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1 | // Copyright 2012-2016 The Rust Project Developers. See the COPYRIGHT |
2 | // file at the top-level directory of this distribution and at | |
3 | // http://rust-lang.org/COPYRIGHT. | |
4 | // | |
5 | // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or | |
6 | // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license | |
7 | // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your | |
8 | // option. This file may not be copied, modified, or distributed | |
9 | // except according to those terms. | |
10 | ||
11 | use self::Constructor::*; | |
12 | use self::Usefulness::*; | |
13 | use self::WitnessPreference::*; | |
14 | ||
15 | use rustc::middle::const_val::ConstVal; | |
16 | use eval::{compare_const_vals}; | |
17 | ||
18 | use rustc_const_math::ConstInt; | |
19 | ||
8bb4bdeb | 20 | use rustc_data_structures::fx::FxHashMap; |
c30ab7b3 SL |
21 | use rustc_data_structures::indexed_vec::Idx; |
22 | ||
23 | use pattern::{FieldPattern, Pattern, PatternKind}; | |
24 | use pattern::{PatternFoldable, PatternFolder}; | |
25 | ||
476ff2be | 26 | use rustc::hir::def_id::DefId; |
32a655c1 SL |
27 | use rustc::hir::RangeEnd; |
28 | use rustc::ty::{self, AdtKind, Ty, TyCtxt, TypeFoldable}; | |
c30ab7b3 | 29 | |
32a655c1 | 30 | use rustc::mir::Field; |
c30ab7b3 SL |
31 | use rustc::util::common::ErrorReported; |
32 | ||
c30ab7b3 SL |
33 | use syntax_pos::{Span, DUMMY_SP}; |
34 | ||
35 | use arena::TypedArena; | |
36 | ||
476ff2be | 37 | use std::cmp::{self, Ordering}; |
c30ab7b3 SL |
38 | use std::fmt; |
39 | use std::iter::{FromIterator, IntoIterator, repeat}; | |
40 | ||
41 | pub fn expand_pattern<'a, 'tcx>(cx: &MatchCheckCtxt<'a, 'tcx>, pat: Pattern<'tcx>) | |
42 | -> &'a Pattern<'tcx> | |
43 | { | |
44 | cx.pattern_arena.alloc(LiteralExpander.fold_pattern(&pat)) | |
45 | } | |
46 | ||
47 | struct LiteralExpander; | |
48 | impl<'tcx> PatternFolder<'tcx> for LiteralExpander { | |
49 | fn fold_pattern(&mut self, pat: &Pattern<'tcx>) -> Pattern<'tcx> { | |
50 | match (&pat.ty.sty, &*pat.kind) { | |
51 | (&ty::TyRef(_, mt), &PatternKind::Constant { ref value }) => { | |
52 | Pattern { | |
53 | ty: pat.ty, | |
54 | span: pat.span, | |
55 | kind: box PatternKind::Deref { | |
56 | subpattern: Pattern { | |
57 | ty: mt.ty, | |
58 | span: pat.span, | |
59 | kind: box PatternKind::Constant { value: value.clone() }, | |
60 | } | |
61 | } | |
62 | } | |
63 | } | |
64 | (_, &PatternKind::Binding { subpattern: Some(ref s), .. }) => { | |
65 | s.fold_with(self) | |
66 | } | |
67 | _ => pat.super_fold_with(self) | |
68 | } | |
69 | } | |
70 | } | |
71 | ||
c30ab7b3 SL |
72 | impl<'tcx> Pattern<'tcx> { |
73 | fn is_wildcard(&self) -> bool { | |
74 | match *self.kind { | |
75 | PatternKind::Binding { subpattern: None, .. } | PatternKind::Wild => | |
76 | true, | |
77 | _ => false | |
78 | } | |
79 | } | |
80 | } | |
81 | ||
82 | pub struct Matrix<'a, 'tcx: 'a>(Vec<Vec<&'a Pattern<'tcx>>>); | |
83 | ||
84 | impl<'a, 'tcx> Matrix<'a, 'tcx> { | |
85 | pub fn empty() -> Self { | |
86 | Matrix(vec![]) | |
87 | } | |
88 | ||
89 | pub fn push(&mut self, row: Vec<&'a Pattern<'tcx>>) { | |
90 | self.0.push(row) | |
91 | } | |
92 | } | |
93 | ||
94 | /// Pretty-printer for matrices of patterns, example: | |
95 | /// ++++++++++++++++++++++++++ | |
96 | /// + _ + [] + | |
97 | /// ++++++++++++++++++++++++++ | |
98 | /// + true + [First] + | |
99 | /// ++++++++++++++++++++++++++ | |
100 | /// + true + [Second(true)] + | |
101 | /// ++++++++++++++++++++++++++ | |
102 | /// + false + [_] + | |
103 | /// ++++++++++++++++++++++++++ | |
104 | /// + _ + [_, _, ..tail] + | |
105 | /// ++++++++++++++++++++++++++ | |
106 | impl<'a, 'tcx> fmt::Debug for Matrix<'a, 'tcx> { | |
107 | fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { | |
108 | write!(f, "\n")?; | |
109 | ||
110 | let &Matrix(ref m) = self; | |
111 | let pretty_printed_matrix: Vec<Vec<String>> = m.iter().map(|row| { | |
112 | row.iter().map(|pat| format!("{:?}", pat)).collect() | |
113 | }).collect(); | |
114 | ||
115 | let column_count = m.iter().map(|row| row.len()).max().unwrap_or(0); | |
116 | assert!(m.iter().all(|row| row.len() == column_count)); | |
117 | let column_widths: Vec<usize> = (0..column_count).map(|col| { | |
118 | pretty_printed_matrix.iter().map(|row| row[col].len()).max().unwrap_or(0) | |
119 | }).collect(); | |
120 | ||
121 | let total_width = column_widths.iter().cloned().sum::<usize>() + column_count * 3 + 1; | |
122 | let br = repeat('+').take(total_width).collect::<String>(); | |
123 | write!(f, "{}\n", br)?; | |
124 | for row in pretty_printed_matrix { | |
125 | write!(f, "+")?; | |
126 | for (column, pat_str) in row.into_iter().enumerate() { | |
127 | write!(f, " ")?; | |
128 | write!(f, "{:1$}", pat_str, column_widths[column])?; | |
129 | write!(f, " +")?; | |
130 | } | |
131 | write!(f, "\n")?; | |
132 | write!(f, "{}\n", br)?; | |
133 | } | |
134 | Ok(()) | |
135 | } | |
136 | } | |
137 | ||
138 | impl<'a, 'tcx> FromIterator<Vec<&'a Pattern<'tcx>>> for Matrix<'a, 'tcx> { | |
139 | fn from_iter<T: IntoIterator<Item=Vec<&'a Pattern<'tcx>>>>(iter: T) -> Self | |
140 | { | |
141 | Matrix(iter.into_iter().collect()) | |
142 | } | |
143 | } | |
144 | ||
145 | //NOTE: appears to be the only place other then InferCtxt to contain a ParamEnv | |
146 | pub struct MatchCheckCtxt<'a, 'tcx: 'a> { | |
147 | pub tcx: TyCtxt<'a, 'tcx, 'tcx>, | |
32a655c1 SL |
148 | /// The module in which the match occurs. This is necessary for |
149 | /// checking inhabited-ness of types because whether a type is (visibly) | |
150 | /// inhabited can depend on whether it was defined in the current module or | |
151 | /// not. eg. `struct Foo { _private: ! }` cannot be seen to be empty | |
152 | /// outside it's module and should not be matchable with an empty match | |
153 | /// statement. | |
154 | pub module: DefId, | |
c30ab7b3 | 155 | pub pattern_arena: &'a TypedArena<Pattern<'tcx>>, |
476ff2be | 156 | pub byte_array_map: FxHashMap<*const Pattern<'tcx>, Vec<&'a Pattern<'tcx>>>, |
c30ab7b3 SL |
157 | } |
158 | ||
159 | impl<'a, 'tcx> MatchCheckCtxt<'a, 'tcx> { | |
160 | pub fn create_and_enter<F, R>( | |
161 | tcx: TyCtxt<'a, 'tcx, 'tcx>, | |
32a655c1 | 162 | module: DefId, |
c30ab7b3 SL |
163 | f: F) -> R |
164 | where F: for<'b> FnOnce(MatchCheckCtxt<'b, 'tcx>) -> R | |
165 | { | |
c30ab7b3 SL |
166 | let pattern_arena = TypedArena::new(); |
167 | ||
168 | f(MatchCheckCtxt { | |
169 | tcx: tcx, | |
32a655c1 | 170 | module: module, |
c30ab7b3 | 171 | pattern_arena: &pattern_arena, |
476ff2be | 172 | byte_array_map: FxHashMap(), |
c30ab7b3 SL |
173 | }) |
174 | } | |
175 | ||
176 | // convert a byte-string pattern to a list of u8 patterns. | |
32a655c1 SL |
177 | fn lower_byte_str_pattern<'p>(&mut self, pat: &'p Pattern<'tcx>) -> Vec<&'p Pattern<'tcx>> |
178 | where 'a: 'p | |
179 | { | |
c30ab7b3 SL |
180 | let pattern_arena = &*self.pattern_arena; |
181 | let tcx = self.tcx; | |
182 | self.byte_array_map.entry(pat).or_insert_with(|| { | |
183 | match pat.kind { | |
184 | box PatternKind::Constant { | |
185 | value: ConstVal::ByteStr(ref data) | |
186 | } => { | |
187 | data.iter().map(|c| &*pattern_arena.alloc(Pattern { | |
188 | ty: tcx.types.u8, | |
189 | span: pat.span, | |
190 | kind: box PatternKind::Constant { | |
191 | value: ConstVal::Integral(ConstInt::U8(*c)) | |
192 | } | |
193 | })).collect() | |
194 | } | |
195 | _ => span_bug!(pat.span, "unexpected byte array pattern {:?}", pat) | |
196 | } | |
197 | }).clone() | |
198 | } | |
32a655c1 SL |
199 | |
200 | fn is_uninhabited(&self, ty: Ty<'tcx>) -> bool { | |
201 | if self.tcx.sess.features.borrow().never_type { | |
202 | ty.is_uninhabited_from(self.module, self.tcx) | |
203 | } else { | |
204 | false | |
205 | } | |
206 | } | |
207 | ||
208 | fn is_variant_uninhabited(&self, | |
209 | variant: &'tcx ty::VariantDef, | |
210 | substs: &'tcx ty::subst::Substs<'tcx>) -> bool | |
211 | { | |
212 | if self.tcx.sess.features.borrow().never_type { | |
213 | let forest = variant.uninhabited_from( | |
8bb4bdeb | 214 | &mut FxHashMap::default(), self.tcx, substs, AdtKind::Enum |
32a655c1 SL |
215 | ); |
216 | forest.contains(self.tcx, self.module) | |
217 | } else { | |
218 | false | |
219 | } | |
220 | } | |
c30ab7b3 SL |
221 | } |
222 | ||
223 | #[derive(Clone, Debug, PartialEq)] | |
8bb4bdeb | 224 | pub enum Constructor<'tcx> { |
c30ab7b3 SL |
225 | /// The constructor of all patterns that don't vary by constructor, |
226 | /// e.g. struct patterns and fixed-length arrays. | |
227 | Single, | |
228 | /// Enum variants. | |
229 | Variant(DefId), | |
230 | /// Literal values. | |
8bb4bdeb | 231 | ConstantValue(ConstVal<'tcx>), |
32a655c1 | 232 | /// Ranges of literal values (`2...5` and `2..5`). |
8bb4bdeb | 233 | ConstantRange(ConstVal<'tcx>, ConstVal<'tcx>, RangeEnd), |
c30ab7b3 SL |
234 | /// Array patterns of length n. |
235 | Slice(usize), | |
236 | } | |
237 | ||
8bb4bdeb | 238 | impl<'tcx> Constructor<'tcx> { |
32a655c1 | 239 | fn variant_index_for_adt(&self, adt: &'tcx ty::AdtDef) -> usize { |
c30ab7b3 | 240 | match self { |
32a655c1 | 241 | &Variant(vid) => adt.variant_index_with_id(vid), |
c30ab7b3 SL |
242 | &Single => { |
243 | assert_eq!(adt.variants.len(), 1); | |
32a655c1 | 244 | 0 |
c30ab7b3 SL |
245 | } |
246 | _ => bug!("bad constructor {:?} for adt {:?}", self, adt) | |
247 | } | |
248 | } | |
249 | } | |
250 | ||
32a655c1 SL |
251 | #[derive(Clone)] |
252 | pub enum Usefulness<'tcx> { | |
c30ab7b3 | 253 | Useful, |
32a655c1 | 254 | UsefulWithWitness(Vec<Witness<'tcx>>), |
c30ab7b3 SL |
255 | NotUseful |
256 | } | |
257 | ||
32a655c1 SL |
258 | impl<'tcx> Usefulness<'tcx> { |
259 | fn is_useful(&self) -> bool { | |
260 | match *self { | |
261 | NotUseful => false, | |
262 | _ => true | |
263 | } | |
264 | } | |
265 | } | |
266 | ||
c30ab7b3 SL |
267 | #[derive(Copy, Clone)] |
268 | pub enum WitnessPreference { | |
269 | ConstructWitness, | |
270 | LeaveOutWitness | |
271 | } | |
272 | ||
273 | #[derive(Copy, Clone, Debug)] | |
274 | struct PatternContext<'tcx> { | |
275 | ty: Ty<'tcx>, | |
276 | max_slice_length: usize, | |
277 | } | |
278 | ||
c30ab7b3 | 279 | /// A stack of patterns in reverse order of construction |
32a655c1 SL |
280 | #[derive(Clone)] |
281 | pub struct Witness<'tcx>(Vec<Pattern<'tcx>>); | |
c30ab7b3 | 282 | |
32a655c1 SL |
283 | impl<'tcx> Witness<'tcx> { |
284 | pub fn single_pattern(&self) -> &Pattern<'tcx> { | |
c30ab7b3 SL |
285 | assert_eq!(self.0.len(), 1); |
286 | &self.0[0] | |
287 | } | |
288 | ||
32a655c1 | 289 | fn push_wild_constructor<'a>( |
c30ab7b3 SL |
290 | mut self, |
291 | cx: &MatchCheckCtxt<'a, 'tcx>, | |
8bb4bdeb | 292 | ctor: &Constructor<'tcx>, |
c30ab7b3 SL |
293 | ty: Ty<'tcx>) |
294 | -> Self | |
295 | { | |
32a655c1 SL |
296 | let sub_pattern_tys = constructor_sub_pattern_tys(cx, ctor, ty); |
297 | self.0.extend(sub_pattern_tys.into_iter().map(|ty| { | |
298 | Pattern { | |
299 | ty: ty, | |
300 | span: DUMMY_SP, | |
301 | kind: box PatternKind::Wild, | |
302 | } | |
303 | })); | |
c30ab7b3 SL |
304 | self.apply_constructor(cx, ctor, ty) |
305 | } | |
306 | ||
307 | ||
308 | /// Constructs a partial witness for a pattern given a list of | |
309 | /// patterns expanded by the specialization step. | |
310 | /// | |
311 | /// When a pattern P is discovered to be useful, this function is used bottom-up | |
312 | /// to reconstruct a complete witness, e.g. a pattern P' that covers a subset | |
313 | /// of values, V, where each value in that set is not covered by any previously | |
314 | /// used patterns and is covered by the pattern P'. Examples: | |
315 | /// | |
316 | /// left_ty: tuple of 3 elements | |
317 | /// pats: [10, 20, _] => (10, 20, _) | |
318 | /// | |
319 | /// left_ty: struct X { a: (bool, &'static str), b: usize} | |
320 | /// pats: [(false, "foo"), 42] => X { a: (false, "foo"), b: 42 } | |
32a655c1 | 321 | fn apply_constructor<'a>( |
c30ab7b3 SL |
322 | mut self, |
323 | cx: &MatchCheckCtxt<'a,'tcx>, | |
8bb4bdeb | 324 | ctor: &Constructor<'tcx>, |
c30ab7b3 SL |
325 | ty: Ty<'tcx>) |
326 | -> Self | |
327 | { | |
328 | let arity = constructor_arity(cx, ctor, ty); | |
329 | let pat = { | |
330 | let len = self.0.len(); | |
331 | let mut pats = self.0.drain(len-arity..).rev(); | |
332 | ||
333 | match ty.sty { | |
32a655c1 SL |
334 | ty::TyAdt(..) | |
335 | ty::TyTuple(..) => { | |
336 | let pats = pats.enumerate().map(|(i, p)| { | |
337 | FieldPattern { | |
338 | field: Field::new(i), | |
339 | pattern: p | |
c30ab7b3 | 340 | } |
32a655c1 SL |
341 | }).collect(); |
342 | ||
343 | if let ty::TyAdt(adt, substs) = ty.sty { | |
344 | if adt.variants.len() > 1 { | |
345 | PatternKind::Variant { | |
346 | adt_def: adt, | |
347 | substs: substs, | |
348 | variant_index: ctor.variant_index_for_adt(adt), | |
349 | subpatterns: pats | |
350 | } | |
351 | } else { | |
352 | PatternKind::Leaf { subpatterns: pats } | |
c30ab7b3 | 353 | } |
32a655c1 SL |
354 | } else { |
355 | PatternKind::Leaf { subpatterns: pats } | |
c30ab7b3 SL |
356 | } |
357 | } | |
358 | ||
32a655c1 SL |
359 | ty::TyRef(..) => { |
360 | PatternKind::Deref { subpattern: pats.nth(0).unwrap() } | |
c30ab7b3 SL |
361 | } |
362 | ||
363 | ty::TySlice(_) | ty::TyArray(..) => { | |
32a655c1 SL |
364 | PatternKind::Slice { |
365 | prefix: pats.collect(), | |
366 | slice: None, | |
367 | suffix: vec![] | |
368 | } | |
c30ab7b3 SL |
369 | } |
370 | ||
371 | _ => { | |
372 | match *ctor { | |
32a655c1 SL |
373 | ConstantValue(ref v) => PatternKind::Constant { value: v.clone() }, |
374 | _ => PatternKind::Wild, | |
c30ab7b3 SL |
375 | } |
376 | } | |
377 | } | |
378 | }; | |
379 | ||
32a655c1 SL |
380 | self.0.push(Pattern { |
381 | ty: ty, | |
382 | span: DUMMY_SP, | |
383 | kind: Box::new(pat), | |
384 | }); | |
c30ab7b3 SL |
385 | |
386 | self | |
387 | } | |
388 | } | |
389 | ||
c30ab7b3 SL |
390 | /// This determines the set of all possible constructors of a pattern matching |
391 | /// values of type `left_ty`. For vectors, this would normally be an infinite set | |
32a655c1 SL |
392 | /// but is instead bounded by the maximum fixed length of slice patterns in |
393 | /// the column of patterns being analyzed. | |
c30ab7b3 SL |
394 | /// |
395 | /// This intentionally does not list ConstantValue specializations for | |
396 | /// non-booleans, because we currently assume that there is always a | |
397 | /// "non-standard constant" that matches. See issue #12483. | |
398 | /// | |
32a655c1 SL |
399 | /// We make sure to omit constructors that are statically impossible. eg for |
400 | /// Option<!> we do not include Some(_) in the returned list of constructors. | |
401 | fn all_constructors<'a, 'tcx: 'a>(cx: &mut MatchCheckCtxt<'a, 'tcx>, | |
8bb4bdeb XL |
402 | pcx: PatternContext<'tcx>) |
403 | -> Vec<Constructor<'tcx>> | |
32a655c1 SL |
404 | { |
405 | debug!("all_constructors({:?})", pcx.ty); | |
c30ab7b3 SL |
406 | match pcx.ty.sty { |
407 | ty::TyBool => | |
408 | [true, false].iter().map(|b| ConstantValue(ConstVal::Bool(*b))).collect(), | |
32a655c1 SL |
409 | ty::TySlice(ref sub_ty) => { |
410 | if cx.is_uninhabited(sub_ty) { | |
411 | vec![Slice(0)] | |
412 | } else { | |
413 | (0..pcx.max_slice_length+1).map(|length| Slice(length)).collect() | |
414 | } | |
415 | } | |
416 | ty::TyArray(ref sub_ty, length) => { | |
417 | if length > 0 && cx.is_uninhabited(sub_ty) { | |
418 | vec![] | |
419 | } else { | |
420 | vec![Slice(length)] | |
421 | } | |
422 | } | |
423 | ty::TyAdt(def, substs) if def.is_enum() && def.variants.len() != 1 => { | |
424 | def.variants.iter() | |
425 | .filter(|v| !cx.is_variant_uninhabited(v, substs)) | |
426 | .map(|v| Variant(v.did)) | |
427 | .collect() | |
428 | } | |
429 | _ => { | |
430 | if cx.is_uninhabited(pcx.ty) { | |
431 | vec![] | |
432 | } else { | |
433 | vec![Single] | |
434 | } | |
435 | } | |
c30ab7b3 SL |
436 | } |
437 | } | |
438 | ||
32a655c1 | 439 | fn max_slice_length<'p, 'a: 'p, 'tcx: 'a, I>( |
476ff2be SL |
440 | _cx: &mut MatchCheckCtxt<'a, 'tcx>, |
441 | patterns: I) -> usize | |
32a655c1 | 442 | where I: Iterator<Item=&'p Pattern<'tcx>> |
476ff2be SL |
443 | { |
444 | // The exhaustiveness-checking paper does not include any details on | |
445 | // checking variable-length slice patterns. However, they are matched | |
446 | // by an infinite collection of fixed-length array patterns. | |
447 | // | |
448 | // Checking the infinite set directly would take an infinite amount | |
449 | // of time. However, it turns out that for each finite set of | |
450 | // patterns `P`, all sufficiently large array lengths are equivalent: | |
451 | // | |
452 | // Each slice `s` with a "sufficiently-large" length `l ≥ L` that applies | |
453 | // to exactly the subset `Pₜ` of `P` can be transformed to a slice | |
454 | // `sₘ` for each sufficiently-large length `m` that applies to exactly | |
455 | // the same subset of `P`. | |
456 | // | |
457 | // Because of that, each witness for reachability-checking from one | |
458 | // of the sufficiently-large lengths can be transformed to an | |
459 | // equally-valid witness from any other length, so we only have | |
460 | // to check slice lengths from the "minimal sufficiently-large length" | |
461 | // and below. | |
462 | // | |
463 | // Note that the fact that there is a *single* `sₘ` for each `m` | |
464 | // not depending on the specific pattern in `P` is important: if | |
465 | // you look at the pair of patterns | |
466 | // `[true, ..]` | |
467 | // `[.., false]` | |
468 | // Then any slice of length ≥1 that matches one of these two | |
469 | // patterns can be be trivially turned to a slice of any | |
470 | // other length ≥1 that matches them and vice-versa - for | |
471 | // but the slice from length 2 `[false, true]` that matches neither | |
472 | // of these patterns can't be turned to a slice from length 1 that | |
473 | // matches neither of these patterns, so we have to consider | |
474 | // slices from length 2 there. | |
475 | // | |
476 | // Now, to see that that length exists and find it, observe that slice | |
477 | // patterns are either "fixed-length" patterns (`[_, _, _]`) or | |
478 | // "variable-length" patterns (`[_, .., _]`). | |
479 | // | |
480 | // For fixed-length patterns, all slices with lengths *longer* than | |
481 | // the pattern's length have the same outcome (of not matching), so | |
482 | // as long as `L` is greater than the pattern's length we can pick | |
483 | // any `sₘ` from that length and get the same result. | |
484 | // | |
485 | // For variable-length patterns, the situation is more complicated, | |
486 | // because as seen above the precise value of `sₘ` matters. | |
487 | // | |
488 | // However, for each variable-length pattern `p` with a prefix of length | |
489 | // `plâ‚š` and suffix of length `slâ‚š`, only the first `plâ‚š` and the last | |
490 | // `slâ‚š` elements are examined. | |
491 | // | |
492 | // Therefore, as long as `L` is positive (to avoid concerns about empty | |
493 | // types), all elements after the maximum prefix length and before | |
494 | // the maximum suffix length are not examined by any variable-length | |
495 | // pattern, and therefore can be added/removed without affecting | |
496 | // them - creating equivalent patterns from any sufficiently-large | |
497 | // length. | |
498 | // | |
499 | // Of course, if fixed-length patterns exist, we must be sure | |
500 | // that our length is large enough to miss them all, so | |
501 | // we can pick `L = max(FIXED_LEN+1 ∪ {max(PREFIX_LEN) + max(SUFFIX_LEN)})` | |
502 | // | |
503 | // for example, with the above pair of patterns, all elements | |
504 | // but the first and last can be added/removed, so any | |
505 | // witness of length ≥2 (say, `[false, false, true]`) can be | |
506 | // turned to a witness from any other length ≥2. | |
507 | ||
508 | let mut max_prefix_len = 0; | |
509 | let mut max_suffix_len = 0; | |
510 | let mut max_fixed_len = 0; | |
511 | ||
512 | for row in patterns { | |
513 | match *row.kind { | |
514 | PatternKind::Constant { value: ConstVal::ByteStr(ref data) } => { | |
515 | max_fixed_len = cmp::max(max_fixed_len, data.len()); | |
516 | } | |
517 | PatternKind::Slice { ref prefix, slice: None, ref suffix } => { | |
518 | let fixed_len = prefix.len() + suffix.len(); | |
519 | max_fixed_len = cmp::max(max_fixed_len, fixed_len); | |
520 | } | |
521 | PatternKind::Slice { ref prefix, slice: Some(_), ref suffix } => { | |
522 | max_prefix_len = cmp::max(max_prefix_len, prefix.len()); | |
523 | max_suffix_len = cmp::max(max_suffix_len, suffix.len()); | |
524 | } | |
525 | _ => {} | |
526 | } | |
527 | } | |
528 | ||
529 | cmp::max(max_fixed_len + 1, max_prefix_len + max_suffix_len) | |
530 | } | |
531 | ||
c30ab7b3 | 532 | /// Algorithm from http://moscova.inria.fr/~maranget/papers/warn/index.html |
32a655c1 SL |
533 | /// The algorithm from the paper has been modified to correctly handle empty |
534 | /// types. The changes are: | |
535 | /// (0) We don't exit early if the pattern matrix has zero rows. We just | |
536 | /// continue to recurse over columns. | |
537 | /// (1) all_constructors will only return constructors that are statically | |
538 | /// possible. eg. it will only return Ok for Result<T, !> | |
c30ab7b3 SL |
539 | /// |
540 | /// Whether a vector `v` of patterns is 'useful' in relation to a set of such | |
541 | /// vectors `m` is defined as there being a set of inputs that will match `v` | |
542 | /// but not any of the sets in `m`. | |
543 | /// | |
544 | /// This is used both for reachability checking (if a pattern isn't useful in | |
545 | /// relation to preceding patterns, it is not reachable) and exhaustiveness | |
546 | /// checking (if a wildcard pattern is useful in relation to a matrix, the | |
547 | /// matrix isn't exhaustive). | |
32a655c1 SL |
548 | pub fn is_useful<'p, 'a: 'p, 'tcx: 'a>(cx: &mut MatchCheckCtxt<'a, 'tcx>, |
549 | matrix: &Matrix<'p, 'tcx>, | |
550 | v: &[&'p Pattern<'tcx>], | |
c30ab7b3 | 551 | witness: WitnessPreference) |
32a655c1 | 552 | -> Usefulness<'tcx> { |
c30ab7b3 SL |
553 | let &Matrix(ref rows) = matrix; |
554 | debug!("is_useful({:?}, {:?})", matrix, v); | |
c30ab7b3 | 555 | |
32a655c1 SL |
556 | // The base case. We are pattern-matching on () and the return value is |
557 | // based on whether our matrix has a row or not. | |
558 | // NOTE: This could potentially be optimized by checking rows.is_empty() | |
559 | // first and then, if v is non-empty, the return value is based on whether | |
560 | // the type of the tuple we're checking is inhabited or not. | |
561 | if v.is_empty() { | |
562 | return if rows.is_empty() { | |
563 | match witness { | |
564 | ConstructWitness => UsefulWithWitness(vec![Witness(vec![])]), | |
565 | LeaveOutWitness => Useful, | |
566 | } | |
567 | } else { | |
568 | NotUseful | |
569 | } | |
570 | }; | |
476ff2be | 571 | |
32a655c1 | 572 | assert!(rows.iter().all(|r| r.len() == v.len())); |
476ff2be | 573 | |
c30ab7b3 SL |
574 | let pcx = PatternContext { |
575 | ty: rows.iter().map(|r| r[0].ty).find(|ty| !ty.references_error()) | |
576 | .unwrap_or(v[0].ty), | |
476ff2be | 577 | max_slice_length: max_slice_length(cx, rows.iter().map(|r| r[0]).chain(Some(v[0]))) |
c30ab7b3 SL |
578 | }; |
579 | ||
580 | debug!("is_useful_expand_first_col: pcx={:?}, expanding {:?}", pcx, v[0]); | |
581 | ||
582 | if let Some(constructors) = pat_constructors(cx, v[0], pcx) { | |
583 | debug!("is_useful - expanding constructors: {:?}", constructors); | |
584 | constructors.into_iter().map(|c| | |
585 | is_useful_specialized(cx, matrix, v, c.clone(), pcx.ty, witness) | |
32a655c1 | 586 | ).find(|result| result.is_useful()).unwrap_or(NotUseful) |
c30ab7b3 SL |
587 | } else { |
588 | debug!("is_useful - expanding wildcard"); | |
32a655c1 SL |
589 | |
590 | let used_ctors: Vec<Constructor> = rows.iter().flat_map(|row| { | |
591 | pat_constructors(cx, row[0], pcx).unwrap_or(vec![]) | |
592 | }).collect(); | |
593 | debug!("used_ctors = {:?}", used_ctors); | |
594 | let all_ctors = all_constructors(cx, pcx); | |
595 | debug!("all_ctors = {:?}", all_ctors); | |
596 | let missing_ctors: Vec<Constructor> = all_ctors.iter().filter(|c| { | |
597 | !used_ctors.contains(*c) | |
598 | }).cloned().collect(); | |
599 | ||
600 | // `missing_ctors` is the set of constructors from the same type as the | |
601 | // first column of `matrix` that are matched only by wildcard patterns | |
602 | // from the first column. | |
603 | // | |
604 | // Therefore, if there is some pattern that is unmatched by `matrix`, | |
605 | // it will still be unmatched if the first constructor is replaced by | |
606 | // any of the constructors in `missing_ctors` | |
607 | // | |
608 | // However, if our scrutinee is *privately* an empty enum, we | |
609 | // must treat it as though it had an "unknown" constructor (in | |
610 | // that case, all other patterns obviously can't be variants) | |
611 | // to avoid exposing its emptyness. See the `match_privately_empty` | |
612 | // test for details. | |
613 | // | |
614 | // FIXME: currently the only way I know of something can | |
615 | // be a privately-empty enum is when the never_type | |
616 | // feature flag is not present, so this is only | |
617 | // needed for that case. | |
618 | ||
619 | let is_privately_empty = | |
620 | all_ctors.is_empty() && !cx.is_uninhabited(pcx.ty); | |
621 | debug!("missing_ctors={:?} is_privately_empty={:?}", missing_ctors, | |
622 | is_privately_empty); | |
623 | if missing_ctors.is_empty() && !is_privately_empty { | |
624 | all_ctors.into_iter().map(|c| { | |
c30ab7b3 | 625 | is_useful_specialized(cx, matrix, v, c.clone(), pcx.ty, witness) |
32a655c1 | 626 | }).find(|result| result.is_useful()).unwrap_or(NotUseful) |
c30ab7b3 SL |
627 | } else { |
628 | let matrix = rows.iter().filter_map(|r| { | |
629 | if r[0].is_wildcard() { | |
630 | Some(r[1..].to_vec()) | |
631 | } else { | |
632 | None | |
633 | } | |
634 | }).collect(); | |
635 | match is_useful(cx, &matrix, &v[1..], witness) { | |
636 | UsefulWithWitness(pats) => { | |
637 | let cx = &*cx; | |
32a655c1 SL |
638 | let new_witnesses = if used_ctors.is_empty() { |
639 | // All constructors are unused. Add wild patterns | |
640 | // rather than each individual constructor | |
641 | pats.into_iter().map(|mut witness| { | |
642 | witness.0.push(Pattern { | |
643 | ty: pcx.ty, | |
644 | span: DUMMY_SP, | |
645 | kind: box PatternKind::Wild, | |
646 | }); | |
647 | witness | |
648 | }).collect() | |
649 | } else { | |
650 | pats.into_iter().flat_map(|witness| { | |
651 | missing_ctors.iter().map(move |ctor| { | |
652 | witness.clone().push_wild_constructor(cx, ctor, pcx.ty) | |
653 | }) | |
654 | }).collect() | |
655 | }; | |
656 | UsefulWithWitness(new_witnesses) | |
c30ab7b3 SL |
657 | } |
658 | result => result | |
659 | } | |
660 | } | |
661 | } | |
662 | } | |
663 | ||
32a655c1 | 664 | fn is_useful_specialized<'p, 'a:'p, 'tcx: 'a>( |
c30ab7b3 | 665 | cx: &mut MatchCheckCtxt<'a, 'tcx>, |
32a655c1 SL |
666 | &Matrix(ref m): &Matrix<'p, 'tcx>, |
667 | v: &[&'p Pattern<'tcx>], | |
8bb4bdeb | 668 | ctor: Constructor<'tcx>, |
c30ab7b3 | 669 | lty: Ty<'tcx>, |
32a655c1 | 670 | witness: WitnessPreference) -> Usefulness<'tcx> |
c30ab7b3 | 671 | { |
32a655c1 SL |
672 | debug!("is_useful_specialized({:?}, {:?}, {:?})", v, ctor, lty); |
673 | let sub_pat_tys = constructor_sub_pattern_tys(cx, &ctor, lty); | |
674 | let wild_patterns_owned: Vec<_> = sub_pat_tys.iter().map(|ty| { | |
675 | Pattern { | |
676 | ty: ty, | |
677 | span: DUMMY_SP, | |
678 | kind: box PatternKind::Wild, | |
679 | } | |
680 | }).collect(); | |
681 | let wild_patterns: Vec<_> = wild_patterns_owned.iter().collect(); | |
c30ab7b3 | 682 | let matrix = Matrix(m.iter().flat_map(|r| { |
cc61c64b | 683 | specialize(cx, &r, &ctor, &wild_patterns) |
c30ab7b3 | 684 | }).collect()); |
32a655c1 | 685 | match specialize(cx, v, &ctor, &wild_patterns) { |
cc61c64b | 686 | Some(v) => match is_useful(cx, &matrix, &v, witness) { |
c30ab7b3 SL |
687 | UsefulWithWitness(witnesses) => UsefulWithWitness( |
688 | witnesses.into_iter() | |
689 | .map(|witness| witness.apply_constructor(cx, &ctor, lty)) | |
690 | .collect() | |
691 | ), | |
692 | result => result | |
693 | }, | |
694 | None => NotUseful | |
695 | } | |
696 | } | |
697 | ||
698 | /// Determines the constructors that the given pattern can be specialized to. | |
699 | /// | |
700 | /// In most cases, there's only one constructor that a specific pattern | |
701 | /// represents, such as a specific enum variant or a specific literal value. | |
702 | /// Slice patterns, however, can match slices of different lengths. For instance, | |
703 | /// `[a, b, ..tail]` can match a slice of length 2, 3, 4 and so on. | |
704 | /// | |
705 | /// Returns None in case of a catch-all, which can't be specialized. | |
8bb4bdeb XL |
706 | fn pat_constructors<'tcx>(_cx: &mut MatchCheckCtxt, |
707 | pat: &Pattern<'tcx>, | |
708 | pcx: PatternContext) | |
709 | -> Option<Vec<Constructor<'tcx>>> | |
c30ab7b3 SL |
710 | { |
711 | match *pat.kind { | |
712 | PatternKind::Binding { .. } | PatternKind::Wild => | |
713 | None, | |
714 | PatternKind::Leaf { .. } | PatternKind::Deref { .. } => | |
715 | Some(vec![Single]), | |
716 | PatternKind::Variant { adt_def, variant_index, .. } => | |
717 | Some(vec![Variant(adt_def.variants[variant_index].did)]), | |
718 | PatternKind::Constant { ref value } => | |
719 | Some(vec![ConstantValue(value.clone())]), | |
32a655c1 SL |
720 | PatternKind::Range { ref lo, ref hi, ref end } => |
721 | Some(vec![ConstantRange(lo.clone(), hi.clone(), end.clone())]), | |
c30ab7b3 SL |
722 | PatternKind::Array { .. } => match pcx.ty.sty { |
723 | ty::TyArray(_, length) => Some(vec![Slice(length)]), | |
724 | _ => span_bug!(pat.span, "bad ty {:?} for array pattern", pcx.ty) | |
725 | }, | |
726 | PatternKind::Slice { ref prefix, ref slice, ref suffix } => { | |
727 | let pat_len = prefix.len() + suffix.len(); | |
728 | if slice.is_some() { | |
729 | Some((pat_len..pcx.max_slice_length+1).map(Slice).collect()) | |
730 | } else { | |
731 | Some(vec![Slice(pat_len)]) | |
732 | } | |
733 | } | |
734 | } | |
735 | } | |
736 | ||
737 | /// This computes the arity of a constructor. The arity of a constructor | |
738 | /// is how many subpattern patterns of that constructor should be expanded to. | |
739 | /// | |
740 | /// For instance, a tuple pattern (_, 42, Some([])) has the arity of 3. | |
741 | /// A struct pattern's arity is the number of fields it contains, etc. | |
742 | fn constructor_arity(_cx: &MatchCheckCtxt, ctor: &Constructor, ty: Ty) -> usize { | |
743 | debug!("constructor_arity({:?}, {:?})", ctor, ty); | |
744 | match ty.sty { | |
8bb4bdeb | 745 | ty::TyTuple(ref fs, _) => fs.len(), |
c30ab7b3 SL |
746 | ty::TySlice(..) | ty::TyArray(..) => match *ctor { |
747 | Slice(length) => length, | |
748 | ConstantValue(_) => 0, | |
749 | _ => bug!("bad slice pattern {:?} {:?}", ctor, ty) | |
750 | }, | |
751 | ty::TyRef(..) => 1, | |
752 | ty::TyAdt(adt, _) => { | |
32a655c1 | 753 | adt.variants[ctor.variant_index_for_adt(adt)].fields.len() |
c30ab7b3 SL |
754 | } |
755 | _ => 0 | |
756 | } | |
757 | } | |
758 | ||
32a655c1 SL |
759 | /// This computes the types of the sub patterns that a constructor should be |
760 | /// expanded to. | |
761 | /// | |
762 | /// For instance, a tuple pattern (43u32, 'a') has sub pattern types [u32, char]. | |
763 | fn constructor_sub_pattern_tys<'a, 'tcx: 'a>(cx: &MatchCheckCtxt<'a, 'tcx>, | |
764 | ctor: &Constructor, | |
765 | ty: Ty<'tcx>) -> Vec<Ty<'tcx>> | |
766 | { | |
767 | debug!("constructor_sub_pattern_tys({:?}, {:?})", ctor, ty); | |
768 | match ty.sty { | |
8bb4bdeb | 769 | ty::TyTuple(ref fs, _) => fs.into_iter().map(|t| *t).collect(), |
32a655c1 SL |
770 | ty::TySlice(ty) | ty::TyArray(ty, _) => match *ctor { |
771 | Slice(length) => repeat(ty).take(length).collect(), | |
772 | ConstantValue(_) => vec![], | |
773 | _ => bug!("bad slice pattern {:?} {:?}", ctor, ty) | |
774 | }, | |
775 | ty::TyRef(_, ref ty_and_mut) => vec![ty_and_mut.ty], | |
776 | ty::TyAdt(adt, substs) => { | |
041b39d2 XL |
777 | if adt.is_box() { |
778 | // Use T as the sub pattern type of Box<T>. | |
779 | vec![substs[0].as_type().unwrap()] | |
780 | } else { | |
781 | adt.variants[ctor.variant_index_for_adt(adt)].fields.iter().map(|field| { | |
782 | let is_visible = adt.is_enum() | |
783 | || field.vis.is_accessible_from(cx.module, cx.tcx); | |
784 | if is_visible { | |
785 | field.ty(cx.tcx, substs) | |
786 | } else { | |
787 | // Treat all non-visible fields as nil. They | |
788 | // can't appear in any other pattern from | |
789 | // this match (because they are private), | |
790 | // so their type does not matter - but | |
791 | // we don't want to know they are | |
792 | // uninhabited. | |
793 | cx.tcx.mk_nil() | |
794 | } | |
795 | }).collect() | |
796 | } | |
32a655c1 SL |
797 | } |
798 | _ => vec![], | |
799 | } | |
800 | } | |
801 | ||
c30ab7b3 SL |
802 | fn slice_pat_covered_by_constructor(_tcx: TyCtxt, _span: Span, |
803 | ctor: &Constructor, | |
804 | prefix: &[Pattern], | |
805 | slice: &Option<Pattern>, | |
806 | suffix: &[Pattern]) | |
807 | -> Result<bool, ErrorReported> { | |
808 | let data = match *ctor { | |
809 | ConstantValue(ConstVal::ByteStr(ref data)) => data, | |
810 | _ => bug!() | |
811 | }; | |
812 | ||
813 | let pat_len = prefix.len() + suffix.len(); | |
814 | if data.len() < pat_len || (slice.is_none() && data.len() > pat_len) { | |
815 | return Ok(false); | |
816 | } | |
817 | ||
818 | for (ch, pat) in | |
819 | data[..prefix.len()].iter().zip(prefix).chain( | |
820 | data[data.len()-suffix.len()..].iter().zip(suffix)) | |
821 | { | |
822 | match pat.kind { | |
823 | box PatternKind::Constant { ref value } => match *value { | |
824 | ConstVal::Integral(ConstInt::U8(u)) => { | |
825 | if u != *ch { | |
826 | return Ok(false); | |
827 | } | |
828 | }, | |
829 | _ => span_bug!(pat.span, "bad const u8 {:?}", value) | |
830 | }, | |
831 | _ => {} | |
832 | } | |
833 | } | |
834 | ||
835 | Ok(true) | |
836 | } | |
837 | ||
041b39d2 | 838 | fn constructor_covered_by_range(tcx: TyCtxt, span: Span, |
c30ab7b3 | 839 | ctor: &Constructor, |
32a655c1 SL |
840 | from: &ConstVal, to: &ConstVal, |
841 | end: RangeEnd) | |
c30ab7b3 | 842 | -> Result<bool, ErrorReported> { |
32a655c1 SL |
843 | let cmp_from = |c_from| Ok(compare_const_vals(tcx, span, c_from, from)? != Ordering::Less); |
844 | let cmp_to = |c_to| compare_const_vals(tcx, span, c_to, to); | |
845 | match *ctor { | |
846 | ConstantValue(ref value) => { | |
847 | let to = cmp_to(value)?; | |
041b39d2 XL |
848 | let end = (to == Ordering::Less) || |
849 | (end == RangeEnd::Included && to == Ordering::Equal); | |
32a655c1 SL |
850 | Ok(cmp_from(value)? && end) |
851 | }, | |
852 | ConstantRange(ref from, ref to, RangeEnd::Included) => { | |
853 | let to = cmp_to(to)?; | |
041b39d2 XL |
854 | let end = (to == Ordering::Less) || |
855 | (end == RangeEnd::Included && to == Ordering::Equal); | |
32a655c1 SL |
856 | Ok(cmp_from(from)? && end) |
857 | }, | |
858 | ConstantRange(ref from, ref to, RangeEnd::Excluded) => { | |
859 | let to = cmp_to(to)?; | |
860 | let end = (to == Ordering::Less) || | |
861 | (end == RangeEnd::Excluded && to == Ordering::Equal); | |
862 | Ok(cmp_from(from)? && end) | |
863 | } | |
864 | Single => Ok(true), | |
865 | _ => bug!(), | |
866 | } | |
c30ab7b3 SL |
867 | } |
868 | ||
32a655c1 SL |
869 | fn patterns_for_variant<'p, 'a: 'p, 'tcx: 'a>( |
870 | subpatterns: &'p [FieldPattern<'tcx>], | |
871 | wild_patterns: &[&'p Pattern<'tcx>]) | |
872 | -> Vec<&'p Pattern<'tcx>> | |
c30ab7b3 | 873 | { |
32a655c1 | 874 | let mut result = wild_patterns.to_owned(); |
c30ab7b3 SL |
875 | |
876 | for subpat in subpatterns { | |
877 | result[subpat.field.index()] = &subpat.pattern; | |
878 | } | |
879 | ||
32a655c1 | 880 | debug!("patterns_for_variant({:?}, {:?}) = {:?}", subpatterns, wild_patterns, result); |
c30ab7b3 SL |
881 | result |
882 | } | |
883 | ||
884 | /// This is the main specialization step. It expands the first pattern in the given row | |
885 | /// into `arity` patterns based on the constructor. For most patterns, the step is trivial, | |
886 | /// for instance tuple patterns are flattened and box patterns expand into their inner pattern. | |
887 | /// | |
888 | /// OTOH, slice patterns with a subslice pattern (..tail) can be expanded into multiple | |
889 | /// different patterns. | |
890 | /// Structure patterns with a partial wild pattern (Foo { a: 42, .. }) have their missing | |
891 | /// fields filled with wild patterns. | |
32a655c1 | 892 | fn specialize<'p, 'a: 'p, 'tcx: 'a>( |
c30ab7b3 | 893 | cx: &mut MatchCheckCtxt<'a, 'tcx>, |
32a655c1 SL |
894 | r: &[&'p Pattern<'tcx>], |
895 | constructor: &Constructor, | |
896 | wild_patterns: &[&'p Pattern<'tcx>]) | |
897 | -> Option<Vec<&'p Pattern<'tcx>>> | |
c30ab7b3 | 898 | { |
32a655c1 | 899 | let pat = &r[0]; |
c30ab7b3 SL |
900 | |
901 | let head: Option<Vec<&Pattern>> = match *pat.kind { | |
32a655c1 SL |
902 | PatternKind::Binding { .. } | PatternKind::Wild => { |
903 | Some(wild_patterns.to_owned()) | |
904 | }, | |
c30ab7b3 | 905 | |
32a655c1 | 906 | PatternKind::Variant { adt_def, variant_index, ref subpatterns, .. } => { |
c30ab7b3 SL |
907 | let ref variant = adt_def.variants[variant_index]; |
908 | if *constructor == Variant(variant.did) { | |
32a655c1 | 909 | Some(patterns_for_variant(subpatterns, wild_patterns)) |
c30ab7b3 SL |
910 | } else { |
911 | None | |
912 | } | |
913 | } | |
914 | ||
32a655c1 SL |
915 | PatternKind::Leaf { ref subpatterns } => { |
916 | Some(patterns_for_variant(subpatterns, wild_patterns)) | |
917 | } | |
918 | PatternKind::Deref { ref subpattern } => { | |
919 | Some(vec![subpattern]) | |
920 | } | |
c30ab7b3 SL |
921 | |
922 | PatternKind::Constant { ref value } => { | |
923 | match *constructor { | |
924 | Slice(..) => match *value { | |
925 | ConstVal::ByteStr(ref data) => { | |
32a655c1 | 926 | if wild_patterns.len() == data.len() { |
c30ab7b3 SL |
927 | Some(cx.lower_byte_str_pattern(pat)) |
928 | } else { | |
929 | None | |
930 | } | |
931 | } | |
932 | _ => span_bug!(pat.span, | |
933 | "unexpected const-val {:?} with ctor {:?}", value, constructor) | |
934 | }, | |
935 | _ => { | |
041b39d2 | 936 | match constructor_covered_by_range( |
32a655c1 | 937 | cx.tcx, pat.span, constructor, value, value, RangeEnd::Included |
c30ab7b3 SL |
938 | ) { |
939 | Ok(true) => Some(vec![]), | |
940 | Ok(false) => None, | |
941 | Err(ErrorReported) => None, | |
942 | } | |
943 | } | |
944 | } | |
945 | } | |
946 | ||
32a655c1 | 947 | PatternKind::Range { ref lo, ref hi, ref end } => { |
041b39d2 | 948 | match constructor_covered_by_range( |
32a655c1 | 949 | cx.tcx, pat.span, constructor, lo, hi, end.clone() |
c30ab7b3 SL |
950 | ) { |
951 | Ok(true) => Some(vec![]), | |
952 | Ok(false) => None, | |
953 | Err(ErrorReported) => None, | |
954 | } | |
955 | } | |
956 | ||
957 | PatternKind::Array { ref prefix, ref slice, ref suffix } | | |
958 | PatternKind::Slice { ref prefix, ref slice, ref suffix } => { | |
959 | match *constructor { | |
960 | Slice(..) => { | |
961 | let pat_len = prefix.len() + suffix.len(); | |
32a655c1 | 962 | if let Some(slice_count) = wild_patterns.len().checked_sub(pat_len) { |
c30ab7b3 SL |
963 | if slice_count == 0 || slice.is_some() { |
964 | Some( | |
965 | prefix.iter().chain( | |
32a655c1 SL |
966 | wild_patterns.iter().map(|p| *p) |
967 | .skip(prefix.len()) | |
968 | .take(slice_count) | |
969 | .chain( | |
c30ab7b3 SL |
970 | suffix.iter() |
971 | )).collect()) | |
972 | } else { | |
973 | None | |
974 | } | |
975 | } else { | |
976 | None | |
977 | } | |
978 | } | |
979 | ConstantValue(..) => { | |
980 | match slice_pat_covered_by_constructor( | |
981 | cx.tcx, pat.span, constructor, prefix, slice, suffix | |
982 | ) { | |
983 | Ok(true) => Some(vec![]), | |
984 | Ok(false) => None, | |
985 | Err(ErrorReported) => None | |
986 | } | |
987 | } | |
988 | _ => span_bug!(pat.span, | |
989 | "unexpected ctor {:?} for slice pat", constructor) | |
990 | } | |
991 | } | |
992 | }; | |
32a655c1 | 993 | debug!("specialize({:?}, {:?}) = {:?}", r[0], wild_patterns, head); |
c30ab7b3 SL |
994 | |
995 | head.map(|mut head| { | |
32a655c1 | 996 | head.extend_from_slice(&r[1 ..]); |
c30ab7b3 SL |
997 | head |
998 | }) | |
999 | } |