1 /// Note: most tests relevant to this file can be found (at the time of writing)
2 /// in src/tests/ui/pattern/usefulness.
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
7 /// (a) the patterns cover every possible constructor for the type [exhaustiveness]
8 /// (b) each pattern is necessary [usefulness]
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).
16 /// The core of the algorithm revolves about a "usefulness" check. In particular, we
17 /// are trying to compute a predicate `U(P, p)` where `P` is a list of patterns (we refer to this as
18 /// a matrix). `U(P, p)` represents whether, given an existing list of patterns
19 /// `P_1 ..= P_m`, adding a new pattern `p` will be "useful" (that is, cover previously-
20 /// uncovered values of the type).
22 /// If we have this predicate, then we can easily compute both exhaustiveness of an
23 /// entire set of patterns and the individual usefulness of each one.
24 /// (a) the set of patterns is exhaustive iff `U(P, _)` is false (i.e., adding a wildcard
25 /// match doesn't increase the number of values we're matching)
26 /// (b) a pattern `P_i` is not useful if `U(P[0..=(i-1), P_i)` is false (i.e., adding a
27 /// pattern to those that have come before it doesn't increase the number of values
30 /// During the course of the algorithm, the rows of the matrix won't just be individual patterns,
31 /// but rather partially-deconstructed patterns in the form of a list of patterns. The paper
32 /// calls those pattern-vectors, and we will call them pattern-stacks. The same holds for the
35 /// For example, say we have the following:
37 /// // x: (Option<bool>, Result<()>)
39 /// (Some(true), _) => {}
40 /// (None, Err(())) => {}
41 /// (None, Err(_)) => {}
44 /// Here, the matrix `P` starts as:
46 /// [(Some(true), _)],
47 /// [(None, Err(()))],
50 /// We can tell it's not exhaustive, because `U(P, _)` is true (we're not covering
51 /// `[(Some(false), _)]`, for instance). In addition, row 3 is not useful, because
52 /// all the values it covers are already covered by row 2.
54 /// A list of patterns can be thought of as a stack, because we are mainly interested in the top of
55 /// the stack at any given point, and we can pop or apply constructors to get new pattern-stacks.
56 /// To match the paper, the top of the stack is at the beginning / on the left.
58 /// There are two important operations on pattern-stacks necessary to understand the algorithm:
59 /// 1. We can pop a given constructor off the top of a stack. This operation is called
60 /// `specialize`, and is denoted `S(c, p)` where `c` is a constructor (like `Some` or
61 /// `None`) and `p` a pattern-stack.
62 /// If the pattern on top of the stack can cover `c`, this removes the constructor and
63 /// pushes its arguments onto the stack. It also expands OR-patterns into distinct patterns.
64 /// Otherwise the pattern-stack is discarded.
65 /// This essentially filters those pattern-stacks whose top covers the constructor `c` and
66 /// discards the others.
68 /// For example, the first pattern above initially gives a stack `[(Some(true), _)]`. If we
69 /// pop the tuple constructor, we are left with `[Some(true), _]`, and if we then pop the
70 /// `Some` constructor we get `[true, _]`. If we had popped `None` instead, we would get
73 /// This returns zero or more new pattern-stacks, as follows. We look at the pattern `p_1`
74 /// on top of the stack, and we have four cases:
75 /// 1.1. `p_1 = c(r_1, .., r_a)`, i.e. the top of the stack has constructor `c`. We
76 /// push onto the stack the arguments of this constructor, and return the result:
77 /// r_1, .., r_a, p_2, .., p_n
78 /// 1.2. `p_1 = c'(r_1, .., r_a')` where `c ≠ c'`. We discard the current stack and
80 /// 1.3. `p_1 = _`. We push onto the stack as many wildcards as the constructor `c` has
81 /// arguments (its arity), and return the resulting stack:
82 /// _, .., _, p_2, .., p_n
83 /// 1.4. `p_1 = r_1 | r_2`. We expand the OR-pattern and then recurse on each resulting
85 /// S(c, (r_1, p_2, .., p_n))
86 /// S(c, (r_2, p_2, .., p_n))
88 /// 2. We can pop a wildcard off the top of the stack. This is called `D(p)`, where `p` is
90 /// This is used when we know there are missing constructor cases, but there might be
91 /// existing wildcard patterns, so to check the usefulness of the matrix, we have to check
92 /// all its *other* components.
94 /// It is computed as follows. We look at the pattern `p_1` on top of the stack,
95 /// and we have three cases:
96 /// 1.1. `p_1 = c(r_1, .., r_a)`. We discard the current stack and return nothing.
97 /// 1.2. `p_1 = _`. We return the rest of the stack:
99 /// 1.3. `p_1 = r_1 | r_2`. We expand the OR-pattern and then recurse on each resulting
101 /// D((r_1, p_2, .., p_n))
102 /// D((r_2, p_2, .., p_n))
104 /// Note that the OR-patterns are not always used directly in Rust, but are used to derive the
105 /// exhaustive integer matching rules, so they're written here for posterity.
107 /// Both those operations extend straightforwardly to a list or pattern-stacks, i.e. a matrix, by
108 /// working row-by-row. Popping a constructor ends up keeping only the matrix rows that start with
109 /// the given constructor, and popping a wildcard keeps those rows that start with a wildcard.
112 /// The algorithm for computing `U`
113 /// -------------------------------
114 /// The algorithm is inductive (on the number of columns: i.e., components of tuple patterns).
115 /// That means we're going to check the components from left-to-right, so the algorithm
116 /// operates principally on the first component of the matrix and new pattern-stack `p`.
117 /// This algorithm is realised in the `is_useful` function.
119 /// Base case. (`n = 0`, i.e., an empty tuple pattern)
120 /// - If `P` already contains an empty pattern (i.e., if the number of patterns `m > 0`),
121 /// then `U(P, p)` is false.
122 /// - Otherwise, `P` must be empty, so `U(P, p)` is true.
124 /// Inductive step. (`n > 0`, i.e., whether there's at least one column
125 /// [which may then be expanded into further columns later])
126 /// We're going to match on the top of the new pattern-stack, `p_1`.
127 /// - If `p_1 == c(r_1, .., r_a)`, i.e. we have a constructor pattern.
128 /// Then, the usefulness of `p_1` can be reduced to whether it is useful when
129 /// we ignore all the patterns in the first column of `P` that involve other constructors.
130 /// This is where `S(c, P)` comes in:
131 /// `U(P, p) := U(S(c, P), S(c, p))`
132 /// This special case is handled in `is_useful_specialized`.
134 /// For example, if `P` is:
139 /// and `p` is [Some(false), 0], then we don't care about row 2 since we know `p` only
140 /// matches values that row 2 doesn't. For row 1 however, we need to dig into the
141 /// arguments of `Some` to know whether some new value is covered. So we compute
142 /// `U([[true, _]], [false, 0])`.
144 /// - If `p_1 == _`, then we look at the list of constructors that appear in the first
145 /// component of the rows of `P`:
146 /// + If there are some constructors that aren't present, then we might think that the
147 /// wildcard `_` is useful, since it covers those constructors that weren't covered
149 /// That's almost correct, but only works if there were no wildcards in those first
150 /// components. So we need to check that `p` is useful with respect to the rows that
151 /// start with a wildcard, if there are any. This is where `D` comes in:
152 /// `U(P, p) := U(D(P), D(p))`
154 /// For example, if `P` is:
157 /// [None, false, 1],
159 /// and `p` is [_, false, _], the `Some` constructor doesn't appear in `P`. So if we
160 /// only had row 2, we'd know that `p` is useful. However row 1 starts with a
161 /// wildcard, so we need to check whether `U([[true, _]], [false, 1])`.
163 /// + Otherwise, all possible constructors (for the relevant type) are present. In this
164 /// case we must check whether the wildcard pattern covers any unmatched value. For
165 /// that, we can think of the `_` pattern as a big OR-pattern that covers all
166 /// possible constructors. For `Option`, that would mean `_ = None | Some(_)` for
167 /// example. The wildcard pattern is useful in this case if it is useful when
168 /// specialized to one of the possible constructors. So we compute:
169 /// `U(P, p) := ∃(k ϵ constructors) U(S(k, P), S(k, p))`
171 /// For example, if `P` is:
176 /// and `p` is [_, false], both `None` and `Some` constructors appear in the first
177 /// components of `P`. We will therefore try popping both constructors in turn: we
178 /// compute U([[true, _]], [_, false]) for the `Some` constructor, and U([[false]],
179 /// [false]) for the `None` constructor. The first case returns true, so we know that
180 /// `p` is useful for `P`. Indeed, it matches `[Some(false), _]` that wasn't matched
183 /// - If `p_1 == r_1 | r_2`, then the usefulness depends on each `r_i` separately:
184 /// `U(P, p) := U(P, (r_1, p_2, .., p_n))
185 /// || U(P, (r_2, p_2, .., p_n))`
187 /// Modifications to the algorithm
188 /// ------------------------------
189 /// The algorithm in the paper doesn't cover some of the special cases that arise in Rust, for
190 /// example uninhabited types and variable-length slice patterns. These are drawn attention to
191 /// throughout the code below. I'll make a quick note here about how exhaustive integer matching is
192 /// accounted for, though.
194 /// Exhaustive integer matching
195 /// ---------------------------
196 /// An integer type can be thought of as a (huge) sum type: 1 | 2 | 3 | ...
197 /// So to support exhaustive integer matching, we can make use of the logic in the paper for
198 /// OR-patterns. However, we obviously can't just treat ranges x..=y as individual sums, because
199 /// they are likely gigantic. So we instead treat ranges as constructors of the integers. This means
200 /// that we have a constructor *of* constructors (the integers themselves). We then need to work
201 /// through all the inductive step rules above, deriving how the ranges would be treated as
202 /// OR-patterns, and making sure that they're treated in the same way even when they're ranges.
203 /// There are really only four special cases here:
204 /// - When we match on a constructor that's actually a range, we have to treat it as if we would
206 /// + It turns out that we can simply extend the case for single-value patterns in
207 /// `specialize` to either be *equal* to a value constructor, or *contained within* a range
209 /// + When the pattern itself is a range, you just want to tell whether any of the values in
210 /// the pattern range coincide with values in the constructor range, which is precisely
212 /// Since when encountering a range pattern for a value constructor, we also use inclusion, it
213 /// means that whenever the constructor is a value/range and the pattern is also a value/range,
214 /// we can simply use intersection to test usefulness.
215 /// - When we're testing for usefulness of a pattern and the pattern's first component is a
217 /// + If all the constructors appear in the matrix, we have a slight complication. By default,
218 /// the behaviour (i.e., a disjunction over specialised matrices for each constructor) is
219 /// invalid, because we want a disjunction over every *integer* in each range, not just a
220 /// disjunction over every range. This is a bit more tricky to deal with: essentially we need
221 /// to form equivalence classes of subranges of the constructor range for which the behaviour
222 /// of the matrix `P` and new pattern `p` are the same. This is described in more
223 /// detail in `split_grouped_constructors`.
224 /// + If some constructors are missing from the matrix, it turns out we don't need to do
225 /// anything special (because we know none of the integers are actually wildcards: i.e., we
226 /// can't span wildcards using ranges).
227 use self::Constructor
::*;
228 use self::SliceKind
::*;
229 use self::Usefulness
::*;
230 use self::WitnessPreference
::*;
232 use rustc_data_structures
::captures
::Captures
;
233 use rustc_index
::vec
::Idx
;
235 use super::{compare_const_vals, PatternFoldable, PatternFolder}
;
236 use super::{FieldPat, Pat, PatKind, PatRange}
;
238 use rustc_attr
::{SignedInt, UnsignedInt}
;
239 use rustc_errors
::ErrorReported
;
240 use rustc_hir
::def_id
::DefId
;
241 use rustc_hir
::{HirId, RangeEnd}
;
242 use rustc_middle
::mir
::interpret
::{truncate, AllocId, ConstValue, Pointer, Scalar}
;
243 use rustc_middle
::mir
::Field
;
244 use rustc_middle
::ty
::layout
::IntegerExt
;
245 use rustc_middle
::ty
::{self, Const, Ty, TyCtxt, TypeFoldable, VariantDef}
;
246 use rustc_session
::lint
;
247 use rustc_span
::{Span, DUMMY_SP}
;
248 use rustc_target
::abi
::{Integer, Size, VariantIdx}
;
250 use arena
::TypedArena
;
252 use smallvec
::{smallvec, SmallVec}
;
253 use std
::borrow
::Cow
;
254 use std
::cmp
::{self, max, min, Ordering}
;
255 use std
::convert
::TryInto
;
257 use std
::iter
::{FromIterator, IntoIterator}
;
258 use std
::ops
::RangeInclusive
;
260 crate fn expand_pattern
<'a
, 'tcx
>(cx
: &MatchCheckCtxt
<'a
, 'tcx
>, pat
: Pat
<'tcx
>) -> Pat
<'tcx
> {
261 LiteralExpander { tcx: cx.tcx, param_env: cx.param_env }
.fold_pattern(&pat
)
264 struct LiteralExpander
<'tcx
> {
266 param_env
: ty
::ParamEnv
<'tcx
>,
269 impl<'tcx
> LiteralExpander
<'tcx
> {
270 /// Derefs `val` and potentially unsizes the value if `crty` is an array and `rty` a slice.
272 /// `crty` and `rty` can differ because you can use array constants in the presence of slice
273 /// patterns. So the pattern may end up being a slice, but the constant is an array. We convert
274 /// the array to a slice in that case.
275 fn fold_const_value_deref(
277 val
: ConstValue
<'tcx
>,
278 // the pattern's pointee type
280 // the constant's pointee type
282 ) -> ConstValue
<'tcx
> {
283 debug
!("fold_const_value_deref {:?} {:?} {:?}", val
, rty
, crty
);
284 match (val
, &crty
.kind
, &rty
.kind
) {
285 // the easy case, deref a reference
286 (ConstValue
::Scalar(p
), x
, y
) if x
== y
=> {
289 let alloc
= self.tcx
.alloc_map
.lock().unwrap_memory(p
.alloc_id
);
290 ConstValue
::ByRef { alloc, offset: p.offset }
292 Scalar
::Raw { .. }
=> {
293 let layout
= self.tcx
.layout_of(self.param_env
.and(rty
)).unwrap();
295 // Deref of a reference to a ZST is a nop.
296 ConstValue
::Scalar(Scalar
::zst())
298 // FIXME(oli-obk): this is reachable for `const FOO: &&&u32 = &&&42;`
299 bug
!("cannot deref {:#?}, {} -> {}", val
, crty
, rty
);
304 // unsize array to slice if pattern is array but match value or other patterns are slice
305 (ConstValue
::Scalar(Scalar
::Ptr(p
)), ty
::Array(t
, n
), ty
::Slice(u
)) => {
308 data
: self.tcx
.alloc_map
.lock().unwrap_memory(p
.alloc_id
),
309 start
: p
.offset
.bytes().try_into().unwrap(),
310 end
: n
.eval_usize(self.tcx
, ty
::ParamEnv
::empty()).try_into().unwrap(),
313 // fat pointers stay the same
314 (ConstValue
::Slice { .. }
, _
, _
)
315 | (_
, ty
::Slice(_
), ty
::Slice(_
))
316 | (_
, ty
::Str
, ty
::Str
) => val
,
317 // FIXME(oli-obk): this is reachable for `const FOO: &&&u32 = &&&42;` being used
318 _
=> bug
!("cannot deref {:#?}, {} -> {}", val
, crty
, rty
),
323 impl<'tcx
> PatternFolder
<'tcx
> for LiteralExpander
<'tcx
> {
324 fn fold_pattern(&mut self, pat
: &Pat
<'tcx
>) -> Pat
<'tcx
> {
325 debug
!("fold_pattern {:?} {:?} {:?}", pat
, pat
.ty
.kind
, pat
.kind
);
326 match (&pat
.ty
.kind
, &*pat
.kind
) {
332 val
: ty
::ConstKind
::Value(val
),
333 ty
: ty
::TyS { kind: ty::Ref(_, crty, _), .. }
,
339 kind
: box PatKind
::Deref
{
343 kind
: box PatKind
::Constant
{
344 value
: Const
::from_value(
346 self.fold_const_value_deref(*val
, rty
, crty
),
357 value
: Const { val, ty: ty::TyS { kind: ty::Ref(_, crty, _), .. }
},
359 ) => bug
!("cannot deref {:#?}, {} -> {}", val
, crty
, rty
),
361 (_
, &PatKind
::Binding { subpattern: Some(ref s), .. }
) => s
.fold_with(self),
362 (_
, &PatKind
::AscribeUserType { subpattern: ref s, .. }
) => s
.fold_with(self),
363 _
=> pat
.super_fold_with(self),
368 impl<'tcx
> Pat
<'tcx
> {
369 pub(super) fn is_wildcard(&self) -> bool
{
371 PatKind
::Binding { subpattern: None, .. }
| PatKind
::Wild
=> true,
377 /// A row of a matrix. Rows of len 1 are very common, which is why `SmallVec[_; 2]`
379 #[derive(Debug, Clone)]
380 crate struct PatStack
<'p
, 'tcx
>(SmallVec
<[&'p Pat
<'tcx
>; 2]>);
382 impl<'p
, 'tcx
> PatStack
<'p
, 'tcx
> {
383 crate fn from_pattern(pat
: &'p Pat
<'tcx
>) -> Self {
384 PatStack(smallvec
![pat
])
387 fn from_vec(vec
: SmallVec
<[&'p Pat
<'tcx
>; 2]>) -> Self {
391 fn from_slice(s
: &[&'p Pat
<'tcx
>]) -> Self {
392 PatStack(SmallVec
::from_slice(s
))
395 fn is_empty(&self) -> bool
{
399 fn len(&self) -> usize {
403 fn head(&self) -> &'p Pat
<'tcx
> {
407 fn to_tail(&self) -> Self {
408 PatStack
::from_slice(&self.0[1..])
411 fn iter(&self) -> impl Iterator
<Item
= &Pat
<'tcx
>> {
412 self.0.iter
().copied()
415 // If the first pattern is an or-pattern, expand this pattern. Otherwise, return `None`.
416 fn expand_or_pat(&self) -> Option
<Vec
<Self>> {
419 } else if let PatKind
::Or { pats }
= &*self.head().kind
{
423 let mut new_patstack
= PatStack
::from_pattern(pat
);
424 new_patstack
.0.extend_from_slice(&self.0[1..]);
434 /// This computes `D(self)`. See top of the file for explanations.
435 fn specialize_wildcard(&self) -> Option
<Self> {
436 if self.head().is_wildcard() { Some(self.to_tail()) }
else { None }
439 /// This computes `S(constructor, self)`. See top of the file for explanations.
440 fn specialize_constructor(
442 cx
: &mut MatchCheckCtxt
<'p
, 'tcx
>,
443 constructor
: &Constructor
<'tcx
>,
444 ctor_wild_subpatterns
: &'p
[Pat
<'tcx
>],
445 ) -> Option
<PatStack
<'p
, 'tcx
>> {
446 let new_heads
= specialize_one_pattern(cx
, self.head(), constructor
, ctor_wild_subpatterns
);
447 new_heads
.map(|mut new_head
| {
448 new_head
.0.extend_from_slice(&self.0[1..]);
454 impl<'p
, 'tcx
> Default
for PatStack
<'p
, 'tcx
> {
455 fn default() -> Self {
456 PatStack(smallvec
![])
460 impl<'p
, 'tcx
> FromIterator
<&'p Pat
<'tcx
>> for PatStack
<'p
, 'tcx
> {
461 fn from_iter
<T
>(iter
: T
) -> Self
463 T
: IntoIterator
<Item
= &'p Pat
<'tcx
>>,
465 PatStack(iter
.into_iter().collect())
471 crate struct Matrix
<'p
, 'tcx
>(Vec
<PatStack
<'p
, 'tcx
>>);
473 impl<'p
, 'tcx
> Matrix
<'p
, 'tcx
> {
474 crate fn empty() -> Self {
478 /// Pushes a new row to the matrix. If the row starts with an or-pattern, this expands it.
479 crate fn push(&mut self, row
: PatStack
<'p
, 'tcx
>) {
480 if let Some(rows
) = row
.expand_or_pat() {
482 // We recursively expand the or-patterns of the new rows.
483 // This is necessary as we might have `0 | (1 | 2)` or e.g., `x @ 0 | x @ (1 | 2)`.
491 /// Iterate over the first component of each row
492 fn heads
<'a
>(&'a
self) -> impl Iterator
<Item
= &'a Pat
<'tcx
>> + Captures
<'p
> {
493 self.0.iter
().map(|r
| r
.head())
496 /// This computes `D(self)`. See top of the file for explanations.
497 fn specialize_wildcard(&self) -> Self {
498 self.0.iter
().filter_map(|r
| r
.specialize_wildcard()).collect()
501 /// This computes `S(constructor, self)`. See top of the file for explanations.
502 fn specialize_constructor(
504 cx
: &mut MatchCheckCtxt
<'p
, 'tcx
>,
505 constructor
: &Constructor
<'tcx
>,
506 ctor_wild_subpatterns
: &'p
[Pat
<'tcx
>],
507 ) -> Matrix
<'p
, 'tcx
> {
510 .filter_map(|r
| r
.specialize_constructor(cx
, constructor
, ctor_wild_subpatterns
))
515 /// Pretty-printer for matrices of patterns, example:
516 /// +++++++++++++++++++++++++++++
518 /// +++++++++++++++++++++++++++++
519 /// + true + [First] +
520 /// +++++++++++++++++++++++++++++
521 /// + true + [Second(true)] +
522 /// +++++++++++++++++++++++++++++
524 /// +++++++++++++++++++++++++++++
525 /// + _ + [_, _, tail @ ..] +
526 /// +++++++++++++++++++++++++++++
527 impl<'p
, 'tcx
> fmt
::Debug
for Matrix
<'p
, 'tcx
> {
528 fn fmt(&self, f
: &mut fmt
::Formatter
<'_
>) -> fmt
::Result
{
531 let &Matrix(ref m
) = self;
532 let pretty_printed_matrix
: Vec
<Vec
<String
>> =
533 m
.iter().map(|row
| row
.iter().map(|pat
| format
!("{:?}", pat
)).collect()).collect();
535 let column_count
= m
.iter().map(|row
| row
.len()).max().unwrap_or(0);
536 assert
!(m
.iter().all(|row
| row
.len() == column_count
));
537 let column_widths
: Vec
<usize> = (0..column_count
)
538 .map(|col
| pretty_printed_matrix
.iter().map(|row
| row
[col
].len()).max().unwrap_or(0))
541 let total_width
= column_widths
.iter().cloned().sum
::<usize>() + column_count
* 3 + 1;
542 let br
= "+".repeat(total_width
);
543 write
!(f
, "{}\n", br
)?
;
544 for row
in pretty_printed_matrix
{
546 for (column
, pat_str
) in row
.into_iter().enumerate() {
548 write
!(f
, "{:1$}", pat_str
, column_widths
[column
])?
;
552 write
!(f
, "{}\n", br
)?
;
558 impl<'p
, 'tcx
> FromIterator
<PatStack
<'p
, 'tcx
>> for Matrix
<'p
, 'tcx
> {
559 fn from_iter
<T
>(iter
: T
) -> Self
561 T
: IntoIterator
<Item
= PatStack
<'p
, 'tcx
>>,
563 let mut matrix
= Matrix
::empty();
565 // Using `push` ensures we correctly expand or-patterns.
572 crate struct MatchCheckCtxt
<'a
, 'tcx
> {
573 crate tcx
: TyCtxt
<'tcx
>,
574 /// The module in which the match occurs. This is necessary for
575 /// checking inhabited-ness of types because whether a type is (visibly)
576 /// inhabited can depend on whether it was defined in the current module or
577 /// not. E.g., `struct Foo { _private: ! }` cannot be seen to be empty
578 /// outside it's module and should not be matchable with an empty match
581 param_env
: ty
::ParamEnv
<'tcx
>,
582 crate pattern_arena
: &'a TypedArena
<Pat
<'tcx
>>,
585 impl<'a
, 'tcx
> MatchCheckCtxt
<'a
, 'tcx
> {
586 crate fn create_and_enter
<R
>(
588 param_env
: ty
::ParamEnv
<'tcx
>,
590 f
: impl FnOnce(MatchCheckCtxt
<'_
, 'tcx
>) -> R
,
592 let pattern_arena
= TypedArena
::default();
594 f(MatchCheckCtxt { tcx, param_env, module, pattern_arena: &pattern_arena }
)
597 fn is_uninhabited(&self, ty
: Ty
<'tcx
>) -> bool
{
598 if self.tcx
.features().exhaustive_patterns
{
599 self.tcx
.is_ty_uninhabited_from(self.module
, ty
, self.param_env
)
605 // Returns whether the given type is an enum from another crate declared `#[non_exhaustive]`.
606 crate fn is_foreign_non_exhaustive_enum(&self, ty
: Ty
<'tcx
>) -> bool
{
608 ty
::Adt(def
, ..) => {
609 def
.is_enum() && def
.is_variant_list_non_exhaustive() && !def
.did
.is_local()
615 // Returns whether the given variant is from another crate and has its fields declared
616 // `#[non_exhaustive]`.
617 fn is_foreign_non_exhaustive_variant(&self, ty
: Ty
<'tcx
>, variant
: &VariantDef
) -> bool
{
619 ty
::Adt(def
, ..) => variant
.is_field_list_non_exhaustive() && !def
.did
.is_local(),
625 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
627 /// Patterns of length `n` (`[x, y]`).
629 /// Patterns using the `..` notation (`[x, .., y]`).
630 /// Captures any array constructor of `length >= i + j`.
631 /// In the case where `array_len` is `Some(_)`,
632 /// this indicates that we only care about the first `i` and the last `j` values of the array,
633 /// and everything in between is a wildcard `_`.
638 fn arity(self) -> u64 {
640 FixedLen(length
) => length
,
641 VarLen(prefix
, suffix
) => prefix
+ suffix
,
645 /// Whether this pattern includes patterns of length `other_len`.
646 fn covers_length(self, other_len
: u64) -> bool
{
648 FixedLen(len
) => len
== other_len
,
649 VarLen(prefix
, suffix
) => prefix
+ suffix
<= other_len
,
653 /// Returns a collection of slices that spans the values covered by `self`, subtracted by the
654 /// values covered by `other`: i.e., `self \ other` (in set notation).
655 fn subtract(self, other
: Self) -> SmallVec
<[Self; 1]> {
656 // Remember, `VarLen(i, j)` covers the union of `FixedLen` from `i + j` to infinity.
657 // Naming: we remove the "neg" constructors from the "pos" ones.
659 FixedLen(pos_len
) => {
660 if other
.covers_length(pos_len
) {
666 VarLen(pos_prefix
, pos_suffix
) => {
667 let pos_len
= pos_prefix
+ pos_suffix
;
669 FixedLen(neg_len
) => {
670 if neg_len
< pos_len
{
675 // We know that `neg_len + 1 >= pos_len >= pos_suffix`.
676 .chain(Some(VarLen(neg_len
+ 1 - pos_suffix
, pos_suffix
)))
680 VarLen(neg_prefix
, neg_suffix
) => {
681 let neg_len
= neg_prefix
+ neg_suffix
;
682 if neg_len
<= pos_len
{
685 (pos_len
..neg_len
).map(FixedLen
).collect()
694 /// A constructor for array and slice patterns.
695 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
697 /// `None` if the matched value is a slice, `Some(n)` if it is an array of size `n`.
698 array_len
: Option
<u64>,
699 /// The kind of pattern it is: fixed-length `[x, y]` or variable length `[x, .., y]`.
704 /// Returns what patterns this constructor covers: either fixed-length patterns or
705 /// variable-length patterns.
706 fn pattern_kind(self) -> SliceKind
{
708 Slice { array_len: Some(len), kind: VarLen(prefix, suffix) }
709 if prefix
+ suffix
== len
=>
717 /// Returns what values this constructor covers: either values of only one given length, or
718 /// values of length above a given length.
719 /// This is different from `pattern_kind()` because in some cases the pattern only takes into
720 /// account a subset of the entries of the array, but still only captures values of a given
722 fn value_kind(self) -> SliceKind
{
724 Slice { array_len: Some(len), kind: VarLen(_, _) }
=> FixedLen(len
),
729 fn arity(self) -> u64 {
730 self.pattern_kind().arity()
734 #[derive(Clone, Debug, PartialEq)]
735 enum Constructor
<'tcx
> {
736 /// The constructor of all patterns that don't vary by constructor,
737 /// e.g., struct patterns and fixed-length arrays.
742 ConstantValue(&'tcx ty
::Const
<'tcx
>),
743 /// Ranges of integer literal values (`2`, `2..=5` or `2..5`).
744 IntRange(IntRange
<'tcx
>),
745 /// Ranges of floating-point literal values (`2.0..=5.2`).
746 FloatRange(&'tcx ty
::Const
<'tcx
>, &'tcx ty
::Const
<'tcx
>, RangeEnd
),
747 /// Array and slice patterns.
749 /// Fake extra constructor for enums that aren't allowed to be matched exhaustively.
753 impl<'tcx
> Constructor
<'tcx
> {
754 fn is_slice(&self) -> bool
{
761 fn variant_index_for_adt
<'a
>(
763 cx
: &MatchCheckCtxt
<'a
, 'tcx
>,
764 adt
: &'tcx ty
::AdtDef
,
767 Variant(id
) => adt
.variant_index_with_id(id
),
769 assert
!(!adt
.is_enum());
772 ConstantValue(c
) => cx
.tcx
.destructure_const(cx
.param_env
.and(c
)).variant
,
773 _
=> bug
!("bad constructor {:?} for adt {:?}", self, adt
),
777 // Returns the set of constructors covered by `self` but not by
778 // anything in `other_ctors`.
779 fn subtract_ctors(&self, other_ctors
: &Vec
<Constructor
<'tcx
>>) -> Vec
<Constructor
<'tcx
>> {
780 if other_ctors
.is_empty() {
781 return vec
![self.clone()];
785 // Those constructors can only match themselves.
786 Single
| Variant(_
) | ConstantValue(..) | FloatRange(..) => {
787 if other_ctors
.iter().any(|c
| c
== self) { vec![] }
else { vec![self.clone()] }
790 let mut other_slices
= other_ctors
792 .filter_map(|c
: &Constructor
<'_
>| match c
{
793 Slice(slice
) => Some(*slice
),
794 // FIXME(oli-obk): implement `deref` for `ConstValue`
795 ConstantValue(..) => None
,
796 _
=> bug
!("bad slice pattern constructor {:?}", c
),
798 .map(Slice
::value_kind
);
800 match slice
.value_kind() {
801 FixedLen(self_len
) => {
802 if other_slices
.any(|other_slice
| other_slice
.covers_length(self_len
)) {
808 kind @
VarLen(..) => {
809 let mut remaining_slices
= vec
![kind
];
811 // For each used slice, subtract from the current set of slices.
812 for other_slice
in other_slices
{
813 remaining_slices
= remaining_slices
815 .flat_map(|remaining_slice
| remaining_slice
.subtract(other_slice
))
818 // If the constructors that have been considered so far already cover
819 // the entire range of `self`, no need to look at more constructors.
820 if remaining_slices
.is_empty() {
827 .map(|kind
| Slice { array_len: slice.array_len, kind }
)
833 IntRange(self_range
) => {
834 let mut remaining_ranges
= vec
![self_range
.clone()];
835 for other_ctor
in other_ctors
{
836 if let IntRange(other_range
) = other_ctor
{
837 if other_range
== self_range
{
838 // If the `self` range appears directly in a `match` arm, we can
839 // eliminate it straight away.
840 remaining_ranges
= vec
![];
842 // Otherwise explicitly compute the remaining ranges.
843 remaining_ranges
= other_range
.subtract_from(remaining_ranges
);
846 // If the ranges that have been considered so far already cover the entire
847 // range of values, we can return early.
848 if remaining_ranges
.is_empty() {
854 // Convert the ranges back into constructors.
855 remaining_ranges
.into_iter().map(IntRange
).collect()
857 // This constructor is never covered by anything else
858 NonExhaustive
=> vec
![NonExhaustive
],
862 /// This returns one wildcard pattern for each argument to this constructor.
864 /// This must be consistent with `apply`, `specialize_one_pattern`, and `arity`.
865 fn wildcard_subpatterns
<'a
>(
867 cx
: &MatchCheckCtxt
<'a
, 'tcx
>,
869 ) -> Vec
<Pat
<'tcx
>> {
870 debug
!("wildcard_subpatterns({:#?}, {:?})", self, ty
);
873 Single
| Variant(_
) => match ty
.kind
{
874 ty
::Tuple(ref fs
) => {
875 fs
.into_iter().map(|t
| t
.expect_ty()).map(Pat
::wildcard_from_ty
).collect()
877 ty
::Ref(_
, rty
, _
) => vec
![Pat
::wildcard_from_ty(rty
)],
878 ty
::Adt(adt
, substs
) => {
880 // Use T as the sub pattern type of Box<T>.
881 vec
![Pat
::wildcard_from_ty(substs
.type_at(0))]
883 let variant
= &adt
.variants
[self.variant_index_for_adt(cx
, adt
)];
884 let is_non_exhaustive
= cx
.is_foreign_non_exhaustive_variant(ty
, variant
);
889 let is_visible
= adt
.is_enum()
890 || field
.vis
.is_accessible_from(cx
.module
, cx
.tcx
);
891 let is_uninhabited
= cx
.is_uninhabited(field
.ty(cx
.tcx
, substs
));
892 match (is_visible
, is_non_exhaustive
, is_uninhabited
) {
893 // Treat all uninhabited types in non-exhaustive variants as
895 (_
, true, true) => cx
.tcx
.types
.err
,
896 // Treat all non-visible fields as `TyErr`. They can't appear
897 // in any other pattern from this match (because they are
898 // private), so their type does not matter - but we don't want
899 // to know they are uninhabited.
900 (false, ..) => cx
.tcx
.types
.err
,
902 let ty
= field
.ty(cx
.tcx
, substs
);
904 // If the field type returned is an array of an unknown
905 // size return an TyErr.
908 .try_eval_usize(cx
.tcx
, cx
.param_env
)
918 .map(Pat
::wildcard_from_ty
)
924 Slice(_
) => match ty
.kind
{
925 ty
::Slice(ty
) | ty
::Array(ty
, _
) => {
926 let arity
= self.arity(cx
, ty
);
927 (0..arity
).map(|_
| Pat
::wildcard_from_ty(ty
)).collect()
929 _
=> bug
!("bad slice pattern {:?} {:?}", self, ty
),
931 ConstantValue(..) | FloatRange(..) | IntRange(..) | NonExhaustive
=> vec
![],
935 /// This computes the arity of a constructor. The arity of a constructor
936 /// is how many subpattern patterns of that constructor should be expanded to.
938 /// For instance, a tuple pattern `(_, 42, Some([]))` has the arity of 3.
939 /// A struct pattern's arity is the number of fields it contains, etc.
941 /// This must be consistent with `wildcard_subpatterns`, `specialize_one_pattern`, and `apply`.
942 fn arity
<'a
>(&self, cx
: &MatchCheckCtxt
<'a
, 'tcx
>, ty
: Ty
<'tcx
>) -> u64 {
943 debug
!("Constructor::arity({:#?}, {:?})", self, ty
);
945 Single
| Variant(_
) => match ty
.kind
{
946 ty
::Tuple(ref fs
) => fs
.len() as u64,
947 ty
::Slice(..) | ty
::Array(..) => bug
!("bad slice pattern {:?} {:?}", self, ty
),
950 adt
.variants
[self.variant_index_for_adt(cx
, adt
)].fields
.len() as u64
954 Slice(slice
) => slice
.arity(),
955 ConstantValue(..) | FloatRange(..) | IntRange(..) | NonExhaustive
=> 0,
959 /// Apply a constructor to a list of patterns, yielding a new pattern. `pats`
960 /// must have as many elements as this constructor's arity.
962 /// This must be consistent with `wildcard_subpatterns`, `specialize_one_pattern`, and `arity`.
965 /// `self`: `Constructor::Single`
966 /// `ty`: `(u32, u32, u32)`
967 /// `pats`: `[10, 20, _]`
968 /// returns `(10, 20, _)`
970 /// `self`: `Constructor::Variant(Option::Some)`
971 /// `ty`: `Option<bool>`
972 /// `pats`: `[false]`
973 /// returns `Some(false)`
976 cx
: &MatchCheckCtxt
<'a
, 'tcx
>,
978 pats
: impl IntoIterator
<Item
= Pat
<'tcx
>>,
980 let mut subpatterns
= pats
.into_iter();
982 let pat
= match self {
983 Single
| Variant(_
) => match ty
.kind
{
984 ty
::Adt(..) | ty
::Tuple(..) => {
985 let subpatterns
= subpatterns
987 .map(|(i
, p
)| FieldPat { field: Field::new(i), pattern: p }
)
990 if let ty
::Adt(adt
, substs
) = ty
.kind
{
995 variant_index
: self.variant_index_for_adt(cx
, adt
),
999 PatKind
::Leaf { subpatterns }
1002 PatKind
::Leaf { subpatterns }
1005 ty
::Ref(..) => PatKind
::Deref { subpattern: subpatterns.next().unwrap() }
,
1006 ty
::Slice(_
) | ty
::Array(..) => bug
!("bad slice pattern {:?} {:?}", self, ty
),
1009 Slice(slice
) => match slice
.pattern_kind() {
1011 PatKind
::Slice { prefix: subpatterns.collect(), slice: None, suffix: vec![] }
1013 VarLen(prefix
, _
) => {
1014 let mut prefix
: Vec
<_
> = subpatterns
.by_ref().take(prefix
as usize).collect();
1015 if slice
.array_len
.is_some() {
1016 // Improves diagnostics a bit: if the type is a known-size array, instead
1017 // of reporting `[x, _, .., _, y]`, we prefer to report `[x, .., y]`.
1018 // This is incorrect if the size is not known, since `[_, ..]` captures
1019 // arrays of lengths `>= 1` whereas `[..]` captures any length.
1020 while !prefix
.is_empty() && prefix
.last().unwrap().is_wildcard() {
1024 let suffix
: Vec
<_
> = if slice
.array_len
.is_some() {
1026 subpatterns
.skip_while(Pat
::is_wildcard
).collect()
1028 subpatterns
.collect()
1030 let wild
= Pat
::wildcard_from_ty(ty
);
1031 PatKind
::Slice { prefix, slice: Some(wild), suffix }
1034 &ConstantValue(value
) => PatKind
::Constant { value }
,
1035 &FloatRange(lo
, hi
, end
) => PatKind
::Range(PatRange { lo, hi, end }
),
1036 IntRange(range
) => return range
.to_pat(cx
.tcx
),
1037 NonExhaustive
=> PatKind
::Wild
,
1040 Pat { ty, span: DUMMY_SP, kind: Box::new(pat) }
1043 /// Like `apply`, but where all the subpatterns are wildcards `_`.
1044 fn apply_wildcards
<'a
>(&self, cx
: &MatchCheckCtxt
<'a
, 'tcx
>, ty
: Ty
<'tcx
>) -> Pat
<'tcx
> {
1045 let subpatterns
= self.wildcard_subpatterns(cx
, ty
).into_iter().rev();
1046 self.apply(cx
, ty
, subpatterns
)
1050 #[derive(Clone, Debug)]
1051 crate enum Usefulness
<'tcx
, 'p
> {
1052 /// Carries a list of unreachable subpatterns. Used only in the presence of or-patterns.
1053 Useful(Vec
<&'p Pat
<'tcx
>>),
1054 /// Carries a list of witnesses of non-exhaustiveness.
1055 UsefulWithWitness(Vec
<Witness
<'tcx
>>),
1059 impl<'tcx
, 'p
> Usefulness
<'tcx
, 'p
> {
1060 fn new_useful(preference
: WitnessPreference
) -> Self {
1062 ConstructWitness
=> UsefulWithWitness(vec
![Witness(vec
![])]),
1063 LeaveOutWitness
=> Useful(vec
![]),
1067 fn is_useful(&self) -> bool
{
1074 fn apply_constructor(
1076 cx
: &MatchCheckCtxt
<'_
, 'tcx
>,
1077 ctor
: &Constructor
<'tcx
>,
1081 UsefulWithWitness(witnesses
) => UsefulWithWitness(
1084 .map(|witness
| witness
.apply_constructor(cx
, &ctor
, ty
))
1091 fn apply_wildcard(self, ty
: Ty
<'tcx
>) -> Self {
1093 UsefulWithWitness(witnesses
) => {
1094 let wild
= Pat
::wildcard_from_ty(ty
);
1098 .map(|mut witness
| {
1099 witness
.0.push(wild
.clone());
1109 fn apply_missing_ctors(
1111 cx
: &MatchCheckCtxt
<'_
, 'tcx
>,
1113 missing_ctors
: &MissingConstructors
<'tcx
>,
1116 UsefulWithWitness(witnesses
) => {
1117 let new_patterns
: Vec
<_
> =
1118 missing_ctors
.iter().map(|ctor
| ctor
.apply_wildcards(cx
, ty
)).collect();
1119 // Add the new patterns to each witness
1123 .flat_map(|witness
| {
1124 new_patterns
.iter().map(move |pat
| {
1125 let mut witness
= witness
.clone();
1126 witness
.0.push(pat
.clone());
1138 #[derive(Copy, Clone, Debug)]
1139 crate enum WitnessPreference
{
1144 #[derive(Copy, Clone, Debug)]
1145 struct PatCtxt
<'tcx
> {
1150 /// A witness of non-exhaustiveness for error reporting, represented
1151 /// as a list of patterns (in reverse order of construction) with
1152 /// wildcards inside to represent elements that can take any inhabitant
1153 /// of the type as a value.
1155 /// A witness against a list of patterns should have the same types
1156 /// and length as the pattern matched against. Because Rust `match`
1157 /// is always against a single pattern, at the end the witness will
1158 /// have length 1, but in the middle of the algorithm, it can contain
1159 /// multiple patterns.
1161 /// For example, if we are constructing a witness for the match against
1163 /// struct Pair(Option<(u32, u32)>, bool);
1165 /// match (p: Pair) {
1166 /// Pair(None, _) => {}
1167 /// Pair(_, false) => {}
1171 /// We'll perform the following steps:
1172 /// 1. Start with an empty witness
1173 /// `Witness(vec![])`
1174 /// 2. Push a witness `Some(_)` against the `None`
1175 /// `Witness(vec![Some(_)])`
1176 /// 3. Push a witness `true` against the `false`
1177 /// `Witness(vec![Some(_), true])`
1178 /// 4. Apply the `Pair` constructor to the witnesses
1179 /// `Witness(vec![Pair(Some(_), true)])`
1181 /// The final `Pair(Some(_), true)` is then the resulting witness.
1182 #[derive(Clone, Debug)]
1183 crate struct Witness
<'tcx
>(Vec
<Pat
<'tcx
>>);
1185 impl<'tcx
> Witness
<'tcx
> {
1186 crate fn single_pattern(self) -> Pat
<'tcx
> {
1187 assert_eq
!(self.0.len(), 1);
1188 self.0.into_iter
().next().unwrap()
1191 /// Constructs a partial witness for a pattern given a list of
1192 /// patterns expanded by the specialization step.
1194 /// When a pattern P is discovered to be useful, this function is used bottom-up
1195 /// to reconstruct a complete witness, e.g., a pattern P' that covers a subset
1196 /// of values, V, where each value in that set is not covered by any previously
1197 /// used patterns and is covered by the pattern P'. Examples:
1199 /// left_ty: tuple of 3 elements
1200 /// pats: [10, 20, _] => (10, 20, _)
1202 /// left_ty: struct X { a: (bool, &'static str), b: usize}
1203 /// pats: [(false, "foo"), 42] => X { a: (false, "foo"), b: 42 }
1204 fn apply_constructor
<'a
>(
1206 cx
: &MatchCheckCtxt
<'a
, 'tcx
>,
1207 ctor
: &Constructor
<'tcx
>,
1210 let arity
= ctor
.arity(cx
, ty
);
1212 let len
= self.0.len() as u64;
1213 let pats
= self.0.drain((len
- arity
) as usize..).rev();
1214 ctor
.apply(cx
, ty
, pats
)
1223 /// This determines the set of all possible constructors of a pattern matching
1224 /// values of type `left_ty`. For vectors, this would normally be an infinite set
1225 /// but is instead bounded by the maximum fixed length of slice patterns in
1226 /// the column of patterns being analyzed.
1228 /// We make sure to omit constructors that are statically impossible. E.g., for
1229 /// `Option<!>`, we do not include `Some(_)` in the returned list of constructors.
1230 /// Invariant: this returns an empty `Vec` if and only if the type is uninhabited (as determined by
1231 /// `cx.is_uninhabited()`).
1232 fn all_constructors
<'a
, 'tcx
>(
1233 cx
: &mut MatchCheckCtxt
<'a
, 'tcx
>,
1235 ) -> Vec
<Constructor
<'tcx
>> {
1236 debug
!("all_constructors({:?})", pcx
.ty
);
1237 let make_range
= |start
, end
| {
1239 // `unwrap()` is ok because we know the type is an integer.
1240 IntRange
::from_range(cx
.tcx
, start
, end
, pcx
.ty
, &RangeEnd
::Included
, pcx
.span
)
1246 [true, false].iter().map(|&b
| ConstantValue(ty
::Const
::from_bool(cx
.tcx
, b
))).collect()
1248 ty
::Array(ref sub_ty
, len
) if len
.try_eval_usize(cx
.tcx
, cx
.param_env
).is_some() => {
1249 let len
= len
.eval_usize(cx
.tcx
, cx
.param_env
);
1250 if len
!= 0 && cx
.is_uninhabited(sub_ty
) {
1253 vec
![Slice(Slice { array_len: Some(len), kind: VarLen(0, 0) }
)]
1256 // Treat arrays of a constant but unknown length like slices.
1257 ty
::Array(ref sub_ty
, _
) | ty
::Slice(ref sub_ty
) => {
1258 let kind
= if cx
.is_uninhabited(sub_ty
) { FixedLen(0) }
else { VarLen(0, 0) }
;
1259 vec
![Slice(Slice { array_len: None, kind }
)]
1261 ty
::Adt(def
, substs
) if def
.is_enum() => {
1262 let ctors
: Vec
<_
> = if cx
.tcx
.features().exhaustive_patterns
{
1263 // If `exhaustive_patterns` is enabled, we exclude variants known to be
1268 !v
.uninhabited_from(cx
.tcx
, substs
, def
.adt_kind(), cx
.param_env
)
1269 .contains(cx
.tcx
, cx
.module
)
1271 .map(|v
| Variant(v
.def_id
))
1274 def
.variants
.iter().map(|v
| Variant(v
.def_id
)).collect()
1277 // If the enum is declared as `#[non_exhaustive]`, we treat it as if it had an
1278 // additional "unknown" constructor.
1279 // There is no point in enumerating all possible variants, because the user can't
1280 // actually match against them all themselves. So we always return only the fictitious
1282 // E.g., in an example like:
1284 // let err: io::ErrorKind = ...;
1286 // io::ErrorKind::NotFound => {},
1289 // we don't want to show every possible IO error, but instead have only `_` as the
1291 let is_declared_nonexhaustive
= cx
.is_foreign_non_exhaustive_enum(pcx
.ty
);
1293 // If `exhaustive_patterns` is disabled and our scrutinee is an empty enum, we treat it
1294 // as though it had an "unknown" constructor to avoid exposing its emptyness. Note that
1295 // an empty match will still be considered exhaustive because that case is handled
1296 // separately in `check_match`.
1297 let is_secretly_empty
=
1298 def
.variants
.is_empty() && !cx
.tcx
.features().exhaustive_patterns
;
1300 if is_secretly_empty
|| is_declared_nonexhaustive { vec![NonExhaustive] }
else { ctors }
1304 // The valid Unicode Scalar Value ranges.
1305 make_range('
\u{0000}'
as u128
, '
\u{D7FF}'
as u128
),
1306 make_range('
\u{E000}'
as u128
, '
\u{10FFFF}'
as u128
),
1309 ty
::Int(_
) | ty
::Uint(_
)
1310 if pcx
.ty
.is_ptr_sized_integral()
1311 && !cx
.tcx
.features().precise_pointer_size_matching
=>
1313 // `usize`/`isize` are not allowed to be matched exhaustively unless the
1314 // `precise_pointer_size_matching` feature is enabled. So we treat those types like
1315 // `#[non_exhaustive]` enums by returning a special unmatcheable constructor.
1319 let bits
= Integer
::from_attr(&cx
.tcx
, SignedInt(ity
)).size().bits() as u128
;
1320 let min
= 1u128 << (bits
- 1);
1322 vec
![make_range(min
, max
)]
1325 let size
= Integer
::from_attr(&cx
.tcx
, UnsignedInt(uty
)).size();
1326 let max
= truncate(u128
::max_value(), size
);
1327 vec
![make_range(0, max
)]
1330 if cx
.is_uninhabited(pcx
.ty
) {
1339 /// An inclusive interval, used for precise integer exhaustiveness checking.
1340 /// `IntRange`s always store a contiguous range. This means that values are
1341 /// encoded such that `0` encodes the minimum value for the integer,
1342 /// regardless of the signedness.
1343 /// For example, the pattern `-128..=127i8` is encoded as `0..=255`.
1344 /// This makes comparisons and arithmetic on interval endpoints much more
1345 /// straightforward. See `signed_bias` for details.
1347 /// `IntRange` is never used to encode an empty range or a "range" that wraps
1348 /// around the (offset) space: i.e., `range.lo <= range.hi`.
1349 #[derive(Clone, Debug)]
1350 struct IntRange
<'tcx
> {
1351 range
: RangeInclusive
<u128
>,
1356 impl<'tcx
> IntRange
<'tcx
> {
1358 fn is_integral(ty
: Ty
<'_
>) -> bool
{
1360 ty
::Char
| ty
::Int(_
) | ty
::Uint(_
) => true,
1365 fn is_singleton(&self) -> bool
{
1366 self.range
.start() == self.range
.end()
1369 fn boundaries(&self) -> (u128
, u128
) {
1370 (*self.range
.start(), *self.range
.end())
1373 /// Don't treat `usize`/`isize` exhaustively unless the `precise_pointer_size_matching` feature
1375 fn treat_exhaustively(&self, tcx
: TyCtxt
<'tcx
>) -> bool
{
1376 !self.ty
.is_ptr_sized_integral() || tcx
.features().precise_pointer_size_matching
1380 fn integral_size_and_signed_bias(tcx
: TyCtxt
<'tcx
>, ty
: Ty
<'_
>) -> Option
<(Size
, u128
)> {
1382 ty
::Char
=> Some((Size
::from_bytes(4), 0)),
1384 let size
= Integer
::from_attr(&tcx
, SignedInt(ity
)).size();
1385 Some((size
, 1u128 << (size
.bits() as u128
- 1)))
1387 ty
::Uint(uty
) => Some((Integer
::from_attr(&tcx
, UnsignedInt(uty
)).size(), 0)),
1395 param_env
: ty
::ParamEnv
<'tcx
>,
1396 value
: &Const
<'tcx
>,
1398 ) -> Option
<IntRange
<'tcx
>> {
1399 if let Some((target_size
, bias
)) = Self::integral_size_and_signed_bias(tcx
, value
.ty
) {
1402 if let ty
::ConstKind
::Value(ConstValue
::Scalar(scalar
)) = value
.val
{
1403 // For this specific pattern we can skip a lot of effort and go
1404 // straight to the result, after doing a bit of checking. (We
1405 // could remove this branch and just fall through, which
1406 // is more general but much slower.)
1407 if let Ok(bits
) = scalar
.to_bits_or_ptr(target_size
, &tcx
) {
1411 // This is a more general form of the previous case.
1412 value
.try_eval_bits(tcx
, param_env
, ty
)
1414 let val
= val ^ bias
;
1415 Some(IntRange { range: val..=val, ty, span }
)
1429 ) -> Option
<IntRange
<'tcx
>> {
1430 if Self::is_integral(ty
) {
1431 // Perform a shift if the underlying types are signed,
1432 // which makes the interval arithmetic simpler.
1433 let bias
= IntRange
::signed_bias(tcx
, ty
);
1434 let (lo
, hi
) = (lo ^ bias
, hi ^ bias
);
1435 let offset
= (*end
== RangeEnd
::Excluded
) as u128
;
1436 if lo
> hi
|| (lo
== hi
&& *end
== RangeEnd
::Excluded
) {
1437 // This should have been caught earlier by E0030.
1438 bug
!("malformed range pattern: {}..={}", lo
, (hi
- offset
));
1440 Some(IntRange { range: lo..=(hi - offset), ty, span }
)
1448 param_env
: ty
::ParamEnv
<'tcx
>,
1450 ) -> Option
<IntRange
<'tcx
>> {
1451 match pat_constructor(tcx
, param_env
, pat
)?
{
1452 IntRange(range
) => Some(range
),
1457 // The return value of `signed_bias` should be XORed with an endpoint to encode/decode it.
1458 fn signed_bias(tcx
: TyCtxt
<'tcx
>, ty
: Ty
<'tcx
>) -> u128
{
1461 let bits
= Integer
::from_attr(&tcx
, SignedInt(ity
)).size().bits() as u128
;
1468 /// Returns a collection of ranges that spans the values covered by `ranges`, subtracted
1469 /// by the values covered by `self`: i.e., `ranges \ self` (in set notation).
1470 fn subtract_from(&self, ranges
: Vec
<IntRange
<'tcx
>>) -> Vec
<IntRange
<'tcx
>> {
1471 let mut remaining_ranges
= vec
![];
1473 let span
= self.span
;
1474 let (lo
, hi
) = self.boundaries();
1475 for subrange
in ranges
{
1476 let (subrange_lo
, subrange_hi
) = subrange
.range
.into_inner();
1477 if lo
> subrange_hi
|| subrange_lo
> hi
{
1478 // The pattern doesn't intersect with the subrange at all,
1479 // so the subrange remains untouched.
1480 remaining_ranges
.push(IntRange { range: subrange_lo..=subrange_hi, ty, span }
);
1482 if lo
> subrange_lo
{
1483 // The pattern intersects an upper section of the
1484 // subrange, so a lower section will remain.
1485 remaining_ranges
.push(IntRange { range: subrange_lo..=(lo - 1), ty, span }
);
1487 if hi
< subrange_hi
{
1488 // The pattern intersects a lower section of the
1489 // subrange, so an upper section will remain.
1490 remaining_ranges
.push(IntRange { range: (hi + 1)..=subrange_hi, ty, span }
);
1497 fn is_subrange(&self, other
: &Self) -> bool
{
1498 other
.range
.start() <= self.range
.start() && self.range
.end() <= other
.range
.end()
1501 fn intersection(&self, tcx
: TyCtxt
<'tcx
>, other
: &Self) -> Option
<Self> {
1503 let (lo
, hi
) = self.boundaries();
1504 let (other_lo
, other_hi
) = other
.boundaries();
1505 if self.treat_exhaustively(tcx
) {
1506 if lo
<= other_hi
&& other_lo
<= hi
{
1507 let span
= other
.span
;
1508 Some(IntRange { range: max(lo, other_lo)..=min(hi, other_hi), ty, span }
)
1513 // If the range should not be treated exhaustively, fallback to checking for inclusion.
1514 if self.is_subrange(other
) { Some(self.clone()) }
else { None }
1518 fn suspicious_intersection(&self, other
: &Self) -> bool
{
1519 // `false` in the following cases:
1520 // 1 ---- // 1 ---------- // 1 ---- // 1 ----
1521 // 2 ---------- // 2 ---- // 2 ---- // 2 ----
1523 // The following are currently `false`, but could be `true` in the future (#64007):
1524 // 1 --------- // 1 ---------
1525 // 2 ---------- // 2 ----------
1527 // `true` in the following cases:
1528 // 1 ------- // 1 -------
1529 // 2 -------- // 2 -------
1530 let (lo
, hi
) = self.boundaries();
1531 let (other_lo
, other_hi
) = other
.boundaries();
1532 lo
== other_hi
|| hi
== other_lo
1535 fn to_pat(&self, tcx
: TyCtxt
<'tcx
>) -> Pat
<'tcx
> {
1536 let (lo
, hi
) = self.boundaries();
1538 let bias
= IntRange
::signed_bias(tcx
, self.ty
);
1539 let (lo
, hi
) = (lo ^ bias
, hi ^ bias
);
1541 let ty
= ty
::ParamEnv
::empty().and(self.ty
);
1542 let lo_const
= ty
::Const
::from_bits(tcx
, lo
, ty
);
1543 let hi_const
= ty
::Const
::from_bits(tcx
, hi
, ty
);
1545 let kind
= if lo
== hi
{
1546 PatKind
::Constant { value: lo_const }
1548 PatKind
::Range(PatRange { lo: lo_const, hi: hi_const, end: RangeEnd::Included }
)
1551 // This is a brand new pattern, so we don't reuse `self.span`.
1552 Pat { ty: self.ty, span: DUMMY_SP, kind: Box::new(kind) }
1556 /// Ignore spans when comparing, they don't carry semantic information as they are only for lints.
1557 impl<'tcx
> std
::cmp
::PartialEq
for IntRange
<'tcx
> {
1558 fn eq(&self, other
: &Self) -> bool
{
1559 self.range
== other
.range
&& self.ty
== other
.ty
1563 // A struct to compute a set of constructors equivalent to `all_ctors \ used_ctors`.
1564 struct MissingConstructors
<'tcx
> {
1565 all_ctors
: Vec
<Constructor
<'tcx
>>,
1566 used_ctors
: Vec
<Constructor
<'tcx
>>,
1569 impl<'tcx
> MissingConstructors
<'tcx
> {
1570 fn new(all_ctors
: Vec
<Constructor
<'tcx
>>, used_ctors
: Vec
<Constructor
<'tcx
>>) -> Self {
1571 MissingConstructors { all_ctors, used_ctors }
1574 fn into_inner(self) -> (Vec
<Constructor
<'tcx
>>, Vec
<Constructor
<'tcx
>>) {
1575 (self.all_ctors
, self.used_ctors
)
1578 fn is_empty(&self) -> bool
{
1579 self.iter().next().is_none()
1581 /// Whether this contains all the constructors for the given type or only a
1583 fn all_ctors_are_missing(&self) -> bool
{
1584 self.used_ctors
.is_empty()
1587 /// Iterate over all_ctors \ used_ctors
1588 fn iter
<'a
>(&'a
self) -> impl Iterator
<Item
= Constructor
<'tcx
>> + Captures
<'a
> {
1589 self.all_ctors
.iter().flat_map(move |req_ctor
| req_ctor
.subtract_ctors(&self.used_ctors
))
1593 impl<'tcx
> fmt
::Debug
for MissingConstructors
<'tcx
> {
1594 fn fmt(&self, f
: &mut fmt
::Formatter
<'_
>) -> fmt
::Result
{
1595 let ctors
: Vec
<_
> = self.iter().collect();
1596 write
!(f
, "{:?}", ctors
)
1600 /// Algorithm from http://moscova.inria.fr/~maranget/papers/warn/index.html.
1601 /// The algorithm from the paper has been modified to correctly handle empty
1602 /// types. The changes are:
1603 /// (0) We don't exit early if the pattern matrix has zero rows. We just
1604 /// continue to recurse over columns.
1605 /// (1) all_constructors will only return constructors that are statically
1606 /// possible. E.g., it will only return `Ok` for `Result<T, !>`.
1608 /// This finds whether a (row) vector `v` of patterns is 'useful' in relation
1609 /// to a set of such vectors `m` - this is defined as there being a set of
1610 /// inputs that will match `v` but not any of the sets in `m`.
1612 /// All the patterns at each column of the `matrix ++ v` matrix must
1613 /// have the same type, except that wildcard (PatKind::Wild) patterns
1614 /// with type `TyErr` are also allowed, even if the "type of the column"
1615 /// is not `TyErr`. That is used to represent private fields, as using their
1616 /// real type would assert that they are inhabited.
1618 /// This is used both for reachability checking (if a pattern isn't useful in
1619 /// relation to preceding patterns, it is not reachable) and exhaustiveness
1620 /// checking (if a wildcard pattern is useful in relation to a matrix, the
1621 /// matrix isn't exhaustive).
1623 /// `is_under_guard` is used to inform if the pattern has a guard. If it
1624 /// has one it must not be inserted into the matrix. This shouldn't be
1625 /// relied on for soundness.
1626 crate fn is_useful
<'p
, 'tcx
>(
1627 cx
: &mut MatchCheckCtxt
<'p
, 'tcx
>,
1628 matrix
: &Matrix
<'p
, 'tcx
>,
1629 v
: &PatStack
<'p
, 'tcx
>,
1630 witness_preference
: WitnessPreference
,
1632 is_under_guard
: bool
,
1634 ) -> Usefulness
<'tcx
, 'p
> {
1635 let &Matrix(ref rows
) = matrix
;
1636 debug
!("is_useful({:#?}, {:#?})", matrix
, v
);
1638 // The base case. We are pattern-matching on () and the return value is
1639 // based on whether our matrix has a row or not.
1640 // NOTE: This could potentially be optimized by checking rows.is_empty()
1641 // first and then, if v is non-empty, the return value is based on whether
1642 // the type of the tuple we're checking is inhabited or not.
1644 return if rows
.is_empty() {
1645 Usefulness
::new_useful(witness_preference
)
1651 assert
!(rows
.iter().all(|r
| r
.len() == v
.len()));
1653 // If the first pattern is an or-pattern, expand it.
1654 if let Some(vs
) = v
.expand_or_pat() {
1655 // We need to push the already-seen patterns into the matrix in order to detect redundant
1656 // branches like `Some(_) | Some(0)`. We also keep track of the unreachable subpatterns.
1657 let mut matrix
= matrix
.clone();
1658 let mut unreachable_pats
= Vec
::new();
1659 let mut any_is_useful
= false;
1661 let res
= is_useful(cx
, &matrix
, &v
, witness_preference
, hir_id
, is_under_guard
, false);
1664 any_is_useful
= true;
1665 unreachable_pats
.extend(pats
);
1667 NotUseful
=> unreachable_pats
.push(v
.head()),
1668 UsefulWithWitness(_
) => {
1669 bug
!("Encountered or-pat in `v` during exhaustiveness checking")
1672 // If pattern has a guard don't add it to the matrix
1673 if !is_under_guard
{
1677 return if any_is_useful { Useful(unreachable_pats) }
else { NotUseful }
;
1680 let (ty
, span
) = matrix
1682 .map(|r
| (r
.ty
, r
.span
))
1683 .find(|(ty
, _
)| !ty
.references_error())
1684 .unwrap_or((v
.head().ty
, v
.head().span
));
1686 // TyErr is used to represent the type of wildcard patterns matching
1687 // against inaccessible (private) fields of structs, so that we won't
1688 // be able to observe whether the types of the struct's fields are
1691 // If the field is truly inaccessible, then all the patterns
1692 // matching against it must be wildcard patterns, so its type
1695 // However, if we are matching against non-wildcard patterns, we
1696 // need to know the real type of the field so we can specialize
1697 // against it. This primarily occurs through constants - they
1698 // can include contents for fields that are inaccessible at the
1699 // location of the match. In that case, the field's type is
1700 // inhabited - by the constant - so we can just use it.
1702 // FIXME: this might lead to "unstable" behavior with macro hygiene
1703 // introducing uninhabited patterns for inaccessible fields. We
1704 // need to figure out how to model that.
1709 debug
!("is_useful_expand_first_col: pcx={:#?}, expanding {:#?}", pcx
, v
.head());
1711 if let Some(constructor
) = pat_constructor(cx
.tcx
, cx
.param_env
, v
.head()) {
1712 debug
!("is_useful - expanding constructor: {:#?}", constructor
);
1713 split_grouped_constructors(
1724 is_useful_specialized(
1735 .find(|result
| result
.is_useful())
1736 .unwrap_or(NotUseful
)
1738 debug
!("is_useful - expanding wildcard");
1740 let used_ctors
: Vec
<Constructor
<'_
>> =
1741 matrix
.heads().filter_map(|p
| pat_constructor(cx
.tcx
, cx
.param_env
, p
)).collect();
1742 debug
!("used_ctors = {:#?}", used_ctors
);
1743 // `all_ctors` are all the constructors for the given type, which
1744 // should all be represented (or caught with the wild pattern `_`).
1745 let all_ctors
= all_constructors(cx
, pcx
);
1746 debug
!("all_ctors = {:#?}", all_ctors
);
1748 // `missing_ctors` is the set of constructors from the same type as the
1749 // first column of `matrix` that are matched only by wildcard patterns
1750 // from the first column.
1752 // Therefore, if there is some pattern that is unmatched by `matrix`,
1753 // it will still be unmatched if the first constructor is replaced by
1754 // any of the constructors in `missing_ctors`
1756 // Missing constructors are those that are not matched by any non-wildcard patterns in the
1757 // current column. We only fully construct them on-demand, because they're rarely used and
1759 let missing_ctors
= MissingConstructors
::new(all_ctors
, used_ctors
);
1761 debug
!("missing_ctors.empty()={:#?}", missing_ctors
.is_empty(),);
1763 if missing_ctors
.is_empty() {
1764 let (all_ctors
, _
) = missing_ctors
.into_inner();
1765 split_grouped_constructors(cx
.tcx
, cx
.param_env
, pcx
, all_ctors
, matrix
, DUMMY_SP
, None
)
1768 is_useful_specialized(
1779 .find(|result
| result
.is_useful())
1780 .unwrap_or(NotUseful
)
1782 let matrix
= matrix
.specialize_wildcard();
1783 let v
= v
.to_tail();
1785 is_useful(cx
, &matrix
, &v
, witness_preference
, hir_id
, is_under_guard
, false);
1787 // In this case, there's at least one "free"
1788 // constructor that is only matched against by
1789 // wildcard patterns.
1791 // There are 2 ways we can report a witness here.
1792 // Commonly, we can report all the "free"
1793 // constructors as witnesses, e.g., if we have:
1796 // enum Direction { N, S, E, W }
1797 // let Direction::N = ...;
1800 // we can report 3 witnesses: `S`, `E`, and `W`.
1802 // However, there is a case where we don't want
1803 // to do this and instead report a single `_` witness:
1804 // if the user didn't actually specify a constructor
1805 // in this arm, e.g., in
1807 // let x: (Direction, Direction, bool) = ...;
1808 // let (_, _, false) = x;
1810 // we don't want to show all 16 possible witnesses
1811 // `(<direction-1>, <direction-2>, true)` - we are
1812 // satisfied with `(_, _, true)`. In this case,
1813 // `used_ctors` is empty.
1814 // The exception is: if we are at the top-level, for example in an empty match, we
1815 // sometimes prefer reporting the list of constructors instead of just `_`.
1816 let report_ctors_rather_than_wildcard
= is_top_level
&& !IntRange
::is_integral(pcx
.ty
);
1817 if missing_ctors
.all_ctors_are_missing() && !report_ctors_rather_than_wildcard
{
1818 // All constructors are unused. Add a wild pattern
1819 // rather than each individual constructor.
1820 usefulness
.apply_wildcard(pcx
.ty
)
1822 // Construct for each missing constructor a "wild" version of this
1823 // constructor, that matches everything that can be built with
1824 // it. For example, if `ctor` is a `Constructor::Variant` for
1825 // `Option::Some`, we get the pattern `Some(_)`.
1826 usefulness
.apply_missing_ctors(cx
, pcx
.ty
, &missing_ctors
)
1832 /// A shorthand for the `U(S(c, P), S(c, q))` operation from the paper. I.e., `is_useful` applied
1833 /// to the specialised version of both the pattern matrix `P` and the new pattern `q`.
1834 fn is_useful_specialized
<'p
, 'tcx
>(
1835 cx
: &mut MatchCheckCtxt
<'p
, 'tcx
>,
1836 matrix
: &Matrix
<'p
, 'tcx
>,
1837 v
: &PatStack
<'p
, 'tcx
>,
1838 ctor
: Constructor
<'tcx
>,
1840 witness_preference
: WitnessPreference
,
1842 is_under_guard
: bool
,
1843 ) -> Usefulness
<'tcx
, 'p
> {
1844 debug
!("is_useful_specialized({:#?}, {:#?}, {:?})", v
, ctor
, lty
);
1846 let ctor_wild_subpatterns
=
1847 cx
.pattern_arena
.alloc_from_iter(ctor
.wildcard_subpatterns(cx
, lty
));
1848 let matrix
= matrix
.specialize_constructor(cx
, &ctor
, ctor_wild_subpatterns
);
1849 v
.specialize_constructor(cx
, &ctor
, ctor_wild_subpatterns
)
1850 .map(|v
| is_useful(cx
, &matrix
, &v
, witness_preference
, hir_id
, is_under_guard
, false))
1851 .map(|u
| u
.apply_constructor(cx
, &ctor
, lty
))
1852 .unwrap_or(NotUseful
)
1855 /// Determines the constructor that the given pattern can be specialized to.
1856 /// Returns `None` in case of a catch-all, which can't be specialized.
1857 fn pat_constructor
<'tcx
>(
1859 param_env
: ty
::ParamEnv
<'tcx
>,
1861 ) -> Option
<Constructor
<'tcx
>> {
1863 PatKind
::AscribeUserType { .. }
=> bug
!(), // Handled by `expand_pattern`
1864 PatKind
::Binding { .. }
| PatKind
::Wild
=> None
,
1865 PatKind
::Leaf { .. }
| PatKind
::Deref { .. }
=> Some(Single
),
1866 PatKind
::Variant { adt_def, variant_index, .. }
=> {
1867 Some(Variant(adt_def
.variants
[variant_index
].def_id
))
1869 PatKind
::Constant { value }
=> {
1870 if let Some(int_range
) = IntRange
::from_const(tcx
, param_env
, value
, pat
.span
) {
1871 Some(IntRange(int_range
))
1873 match (value
.val
, &value
.ty
.kind
) {
1874 (_
, ty
::Array(_
, n
)) => {
1875 let len
= n
.eval_usize(tcx
, param_env
);
1876 Some(Slice(Slice { array_len: Some(len), kind: FixedLen(len) }
))
1878 (ty
::ConstKind
::Value(ConstValue
::Slice { start, end, .. }
), ty
::Slice(_
)) => {
1879 let len
= (end
- start
) as u64;
1880 Some(Slice(Slice { array_len: None, kind: FixedLen(len) }
))
1882 // FIXME(oli-obk): implement `deref` for `ConstValue`
1883 // (ty::ConstKind::Value(ConstValue::ByRef { .. }), ty::Slice(_)) => { ... }
1884 _
=> Some(ConstantValue(value
)),
1888 PatKind
::Range(PatRange { lo, hi, end }
) => {
1890 if let Some(int_range
) = IntRange
::from_range(
1892 lo
.eval_bits(tcx
, param_env
, lo
.ty
),
1893 hi
.eval_bits(tcx
, param_env
, hi
.ty
),
1898 Some(IntRange(int_range
))
1900 Some(FloatRange(lo
, hi
, end
))
1903 PatKind
::Array { ref prefix, ref slice, ref suffix }
1904 | PatKind
::Slice { ref prefix, ref slice, ref suffix }
=> {
1905 let array_len
= match pat
.ty
.kind
{
1906 ty
::Array(_
, length
) => Some(length
.eval_usize(tcx
, param_env
)),
1907 ty
::Slice(_
) => None
,
1908 _
=> span_bug
!(pat
.span
, "bad ty {:?} for slice pattern", pat
.ty
),
1910 let prefix
= prefix
.len() as u64;
1911 let suffix
= suffix
.len() as u64;
1913 if slice
.is_some() { VarLen(prefix, suffix) }
else { FixedLen(prefix + suffix) }
;
1914 Some(Slice(Slice { array_len, kind }
))
1916 PatKind
::Or { .. }
=> bug
!("Or-pattern should have been expanded earlier on."),
1920 // checks whether a constant is equal to a user-written slice pattern. Only supports byte slices,
1921 // meaning all other types will compare unequal and thus equal patterns often do not cause the
1922 // second pattern to lint about unreachable match arms.
1923 fn slice_pat_covered_by_const
<'tcx
>(
1926 const_val
: &'tcx ty
::Const
<'tcx
>,
1927 prefix
: &[Pat
<'tcx
>],
1928 slice
: &Option
<Pat
<'tcx
>>,
1929 suffix
: &[Pat
<'tcx
>],
1930 param_env
: ty
::ParamEnv
<'tcx
>,
1931 ) -> Result
<bool
, ErrorReported
> {
1932 let const_val_val
= if let ty
::ConstKind
::Value(val
) = const_val
.val
{
1936 "slice_pat_covered_by_const: {:#?}, {:#?}, {:#?}, {:#?}",
1944 let data
: &[u8] = match (const_val_val
, &const_val
.ty
.kind
) {
1945 (ConstValue
::ByRef { offset, alloc, .. }
, ty
::Array(t
, n
)) => {
1946 assert_eq
!(*t
, tcx
.types
.u8);
1947 let n
= n
.eval_usize(tcx
, param_env
);
1948 let ptr
= Pointer
::new(AllocId(0), offset
);
1949 alloc
.get_bytes(&tcx
, ptr
, Size
::from_bytes(n
)).unwrap()
1951 (ConstValue
::Slice { data, start, end }
, ty
::Slice(t
)) => {
1952 assert_eq
!(*t
, tcx
.types
.u8);
1953 let ptr
= Pointer
::new(AllocId(0), Size
::from_bytes(start
));
1954 data
.get_bytes(&tcx
, ptr
, Size
::from_bytes(end
- start
)).unwrap()
1956 // FIXME(oli-obk): create a way to extract fat pointers from ByRef
1957 (_
, ty
::Slice(_
)) => return Ok(false),
1959 "slice_pat_covered_by_const: {:#?}, {:#?}, {:#?}, {:#?}",
1967 let pat_len
= prefix
.len() + suffix
.len();
1968 if data
.len() < pat_len
|| (slice
.is_none() && data
.len() > pat_len
) {
1972 for (ch
, pat
) in data
[..prefix
.len()]
1975 .chain(data
[data
.len() - suffix
.len()..].iter().zip(suffix
))
1977 if let box PatKind
::Constant { value }
= pat
.kind
{
1978 let b
= value
.eval_bits(tcx
, param_env
, pat
.ty
);
1979 assert_eq
!(b
as u8 as u128
, b
);
1989 /// For exhaustive integer matching, some constructors are grouped within other constructors
1990 /// (namely integer typed values are grouped within ranges). However, when specialising these
1991 /// constructors, we want to be specialising for the underlying constructors (the integers), not
1992 /// the groups (the ranges). Thus we need to split the groups up. Splitting them up naïvely would
1993 /// mean creating a separate constructor for every single value in the range, which is clearly
1994 /// impractical. However, observe that for some ranges of integers, the specialisation will be
1995 /// identical across all values in that range (i.e., there are equivalence classes of ranges of
1996 /// constructors based on their `is_useful_specialized` outcome). These classes are grouped by
1997 /// the patterns that apply to them (in the matrix `P`). We can split the range whenever the
1998 /// patterns that apply to that range (specifically: the patterns that *intersect* with that range)
2000 /// Our solution, therefore, is to split the range constructor into subranges at every single point
2001 /// the group of intersecting patterns changes (using the method described below).
2002 /// And voilà! We're testing precisely those ranges that we need to, without any exhaustive matching
2003 /// on actual integers. The nice thing about this is that the number of subranges is linear in the
2004 /// number of rows in the matrix (i.e., the number of cases in the `match` statement), so we don't
2005 /// need to be worried about matching over gargantuan ranges.
2007 /// Essentially, given the first column of a matrix representing ranges, looking like the following:
2009 /// |------| |----------| |-------| ||
2010 /// |-------| |-------| |----| ||
2013 /// We split the ranges up into equivalence classes so the ranges are no longer overlapping:
2015 /// |--|--|||-||||--||---|||-------| |-|||| ||
2017 /// The logic for determining how to split the ranges is fairly straightforward: we calculate
2018 /// boundaries for each interval range, sort them, then create constructors for each new interval
2019 /// between every pair of boundary points. (This essentially sums up to performing the intuitive
2020 /// merging operation depicted above.)
2022 /// `hir_id` is `None` when we're evaluating the wildcard pattern, do not lint for overlapping in
2023 /// ranges that case.
2025 /// This also splits variable-length slices into fixed-length slices.
2026 fn split_grouped_constructors
<'p
, 'tcx
>(
2028 param_env
: ty
::ParamEnv
<'tcx
>,
2030 ctors
: Vec
<Constructor
<'tcx
>>,
2031 matrix
: &Matrix
<'p
, 'tcx
>,
2033 hir_id
: Option
<HirId
>,
2034 ) -> Vec
<Constructor
<'tcx
>> {
2036 let mut split_ctors
= Vec
::with_capacity(ctors
.len());
2037 debug
!("split_grouped_constructors({:#?}, {:#?})", matrix
, ctors
);
2039 for ctor
in ctors
.into_iter() {
2041 IntRange(ctor_range
) if ctor_range
.treat_exhaustively(tcx
) => {
2042 // Fast-track if the range is trivial. In particular, don't do the overlapping
2044 if ctor_range
.is_singleton() {
2045 split_ctors
.push(IntRange(ctor_range
));
2049 /// Represents a border between 2 integers. Because the intervals spanning borders
2050 /// must be able to cover every integer, we need to be able to represent
2051 /// 2^128 + 1 such borders.
2052 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Debug)]
2058 // A function for extracting the borders of an integer interval.
2059 fn range_borders(r
: IntRange
<'_
>) -> impl Iterator
<Item
= Border
> {
2060 let (lo
, hi
) = r
.range
.into_inner();
2061 let from
= Border
::JustBefore(lo
);
2062 let to
= match hi
.checked_add(1) {
2063 Some(m
) => Border
::JustBefore(m
),
2064 None
=> Border
::AfterMax
,
2066 vec
![from
, to
].into_iter()
2069 // Collect the span and range of all the intersecting ranges to lint on likely
2070 // incorrect range patterns. (#63987)
2071 let mut overlaps
= vec
![];
2072 // `borders` is the set of borders between equivalence classes: each equivalence
2073 // class lies between 2 borders.
2074 let row_borders
= matrix
2078 IntRange
::from_pat(tcx
, param_env
, row
.head()).map(|r
| (r
, row
.len()))
2080 .flat_map(|(range
, row_len
)| {
2081 let intersection
= ctor_range
.intersection(tcx
, &range
);
2082 let should_lint
= ctor_range
.suspicious_intersection(&range
);
2083 if let (Some(range
), 1, true) = (&intersection
, row_len
, should_lint
) {
2084 // FIXME: for now, only check for overlapping ranges on simple range
2085 // patterns. Otherwise with the current logic the following is detected
2087 // match (10u8, true) {
2088 // (0 ..= 125, false) => {}
2089 // (126 ..= 255, false) => {}
2090 // (0 ..= 255, true) => {}
2092 overlaps
.push(range
.clone());
2096 .flat_map(range_borders
);
2097 let ctor_borders
= range_borders(ctor_range
.clone());
2098 let mut borders
: Vec
<_
> = row_borders
.chain(ctor_borders
).collect();
2099 borders
.sort_unstable();
2101 lint_overlapping_patterns(tcx
, hir_id
, ctor_range
, ty
, overlaps
);
2103 // We're going to iterate through every adjacent pair of borders, making sure that
2104 // each represents an interval of nonnegative length, and convert each such
2105 // interval into a constructor.
2109 .filter_map(|window
| match (window
[0], window
[1]) {
2110 (Border
::JustBefore(n
), Border
::JustBefore(m
)) => {
2112 Some(IntRange { range: n..=(m - 1), ty, span }
)
2117 (Border
::JustBefore(n
), Border
::AfterMax
) => {
2118 Some(IntRange { range: n..=u128::MAX, ty, span }
)
2120 (Border
::AfterMax
, _
) => None
,
2125 Slice(Slice { array_len, kind: VarLen(self_prefix, self_suffix) }
) => {
2126 // The exhaustiveness-checking paper does not include any details on
2127 // checking variable-length slice patterns. However, they are matched
2128 // by an infinite collection of fixed-length array patterns.
2130 // Checking the infinite set directly would take an infinite amount
2131 // of time. However, it turns out that for each finite set of
2132 // patterns `P`, all sufficiently large array lengths are equivalent:
2134 // Each slice `s` with a "sufficiently-large" length `l ≥ L` that applies
2135 // to exactly the subset `Pₜ` of `P` can be transformed to a slice
2136 // `sₘ` for each sufficiently-large length `m` that applies to exactly
2137 // the same subset of `P`.
2139 // Because of that, each witness for reachability-checking from one
2140 // of the sufficiently-large lengths can be transformed to an
2141 // equally-valid witness from any other length, so we only have
2142 // to check slice lengths from the "minimal sufficiently-large length"
2145 // Note that the fact that there is a *single* `sₘ` for each `m`
2146 // not depending on the specific pattern in `P` is important: if
2147 // you look at the pair of patterns
2150 // Then any slice of length ≥1 that matches one of these two
2151 // patterns can be trivially turned to a slice of any
2152 // other length ≥1 that matches them and vice-versa - for
2153 // but the slice from length 2 `[false, true]` that matches neither
2154 // of these patterns can't be turned to a slice from length 1 that
2155 // matches neither of these patterns, so we have to consider
2156 // slices from length 2 there.
2158 // Now, to see that that length exists and find it, observe that slice
2159 // patterns are either "fixed-length" patterns (`[_, _, _]`) or
2160 // "variable-length" patterns (`[_, .., _]`).
2162 // For fixed-length patterns, all slices with lengths *longer* than
2163 // the pattern's length have the same outcome (of not matching), so
2164 // as long as `L` is greater than the pattern's length we can pick
2165 // any `sₘ` from that length and get the same result.
2167 // For variable-length patterns, the situation is more complicated,
2168 // because as seen above the precise value of `sₘ` matters.
2170 // However, for each variable-length pattern `p` with a prefix of length
2171 // `plₚ` and suffix of length `slₚ`, only the first `plₚ` and the last
2172 // `slₚ` elements are examined.
2174 // Therefore, as long as `L` is positive (to avoid concerns about empty
2175 // types), all elements after the maximum prefix length and before
2176 // the maximum suffix length are not examined by any variable-length
2177 // pattern, and therefore can be added/removed without affecting
2178 // them - creating equivalent patterns from any sufficiently-large
2181 // Of course, if fixed-length patterns exist, we must be sure
2182 // that our length is large enough to miss them all, so
2183 // we can pick `L = max(max(FIXED_LEN)+1, max(PREFIX_LEN) + max(SUFFIX_LEN))`
2185 // for example, with the above pair of patterns, all elements
2186 // but the first and last can be added/removed, so any
2187 // witness of length ≥2 (say, `[false, false, true]`) can be
2188 // turned to a witness from any other length ≥2.
2190 let mut max_prefix_len
= self_prefix
;
2191 let mut max_suffix_len
= self_suffix
;
2192 let mut max_fixed_len
= 0;
2195 matrix
.heads().filter_map(|pat
| pat_constructor(tcx
, param_env
, pat
));
2196 for ctor
in head_ctors
{
2197 if let Slice(slice
) = ctor
{
2198 match slice
.pattern_kind() {
2200 max_fixed_len
= cmp
::max(max_fixed_len
, len
);
2202 VarLen(prefix
, suffix
) => {
2203 max_prefix_len
= cmp
::max(max_prefix_len
, prefix
);
2204 max_suffix_len
= cmp
::max(max_suffix_len
, suffix
);
2210 // For diagnostics, we keep the prefix and suffix lengths separate, so in the case
2211 // where `max_fixed_len + 1` is the largest, we adapt `max_prefix_len` accordingly,
2212 // so that `L = max_prefix_len + max_suffix_len`.
2213 if max_fixed_len
+ 1 >= max_prefix_len
+ max_suffix_len
{
2214 // The subtraction can't overflow thanks to the above check.
2215 // The new `max_prefix_len` is also guaranteed to be larger than its previous
2217 max_prefix_len
= max_fixed_len
+ 1 - max_suffix_len
;
2222 let kind
= if max_prefix_len
+ max_suffix_len
< len
{
2223 VarLen(max_prefix_len
, max_suffix_len
)
2227 split_ctors
.push(Slice(Slice { array_len, kind }
));
2230 // `ctor` originally covered the range `(self_prefix +
2231 // self_suffix..infinity)`. We now split it into two: lengths smaller than
2232 // `max_prefix_len + max_suffix_len` are treated independently as
2233 // fixed-lengths slices, and lengths above are captured by a final VarLen
2236 (self_prefix
+ self_suffix
..max_prefix_len
+ max_suffix_len
)
2237 .map(|len
| Slice(Slice { array_len, kind: FixedLen(len) }
)),
2239 split_ctors
.push(Slice(Slice
{
2241 kind
: VarLen(max_prefix_len
, max_suffix_len
),
2246 // Any other constructor can be used unchanged.
2247 _
=> split_ctors
.push(ctor
),
2251 debug
!("split_grouped_constructors(..)={:#?}", split_ctors
);
2255 fn lint_overlapping_patterns
<'tcx
>(
2257 hir_id
: Option
<HirId
>,
2258 ctor_range
: IntRange
<'tcx
>,
2260 overlaps
: Vec
<IntRange
<'tcx
>>,
2262 if let (true, Some(hir_id
)) = (!overlaps
.is_empty(), hir_id
) {
2263 tcx
.struct_span_lint_hir(
2264 lint
::builtin
::OVERLAPPING_PATTERNS
,
2268 let mut err
= lint
.build("multiple patterns covering the same range");
2269 err
.span_label(ctor_range
.span
, "overlapping patterns");
2270 for int_range
in overlaps
{
2271 // Use the real type for user display of the ranges:
2275 "this range overlaps on `{}`",
2276 IntRange { range: int_range.range, ty, span: DUMMY_SP }
.to_pat(tcx
),
2286 fn constructor_covered_by_range
<'tcx
>(
2288 param_env
: ty
::ParamEnv
<'tcx
>,
2289 ctor
: &Constructor
<'tcx
>,
2292 if let Single
= ctor
{
2296 let (pat_from
, pat_to
, pat_end
, ty
) = match *pat
.kind
{
2297 PatKind
::Constant { value }
=> (value
, value
, RangeEnd
::Included
, value
.ty
),
2298 PatKind
::Range(PatRange { lo, hi, end }
) => (lo
, hi
, end
, lo
.ty
),
2299 _
=> bug
!("`constructor_covered_by_range` called with {:?}", pat
),
2301 let (ctor_from
, ctor_to
, ctor_end
) = match *ctor
{
2302 ConstantValue(value
) => (value
, value
, RangeEnd
::Included
),
2303 FloatRange(from
, to
, ctor_end
) => (from
, to
, ctor_end
),
2304 _
=> bug
!("`constructor_covered_by_range` called with {:?}", ctor
),
2306 trace
!("constructor_covered_by_range {:#?}, {:#?}, {:#?}, {}", ctor
, pat_from
, pat_to
, ty
);
2308 let to
= compare_const_vals(tcx
, ctor_to
, pat_to
, param_env
, ty
)?
;
2309 let from
= compare_const_vals(tcx
, ctor_from
, pat_from
, param_env
, ty
)?
;
2310 let intersects
= (from
== Ordering
::Greater
|| from
== Ordering
::Equal
)
2311 && (to
== Ordering
::Less
|| (pat_end
== ctor_end
&& to
== Ordering
::Equal
));
2312 if intersects { Some(()) }
else { None }
2315 fn patterns_for_variant
<'p
, 'tcx
>(
2316 cx
: &mut MatchCheckCtxt
<'p
, 'tcx
>,
2317 subpatterns
: &'p
[FieldPat
<'tcx
>],
2318 ctor_wild_subpatterns
: &'p
[Pat
<'tcx
>],
2319 is_non_exhaustive
: bool
,
2320 ) -> PatStack
<'p
, 'tcx
> {
2321 let mut result
: SmallVec
<_
> = ctor_wild_subpatterns
.iter().collect();
2323 for subpat
in subpatterns
{
2324 if !is_non_exhaustive
|| !cx
.is_uninhabited(subpat
.pattern
.ty
) {
2325 result
[subpat
.field
.index()] = &subpat
.pattern
;
2330 "patterns_for_variant({:#?}, {:#?}) = {:#?}",
2331 subpatterns
, ctor_wild_subpatterns
, result
2333 PatStack
::from_vec(result
)
2336 /// This is the main specialization step. It expands the pattern
2337 /// into `arity` patterns based on the constructor. For most patterns, the step is trivial,
2338 /// for instance tuple patterns are flattened and box patterns expand into their inner pattern.
2339 /// Returns `None` if the pattern does not have the given constructor.
2341 /// OTOH, slice patterns with a subslice pattern (tail @ ..) can be expanded into multiple
2342 /// different patterns.
2343 /// Structure patterns with a partial wild pattern (Foo { a: 42, .. }) have their missing
2344 /// fields filled with wild patterns.
2345 fn specialize_one_pattern
<'p
, 'tcx
>(
2346 cx
: &mut MatchCheckCtxt
<'p
, 'tcx
>,
2348 constructor
: &Constructor
<'tcx
>,
2349 ctor_wild_subpatterns
: &'p
[Pat
<'tcx
>],
2350 ) -> Option
<PatStack
<'p
, 'tcx
>> {
2351 if let NonExhaustive
= constructor
{
2352 // Only a wildcard pattern can match the special extra constructor
2353 return if pat
.is_wildcard() { Some(PatStack::default()) }
else { None }
;
2356 let result
= match *pat
.kind
{
2357 PatKind
::AscribeUserType { .. }
=> bug
!(), // Handled by `expand_pattern`
2359 PatKind
::Binding { .. }
| PatKind
::Wild
=> Some(ctor_wild_subpatterns
.iter().collect()),
2361 PatKind
::Variant { adt_def, variant_index, ref subpatterns, .. }
=> {
2362 let variant
= &adt_def
.variants
[variant_index
];
2363 let is_non_exhaustive
= cx
.is_foreign_non_exhaustive_variant(pat
.ty
, variant
);
2364 Some(Variant(variant
.def_id
))
2365 .filter(|variant_constructor
| variant_constructor
== constructor
)
2367 patterns_for_variant(cx
, subpatterns
, ctor_wild_subpatterns
, is_non_exhaustive
)
2371 PatKind
::Leaf { ref subpatterns }
=> {
2372 Some(patterns_for_variant(cx
, subpatterns
, ctor_wild_subpatterns
, false))
2375 PatKind
::Deref { ref subpattern }
=> Some(PatStack
::from_pattern(subpattern
)),
2377 PatKind
::Constant { value }
if constructor
.is_slice() => {
2378 // We extract an `Option` for the pointer because slices of zero
2379 // elements don't necessarily point to memory, they are usually
2380 // just integers. The only time they should be pointing to memory
2381 // is when they are subslices of nonzero slices.
2382 let (alloc
, offset
, n
, ty
) = match value
.ty
.kind
{
2383 ty
::Array(t
, n
) => {
2384 let n
= n
.eval_usize(cx
.tcx
, cx
.param_env
);
2385 // Shortcut for `n == 0` where no matter what `alloc` and `offset` we produce,
2386 // the result would be exactly what we early return here.
2388 if ctor_wild_subpatterns
.len() as u64 == 0 {
2389 return Some(PatStack
::from_slice(&[]));
2395 ty
::ConstKind
::Value(ConstValue
::ByRef { offset, alloc, .. }
) => {
2396 (Cow
::Borrowed(alloc
), offset
, n
, t
)
2398 _
=> span_bug
!(pat
.span
, "array pattern is {:?}", value
,),
2403 ty
::ConstKind
::Value(ConstValue
::Slice { data, start, end }
) => {
2404 let offset
= Size
::from_bytes(start
);
2405 let n
= (end
- start
) as u64;
2406 (Cow
::Borrowed(data
), offset
, n
, t
)
2408 ty
::ConstKind
::Value(ConstValue
::ByRef { .. }
) => {
2409 // FIXME(oli-obk): implement `deref` for `ConstValue`
2414 "slice pattern constant must be scalar pair but is {:?}",
2421 "unexpected const-val {:?} with ctor {:?}",
2426 if ctor_wild_subpatterns
.len() as u64 == n
{
2427 // convert a constant slice/array pattern to a list of patterns.
2428 let layout
= cx
.tcx
.layout_of(cx
.param_env
.and(ty
)).ok()?
;
2429 let ptr
= Pointer
::new(AllocId(0), offset
);
2432 let ptr
= ptr
.offset(layout
.size
* i
, &cx
.tcx
).ok()?
;
2433 let scalar
= alloc
.read_scalar(&cx
.tcx
, ptr
, layout
.size
).ok()?
;
2434 let scalar
= scalar
.not_undef().ok()?
;
2435 let value
= ty
::Const
::from_scalar(cx
.tcx
, scalar
, ty
);
2437 Pat { ty, span: pat.span, kind: box PatKind::Constant { value }
};
2438 Some(&*cx
.pattern_arena
.alloc(pattern
))
2446 PatKind
::Constant { .. }
| PatKind
::Range { .. }
=> {
2447 // If the constructor is a:
2448 // - Single value: add a row if the pattern contains the constructor.
2449 // - Range: add a row if the constructor intersects the pattern.
2450 if let IntRange(ctor
) = constructor
{
2451 match IntRange
::from_pat(cx
.tcx
, cx
.param_env
, pat
) {
2452 Some(pat
) => ctor
.intersection(cx
.tcx
, &pat
).map(|_
| {
2453 // Constructor splitting should ensure that all intersections we encounter
2454 // are actually inclusions.
2455 assert
!(ctor
.is_subrange(&pat
));
2461 // Fallback for non-ranges and ranges that involve
2462 // floating-point numbers, which are not conveniently handled
2463 // by `IntRange`. For these cases, the constructor may not be a
2464 // range so intersection actually devolves into being covered
2466 constructor_covered_by_range(cx
.tcx
, cx
.param_env
, constructor
, pat
)
2467 .map(|()| PatStack
::default())
2471 PatKind
::Array { ref prefix, ref slice, ref suffix }
2472 | PatKind
::Slice { ref prefix, ref slice, ref suffix }
=> match *constructor
{
2474 let pat_len
= prefix
.len() + suffix
.len();
2475 if let Some(slice_count
) = ctor_wild_subpatterns
.len().checked_sub(pat_len
) {
2476 if slice_count
== 0 || slice
.is_some() {
2481 ctor_wild_subpatterns
2485 .chain(suffix
.iter()),
2496 ConstantValue(cv
) => {
2497 match slice_pat_covered_by_const(
2506 Ok(true) => Some(PatStack
::default()),
2508 Err(ErrorReported
) => None
,
2511 _
=> span_bug
!(pat
.span
, "unexpected ctor {:?} for slice pat", constructor
),
2514 PatKind
::Or { .. }
=> bug
!("Or-pattern should have been expanded earlier on."),
2516 debug
!("specialize({:#?}, {:#?}) = {:#?}", pat
, ctor_wild_subpatterns
, result
);