]>, | |
1037 | kept_count: usize, | |
1038 | }, | |
1039 | } | |
1040 | ||
1041 | impl<'p, 'tcx> Fields<'p, 'tcx> { | |
1042 | fn empty() -> Self { | |
1043 | Fields::Slice(&[]) | |
1044 | } | |
1045 | ||
1046 | /// Construct a new `Fields` from the given pattern. Must not be used if the pattern is a field | |
1047 | /// of a struct/tuple/variant. | |
1048 | fn from_single_pattern(pat: &'p Pat<'tcx>) -> Self { | |
1049 | Fields::Slice(std::slice::from_ref(pat)) | |
1050 | } | |
1051 | ||
1052 | /// Construct a new `Fields` from the given patterns. You must be sure those patterns can't | |
1053 | /// contain fields that need to be filtered out. When in doubt, prefer `replace_fields`. | |
1054 | fn from_slice_unfiltered(pats: &'p [Pat<'tcx>]) -> Self { | |
1055 | Fields::Slice(pats) | |
1056 | } | |
1057 | ||
1058 | /// Convenience; internal use. | |
1059 | fn wildcards_from_tys( | |
1060 | cx: &MatchCheckCtxt<'p, 'tcx>, | |
1061 | tys: impl IntoIterator<Item = Ty<'tcx>>, | |
1062 | ) -> Self { | |
1063 | let wilds = tys.into_iter().map(Pat::wildcard_from_ty); | |
1064 | let pats = cx.pattern_arena.alloc_from_iter(wilds); | |
1065 | Fields::Slice(pats) | |
1066 | } | |
1067 | ||
1068 | /// Creates a new list of wildcard fields for a given constructor. | |
1069 | fn wildcards( | |
1070 | cx: &MatchCheckCtxt<'p, 'tcx>, | |
1071 | constructor: &Constructor<'tcx>, | |
1072 | ty: Ty<'tcx>, | |
1073 | ) -> Self { | |
1074 | let wildcard_from_ty = |ty| &*cx.pattern_arena.alloc(Pat::wildcard_from_ty(ty)); | |
1075 | ||
1076 | let ret = match constructor { | |
1077 | Single | Variant(_) => match ty.kind { | |
1078 | ty::Tuple(ref fs) => { | |
1079 | Fields::wildcards_from_tys(cx, fs.into_iter().map(|ty| ty.expect_ty())) | |
1080 | } | |
1081 | ty::Ref(_, rty, _) => Fields::from_single_pattern(wildcard_from_ty(rty)), | |
1082 | ty::Adt(adt, substs) => { | |
1083 | if adt.is_box() { | |
1084 | // Use T as the sub pattern type of Box<T>. | |
1085 | Fields::from_single_pattern(wildcard_from_ty(substs.type_at(0))) | |
1086 | } else { | |
1087 | let variant = &adt.variants[constructor.variant_index_for_adt(cx, adt)]; | |
1088 | // Whether we must not match the fields of this variant exhaustively. | |
1089 | let is_non_exhaustive = | |
1090 | variant.is_field_list_non_exhaustive() && !adt.did.is_local(); | |
1091 | let field_tys = variant.fields.iter().map(|field| field.ty(cx.tcx, substs)); | |
1092 | // In the following cases, we don't need to filter out any fields. This is | |
1093 | // the vast majority of real cases, since uninhabited fields are uncommon. | |
1094 | let has_no_hidden_fields = (adt.is_enum() && !is_non_exhaustive) | |
1095 | || !field_tys.clone().any(|ty| cx.is_uninhabited(ty)); | |
1096 | ||
1097 | if has_no_hidden_fields { | |
1098 | Fields::wildcards_from_tys(cx, field_tys) | |
1099 | } else { | |
1100 | let mut kept_count = 0; | |
1101 | let fields = variant | |
1102 | .fields | |
1103 | .iter() | |
1104 | .map(|field| { | |
1105 | let ty = field.ty(cx.tcx, substs); | |
1106 | let is_visible = adt.is_enum() | |
1107 | || field.vis.is_accessible_from(cx.module, cx.tcx); | |
1108 | let is_uninhabited = cx.is_uninhabited(ty); | |
1109 | ||
1110 | // In the cases of either a `#[non_exhaustive]` field list | |
1111 | // or a non-public field, we hide uninhabited fields in | |
1112 | // order not to reveal the uninhabitedness of the whole | |
1113 | // variant. | |
1114 | if is_uninhabited && (!is_visible || is_non_exhaustive) { | |
1115 | FilteredField::Hidden(ty) | |
1116 | } else { | |
1117 | kept_count += 1; | |
1118 | FilteredField::Kept(wildcard_from_ty(ty)) | |
1119 | } | |
1120 | }) | |
1121 | .collect(); | |
1122 | Fields::Filtered { fields, kept_count } | |
1123 | } | |
1124 | } | |
1125 | } | |
1126 | _ => Fields::empty(), | |
1127 | }, | |
1128 | Slice(slice) => match ty.kind { | |
1129 | ty::Slice(ty) | ty::Array(ty, _) => { | |
1130 | let arity = slice.arity(); | |
1131 | Fields::wildcards_from_tys(cx, (0..arity).map(|_| ty)) | |
1132 | } | |
1133 | _ => bug!("bad slice pattern {:?} {:?}", constructor, ty), | |
1134 | }, | |
1135 | ConstantValue(..) | FloatRange(..) | IntRange(..) | NonExhaustive => Fields::empty(), | |
1136 | }; | |
1137 | debug!("Fields::wildcards({:?}, {:?}) = {:#?}", constructor, ty, ret); | |
1138 | ret | |
1139 | } | |
1140 | ||
1141 | /// Returns the number of patterns from the viewpoint of match-checking, i.e. excluding hidden | |
1142 | /// fields. This is what we want in most cases in this file, the only exception being | |
1143 | /// conversion to/from `Pat`. | |
1144 | fn len(&self) -> usize { | |
1145 | match self { | |
1146 | Fields::Slice(pats) => pats.len(), | |
1147 | Fields::Vec(pats) => pats.len(), | |
1148 | Fields::Filtered { kept_count, .. } => *kept_count, | |
1149 | } | |
1150 | } | |
1151 | ||
1152 | /// Returns the complete list of patterns, including hidden fields. | |
1153 | fn all_patterns(self) -> impl Iterator<Item = Pat<'tcx>> { | |
1154 | let pats: SmallVec<[_; 2]> = match self { | |
1155 | Fields::Slice(pats) => pats.iter().cloned().collect(), | |
1156 | Fields::Vec(pats) => pats.into_iter().cloned().collect(), | |
1157 | Fields::Filtered { fields, .. } => { | |
1158 | // We don't skip any fields here. | |
1159 | fields.into_iter().map(|p| p.to_pattern()).collect() | |
1160 | } | |
1161 | }; | |
1162 | pats.into_iter() | |
1163 | } | |
1164 | ||
1165 | /// Overrides some of the fields with the provided patterns. Exactly like | |
1166 | /// `replace_fields_indexed`, except that it takes `FieldPat`s as input. | |
1167 | fn replace_with_fieldpats( | |
1168 | &self, | |
1169 | new_pats: impl IntoIterator<Item = &'p FieldPat<'tcx>>, | |
1170 | ) -> Self { | |
1171 | self.replace_fields_indexed( | |
1172 | new_pats.into_iter().map(|pat| (pat.field.index(), &pat.pattern)), | |
1173 | ) | |
1174 | } | |
1175 | ||
1176 | /// Overrides some of the fields with the provided patterns. This is used when a pattern | |
1177 | /// defines some fields but not all, for example `Foo { field1: Some(_), .. }`: here we start with a | |
1178 | /// `Fields` that is just one wildcard per field of the `Foo` struct, and override the entry | |
1179 | /// corresponding to `field1` with the pattern `Some(_)`. This is also used for slice patterns | |
1180 | /// for the same reason. | |
1181 | fn replace_fields_indexed( | |
1182 | &self, | |
1183 | new_pats: impl IntoIterator<Item = (usize, &'p Pat<'tcx>)>, | |
1184 | ) -> Self { | |
1185 | let mut fields = self.clone(); | |
1186 | if let Fields::Slice(pats) = fields { | |
1187 | fields = Fields::Vec(pats.iter().collect()); | |
1188 | } | |
1189 | ||
1190 | match &mut fields { | |
1191 | Fields::Vec(pats) => { | |
1192 | for (i, pat) in new_pats { | |
1193 | pats[i] = pat | |
1194 | } | |
1195 | } | |
1196 | Fields::Filtered { fields, .. } => { | |
1197 | for (i, pat) in new_pats { | |
1198 | if let FilteredField::Kept(p) = &mut fields[i] { | |
1199 | *p = pat | |
1200 | } | |
1201 | } | |
1202 | } | |
1203 | Fields::Slice(_) => unreachable!(), | |
1204 | } | |
1205 | fields | |
1206 | } | |
1207 | ||
1208 | /// Replaces contained fields with the given filtered list of patterns, e.g. taken from the | |
1209 | /// matrix. There must be `len()` patterns in `pats`. | |
1210 | fn replace_fields( | |
1211 | &self, | |
1212 | cx: &MatchCheckCtxt<'p, 'tcx>, | |
1213 | pats: impl IntoIterator<Item = Pat<'tcx>>, | |
1214 | ) -> Self { | |
1215 | let pats: &[_] = cx.pattern_arena.alloc_from_iter(pats); | |
1216 | ||
1217 | match self { | |
1218 | Fields::Filtered { fields, kept_count } => { | |
1219 | let mut pats = pats.iter(); | |
1220 | let mut fields = fields.clone(); | |
1221 | for f in &mut fields { | |
1222 | if let FilteredField::Kept(p) = f { | |
1223 | // We take one input pattern for each `Kept` field, in order. | |
1224 | *p = pats.next().unwrap(); | |
1225 | } | |
1226 | } | |
1227 | Fields::Filtered { fields, kept_count: *kept_count } | |
1228 | } | |
1229 | _ => Fields::Slice(pats), | |
1230 | } | |
1231 | } | |
1232 | ||
1233 | fn push_on_patstack(self, stack: &[&'p Pat<'tcx>]) -> PatStack<'p, 'tcx> { | |
1234 | let pats: SmallVec<_> = match self { | |
1235 | Fields::Slice(pats) => pats.iter().chain(stack.iter().copied()).collect(), | |
1236 | Fields::Vec(mut pats) => { | |
1237 | pats.extend_from_slice(stack); | |
1238 | pats | |
1239 | } | |
1240 | Fields::Filtered { fields, .. } => { | |
1241 | // We skip hidden fields here | |
1242 | fields.into_iter().filter_map(|p| p.kept()).chain(stack.iter().copied()).collect() | |
1243 | } | |
1244 | }; | |
1245 | PatStack::from_vec(pats) | |
c30ab7b3 SL |
1246 | } |
1247 | } | |
1248 | ||
b7449926 | 1249 | #[derive(Clone, Debug)] |
f035d41b | 1250 | crate enum Usefulness<'tcx> { |
60c5eb7d | 1251 | /// Carries a list of unreachable subpatterns. Used only in the presence of or-patterns. |
f035d41b | 1252 | Useful(Vec<Span>), |
60c5eb7d | 1253 | /// Carries a list of witnesses of non-exhaustiveness. |
32a655c1 | 1254 | UsefulWithWitness(Vec<Witness<'tcx>>), |
e74abb32 | 1255 | NotUseful, |
c30ab7b3 SL |
1256 | } |
1257 | ||
f035d41b | 1258 | impl<'tcx> Usefulness<'tcx> { |
e74abb32 XL |
1259 | fn new_useful(preference: WitnessPreference) -> Self { |
1260 | match preference { | |
1261 | ConstructWitness => UsefulWithWitness(vec![Witness(vec![])]), | |
60c5eb7d | 1262 | LeaveOutWitness => Useful(vec![]), |
e74abb32 XL |
1263 | } |
1264 | } | |
1265 | ||
32a655c1 SL |
1266 | fn is_useful(&self) -> bool { |
1267 | match *self { | |
1268 | NotUseful => false, | |
e74abb32 XL |
1269 | _ => true, |
1270 | } | |
1271 | } | |
1272 | ||
f035d41b | 1273 | fn apply_constructor<'p>( |
e74abb32 | 1274 | self, |
f9f354fc | 1275 | cx: &MatchCheckCtxt<'p, 'tcx>, |
e74abb32 XL |
1276 | ctor: &Constructor<'tcx>, |
1277 | ty: Ty<'tcx>, | |
f9f354fc | 1278 | ctor_wild_subpatterns: &Fields<'p, 'tcx>, |
e74abb32 XL |
1279 | ) -> Self { |
1280 | match self { | |
1281 | UsefulWithWitness(witnesses) => UsefulWithWitness( | |
1282 | witnesses | |
1283 | .into_iter() | |
f9f354fc | 1284 | .map(|witness| witness.apply_constructor(cx, &ctor, ty, ctor_wild_subpatterns)) |
e74abb32 XL |
1285 | .collect(), |
1286 | ), | |
1287 | x => x, | |
1288 | } | |
1289 | } | |
1290 | ||
1291 | fn apply_wildcard(self, ty: Ty<'tcx>) -> Self { | |
1292 | match self { | |
1293 | UsefulWithWitness(witnesses) => { | |
60c5eb7d | 1294 | let wild = Pat::wildcard_from_ty(ty); |
e74abb32 XL |
1295 | UsefulWithWitness( |
1296 | witnesses | |
1297 | .into_iter() | |
1298 | .map(|mut witness| { | |
1299 | witness.0.push(wild.clone()); | |
1300 | witness | |
1301 | }) | |
1302 | .collect(), | |
1303 | ) | |
1304 | } | |
1305 | x => x, | |
1306 | } | |
1307 | } | |
1308 | ||
1309 | fn apply_missing_ctors( | |
1310 | self, | |
1311 | cx: &MatchCheckCtxt<'_, 'tcx>, | |
1312 | ty: Ty<'tcx>, | |
1313 | missing_ctors: &MissingConstructors<'tcx>, | |
1314 | ) -> Self { | |
1315 | match self { | |
1316 | UsefulWithWitness(witnesses) => { | |
1317 | let new_patterns: Vec<_> = | |
1318 | missing_ctors.iter().map(|ctor| ctor.apply_wildcards(cx, ty)).collect(); | |
1319 | // Add the new patterns to each witness | |
1320 | UsefulWithWitness( | |
1321 | witnesses | |
1322 | .into_iter() | |
1323 | .flat_map(|witness| { | |
1324 | new_patterns.iter().map(move |pat| { | |
1325 | let mut witness = witness.clone(); | |
1326 | witness.0.push(pat.clone()); | |
1327 | witness | |
1328 | }) | |
1329 | }) | |
1330 | .collect(), | |
1331 | ) | |
1332 | } | |
1333 | x => x, | |
32a655c1 SL |
1334 | } |
1335 | } | |
1336 | } | |
1337 | ||
b7449926 | 1338 | #[derive(Copy, Clone, Debug)] |
dfeec247 | 1339 | crate enum WitnessPreference { |
c30ab7b3 | 1340 | ConstructWitness, |
e74abb32 | 1341 | LeaveOutWitness, |
c30ab7b3 SL |
1342 | } |
1343 | ||
1344 | #[derive(Copy, Clone, Debug)] | |
e74abb32 | 1345 | struct PatCtxt<'tcx> { |
c30ab7b3 | 1346 | ty: Ty<'tcx>, |
e74abb32 | 1347 | span: Span, |
c30ab7b3 SL |
1348 | } |
1349 | ||
b7449926 XL |
1350 | /// A witness of non-exhaustiveness for error reporting, represented |
1351 | /// as a list of patterns (in reverse order of construction) with | |
1352 | /// wildcards inside to represent elements that can take any inhabitant | |
1353 | /// of the type as a value. | |
1354 | /// | |
1355 | /// A witness against a list of patterns should have the same types | |
1356 | /// and length as the pattern matched against. Because Rust `match` | |
1357 | /// is always against a single pattern, at the end the witness will | |
1358 | /// have length 1, but in the middle of the algorithm, it can contain | |
1359 | /// multiple patterns. | |
1360 | /// | |
1361 | /// For example, if we are constructing a witness for the match against | |
1362 | /// ``` | |
1363 | /// struct Pair(Option<(u32, u32)>, bool); | |
1364 | /// | |
1365 | /// match (p: Pair) { | |
1366 | /// Pair(None, _) => {} | |
1367 | /// Pair(_, false) => {} | |
1368 | /// } | |
1369 | /// ``` | |
1370 | /// | |
1371 | /// We'll perform the following steps: | |
1372 | /// 1. Start with an empty witness | |
1373 | /// `Witness(vec![])` | |
1374 | /// 2. Push a witness `Some(_)` against the `None` | |
1375 | /// `Witness(vec![Some(_)])` | |
1376 | /// 3. Push a witness `true` against the `false` | |
1377 | /// `Witness(vec![Some(_), true])` | |
1378 | /// 4. Apply the `Pair` constructor to the witnesses | |
1379 | /// `Witness(vec![Pair(Some(_), true)])` | |
1380 | /// | |
1381 | /// The final `Pair(Some(_), true)` is then the resulting witness. | |
1382 | #[derive(Clone, Debug)] | |
dfeec247 | 1383 | crate struct Witness<'tcx>(Vec<Pat<'tcx>>); |
c30ab7b3 | 1384 | |
32a655c1 | 1385 | impl<'tcx> Witness<'tcx> { |
dfeec247 | 1386 | crate fn single_pattern(self) -> Pat<'tcx> { |
c30ab7b3 | 1387 | assert_eq!(self.0.len(), 1); |
e1599b0c | 1388 | self.0.into_iter().next().unwrap() |
c30ab7b3 SL |
1389 | } |
1390 | ||
c30ab7b3 SL |
1391 | /// Constructs a partial witness for a pattern given a list of |
1392 | /// patterns expanded by the specialization step. | |
1393 | /// | |
1394 | /// When a pattern P is discovered to be useful, this function is used bottom-up | |
0731742a | 1395 | /// to reconstruct a complete witness, e.g., a pattern P' that covers a subset |
c30ab7b3 SL |
1396 | /// of values, V, where each value in that set is not covered by any previously |
1397 | /// used patterns and is covered by the pattern P'. Examples: | |
1398 | /// | |
1399 | /// left_ty: tuple of 3 elements | |
1400 | /// pats: [10, 20, _] => (10, 20, _) | |
1401 | /// | |
1402 | /// left_ty: struct X { a: (bool, &'static str), b: usize} | |
1403 | /// pats: [(false, "foo"), 42] => X { a: (false, "foo"), b: 42 } | |
f9f354fc | 1404 | fn apply_constructor<'p>( |
c30ab7b3 | 1405 | mut self, |
f9f354fc | 1406 | cx: &MatchCheckCtxt<'p, 'tcx>, |
8bb4bdeb | 1407 | ctor: &Constructor<'tcx>, |
e74abb32 | 1408 | ty: Ty<'tcx>, |
f9f354fc | 1409 | ctor_wild_subpatterns: &Fields<'p, 'tcx>, |
e74abb32 | 1410 | ) -> Self { |
c30ab7b3 | 1411 | let pat = { |
f9f354fc XL |
1412 | let len = self.0.len(); |
1413 | let arity = ctor_wild_subpatterns.len(); | |
1414 | let pats = self.0.drain((len - arity)..).rev(); | |
1415 | let fields = ctor_wild_subpatterns.replace_fields(cx, pats); | |
1416 | ctor.apply(cx, ty, fields) | |
c30ab7b3 SL |
1417 | }; |
1418 | ||
e74abb32 | 1419 | self.0.push(pat); |
c30ab7b3 SL |
1420 | |
1421 | self | |
1422 | } | |
1423 | } | |
1424 | ||
c30ab7b3 SL |
1425 | /// This determines the set of all possible constructors of a pattern matching |
1426 | /// values of type `left_ty`. For vectors, this would normally be an infinite set | |
32a655c1 SL |
1427 | /// but is instead bounded by the maximum fixed length of slice patterns in |
1428 | /// the column of patterns being analyzed. | |
c30ab7b3 | 1429 | /// |
9fa01778 XL |
1430 | /// We make sure to omit constructors that are statically impossible. E.g., for |
1431 | /// `Option<!>`, we do not include `Some(_)` in the returned list of constructors. | |
60c5eb7d XL |
1432 | /// Invariant: this returns an empty `Vec` if and only if the type is uninhabited (as determined by |
1433 | /// `cx.is_uninhabited()`). | |
dc9dc135 XL |
1434 | fn all_constructors<'a, 'tcx>( |
1435 | cx: &mut MatchCheckCtxt<'a, 'tcx>, | |
e74abb32 | 1436 | pcx: PatCtxt<'tcx>, |
dc9dc135 | 1437 | ) -> Vec<Constructor<'tcx>> { |
32a655c1 | 1438 | debug!("all_constructors({:?})", pcx.ty); |
60c5eb7d XL |
1439 | let make_range = |start, end| { |
1440 | IntRange( | |
1441 | // `unwrap()` is ok because we know the type is an integer. | |
1442 | IntRange::from_range(cx.tcx, start, end, pcx.ty, &RangeEnd::Included, pcx.span) | |
1443 | .unwrap(), | |
1444 | ) | |
1445 | }; | |
1446 | match pcx.ty.kind { | |
1447 | ty::Bool => { | |
1448 | [true, false].iter().map(|&b| ConstantValue(ty::Const::from_bool(cx.tcx, b))).collect() | |
1449 | } | |
416331ca XL |
1450 | ty::Array(ref sub_ty, len) if len.try_eval_usize(cx.tcx, cx.param_env).is_some() => { |
1451 | let len = len.eval_usize(cx.tcx, cx.param_env); | |
60c5eb7d XL |
1452 | if len != 0 && cx.is_uninhabited(sub_ty) { |
1453 | vec![] | |
1454 | } else { | |
1455 | vec![Slice(Slice { array_len: Some(len), kind: VarLen(0, 0) })] | |
1456 | } | |
ea8adc8c XL |
1457 | } |
1458 | // Treat arrays of a constant but unknown length like slices. | |
e74abb32 | 1459 | ty::Array(ref sub_ty, _) | ty::Slice(ref sub_ty) => { |
60c5eb7d XL |
1460 | let kind = if cx.is_uninhabited(sub_ty) { FixedLen(0) } else { VarLen(0, 0) }; |
1461 | vec![Slice(Slice { array_len: None, kind })] | |
1462 | } | |
1463 | ty::Adt(def, substs) if def.is_enum() => { | |
1464 | let ctors: Vec<_> = if cx.tcx.features().exhaustive_patterns { | |
1465 | // If `exhaustive_patterns` is enabled, we exclude variants known to be | |
1466 | // uninhabited. | |
1467 | def.variants | |
1468 | .iter() | |
1469 | .filter(|v| { | |
ba9703b0 | 1470 | !v.uninhabited_from(cx.tcx, substs, def.adt_kind(), cx.param_env) |
60c5eb7d XL |
1471 | .contains(cx.tcx, cx.module) |
1472 | }) | |
1473 | .map(|v| Variant(v.def_id)) | |
1474 | .collect() | |
32a655c1 | 1475 | } else { |
60c5eb7d XL |
1476 | def.variants.iter().map(|v| Variant(v.def_id)).collect() |
1477 | }; | |
1478 | ||
1479 | // If the enum is declared as `#[non_exhaustive]`, we treat it as if it had an | |
1480 | // additional "unknown" constructor. | |
1481 | // There is no point in enumerating all possible variants, because the user can't | |
1482 | // actually match against them all themselves. So we always return only the fictitious | |
1483 | // constructor. | |
1484 | // E.g., in an example like: | |
1485 | // ``` | |
1486 | // let err: io::ErrorKind = ...; | |
1487 | // match err { | |
1488 | // io::ErrorKind::NotFound => {}, | |
1489 | // } | |
1490 | // ``` | |
1491 | // we don't want to show every possible IO error, but instead have only `_` as the | |
1492 | // witness. | |
1493 | let is_declared_nonexhaustive = cx.is_foreign_non_exhaustive_enum(pcx.ty); | |
1494 | ||
1495 | // If `exhaustive_patterns` is disabled and our scrutinee is an empty enum, we treat it | |
1496 | // as though it had an "unknown" constructor to avoid exposing its emptyness. Note that | |
1497 | // an empty match will still be considered exhaustive because that case is handled | |
1498 | // separately in `check_match`. | |
1499 | let is_secretly_empty = | |
1500 | def.variants.is_empty() && !cx.tcx.features().exhaustive_patterns; | |
1501 | ||
1502 | if is_secretly_empty || is_declared_nonexhaustive { vec![NonExhaustive] } else { ctors } | |
32a655c1 | 1503 | } |
0731742a | 1504 | ty::Char => { |
b7449926 XL |
1505 | vec![ |
1506 | // The valid Unicode Scalar Value ranges. | |
60c5eb7d XL |
1507 | make_range('\u{0000}' as u128, '\u{D7FF}' as u128), |
1508 | make_range('\u{E000}' as u128, '\u{10FFFF}' as u128), | |
b7449926 XL |
1509 | ] |
1510 | } | |
60c5eb7d XL |
1511 | ty::Int(_) | ty::Uint(_) |
1512 | if pcx.ty.is_ptr_sized_integral() | |
1513 | && !cx.tcx.features().precise_pointer_size_matching => | |
1514 | { | |
1515 | // `usize`/`isize` are not allowed to be matched exhaustively unless the | |
1516 | // `precise_pointer_size_matching` feature is enabled. So we treat those types like | |
1517 | // `#[non_exhaustive]` enums by returning a special unmatcheable constructor. | |
1518 | vec![NonExhaustive] | |
1519 | } | |
0731742a | 1520 | ty::Int(ity) => { |
a1dfa0c6 | 1521 | let bits = Integer::from_attr(&cx.tcx, SignedInt(ity)).size().bits() as u128; |
b7449926 | 1522 | let min = 1u128 << (bits - 1); |
532ac7d7 | 1523 | let max = min - 1; |
60c5eb7d | 1524 | vec![make_range(min, max)] |
b7449926 | 1525 | } |
0731742a | 1526 | ty::Uint(uty) => { |
532ac7d7 | 1527 | let size = Integer::from_attr(&cx.tcx, UnsignedInt(uty)).size(); |
f035d41b | 1528 | let max = truncate(u128::MAX, size); |
60c5eb7d | 1529 | vec![make_range(0, max)] |
b7449926 | 1530 | } |
32a655c1 SL |
1531 | _ => { |
1532 | if cx.is_uninhabited(pcx.ty) { | |
1533 | vec![] | |
1534 | } else { | |
1535 | vec![Single] | |
1536 | } | |
1537 | } | |
476ff2be | 1538 | } |
476ff2be SL |
1539 | } |
1540 | ||
b7449926 XL |
1541 | /// An inclusive interval, used for precise integer exhaustiveness checking. |
1542 | /// `IntRange`s always store a contiguous range. This means that values are | |
1543 | /// encoded such that `0` encodes the minimum value for the integer, | |
1544 | /// regardless of the signedness. | |
dc9dc135 | 1545 | /// For example, the pattern `-128..=127i8` is encoded as `0..=255`. |
b7449926 XL |
1546 | /// This makes comparisons and arithmetic on interval endpoints much more |
1547 | /// straightforward. See `signed_bias` for details. | |
1548 | /// | |
1549 | /// `IntRange` is never used to encode an empty range or a "range" that wraps | |
0731742a | 1550 | /// around the (offset) space: i.e., `range.lo <= range.hi`. |
e74abb32 | 1551 | #[derive(Clone, Debug)] |
b7449926 | 1552 | struct IntRange<'tcx> { |
dfeec247 XL |
1553 | range: RangeInclusive<u128>, |
1554 | ty: Ty<'tcx>, | |
1555 | span: Span, | |
b7449926 XL |
1556 | } |
1557 | ||
1558 | impl<'tcx> IntRange<'tcx> { | |
e74abb32 XL |
1559 | #[inline] |
1560 | fn is_integral(ty: Ty<'_>) -> bool { | |
1561 | match ty.kind { | |
1562 | ty::Char | ty::Int(_) | ty::Uint(_) => true, | |
1563 | _ => false, | |
1564 | } | |
1565 | } | |
1566 | ||
60c5eb7d XL |
1567 | fn is_singleton(&self) -> bool { |
1568 | self.range.start() == self.range.end() | |
1569 | } | |
1570 | ||
1571 | fn boundaries(&self) -> (u128, u128) { | |
1572 | (*self.range.start(), *self.range.end()) | |
1573 | } | |
1574 | ||
1575 | /// Don't treat `usize`/`isize` exhaustively unless the `precise_pointer_size_matching` feature | |
1576 | /// is enabled. | |
1577 | fn treat_exhaustively(&self, tcx: TyCtxt<'tcx>) -> bool { | |
1578 | !self.ty.is_ptr_sized_integral() || tcx.features().precise_pointer_size_matching | |
1579 | } | |
1580 | ||
e74abb32 XL |
1581 | #[inline] |
1582 | fn integral_size_and_signed_bias(tcx: TyCtxt<'tcx>, ty: Ty<'_>) -> Option<(Size, u128)> { | |
1583 | match ty.kind { | |
1584 | ty::Char => Some((Size::from_bytes(4), 0)), | |
1585 | ty::Int(ity) => { | |
1586 | let size = Integer::from_attr(&tcx, SignedInt(ity)).size(); | |
1587 | Some((size, 1u128 << (size.bits() as u128 - 1))) | |
1588 | } | |
1589 | ty::Uint(uty) => Some((Integer::from_attr(&tcx, UnsignedInt(uty)).size(), 0)), | |
1590 | _ => None, | |
1591 | } | |
1592 | } | |
1593 | ||
1594 | #[inline] | |
1595 | fn from_const( | |
1596 | tcx: TyCtxt<'tcx>, | |
1597 | param_env: ty::ParamEnv<'tcx>, | |
1598 | value: &Const<'tcx>, | |
1599 | span: Span, | |
1600 | ) -> Option<IntRange<'tcx>> { | |
1601 | if let Some((target_size, bias)) = Self::integral_size_and_signed_bias(tcx, value.ty) { | |
1602 | let ty = value.ty; | |
74b04a01 XL |
1603 | let val = (|| { |
1604 | if let ty::ConstKind::Value(ConstValue::Scalar(scalar)) = value.val { | |
1605 | // For this specific pattern we can skip a lot of effort and go | |
1606 | // straight to the result, after doing a bit of checking. (We | |
1607 | // could remove this branch and just fall through, which | |
1608 | // is more general but much slower.) | |
1609 | if let Ok(bits) = scalar.to_bits_or_ptr(target_size, &tcx) { | |
1610 | return Some(bits); | |
1611 | } | |
1612 | } | |
1613 | // This is a more general form of the previous case. | |
1614 | value.try_eval_bits(tcx, param_env, ty) | |
1615 | })()?; | |
e74abb32 XL |
1616 | let val = val ^ bias; |
1617 | Some(IntRange { range: val..=val, ty, span }) | |
1618 | } else { | |
1619 | None | |
1620 | } | |
1621 | } | |
1622 | ||
1623 | #[inline] | |
1624 | fn from_range( | |
1625 | tcx: TyCtxt<'tcx>, | |
1626 | lo: u128, | |
1627 | hi: u128, | |
1628 | ty: Ty<'tcx>, | |
1629 | end: &RangeEnd, | |
1630 | span: Span, | |
1631 | ) -> Option<IntRange<'tcx>> { | |
1632 | if Self::is_integral(ty) { | |
1633 | // Perform a shift if the underlying types are signed, | |
1634 | // which makes the interval arithmetic simpler. | |
1635 | let bias = IntRange::signed_bias(tcx, ty); | |
1636 | let (lo, hi) = (lo ^ bias, hi ^ bias); | |
60c5eb7d XL |
1637 | let offset = (*end == RangeEnd::Excluded) as u128; |
1638 | if lo > hi || (lo == hi && *end == RangeEnd::Excluded) { | |
1639 | // This should have been caught earlier by E0030. | |
1640 | bug!("malformed range pattern: {}..={}", lo, (hi - offset)); | |
e74abb32 | 1641 | } |
60c5eb7d | 1642 | Some(IntRange { range: lo..=(hi - offset), ty, span }) |
e74abb32 XL |
1643 | } else { |
1644 | None | |
1645 | } | |
1646 | } | |
1647 | ||
416331ca XL |
1648 | fn from_pat( |
1649 | tcx: TyCtxt<'tcx>, | |
1650 | param_env: ty::ParamEnv<'tcx>, | |
60c5eb7d | 1651 | pat: &Pat<'tcx>, |
416331ca | 1652 | ) -> Option<IntRange<'tcx>> { |
60c5eb7d XL |
1653 | match pat_constructor(tcx, param_env, pat)? { |
1654 | IntRange(range) => Some(range), | |
1655 | _ => None, | |
e74abb32 | 1656 | } |
b7449926 XL |
1657 | } |
1658 | ||
1659 | // The return value of `signed_bias` should be XORed with an endpoint to encode/decode it. | |
dc9dc135 | 1660 | fn signed_bias(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> u128 { |
e74abb32 | 1661 | match ty.kind { |
b7449926 | 1662 | ty::Int(ity) => { |
a1dfa0c6 | 1663 | let bits = Integer::from_attr(&tcx, SignedInt(ity)).size().bits() as u128; |
b7449926 XL |
1664 | 1u128 << (bits - 1) |
1665 | } | |
e74abb32 | 1666 | _ => 0, |
b7449926 XL |
1667 | } |
1668 | } | |
1669 | ||
9fa01778 | 1670 | /// Returns a collection of ranges that spans the values covered by `ranges`, subtracted |
0731742a | 1671 | /// by the values covered by `self`: i.e., `ranges \ self` (in set notation). |
60c5eb7d | 1672 | fn subtract_from(&self, ranges: Vec<IntRange<'tcx>>) -> Vec<IntRange<'tcx>> { |
b7449926 XL |
1673 | let mut remaining_ranges = vec![]; |
1674 | let ty = self.ty; | |
60c5eb7d XL |
1675 | let span = self.span; |
1676 | let (lo, hi) = self.boundaries(); | |
b7449926 | 1677 | for subrange in ranges { |
60c5eb7d | 1678 | let (subrange_lo, subrange_hi) = subrange.range.into_inner(); |
e74abb32 | 1679 | if lo > subrange_hi || subrange_lo > hi { |
b7449926 XL |
1680 | // The pattern doesn't intersect with the subrange at all, |
1681 | // so the subrange remains untouched. | |
60c5eb7d | 1682 | remaining_ranges.push(IntRange { range: subrange_lo..=subrange_hi, ty, span }); |
b7449926 XL |
1683 | } else { |
1684 | if lo > subrange_lo { | |
1685 | // The pattern intersects an upper section of the | |
1686 | // subrange, so a lower section will remain. | |
60c5eb7d | 1687 | remaining_ranges.push(IntRange { range: subrange_lo..=(lo - 1), ty, span }); |
b7449926 XL |
1688 | } |
1689 | if hi < subrange_hi { | |
1690 | // The pattern intersects a lower section of the | |
1691 | // subrange, so an upper section will remain. | |
60c5eb7d | 1692 | remaining_ranges.push(IntRange { range: (hi + 1)..=subrange_hi, ty, span }); |
b7449926 XL |
1693 | } |
1694 | } | |
1695 | } | |
1696 | remaining_ranges | |
1697 | } | |
1698 | ||
60c5eb7d XL |
1699 | fn is_subrange(&self, other: &Self) -> bool { |
1700 | other.range.start() <= self.range.start() && self.range.end() <= other.range.end() | |
1701 | } | |
1702 | ||
1703 | fn intersection(&self, tcx: TyCtxt<'tcx>, other: &Self) -> Option<Self> { | |
b7449926 | 1704 | let ty = self.ty; |
60c5eb7d XL |
1705 | let (lo, hi) = self.boundaries(); |
1706 | let (other_lo, other_hi) = other.boundaries(); | |
1707 | if self.treat_exhaustively(tcx) { | |
1708 | if lo <= other_hi && other_lo <= hi { | |
1709 | let span = other.span; | |
1710 | Some(IntRange { range: max(lo, other_lo)..=min(hi, other_hi), ty, span }) | |
1711 | } else { | |
1712 | None | |
1713 | } | |
b7449926 | 1714 | } else { |
60c5eb7d XL |
1715 | // If the range should not be treated exhaustively, fallback to checking for inclusion. |
1716 | if self.is_subrange(other) { Some(self.clone()) } else { None } | |
b7449926 XL |
1717 | } |
1718 | } | |
e74abb32 XL |
1719 | |
1720 | fn suspicious_intersection(&self, other: &Self) -> bool { | |
1721 | // `false` in the following cases: | |
1722 | // 1 ---- // 1 ---------- // 1 ---- // 1 ---- | |
1723 | // 2 ---------- // 2 ---- // 2 ---- // 2 ---- | |
1724 | // | |
1725 | // The following are currently `false`, but could be `true` in the future (#64007): | |
1726 | // 1 --------- // 1 --------- | |
1727 | // 2 ---------- // 2 ---------- | |
1728 | // | |
1729 | // `true` in the following cases: | |
1730 | // 1 ------- // 1 ------- | |
1731 | // 2 -------- // 2 ------- | |
60c5eb7d XL |
1732 | let (lo, hi) = self.boundaries(); |
1733 | let (other_lo, other_hi) = other.boundaries(); | |
dfeec247 | 1734 | lo == other_hi || hi == other_lo |
e74abb32 | 1735 | } |
60c5eb7d XL |
1736 | |
1737 | fn to_pat(&self, tcx: TyCtxt<'tcx>) -> Pat<'tcx> { | |
1738 | let (lo, hi) = self.boundaries(); | |
1739 | ||
1740 | let bias = IntRange::signed_bias(tcx, self.ty); | |
1741 | let (lo, hi) = (lo ^ bias, hi ^ bias); | |
1742 | ||
1743 | let ty = ty::ParamEnv::empty().and(self.ty); | |
1744 | let lo_const = ty::Const::from_bits(tcx, lo, ty); | |
1745 | let hi_const = ty::Const::from_bits(tcx, hi, ty); | |
1746 | ||
1747 | let kind = if lo == hi { | |
1748 | PatKind::Constant { value: lo_const } | |
1749 | } else { | |
1750 | PatKind::Range(PatRange { lo: lo_const, hi: hi_const, end: RangeEnd::Included }) | |
1751 | }; | |
1752 | ||
1753 | // This is a brand new pattern, so we don't reuse `self.span`. | |
1754 | Pat { ty: self.ty, span: DUMMY_SP, kind: Box::new(kind) } | |
1755 | } | |
1756 | } | |
1757 | ||
1758 | /// Ignore spans when comparing, they don't carry semantic information as they are only for lints. | |
1759 | impl<'tcx> std::cmp::PartialEq for IntRange<'tcx> { | |
1760 | fn eq(&self, other: &Self) -> bool { | |
1761 | self.range == other.range && self.ty == other.ty | |
1762 | } | |
b7449926 XL |
1763 | } |
1764 | ||
e74abb32 XL |
1765 | // A struct to compute a set of constructors equivalent to `all_ctors \ used_ctors`. |
1766 | struct MissingConstructors<'tcx> { | |
e74abb32 XL |
1767 | all_ctors: Vec<Constructor<'tcx>>, |
1768 | used_ctors: Vec<Constructor<'tcx>>, | |
a1dfa0c6 XL |
1769 | } |
1770 | ||
e74abb32 | 1771 | impl<'tcx> MissingConstructors<'tcx> { |
60c5eb7d XL |
1772 | fn new(all_ctors: Vec<Constructor<'tcx>>, used_ctors: Vec<Constructor<'tcx>>) -> Self { |
1773 | MissingConstructors { all_ctors, used_ctors } | |
e74abb32 | 1774 | } |
a1dfa0c6 | 1775 | |
e74abb32 XL |
1776 | fn into_inner(self) -> (Vec<Constructor<'tcx>>, Vec<Constructor<'tcx>>) { |
1777 | (self.all_ctors, self.used_ctors) | |
1778 | } | |
a1dfa0c6 | 1779 | |
e74abb32 XL |
1780 | fn is_empty(&self) -> bool { |
1781 | self.iter().next().is_none() | |
1782 | } | |
1783 | /// Whether this contains all the constructors for the given type or only a | |
1784 | /// subset. | |
1785 | fn all_ctors_are_missing(&self) -> bool { | |
1786 | self.used_ctors.is_empty() | |
1787 | } | |
b7449926 | 1788 | |
e74abb32 XL |
1789 | /// Iterate over all_ctors \ used_ctors |
1790 | fn iter<'a>(&'a self) -> impl Iterator<Item = Constructor<'tcx>> + Captures<'a> { | |
60c5eb7d | 1791 | self.all_ctors.iter().flat_map(move |req_ctor| req_ctor.subtract_ctors(&self.used_ctors)) |
b7449926 | 1792 | } |
e74abb32 | 1793 | } |
b7449926 | 1794 | |
e74abb32 XL |
1795 | impl<'tcx> fmt::Debug for MissingConstructors<'tcx> { |
1796 | fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { | |
1797 | let ctors: Vec<_> = self.iter().collect(); | |
1798 | write!(f, "{:?}", ctors) | |
a1dfa0c6 | 1799 | } |
b7449926 XL |
1800 | } |
1801 | ||
9fa01778 | 1802 | /// Algorithm from http://moscova.inria.fr/~maranget/papers/warn/index.html. |
32a655c1 SL |
1803 | /// The algorithm from the paper has been modified to correctly handle empty |
1804 | /// types. The changes are: | |
1805 | /// (0) We don't exit early if the pattern matrix has zero rows. We just | |
1806 | /// continue to recurse over columns. | |
1807 | /// (1) all_constructors will only return constructors that are statically | |
9fa01778 | 1808 | /// possible. E.g., it will only return `Ok` for `Result<T, !>`. |
c30ab7b3 | 1809 | /// |
2c00a5a8 XL |
1810 | /// This finds whether a (row) vector `v` of patterns is 'useful' in relation |
1811 | /// to a set of such vectors `m` - this is defined as there being a set of | |
1812 | /// inputs that will match `v` but not any of the sets in `m`. | |
1813 | /// | |
f9f354fc | 1814 | /// All the patterns at each column of the `matrix ++ v` matrix must have the same type. |
c30ab7b3 SL |
1815 | /// |
1816 | /// This is used both for reachability checking (if a pattern isn't useful in | |
1817 | /// relation to preceding patterns, it is not reachable) and exhaustiveness | |
1818 | /// checking (if a wildcard pattern is useful in relation to a matrix, the | |
1819 | /// matrix isn't exhaustive). | |
ba9703b0 XL |
1820 | /// |
1821 | /// `is_under_guard` is used to inform if the pattern has a guard. If it | |
1822 | /// has one it must not be inserted into the matrix. This shouldn't be | |
1823 | /// relied on for soundness. | |
dfeec247 | 1824 | crate fn is_useful<'p, 'tcx>( |
60c5eb7d | 1825 | cx: &mut MatchCheckCtxt<'p, 'tcx>, |
dc9dc135 | 1826 | matrix: &Matrix<'p, 'tcx>, |
60c5eb7d | 1827 | v: &PatStack<'p, 'tcx>, |
e74abb32 XL |
1828 | witness_preference: WitnessPreference, |
1829 | hir_id: HirId, | |
ba9703b0 | 1830 | is_under_guard: bool, |
60c5eb7d | 1831 | is_top_level: bool, |
f035d41b | 1832 | ) -> Usefulness<'tcx> { |
c30ab7b3 | 1833 | let &Matrix(ref rows) = matrix; |
0531ce1d | 1834 | debug!("is_useful({:#?}, {:#?})", matrix, v); |
c30ab7b3 | 1835 | |
32a655c1 SL |
1836 | // The base case. We are pattern-matching on () and the return value is |
1837 | // based on whether our matrix has a row or not. | |
1838 | // NOTE: This could potentially be optimized by checking rows.is_empty() | |
1839 | // first and then, if v is non-empty, the return value is based on whether | |
1840 | // the type of the tuple we're checking is inhabited or not. | |
1841 | if v.is_empty() { | |
1842 | return if rows.is_empty() { | |
e74abb32 | 1843 | Usefulness::new_useful(witness_preference) |
32a655c1 SL |
1844 | } else { |
1845 | NotUseful | |
e74abb32 | 1846 | }; |
32a655c1 | 1847 | }; |
476ff2be | 1848 | |
32a655c1 | 1849 | assert!(rows.iter().all(|r| r.len() == v.len())); |
476ff2be | 1850 | |
60c5eb7d XL |
1851 | // If the first pattern is an or-pattern, expand it. |
1852 | if let Some(vs) = v.expand_or_pat() { | |
1853 | // We need to push the already-seen patterns into the matrix in order to detect redundant | |
1854 | // branches like `Some(_) | Some(0)`. We also keep track of the unreachable subpatterns. | |
1855 | let mut matrix = matrix.clone(); | |
f035d41b XL |
1856 | // `Vec` of all the unreachable branches of the current or-pattern. |
1857 | let mut unreachable_branches = Vec::new(); | |
1858 | // Subpatterns that are unreachable from all branches. E.g. in the following case, the last | |
1859 | // `true` is unreachable only from one branch, so it is overall reachable. | |
1860 | // ``` | |
1861 | // match (true, true) { | |
1862 | // (true, true) => {} | |
1863 | // (false | true, false | true) => {} | |
1864 | // } | |
1865 | // ``` | |
1866 | let mut unreachable_subpats = FxHashSet::default(); | |
1867 | // Whether any branch at all is useful. | |
60c5eb7d | 1868 | let mut any_is_useful = false; |
f035d41b | 1869 | |
60c5eb7d | 1870 | for v in vs { |
ba9703b0 | 1871 | let res = is_useful(cx, &matrix, &v, witness_preference, hir_id, is_under_guard, false); |
60c5eb7d XL |
1872 | match res { |
1873 | Useful(pats) => { | |
f035d41b XL |
1874 | if !any_is_useful { |
1875 | any_is_useful = true; | |
1876 | // Initialize with the first set of unreachable subpatterns encountered. | |
1877 | unreachable_subpats = pats.into_iter().collect(); | |
1878 | } else { | |
1879 | // Keep the patterns unreachable from both this and previous branches. | |
1880 | unreachable_subpats = | |
1881 | pats.into_iter().filter(|p| unreachable_subpats.contains(p)).collect(); | |
1882 | } | |
60c5eb7d | 1883 | } |
f035d41b | 1884 | NotUseful => unreachable_branches.push(v.head().span), |
60c5eb7d XL |
1885 | UsefulWithWitness(_) => { |
1886 | bug!("Encountered or-pat in `v` during exhaustiveness checking") | |
1887 | } | |
1888 | } | |
ba9703b0 XL |
1889 | // If pattern has a guard don't add it to the matrix |
1890 | if !is_under_guard { | |
1891 | matrix.push(v); | |
1892 | } | |
60c5eb7d | 1893 | } |
f035d41b XL |
1894 | if any_is_useful { |
1895 | // Collect all the unreachable patterns. | |
1896 | unreachable_branches.extend(unreachable_subpats); | |
1897 | return Useful(unreachable_branches); | |
1898 | } else { | |
1899 | return NotUseful; | |
1900 | } | |
60c5eb7d XL |
1901 | } |
1902 | ||
f9f354fc XL |
1903 | // FIXME(Nadrieril): Hack to work around type normalization issues (see #72476). |
1904 | let ty = matrix.heads().next().map(|r| r.ty).unwrap_or(v.head().ty); | |
1905 | let pcx = PatCtxt { ty, span: v.head().span }; | |
c30ab7b3 | 1906 | |
e74abb32 XL |
1907 | debug!("is_useful_expand_first_col: pcx={:#?}, expanding {:#?}", pcx, v.head()); |
1908 | ||
f9f354fc | 1909 | let ret = if let Some(constructor) = pat_constructor(cx.tcx, cx.param_env, v.head()) { |
60c5eb7d | 1910 | debug!("is_useful - expanding constructor: {:#?}", constructor); |
e74abb32 XL |
1911 | split_grouped_constructors( |
1912 | cx.tcx, | |
1913 | cx.param_env, | |
60c5eb7d XL |
1914 | pcx, |
1915 | vec![constructor], | |
e74abb32 | 1916 | matrix, |
e74abb32 XL |
1917 | pcx.span, |
1918 | Some(hir_id), | |
1919 | ) | |
1920 | .into_iter() | |
ba9703b0 XL |
1921 | .map(|c| { |
1922 | is_useful_specialized( | |
1923 | cx, | |
1924 | matrix, | |
1925 | v, | |
1926 | c, | |
1927 | pcx.ty, | |
1928 | witness_preference, | |
1929 | hir_id, | |
1930 | is_under_guard, | |
1931 | ) | |
1932 | }) | |
e74abb32 XL |
1933 | .find(|result| result.is_useful()) |
1934 | .unwrap_or(NotUseful) | |
c30ab7b3 SL |
1935 | } else { |
1936 | debug!("is_useful - expanding wildcard"); | |
32a655c1 | 1937 | |
e74abb32 | 1938 | let used_ctors: Vec<Constructor<'_>> = |
60c5eb7d | 1939 | matrix.heads().filter_map(|p| pat_constructor(cx.tcx, cx.param_env, p)).collect(); |
f9f354fc | 1940 | debug!("is_useful_used_ctors = {:#?}", used_ctors); |
b7449926 XL |
1941 | // `all_ctors` are all the constructors for the given type, which |
1942 | // should all be represented (or caught with the wild pattern `_`). | |
32a655c1 | 1943 | let all_ctors = all_constructors(cx, pcx); |
f9f354fc | 1944 | debug!("is_useful_all_ctors = {:#?}", all_ctors); |
32a655c1 SL |
1945 | |
1946 | // `missing_ctors` is the set of constructors from the same type as the | |
1947 | // first column of `matrix` that are matched only by wildcard patterns | |
1948 | // from the first column. | |
1949 | // | |
1950 | // Therefore, if there is some pattern that is unmatched by `matrix`, | |
1951 | // it will still be unmatched if the first constructor is replaced by | |
1952 | // any of the constructors in `missing_ctors` | |
b7449926 | 1953 | |
60c5eb7d XL |
1954 | // Missing constructors are those that are not matched by any non-wildcard patterns in the |
1955 | // current column. We only fully construct them on-demand, because they're rarely used and | |
1956 | // can be big. | |
1957 | let missing_ctors = MissingConstructors::new(all_ctors, used_ctors); | |
1958 | ||
f9f354fc | 1959 | debug!("is_useful_missing_ctors.empty()={:#?}", missing_ctors.is_empty(),); |
e74abb32 | 1960 | |
60c5eb7d | 1961 | if missing_ctors.is_empty() { |
e74abb32 | 1962 | let (all_ctors, _) = missing_ctors.into_inner(); |
60c5eb7d XL |
1963 | split_grouped_constructors(cx.tcx, cx.param_env, pcx, all_ctors, matrix, DUMMY_SP, None) |
1964 | .into_iter() | |
1965 | .map(|c| { | |
ba9703b0 XL |
1966 | is_useful_specialized( |
1967 | cx, | |
1968 | matrix, | |
1969 | v, | |
1970 | c, | |
1971 | pcx.ty, | |
1972 | witness_preference, | |
1973 | hir_id, | |
1974 | is_under_guard, | |
1975 | ) | |
60c5eb7d XL |
1976 | }) |
1977 | .find(|result| result.is_useful()) | |
1978 | .unwrap_or(NotUseful) | |
c30ab7b3 | 1979 | } else { |
e74abb32 XL |
1980 | let matrix = matrix.specialize_wildcard(); |
1981 | let v = v.to_tail(); | |
ba9703b0 XL |
1982 | let usefulness = |
1983 | is_useful(cx, &matrix, &v, witness_preference, hir_id, is_under_guard, false); | |
e74abb32 XL |
1984 | |
1985 | // In this case, there's at least one "free" | |
1986 | // constructor that is only matched against by | |
1987 | // wildcard patterns. | |
1988 | // | |
1989 | // There are 2 ways we can report a witness here. | |
1990 | // Commonly, we can report all the "free" | |
1991 | // constructors as witnesses, e.g., if we have: | |
1992 | // | |
1993 | // ``` | |
1994 | // enum Direction { N, S, E, W } | |
1995 | // let Direction::N = ...; | |
1996 | // ``` | |
1997 | // | |
1998 | // we can report 3 witnesses: `S`, `E`, and `W`. | |
1999 | // | |
60c5eb7d | 2000 | // However, there is a case where we don't want |
e74abb32 | 2001 | // to do this and instead report a single `_` witness: |
60c5eb7d | 2002 | // if the user didn't actually specify a constructor |
e74abb32 XL |
2003 | // in this arm, e.g., in |
2004 | // ``` | |
2005 | // let x: (Direction, Direction, bool) = ...; | |
2006 | // let (_, _, false) = x; | |
2007 | // ``` | |
2008 | // we don't want to show all 16 possible witnesses | |
2009 | // `(<direction-1>, <direction-2>, true)` - we are | |
2010 | // satisfied with `(_, _, true)`. In this case, | |
2011 | // `used_ctors` is empty. | |
60c5eb7d XL |
2012 | // The exception is: if we are at the top-level, for example in an empty match, we |
2013 | // sometimes prefer reporting the list of constructors instead of just `_`. | |
2014 | let report_ctors_rather_than_wildcard = is_top_level && !IntRange::is_integral(pcx.ty); | |
2015 | if missing_ctors.all_ctors_are_missing() && !report_ctors_rather_than_wildcard { | |
e74abb32 XL |
2016 | // All constructors are unused. Add a wild pattern |
2017 | // rather than each individual constructor. | |
2018 | usefulness.apply_wildcard(pcx.ty) | |
2019 | } else { | |
2020 | // Construct for each missing constructor a "wild" version of this | |
2021 | // constructor, that matches everything that can be built with | |
2022 | // it. For example, if `ctor` is a `Constructor::Variant` for | |
2023 | // `Option::Some`, we get the pattern `Some(_)`. | |
2024 | usefulness.apply_missing_ctors(cx, pcx.ty, &missing_ctors) | |
c30ab7b3 SL |
2025 | } |
2026 | } | |
f9f354fc XL |
2027 | }; |
2028 | debug!("is_useful::returns({:#?}, {:#?}) = {:?}", matrix, v, ret); | |
2029 | ret | |
c30ab7b3 SL |
2030 | } |
2031 | ||
0731742a | 2032 | /// A shorthand for the `U(S(c, P), S(c, q))` operation from the paper. I.e., `is_useful` applied |
b7449926 | 2033 | /// to the specialised version of both the pattern matrix `P` and the new pattern `q`. |
60c5eb7d XL |
2034 | fn is_useful_specialized<'p, 'tcx>( |
2035 | cx: &mut MatchCheckCtxt<'p, 'tcx>, | |
e74abb32 | 2036 | matrix: &Matrix<'p, 'tcx>, |
60c5eb7d | 2037 | v: &PatStack<'p, 'tcx>, |
8bb4bdeb | 2038 | ctor: Constructor<'tcx>, |
f9f354fc | 2039 | ty: Ty<'tcx>, |
e74abb32 XL |
2040 | witness_preference: WitnessPreference, |
2041 | hir_id: HirId, | |
ba9703b0 | 2042 | is_under_guard: bool, |
f035d41b | 2043 | ) -> Usefulness<'tcx> { |
f9f354fc | 2044 | debug!("is_useful_specialized({:#?}, {:#?}, {:?})", v, ctor, ty); |
e74abb32 | 2045 | |
f9f354fc XL |
2046 | // We cache the result of `Fields::wildcards` because it is used a lot. |
2047 | let ctor_wild_subpatterns = Fields::wildcards(cx, &ctor, ty); | |
2048 | let matrix = matrix.specialize_constructor(cx, &ctor, &ctor_wild_subpatterns); | |
2049 | v.specialize_constructor(cx, &ctor, &ctor_wild_subpatterns) | |
ba9703b0 | 2050 | .map(|v| is_useful(cx, &matrix, &v, witness_preference, hir_id, is_under_guard, false)) |
f9f354fc | 2051 | .map(|u| u.apply_constructor(cx, &ctor, ty, &ctor_wild_subpatterns)) |
e74abb32 | 2052 | .unwrap_or(NotUseful) |
c30ab7b3 SL |
2053 | } |
2054 | ||
60c5eb7d | 2055 | /// Determines the constructor that the given pattern can be specialized to. |
9fa01778 | 2056 | /// Returns `None` in case of a catch-all, which can't be specialized. |
60c5eb7d XL |
2057 | fn pat_constructor<'tcx>( |
2058 | tcx: TyCtxt<'tcx>, | |
2059 | param_env: ty::ParamEnv<'tcx>, | |
e74abb32 | 2060 | pat: &Pat<'tcx>, |
60c5eb7d | 2061 | ) -> Option<Constructor<'tcx>> { |
c30ab7b3 | 2062 | match *pat.kind { |
60c5eb7d | 2063 | PatKind::AscribeUserType { .. } => bug!(), // Handled by `expand_pattern` |
e74abb32 | 2064 | PatKind::Binding { .. } | PatKind::Wild => None, |
60c5eb7d | 2065 | PatKind::Leaf { .. } | PatKind::Deref { .. } => Some(Single), |
e74abb32 | 2066 | PatKind::Variant { adt_def, variant_index, .. } => { |
60c5eb7d | 2067 | Some(Variant(adt_def.variants[variant_index].def_id)) |
b7449926 | 2068 | } |
60c5eb7d XL |
2069 | PatKind::Constant { value } => { |
2070 | if let Some(int_range) = IntRange::from_const(tcx, param_env, value, pat.span) { | |
2071 | Some(IntRange(int_range)) | |
c30ab7b3 | 2072 | } else { |
60c5eb7d XL |
2073 | match (value.val, &value.ty.kind) { |
2074 | (_, ty::Array(_, n)) => { | |
2075 | let len = n.eval_usize(tcx, param_env); | |
2076 | Some(Slice(Slice { array_len: Some(len), kind: FixedLen(len) })) | |
2077 | } | |
2078 | (ty::ConstKind::Value(ConstValue::Slice { start, end, .. }), ty::Slice(_)) => { | |
2079 | let len = (end - start) as u64; | |
2080 | Some(Slice(Slice { array_len: None, kind: FixedLen(len) })) | |
2081 | } | |
2082 | // FIXME(oli-obk): implement `deref` for `ConstValue` | |
2083 | // (ty::ConstKind::Value(ConstValue::ByRef { .. }), ty::Slice(_)) => { ... } | |
2084 | _ => Some(ConstantValue(value)), | |
2085 | } | |
c30ab7b3 SL |
2086 | } |
2087 | } | |
60c5eb7d XL |
2088 | PatKind::Range(PatRange { lo, hi, end }) => { |
2089 | let ty = lo.ty; | |
2090 | if let Some(int_range) = IntRange::from_range( | |
2091 | tcx, | |
2092 | lo.eval_bits(tcx, param_env, lo.ty), | |
2093 | hi.eval_bits(tcx, param_env, hi.ty), | |
2094 | ty, | |
2095 | &end, | |
2096 | pat.span, | |
2097 | ) { | |
2098 | Some(IntRange(int_range)) | |
041b39d2 | 2099 | } else { |
60c5eb7d | 2100 | Some(FloatRange(lo, hi, end)) |
041b39d2 | 2101 | } |
32a655c1 | 2102 | } |
60c5eb7d XL |
2103 | PatKind::Array { ref prefix, ref slice, ref suffix } |
2104 | | PatKind::Slice { ref prefix, ref slice, ref suffix } => { | |
2105 | let array_len = match pat.ty.kind { | |
2106 | ty::Array(_, length) => Some(length.eval_usize(tcx, param_env)), | |
2107 | ty::Slice(_) => None, | |
2108 | _ => span_bug!(pat.span, "bad ty {:?} for slice pattern", pat.ty), | |
2109 | }; | |
2110 | let prefix = prefix.len() as u64; | |
2111 | let suffix = suffix.len() as u64; | |
2112 | let kind = | |
2113 | if slice.is_some() { VarLen(prefix, suffix) } else { FixedLen(prefix + suffix) }; | |
2114 | Some(Slice(Slice { array_len, kind })) | |
2115 | } | |
2116 | PatKind::Or { .. } => bug!("Or-pattern should have been expanded earlier on."), | |
32a655c1 SL |
2117 | } |
2118 | } | |
2119 | ||
0731742a XL |
2120 | // checks whether a constant is equal to a user-written slice pattern. Only supports byte slices, |
2121 | // meaning all other types will compare unequal and thus equal patterns often do not cause the | |
2122 | // second pattern to lint about unreachable match arms. | |
2123 | fn slice_pat_covered_by_const<'tcx>( | |
dc9dc135 | 2124 | tcx: TyCtxt<'tcx>, |
94b46f34 | 2125 | _span: Span, |
dc9dc135 | 2126 | const_val: &'tcx ty::Const<'tcx>, |
e74abb32 XL |
2127 | prefix: &[Pat<'tcx>], |
2128 | slice: &Option<Pat<'tcx>>, | |
2129 | suffix: &[Pat<'tcx>], | |
416331ca | 2130 | param_env: ty::ParamEnv<'tcx>, |
94b46f34 | 2131 | ) -> Result<bool, ErrorReported> { |
60c5eb7d XL |
2132 | let const_val_val = if let ty::ConstKind::Value(val) = const_val.val { |
2133 | val | |
2134 | } else { | |
2135 | bug!( | |
2136 | "slice_pat_covered_by_const: {:#?}, {:#?}, {:#?}, {:#?}", | |
2137 | const_val, | |
2138 | prefix, | |
2139 | slice, | |
2140 | suffix, | |
2141 | ) | |
2142 | }; | |
2143 | ||
2144 | let data: &[u8] = match (const_val_val, &const_val.ty.kind) { | |
dc9dc135 XL |
2145 | (ConstValue::ByRef { offset, alloc, .. }, ty::Array(t, n)) => { |
2146 | assert_eq!(*t, tcx.types.u8); | |
416331ca | 2147 | let n = n.eval_usize(tcx, param_env); |
dc9dc135 | 2148 | let ptr = Pointer::new(AllocId(0), offset); |
0731742a | 2149 | alloc.get_bytes(&tcx, ptr, Size::from_bytes(n)).unwrap() |
e74abb32 | 2150 | } |
dc9dc135 XL |
2151 | (ConstValue::Slice { data, start, end }, ty::Slice(t)) => { |
2152 | assert_eq!(*t, tcx.types.u8); | |
ba9703b0 XL |
2153 | let ptr = Pointer::new(AllocId(0), Size::from_bytes(start)); |
2154 | data.get_bytes(&tcx, ptr, Size::from_bytes(end - start)).unwrap() | |
e74abb32 | 2155 | } |
dc9dc135 XL |
2156 | // FIXME(oli-obk): create a way to extract fat pointers from ByRef |
2157 | (_, ty::Slice(_)) => return Ok(false), | |
0731742a XL |
2158 | _ => bug!( |
2159 | "slice_pat_covered_by_const: {:#?}, {:#?}, {:#?}, {:#?}", | |
e74abb32 XL |
2160 | const_val, |
2161 | prefix, | |
2162 | slice, | |
2163 | suffix, | |
0731742a | 2164 | ), |
c30ab7b3 SL |
2165 | }; |
2166 | ||
2167 | let pat_len = prefix.len() + suffix.len(); | |
2168 | if data.len() < pat_len || (slice.is_none() && data.len() > pat_len) { | |
2169 | return Ok(false); | |
2170 | } | |
2171 | ||
e74abb32 XL |
2172 | for (ch, pat) in data[..prefix.len()] |
2173 | .iter() | |
2174 | .zip(prefix) | |
2175 | .chain(data[data.len() - suffix.len()..].iter().zip(suffix)) | |
c30ab7b3 | 2176 | { |
ba9703b0 XL |
2177 | if let box PatKind::Constant { value } = pat.kind { |
2178 | let b = value.eval_bits(tcx, param_env, pat.ty); | |
2179 | assert_eq!(b as u8 as u128, b); | |
2180 | if b as u8 != *ch { | |
2181 | return Ok(false); | |
94b46f34 | 2182 | } |
c30ab7b3 SL |
2183 | } |
2184 | } | |
2185 | ||
2186 | Ok(true) | |
2187 | } | |
2188 | ||
b7449926 XL |
2189 | /// For exhaustive integer matching, some constructors are grouped within other constructors |
2190 | /// (namely integer typed values are grouped within ranges). However, when specialising these | |
2191 | /// constructors, we want to be specialising for the underlying constructors (the integers), not | |
2192 | /// the groups (the ranges). Thus we need to split the groups up. Splitting them up naïvely would | |
2193 | /// mean creating a separate constructor for every single value in the range, which is clearly | |
2194 | /// impractical. However, observe that for some ranges of integers, the specialisation will be | |
0731742a | 2195 | /// identical across all values in that range (i.e., there are equivalence classes of ranges of |
a1dfa0c6 | 2196 | /// constructors based on their `is_useful_specialized` outcome). These classes are grouped by |
b7449926 XL |
2197 | /// the patterns that apply to them (in the matrix `P`). We can split the range whenever the |
2198 | /// patterns that apply to that range (specifically: the patterns that *intersect* with that range) | |
2199 | /// change. | |
2200 | /// Our solution, therefore, is to split the range constructor into subranges at every single point | |
2201 | /// the group of intersecting patterns changes (using the method described below). | |
2202 | /// And voilà! We're testing precisely those ranges that we need to, without any exhaustive matching | |
2203 | /// on actual integers. The nice thing about this is that the number of subranges is linear in the | |
0731742a | 2204 | /// number of rows in the matrix (i.e., the number of cases in the `match` statement), so we don't |
b7449926 XL |
2205 | /// need to be worried about matching over gargantuan ranges. |
2206 | /// | |
2207 | /// Essentially, given the first column of a matrix representing ranges, looking like the following: | |
2208 | /// | |
2209 | /// |------| |----------| |-------| || | |
2210 | /// |-------| |-------| |----| || | |
2211 | /// |---------| | |
2212 | /// | |
2213 | /// We split the ranges up into equivalence classes so the ranges are no longer overlapping: | |
2214 | /// | |
2215 | /// |--|--|||-||||--||---|||-------| |-|||| || | |
2216 | /// | |
2217 | /// The logic for determining how to split the ranges is fairly straightforward: we calculate | |
2218 | /// boundaries for each interval range, sort them, then create constructors for each new interval | |
2219 | /// between every pair of boundary points. (This essentially sums up to performing the intuitive | |
2220 | /// merging operation depicted above.) | |
e74abb32 XL |
2221 | /// |
2222 | /// `hir_id` is `None` when we're evaluating the wildcard pattern, do not lint for overlapping in | |
2223 | /// ranges that case. | |
60c5eb7d XL |
2224 | /// |
2225 | /// This also splits variable-length slices into fixed-length slices. | |
dc9dc135 XL |
2226 | fn split_grouped_constructors<'p, 'tcx>( |
2227 | tcx: TyCtxt<'tcx>, | |
416331ca | 2228 | param_env: ty::ParamEnv<'tcx>, |
60c5eb7d | 2229 | pcx: PatCtxt<'tcx>, |
b7449926 | 2230 | ctors: Vec<Constructor<'tcx>>, |
e74abb32 | 2231 | matrix: &Matrix<'p, 'tcx>, |
e74abb32 XL |
2232 | span: Span, |
2233 | hir_id: Option<HirId>, | |
b7449926 | 2234 | ) -> Vec<Constructor<'tcx>> { |
60c5eb7d | 2235 | let ty = pcx.ty; |
b7449926 | 2236 | let mut split_ctors = Vec::with_capacity(ctors.len()); |
60c5eb7d | 2237 | debug!("split_grouped_constructors({:#?}, {:#?})", matrix, ctors); |
b7449926 XL |
2238 | |
2239 | for ctor in ctors.into_iter() { | |
2240 | match ctor { | |
60c5eb7d XL |
2241 | IntRange(ctor_range) if ctor_range.treat_exhaustively(tcx) => { |
2242 | // Fast-track if the range is trivial. In particular, don't do the overlapping | |
2243 | // ranges check. | |
2244 | if ctor_range.is_singleton() { | |
2245 | split_ctors.push(IntRange(ctor_range)); | |
2246 | continue; | |
2247 | } | |
b7449926 XL |
2248 | |
2249 | /// Represents a border between 2 integers. Because the intervals spanning borders | |
2250 | /// must be able to cover every integer, we need to be able to represent | |
2251 | /// 2^128 + 1 such borders. | |
e74abb32 | 2252 | #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Debug)] |
b7449926 XL |
2253 | enum Border { |
2254 | JustBefore(u128), | |
2255 | AfterMax, | |
2256 | } | |
2257 | ||
2258 | // A function for extracting the borders of an integer interval. | |
2259 | fn range_borders(r: IntRange<'_>) -> impl Iterator<Item = Border> { | |
2260 | let (lo, hi) = r.range.into_inner(); | |
2261 | let from = Border::JustBefore(lo); | |
2262 | let to = match hi.checked_add(1) { | |
2263 | Some(m) => Border::JustBefore(m), | |
2264 | None => Border::AfterMax, | |
2265 | }; | |
2266 | vec![from, to].into_iter() | |
2267 | } | |
2268 | ||
e74abb32 XL |
2269 | // Collect the span and range of all the intersecting ranges to lint on likely |
2270 | // incorrect range patterns. (#63987) | |
2271 | let mut overlaps = vec![]; | |
b7449926 XL |
2272 | // `borders` is the set of borders between equivalence classes: each equivalence |
2273 | // class lies between 2 borders. | |
e74abb32 XL |
2274 | let row_borders = matrix |
2275 | .0 | |
2276 | .iter() | |
2277 | .flat_map(|row| { | |
2278 | IntRange::from_pat(tcx, param_env, row.head()).map(|r| (r, row.len())) | |
2279 | }) | |
2280 | .flat_map(|(range, row_len)| { | |
60c5eb7d | 2281 | let intersection = ctor_range.intersection(tcx, &range); |
e74abb32 XL |
2282 | let should_lint = ctor_range.suspicious_intersection(&range); |
2283 | if let (Some(range), 1, true) = (&intersection, row_len, should_lint) { | |
2284 | // FIXME: for now, only check for overlapping ranges on simple range | |
2285 | // patterns. Otherwise with the current logic the following is detected | |
2286 | // as overlapping: | |
2287 | // match (10u8, true) { | |
2288 | // (0 ..= 125, false) => {} | |
2289 | // (126 ..= 255, false) => {} | |
2290 | // (0 ..= 255, true) => {} | |
2291 | // } | |
2292 | overlaps.push(range.clone()); | |
2293 | } | |
2294 | intersection | |
2295 | }) | |
ba9703b0 | 2296 | .flat_map(range_borders); |
b7449926 XL |
2297 | let ctor_borders = range_borders(ctor_range.clone()); |
2298 | let mut borders: Vec<_> = row_borders.chain(ctor_borders).collect(); | |
2299 | borders.sort_unstable(); | |
2300 | ||
e74abb32 XL |
2301 | lint_overlapping_patterns(tcx, hir_id, ctor_range, ty, overlaps); |
2302 | ||
2303 | // We're going to iterate through every adjacent pair of borders, making sure that | |
2304 | // each represents an interval of nonnegative length, and convert each such | |
2305 | // interval into a constructor. | |
60c5eb7d XL |
2306 | split_ctors.extend( |
2307 | borders | |
2308 | .windows(2) | |
2309 | .filter_map(|window| match (window[0], window[1]) { | |
2310 | (Border::JustBefore(n), Border::JustBefore(m)) => { | |
2311 | if n < m { | |
2312 | Some(IntRange { range: n..=(m - 1), ty, span }) | |
2313 | } else { | |
2314 | None | |
2315 | } | |
b7449926 | 2316 | } |
60c5eb7d XL |
2317 | (Border::JustBefore(n), Border::AfterMax) => { |
2318 | Some(IntRange { range: n..=u128::MAX, ty, span }) | |
2319 | } | |
2320 | (Border::AfterMax, _) => None, | |
2321 | }) | |
2322 | .map(IntRange), | |
2323 | ); | |
2324 | } | |
2325 | Slice(Slice { array_len, kind: VarLen(self_prefix, self_suffix) }) => { | |
2326 | // The exhaustiveness-checking paper does not include any details on | |
2327 | // checking variable-length slice patterns. However, they are matched | |
2328 | // by an infinite collection of fixed-length array patterns. | |
2329 | // | |
2330 | // Checking the infinite set directly would take an infinite amount | |
2331 | // of time. However, it turns out that for each finite set of | |
2332 | // patterns `P`, all sufficiently large array lengths are equivalent: | |
2333 | // | |
2334 | // Each slice `s` with a "sufficiently-large" length `l ≥ L` that applies | |
2335 | // to exactly the subset `Pₜ` of `P` can be transformed to a slice | |
2336 | // `sₘ` for each sufficiently-large length `m` that applies to exactly | |
2337 | // the same subset of `P`. | |
2338 | // | |
2339 | // Because of that, each witness for reachability-checking from one | |
2340 | // of the sufficiently-large lengths can be transformed to an | |
2341 | // equally-valid witness from any other length, so we only have | |
2342 | // to check slice lengths from the "minimal sufficiently-large length" | |
2343 | // and below. | |
2344 | // | |
2345 | // Note that the fact that there is a *single* `sₘ` for each `m` | |
2346 | // not depending on the specific pattern in `P` is important: if | |
2347 | // you look at the pair of patterns | |
2348 | // `[true, ..]` | |
2349 | // `[.., false]` | |
2350 | // Then any slice of length ≥1 that matches one of these two | |
2351 | // patterns can be trivially turned to a slice of any | |
2352 | // other length ≥1 that matches them and vice-versa - for | |
2353 | // but the slice from length 2 `[false, true]` that matches neither | |
2354 | // of these patterns can't be turned to a slice from length 1 that | |
2355 | // matches neither of these patterns, so we have to consider | |
2356 | // slices from length 2 there. | |
2357 | // | |
2358 | // Now, to see that that length exists and find it, observe that slice | |
2359 | // patterns are either "fixed-length" patterns (`[_, _, _]`) or | |
2360 | // "variable-length" patterns (`[_, .., _]`). | |
2361 | // | |
2362 | // For fixed-length patterns, all slices with lengths *longer* than | |
2363 | // the pattern's length have the same outcome (of not matching), so | |
2364 | // as long as `L` is greater than the pattern's length we can pick | |
2365 | // any `sₘ` from that length and get the same result. | |
2366 | // | |
2367 | // For variable-length patterns, the situation is more complicated, | |
2368 | // because as seen above the precise value of `sₘ` matters. | |
2369 | // | |
2370 | // However, for each variable-length pattern `p` with a prefix of length | |
2371 | // `plₚ` and suffix of length `slₚ`, only the first `plₚ` and the last | |
2372 | // `slₚ` elements are examined. | |
2373 | // | |
2374 | // Therefore, as long as `L` is positive (to avoid concerns about empty | |
2375 | // types), all elements after the maximum prefix length and before | |
2376 | // the maximum suffix length are not examined by any variable-length | |
2377 | // pattern, and therefore can be added/removed without affecting | |
2378 | // them - creating equivalent patterns from any sufficiently-large | |
2379 | // length. | |
2380 | // | |
2381 | // Of course, if fixed-length patterns exist, we must be sure | |
2382 | // that our length is large enough to miss them all, so | |
2383 | // we can pick `L = max(max(FIXED_LEN)+1, max(PREFIX_LEN) + max(SUFFIX_LEN))` | |
2384 | // | |
2385 | // for example, with the above pair of patterns, all elements | |
2386 | // but the first and last can be added/removed, so any | |
2387 | // witness of length ≥2 (say, `[false, false, true]`) can be | |
2388 | // turned to a witness from any other length ≥2. | |
2389 | ||
2390 | let mut max_prefix_len = self_prefix; | |
2391 | let mut max_suffix_len = self_suffix; | |
2392 | let mut max_fixed_len = 0; | |
2393 | ||
2394 | let head_ctors = | |
2395 | matrix.heads().filter_map(|pat| pat_constructor(tcx, param_env, pat)); | |
2396 | for ctor in head_ctors { | |
ba9703b0 XL |
2397 | if let Slice(slice) = ctor { |
2398 | match slice.pattern_kind() { | |
60c5eb7d XL |
2399 | FixedLen(len) => { |
2400 | max_fixed_len = cmp::max(max_fixed_len, len); | |
2401 | } | |
2402 | VarLen(prefix, suffix) => { | |
2403 | max_prefix_len = cmp::max(max_prefix_len, prefix); | |
2404 | max_suffix_len = cmp::max(max_suffix_len, suffix); | |
2405 | } | |
ba9703b0 | 2406 | } |
60c5eb7d XL |
2407 | } |
2408 | } | |
2409 | ||
2410 | // For diagnostics, we keep the prefix and suffix lengths separate, so in the case | |
2411 | // where `max_fixed_len + 1` is the largest, we adapt `max_prefix_len` accordingly, | |
2412 | // so that `L = max_prefix_len + max_suffix_len`. | |
2413 | if max_fixed_len + 1 >= max_prefix_len + max_suffix_len { | |
2414 | // The subtraction can't overflow thanks to the above check. | |
2415 | // The new `max_prefix_len` is also guaranteed to be larger than its previous | |
2416 | // value. | |
2417 | max_prefix_len = max_fixed_len + 1 - max_suffix_len; | |
2418 | } | |
2419 | ||
2420 | match array_len { | |
2421 | Some(len) => { | |
2422 | let kind = if max_prefix_len + max_suffix_len < len { | |
2423 | VarLen(max_prefix_len, max_suffix_len) | |
2424 | } else { | |
2425 | FixedLen(len) | |
2426 | }; | |
2427 | split_ctors.push(Slice(Slice { array_len, kind })); | |
2428 | } | |
2429 | None => { | |
2430 | // `ctor` originally covered the range `(self_prefix + | |
2431 | // self_suffix..infinity)`. We now split it into two: lengths smaller than | |
2432 | // `max_prefix_len + max_suffix_len` are treated independently as | |
2433 | // fixed-lengths slices, and lengths above are captured by a final VarLen | |
2434 | // constructor. | |
2435 | split_ctors.extend( | |
2436 | (self_prefix + self_suffix..max_prefix_len + max_suffix_len) | |
2437 | .map(|len| Slice(Slice { array_len, kind: FixedLen(len) })), | |
2438 | ); | |
2439 | split_ctors.push(Slice(Slice { | |
2440 | array_len, | |
2441 | kind: VarLen(max_prefix_len, max_suffix_len), | |
2442 | })); | |
2443 | } | |
b7449926 XL |
2444 | } |
2445 | } | |
2446 | // Any other constructor can be used unchanged. | |
2447 | _ => split_ctors.push(ctor), | |
2448 | } | |
2449 | } | |
2450 | ||
60c5eb7d | 2451 | debug!("split_grouped_constructors(..)={:#?}", split_ctors); |
b7449926 XL |
2452 | split_ctors |
2453 | } | |
2454 | ||
dfeec247 | 2455 | fn lint_overlapping_patterns<'tcx>( |
dc9dc135 | 2456 | tcx: TyCtxt<'tcx>, |
e74abb32 XL |
2457 | hir_id: Option<HirId>, |
2458 | ctor_range: IntRange<'tcx>, | |
2459 | ty: Ty<'tcx>, | |
2460 | overlaps: Vec<IntRange<'tcx>>, | |
2461 | ) { | |
2462 | if let (true, Some(hir_id)) = (!overlaps.is_empty(), hir_id) { | |
74b04a01 | 2463 | tcx.struct_span_lint_hir( |
e74abb32 XL |
2464 | lint::builtin::OVERLAPPING_PATTERNS, |
2465 | hir_id, | |
2466 | ctor_range.span, | |
74b04a01 XL |
2467 | |lint| { |
2468 | let mut err = lint.build("multiple patterns covering the same range"); | |
2469 | err.span_label(ctor_range.span, "overlapping patterns"); | |
2470 | for int_range in overlaps { | |
2471 | // Use the real type for user display of the ranges: | |
2472 | err.span_label( | |
2473 | int_range.span, | |
2474 | &format!( | |
2475 | "this range overlaps on `{}`", | |
2476 | IntRange { range: int_range.range, ty, span: DUMMY_SP }.to_pat(tcx), | |
2477 | ), | |
2478 | ); | |
2479 | } | |
2480 | err.emit(); | |
2481 | }, | |
e74abb32 | 2482 | ); |
b7449926 XL |
2483 | } |
2484 | } | |
2485 | ||
dc9dc135 XL |
2486 | fn constructor_covered_by_range<'tcx>( |
2487 | tcx: TyCtxt<'tcx>, | |
416331ca | 2488 | param_env: ty::ParamEnv<'tcx>, |
94b46f34 | 2489 | ctor: &Constructor<'tcx>, |
e74abb32 | 2490 | pat: &Pat<'tcx>, |
60c5eb7d XL |
2491 | ) -> Option<()> { |
2492 | if let Single = ctor { | |
2493 | return Some(()); | |
2494 | } | |
2495 | ||
2496 | let (pat_from, pat_to, pat_end, ty) = match *pat.kind { | |
2497 | PatKind::Constant { value } => (value, value, RangeEnd::Included, value.ty), | |
2498 | PatKind::Range(PatRange { lo, hi, end }) => (lo, hi, end, lo.ty), | |
b7449926 XL |
2499 | _ => bug!("`constructor_covered_by_range` called with {:?}", pat), |
2500 | }; | |
60c5eb7d XL |
2501 | let (ctor_from, ctor_to, ctor_end) = match *ctor { |
2502 | ConstantValue(value) => (value, value, RangeEnd::Included), | |
2503 | FloatRange(from, to, ctor_end) => (from, to, ctor_end), | |
2504 | _ => bug!("`constructor_covered_by_range` called with {:?}", ctor), | |
e74abb32 | 2505 | }; |
60c5eb7d XL |
2506 | trace!("constructor_covered_by_range {:#?}, {:#?}, {:#?}, {}", ctor, pat_from, pat_to, ty); |
2507 | ||
2508 | let to = compare_const_vals(tcx, ctor_to, pat_to, param_env, ty)?; | |
2509 | let from = compare_const_vals(tcx, ctor_from, pat_from, param_env, ty)?; | |
2510 | let intersects = (from == Ordering::Greater || from == Ordering::Equal) | |
2511 | && (to == Ordering::Less || (pat_end == ctor_end && to == Ordering::Equal)); | |
2512 | if intersects { Some(()) } else { None } | |
c30ab7b3 SL |
2513 | } |
2514 | ||
e74abb32 | 2515 | /// This is the main specialization step. It expands the pattern |
c30ab7b3 SL |
2516 | /// into `arity` patterns based on the constructor. For most patterns, the step is trivial, |
2517 | /// for instance tuple patterns are flattened and box patterns expand into their inner pattern. | |
e74abb32 | 2518 | /// Returns `None` if the pattern does not have the given constructor. |
c30ab7b3 | 2519 | /// |
e74abb32 | 2520 | /// OTOH, slice patterns with a subslice pattern (tail @ ..) can be expanded into multiple |
c30ab7b3 SL |
2521 | /// different patterns. |
2522 | /// Structure patterns with a partial wild pattern (Foo { a: 42, .. }) have their missing | |
2523 | /// fields filled with wild patterns. | |
f9f354fc XL |
2524 | /// |
2525 | /// This is roughly the inverse of `Constructor::apply`. | |
60c5eb7d XL |
2526 | fn specialize_one_pattern<'p, 'tcx>( |
2527 | cx: &mut MatchCheckCtxt<'p, 'tcx>, | |
2528 | pat: &'p Pat<'tcx>, | |
0531ce1d | 2529 | constructor: &Constructor<'tcx>, |
f9f354fc XL |
2530 | ctor_wild_subpatterns: &Fields<'p, 'tcx>, |
2531 | ) -> Option<Fields<'p, 'tcx>> { | |
60c5eb7d XL |
2532 | if let NonExhaustive = constructor { |
2533 | // Only a wildcard pattern can match the special extra constructor | |
f9f354fc XL |
2534 | if !pat.is_wildcard() { |
2535 | return None; | |
2536 | } | |
2537 | return Some(Fields::empty()); | |
60c5eb7d XL |
2538 | } |
2539 | ||
e74abb32 | 2540 | let result = match *pat.kind { |
60c5eb7d | 2541 | PatKind::AscribeUserType { .. } => bug!(), // Handled by `expand_pattern` |
e74abb32 | 2542 | |
f9f354fc | 2543 | PatKind::Binding { .. } | PatKind::Wild => Some(ctor_wild_subpatterns.clone()), |
b7449926 | 2544 | |
e74abb32 | 2545 | PatKind::Variant { adt_def, variant_index, ref subpatterns, .. } => { |
74b04a01 | 2546 | let variant = &adt_def.variants[variant_index]; |
f9f354fc XL |
2547 | if constructor != &Variant(variant.def_id) { |
2548 | return None; | |
2549 | } | |
2550 | Some(ctor_wild_subpatterns.replace_with_fieldpats(subpatterns)) | |
32a655c1 | 2551 | } |
b7449926 | 2552 | |
e74abb32 | 2553 | PatKind::Leaf { ref subpatterns } => { |
f9f354fc | 2554 | Some(ctor_wild_subpatterns.replace_with_fieldpats(subpatterns)) |
32a655c1 | 2555 | } |
c30ab7b3 | 2556 | |
f9f354fc | 2557 | PatKind::Deref { ref subpattern } => Some(Fields::from_single_pattern(subpattern)), |
e74abb32 XL |
2558 | |
2559 | PatKind::Constant { value } if constructor.is_slice() => { | |
2560 | // We extract an `Option` for the pointer because slices of zero | |
2561 | // elements don't necessarily point to memory, they are usually | |
2562 | // just integers. The only time they should be pointing to memory | |
2563 | // is when they are subslices of nonzero slices. | |
2564 | let (alloc, offset, n, ty) = match value.ty.kind { | |
dfeec247 XL |
2565 | ty::Array(t, n) => { |
2566 | let n = n.eval_usize(cx.tcx, cx.param_env); | |
2567 | // Shortcut for `n == 0` where no matter what `alloc` and `offset` we produce, | |
2568 | // the result would be exactly what we early return here. | |
2569 | if n == 0 { | |
f9f354fc | 2570 | if ctor_wild_subpatterns.len() as u64 != n { |
dfeec247 XL |
2571 | return None; |
2572 | } | |
f9f354fc | 2573 | return Some(Fields::empty()); |
e74abb32 | 2574 | } |
dfeec247 XL |
2575 | match value.val { |
2576 | ty::ConstKind::Value(ConstValue::ByRef { offset, alloc, .. }) => { | |
2577 | (Cow::Borrowed(alloc), offset, n, t) | |
2578 | } | |
2579 | _ => span_bug!(pat.span, "array pattern is {:?}", value,), | |
2580 | } | |
2581 | } | |
e74abb32 XL |
2582 | ty::Slice(t) => { |
2583 | match value.val { | |
60c5eb7d | 2584 | ty::ConstKind::Value(ConstValue::Slice { data, start, end }) => { |
ba9703b0 | 2585 | let offset = Size::from_bytes(start); |
dfeec247 XL |
2586 | let n = (end - start) as u64; |
2587 | (Cow::Borrowed(data), offset, n, t) | |
e74abb32 | 2588 | } |
60c5eb7d | 2589 | ty::ConstKind::Value(ConstValue::ByRef { .. }) => { |
e74abb32 XL |
2590 | // FIXME(oli-obk): implement `deref` for `ConstValue` |
2591 | return None; | |
2592 | } | |
0731742a XL |
2593 | _ => span_bug!( |
2594 | pat.span, | |
e74abb32 | 2595 | "slice pattern constant must be scalar pair but is {:?}", |
0731742a | 2596 | value, |
0731742a | 2597 | ), |
94b46f34 | 2598 | } |
b7449926 | 2599 | } |
e74abb32 XL |
2600 | _ => span_bug!( |
2601 | pat.span, | |
2602 | "unexpected const-val {:?} with ctor {:?}", | |
2603 | value, | |
2604 | constructor, | |
2605 | ), | |
2606 | }; | |
f9f354fc XL |
2607 | if ctor_wild_subpatterns.len() as u64 != n { |
2608 | return None; | |
c30ab7b3 | 2609 | } |
f9f354fc XL |
2610 | |
2611 | // Convert a constant slice/array pattern to a list of patterns. | |
2612 | let layout = cx.tcx.layout_of(cx.param_env.and(ty)).ok()?; | |
2613 | let ptr = Pointer::new(AllocId(0), offset); | |
2614 | let pats = cx.pattern_arena.alloc_from_iter((0..n).filter_map(|i| { | |
2615 | let ptr = ptr.offset(layout.size * i, &cx.tcx).ok()?; | |
2616 | let scalar = alloc.read_scalar(&cx.tcx, ptr, layout.size).ok()?; | |
3dfed10e | 2617 | let scalar = scalar.check_init().ok()?; |
f9f354fc XL |
2618 | let value = ty::Const::from_scalar(cx.tcx, scalar, ty); |
2619 | let pattern = Pat { ty, span: pat.span, kind: box PatKind::Constant { value } }; | |
2620 | Some(pattern) | |
2621 | })); | |
2622 | // Ensure none of the dereferences failed. | |
2623 | if pats.len() as u64 != n { | |
2624 | return None; | |
2625 | } | |
2626 | Some(Fields::from_slice_unfiltered(pats)) | |
c30ab7b3 SL |
2627 | } |
2628 | ||
e74abb32 | 2629 | PatKind::Constant { .. } | PatKind::Range { .. } => { |
b7449926 | 2630 | // If the constructor is a: |
e74abb32 XL |
2631 | // - Single value: add a row if the pattern contains the constructor. |
2632 | // - Range: add a row if the constructor intersects the pattern. | |
60c5eb7d | 2633 | if let IntRange(ctor) = constructor { |
f9f354fc XL |
2634 | let pat = IntRange::from_pat(cx.tcx, cx.param_env, pat)?; |
2635 | ctor.intersection(cx.tcx, &pat)?; | |
2636 | // Constructor splitting should ensure that all intersections we encounter | |
2637 | // are actually inclusions. | |
2638 | assert!(ctor.is_subrange(&pat)); | |
e74abb32 XL |
2639 | } else { |
2640 | // Fallback for non-ranges and ranges that involve | |
2641 | // floating-point numbers, which are not conveniently handled | |
2642 | // by `IntRange`. For these cases, the constructor may not be a | |
2643 | // range so intersection actually devolves into being covered | |
2644 | // by the pattern. | |
f9f354fc | 2645 | constructor_covered_by_range(cx.tcx, cx.param_env, constructor, pat)?; |
e74abb32 | 2646 | } |
f9f354fc | 2647 | Some(Fields::empty()) |
c30ab7b3 SL |
2648 | } |
2649 | ||
e74abb32 XL |
2650 | PatKind::Array { ref prefix, ref slice, ref suffix } |
2651 | | PatKind::Slice { ref prefix, ref slice, ref suffix } => match *constructor { | |
60c5eb7d | 2652 | Slice(_) => { |
f9f354fc | 2653 | // Number of subpatterns for this pattern |
e74abb32 | 2654 | let pat_len = prefix.len() + suffix.len(); |
f9f354fc XL |
2655 | // Number of subpatterns for this constructor |
2656 | let arity = ctor_wild_subpatterns.len(); | |
2657 | ||
2658 | if (slice.is_none() && arity != pat_len) || pat_len > arity { | |
2659 | return None; | |
c30ab7b3 | 2660 | } |
f9f354fc XL |
2661 | |
2662 | // Replace the prefix and the suffix with the given patterns, leaving wildcards in | |
2663 | // the middle if there was a subslice pattern `..`. | |
2664 | let prefix = prefix.iter().enumerate(); | |
2665 | let suffix = suffix.iter().enumerate().map(|(i, p)| (arity - suffix.len() + i, p)); | |
2666 | Some(ctor_wild_subpatterns.replace_fields_indexed(prefix.chain(suffix))) | |
e74abb32 | 2667 | } |
60c5eb7d | 2668 | ConstantValue(cv) => { |
e74abb32 XL |
2669 | match slice_pat_covered_by_const( |
2670 | cx.tcx, | |
2671 | pat.span, | |
2672 | cv, | |
2673 | prefix, | |
2674 | slice, | |
2675 | suffix, | |
2676 | cx.param_env, | |
2677 | ) { | |
f9f354fc | 2678 | Ok(true) => Some(Fields::empty()), |
e74abb32 XL |
2679 | Ok(false) => None, |
2680 | Err(ErrorReported) => None, | |
c30ab7b3 | 2681 | } |
c30ab7b3 | 2682 | } |
e74abb32 XL |
2683 | _ => span_bug!(pat.span, "unexpected ctor {:?} for slice pat", constructor), |
2684 | }, | |
e1599b0c | 2685 | |
60c5eb7d | 2686 | PatKind::Or { .. } => bug!("Or-pattern should have been expanded earlier on."), |
c30ab7b3 | 2687 | }; |
f9f354fc XL |
2688 | debug!( |
2689 | "specialize({:#?}, {:#?}, {:#?}) = {:#?}", | |
2690 | pat, constructor, ctor_wild_subpatterns, result | |
2691 | ); | |
c30ab7b3 | 2692 | |
e74abb32 | 2693 | result |
c30ab7b3 | 2694 | } |