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1//! This module implements match statement exhaustiveness checking and usefulness checking
2//! for match arms.
3//!
4//! It is modeled on the rustc module `librustc_mir_build::hair::pattern::_match`, which
5//! contains very detailed documentation about the algorithms used here. I've duplicated
6//! most of that documentation below.
7//!
8//! This file includes the logic for exhaustiveness and usefulness checking for
9//! pattern-matching. Specifically, given a list of patterns for a type, we can
10//! tell whether:
11//! - (a) the patterns cover every possible constructor for the type (exhaustiveness).
12//! - (b) each pattern is necessary (usefulness).
13//!
14//! The algorithm implemented here is a modified version of the one described in
15//! <http://moscova.inria.fr/~maranget/papers/warn/index.html>.
16//! However, to save future implementors from reading the original paper, we
17//! summarise the algorithm here to hopefully save time and be a little clearer
18//! (without being so rigorous).
19//!
20//! The core of the algorithm revolves about a "usefulness" check. In particular, we
21//! are trying to compute a predicate `U(P, p)` where `P` is a list of patterns (we refer to this as
22//! a matrix). `U(P, p)` represents whether, given an existing list of patterns
23//! `P_1 ..= P_m`, adding a new pattern `p` will be "useful" (that is, cover previously-
24//! uncovered values of the type).
25//!
26//! If we have this predicate, then we can easily compute both exhaustiveness of an
27//! entire set of patterns and the individual usefulness of each one.
28//! (a) the set of patterns is exhaustive iff `U(P, _)` is false (i.e., adding a wildcard
29//! match doesn't increase the number of values we're matching)
30//! (b) a pattern `P_i` is not useful if `U(P[0..=(i-1), P_i)` is false (i.e., adding a
31//! pattern to those that have come before it doesn't increase the number of values
32//! we're matching).
33//!
34//! During the course of the algorithm, the rows of the matrix won't just be individual patterns,
35//! but rather partially-deconstructed patterns in the form of a list of patterns. The paper
36//! calls those pattern-vectors, and we will call them pattern-stacks. The same holds for the
37//! new pattern `p`.
38//!
39//! For example, say we have the following:
40//!
41//! ```ignore
42//! // x: (Option<bool>, Result<()>)
43//! match x {
44//! (Some(true), _) => {}
45//! (None, Err(())) => {}
46//! (None, Err(_)) => {}
47//! }
48//! ```
49//!
50//! Here, the matrix `P` starts as:
51//!
52//! ```text
53//! [
54//! [(Some(true), _)],
55//! [(None, Err(()))],
56//! [(None, Err(_))],
57//! ]
58//! ```
59//!
60//! We can tell it's not exhaustive, because `U(P, _)` is true (we're not covering
61//! `[(Some(false), _)]`, for instance). In addition, row 3 is not useful, because
62//! all the values it covers are already covered by row 2.
63//!
64//! A list of patterns can be thought of as a stack, because we are mainly interested in the top of
65//! the stack at any given point, and we can pop or apply constructors to get new pattern-stacks.
66//! To match the paper, the top of the stack is at the beginning / on the left.
67//!
68//! There are two important operations on pattern-stacks necessary to understand the algorithm:
69//!
70//! 1. We can pop a given constructor off the top of a stack. This operation is called
71//! `specialize`, and is denoted `S(c, p)` where `c` is a constructor (like `Some` or
72//! `None`) and `p` a pattern-stack.
73//! If the pattern on top of the stack can cover `c`, this removes the constructor and
74//! pushes its arguments onto the stack. It also expands OR-patterns into distinct patterns.
75//! Otherwise the pattern-stack is discarded.
76//! This essentially filters those pattern-stacks whose top covers the constructor `c` and
77//! discards the others.
78//!
79//! For example, the first pattern above initially gives a stack `[(Some(true), _)]`. If we
80//! pop the tuple constructor, we are left with `[Some(true), _]`, and if we then pop the
81//! `Some` constructor we get `[true, _]`. If we had popped `None` instead, we would get
82//! nothing back.
83//!
84//! This returns zero or more new pattern-stacks, as follows. We look at the pattern `p_1`
85//! on top of the stack, and we have four cases:
86//!
87//! * 1.1. `p_1 = c(r_1, .., r_a)`, i.e. the top of the stack has constructor `c`. We push onto
88//! the stack the arguments of this constructor, and return the result:
89//!
90//! r_1, .., r_a, p_2, .., p_n
91//!
92//! * 1.2. `p_1 = c'(r_1, .., r_a')` where `c ≠ c'`. We discard the current stack and return
93//! nothing.
94//! * 1.3. `p_1 = _`. We push onto the stack as many wildcards as the constructor `c` has
95//! arguments (its arity), and return the resulting stack:
96//!
97//! _, .., _, p_2, .., p_n
98//!
99//! * 1.4. `p_1 = r_1 | r_2`. We expand the OR-pattern and then recurse on each resulting stack:
100//!
101//! S(c, (r_1, p_2, .., p_n))
102//! S(c, (r_2, p_2, .., p_n))
103//!
104//! 2. We can pop a wildcard off the top of the stack. This is called `D(p)`, where `p` is
105//! a pattern-stack.
106//! This is used when we know there are missing constructor cases, but there might be
107//! existing wildcard patterns, so to check the usefulness of the matrix, we have to check
108//! all its *other* components.
109//!
110//! It is computed as follows. We look at the pattern `p_1` on top of the stack,
111//! and we have three cases:
112//! * 1.1. `p_1 = c(r_1, .., r_a)`. We discard the current stack and return nothing.
113//! * 1.2. `p_1 = _`. We return the rest of the stack:
114//!
115//! p_2, .., p_n
116//!
117//! * 1.3. `p_1 = r_1 | r_2`. We expand the OR-pattern and then recurse on each resulting stack:
118//!
119//! D((r_1, p_2, .., p_n))
120//! D((r_2, p_2, .., p_n))
121//!
122//! Note that the OR-patterns are not always used directly in Rust, but are used to derive the
123//! exhaustive integer matching rules, so they're written here for posterity.
124//!
125//! Both those operations extend straightforwardly to a list or pattern-stacks, i.e. a matrix, by
126//! working row-by-row. Popping a constructor ends up keeping only the matrix rows that start with
127//! the given constructor, and popping a wildcard keeps those rows that start with a wildcard.
128//!
129//!
130//! The algorithm for computing `U`
131//! -------------------------------
132//! The algorithm is inductive (on the number of columns: i.e., components of tuple patterns).
133//! That means we're going to check the components from left-to-right, so the algorithm
134//! operates principally on the first component of the matrix and new pattern-stack `p`.
135//! This algorithm is realised in the `is_useful` function.
136//!
137//! Base case (`n = 0`, i.e., an empty tuple pattern):
138//! - If `P` already contains an empty pattern (i.e., if the number of patterns `m > 0`), then
139//! `U(P, p)` is false.
140//! - Otherwise, `P` must be empty, so `U(P, p)` is true.
141//!
142//! Inductive step (`n > 0`, i.e., whether there's at least one column [which may then be expanded
143//! into further columns later]). We're going to match on the top of the new pattern-stack, `p_1`:
144//!
145//! - If `p_1 == c(r_1, .., r_a)`, i.e. we have a constructor pattern.
146//! Then, the usefulness of `p_1` can be reduced to whether it is useful when
147//! we ignore all the patterns in the first column of `P` that involve other constructors.
148//! This is where `S(c, P)` comes in:
149//!
150//! ```text
151//! U(P, p) := U(S(c, P), S(c, p))
152//! ```
153//!
154//! This special case is handled in `is_useful_specialized`.
155//!
156//! For example, if `P` is:
157//!
158//! ```text
159//! [
160//! [Some(true), _],
161//! [None, 0],
162//! ]
163//! ```
164//!
165//! and `p` is `[Some(false), 0]`, then we don't care about row 2 since we know `p` only
166//! matches values that row 2 doesn't. For row 1 however, we need to dig into the
167//! arguments of `Some` to know whether some new value is covered. So we compute
168//! `U([[true, _]], [false, 0])`.
169//!
170//! - If `p_1 == _`, then we look at the list of constructors that appear in the first component of
171//! the rows of `P`:
172//! - If there are some constructors that aren't present, then we might think that the
173//! wildcard `_` is useful, since it covers those constructors that weren't covered
174//! before.
175//! That's almost correct, but only works if there were no wildcards in those first
176//! components. So we need to check that `p` is useful with respect to the rows that
177//! start with a wildcard, if there are any. This is where `D` comes in:
178//! `U(P, p) := U(D(P), D(p))`
179//!
180//! For example, if `P` is:
181//! ```text
182//! [
183//! [_, true, _],
184//! [None, false, 1],
185//! ]
186//! ```
187//! and `p` is `[_, false, _]`, the `Some` constructor doesn't appear in `P`. So if we
188//! only had row 2, we'd know that `p` is useful. However row 1 starts with a
189//! wildcard, so we need to check whether `U([[true, _]], [false, 1])`.
190//!
191//! - Otherwise, all possible constructors (for the relevant type) are present. In this
192//! case we must check whether the wildcard pattern covers any unmatched value. For
193//! that, we can think of the `_` pattern as a big OR-pattern that covers all
194//! possible constructors. For `Option`, that would mean `_ = None | Some(_)` for
195//! example. The wildcard pattern is useful in this case if it is useful when
196//! specialized to one of the possible constructors. So we compute:
197//! `U(P, p) := ∃(k ϵ constructors) U(S(k, P), S(k, p))`
198//!
199//! For example, if `P` is:
200//! ```text
201//! [
202//! [Some(true), _],
203//! [None, false],
204//! ]
205//! ```
206//! and `p` is `[_, false]`, both `None` and `Some` constructors appear in the first
207//! components of `P`. We will therefore try popping both constructors in turn: we
208//! compute `U([[true, _]], [_, false])` for the `Some` constructor, and `U([[false]],
209//! [false])` for the `None` constructor. The first case returns true, so we know that
210//! `p` is useful for `P`. Indeed, it matches `[Some(false), _]` that wasn't matched
211//! before.
212//!
213//! - If `p_1 == r_1 | r_2`, then the usefulness depends on each `r_i` separately:
214//!
215//! ```text
216//! U(P, p) := U(P, (r_1, p_2, .., p_n))
217//! || U(P, (r_2, p_2, .., p_n))
218//! ```
219use std::sync::Arc;
220
221use smallvec::{smallvec, SmallVec};
222
223use crate::{
224 db::HirDatabase,
225 expr::{Body, Expr, Literal, Pat, PatId},
226 ApplicationTy, InferenceResult, Ty, TypeCtor,
227};
228use hir_def::{adt::VariantData, AdtId, EnumVariantId, VariantId};
229use ra_arena::Idx;
230
231#[derive(Debug, Clone, Copy)]
232/// Either a pattern from the source code being analyzed, represented as
233/// as `PatId`, or a `Wild` pattern which is created as an intermediate
234/// step in the match checking algorithm and thus is not backed by a
235/// real `PatId`.
236///
237/// Note that it is totally valid for the `PatId` variant to contain
238/// a `PatId` which resolves to a `Wild` pattern, if that wild pattern
239/// exists in the source code being analyzed.
240enum PatIdOrWild {
241 PatId(PatId),
242 Wild,
243}
244
245impl PatIdOrWild {
246 fn as_pat(self, cx: &MatchCheckCtx) -> Pat {
247 match self {
248 PatIdOrWild::PatId(id) => cx.body.pats[id].clone(),
249 PatIdOrWild::Wild => Pat::Wild,
250 }
251 }
252
253 fn as_id(self) -> Option<PatId> {
254 match self {
255 PatIdOrWild::PatId(id) => Some(id),
256 PatIdOrWild::Wild => None,
257 }
258 }
259}
260
261impl From<PatId> for PatIdOrWild {
262 fn from(pat_id: PatId) -> Self {
263 Self::PatId(pat_id)
264 }
265}
266
267impl From<&PatId> for PatIdOrWild {
268 fn from(pat_id: &PatId) -> Self {
269 Self::PatId(*pat_id)
270 }
271}
272
273#[derive(Debug, Clone, Copy, PartialEq)]
274pub enum MatchCheckErr {
275 NotImplemented,
276 MalformedMatchArm,
277 /// Used when type inference cannot resolve the type of
278 /// a pattern or expression.
279 Unknown,
280}
281
282/// The return type of `is_useful` is either an indication of usefulness
283/// of the match arm, or an error in the case the match statement
284/// is made up of types for which exhaustiveness checking is currently
285/// not completely implemented.
286///
287/// The `std::result::Result` type is used here rather than a custom enum
288/// to allow the use of `?`.
289pub type MatchCheckResult<T> = Result<T, MatchCheckErr>;
290
291#[derive(Debug)]
292/// A row in a Matrix.
293///
294/// This type is modeled from the struct of the same name in `rustc`.
295pub(crate) struct PatStack(PatStackInner);
296type PatStackInner = SmallVec<[PatIdOrWild; 2]>;
297
298impl PatStack {
299 pub(crate) fn from_pattern(pat_id: PatId) -> PatStack {
300 Self(smallvec!(pat_id.into()))
301 }
302
303 pub(crate) fn from_wild() -> PatStack {
304 Self(smallvec!(PatIdOrWild::Wild))
305 }
306
307 fn from_slice(slice: &[PatIdOrWild]) -> PatStack {
308 Self(SmallVec::from_slice(slice))
309 }
310
311 fn from_vec(v: PatStackInner) -> PatStack {
312 Self(v)
313 }
314
315 fn get_head(&self) -> Option<PatIdOrWild> {
316 self.0.first().copied()
317 }
318
319 fn tail(&self) -> &[PatIdOrWild] {
320 self.0.get(1..).unwrap_or(&[])
321 }
322
323 fn to_tail(&self) -> PatStack {
324 Self::from_slice(self.tail())
325 }
326
327 fn replace_head_with<I, T>(&self, pats: I) -> PatStack
328 where
329 I: Iterator<Item = T>,
330 T: Into<PatIdOrWild>,
331 {
332 let mut patterns: PatStackInner = smallvec![];
333 for pat in pats {
334 patterns.push(pat.into());
335 }
336 for pat in &self.0[1..] {
337 patterns.push(*pat);
338 }
339 PatStack::from_vec(patterns)
340 }
341
342 /// Computes `D(self)`.
343 ///
344 /// See the module docs and the associated documentation in rustc for details.
345 fn specialize_wildcard(&self, cx: &MatchCheckCtx) -> Option<PatStack> {
346 if matches!(self.get_head()?.as_pat(cx), Pat::Wild) {
347 Some(self.to_tail())
348 } else {
349 None
350 }
351 }
352
353 /// Computes `S(constructor, self)`.
354 ///
355 /// See the module docs and the associated documentation in rustc for details.
356 fn specialize_constructor(
357 &self,
358 cx: &MatchCheckCtx,
359 constructor: &Constructor,
360 ) -> MatchCheckResult<Option<PatStack>> {
361 let head = match self.get_head() {
362 Some(head) => head,
363 None => return Ok(None),
364 };
365
366 let head_pat = head.as_pat(cx);
367 let result = match (head_pat, constructor) {
368 (Pat::Tuple { args: ref pat_ids, ellipsis }, Constructor::Tuple { arity: _ }) => {
369 if ellipsis.is_some() {
370 // If there are ellipsis here, we should add the correct number of
371 // Pat::Wild patterns to `pat_ids`. We should be able to use the
372 // constructors arity for this, but at the time of writing we aren't
373 // correctly calculating this arity when ellipsis are present.
374 return Err(MatchCheckErr::NotImplemented);
375 }
376
377 Some(self.replace_head_with(pat_ids.iter()))
378 }
379 (Pat::Lit(lit_expr), Constructor::Bool(constructor_val)) => {
380 match cx.body.exprs[lit_expr] {
381 Expr::Literal(Literal::Bool(pat_val)) if *constructor_val == pat_val => {
382 Some(self.to_tail())
383 }
384 // it was a bool but the value doesn't match
385 Expr::Literal(Literal::Bool(_)) => None,
386 // perhaps this is actually unreachable given we have
387 // already checked that these match arms have the appropriate type?
388 _ => return Err(MatchCheckErr::NotImplemented),
389 }
390 }
391 (Pat::Wild, constructor) => Some(self.expand_wildcard(cx, constructor)?),
392 (Pat::Path(_), Constructor::Enum(constructor)) => {
393 // unit enum variants become `Pat::Path`
394 let pat_id = head.as_id().expect("we know this isn't a wild");
395 if !enum_variant_matches(cx, pat_id, *constructor) {
396 None
397 } else {
398 Some(self.to_tail())
399 }
400 }
401 (
402 Pat::TupleStruct { args: ref pat_ids, ellipsis, .. },
403 Constructor::Enum(enum_constructor),
404 ) => {
405 let pat_id = head.as_id().expect("we know this isn't a wild");
406 if !enum_variant_matches(cx, pat_id, *enum_constructor) {
407 None
408 } else {
409 let constructor_arity = constructor.arity(cx)?;
410 if let Some(ellipsis_position) = ellipsis {
411 // If there are ellipsis in the pattern, the ellipsis must take the place
412 // of at least one sub-pattern, so `pat_ids` should be smaller than the
413 // constructor arity.
414 if pat_ids.len() < constructor_arity {
415 let mut new_patterns: Vec<PatIdOrWild> = vec![];
416
417 for pat_id in &pat_ids[0..ellipsis_position] {
418 new_patterns.push((*pat_id).into());
419 }
420
421 for _ in 0..(constructor_arity - pat_ids.len()) {
422 new_patterns.push(PatIdOrWild::Wild);
423 }
424
425 for pat_id in &pat_ids[ellipsis_position..pat_ids.len()] {
426 new_patterns.push((*pat_id).into());
427 }
428
429 Some(self.replace_head_with(new_patterns.into_iter()))
430 } else {
431 return Err(MatchCheckErr::MalformedMatchArm);
432 }
433 } else {
434 // If there is no ellipsis in the tuple pattern, the number
435 // of patterns must equal the constructor arity.
436 if pat_ids.len() == constructor_arity {
437 Some(self.replace_head_with(pat_ids.into_iter()))
438 } else {
439 return Err(MatchCheckErr::MalformedMatchArm);
440 }
441 }
442 }
443 }
444 (Pat::Record { args: ref arg_patterns, .. }, Constructor::Enum(e)) => {
445 let pat_id = head.as_id().expect("we know this isn't a wild");
446 if !enum_variant_matches(cx, pat_id, *e) {
447 None
448 } else {
449 match cx.db.enum_data(e.parent).variants[e.local_id].variant_data.as_ref() {
450 VariantData::Record(struct_field_arena) => {
451 // Here we treat any missing fields in the record as the wild pattern, as
452 // if the record has ellipsis. We want to do this here even if the
453 // record does not contain ellipsis, because it allows us to continue
454 // enforcing exhaustiveness for the rest of the match statement.
455 //
456 // Creating the diagnostic for the missing field in the pattern
457 // should be done in a different diagnostic.
458 let patterns = struct_field_arena.iter().map(|(_, struct_field)| {
459 arg_patterns
460 .iter()
461 .find(|pat| pat.name == struct_field.name)
462 .map(|pat| PatIdOrWild::from(pat.pat))
463 .unwrap_or(PatIdOrWild::Wild)
464 });
465
466 Some(self.replace_head_with(patterns))
467 }
468 _ => return Err(MatchCheckErr::Unknown),
469 }
470 }
471 }
472 (Pat::Or(_), _) => return Err(MatchCheckErr::NotImplemented),
473 (_, _) => return Err(MatchCheckErr::NotImplemented),
474 };
475
476 Ok(result)
477 }
478
479 /// A special case of `specialize_constructor` where the head of the pattern stack
480 /// is a Wild pattern.
481 ///
482 /// Replaces the Wild pattern at the head of the pattern stack with N Wild patterns
483 /// (N >= 0), where N is the arity of the given constructor.
484 fn expand_wildcard(
485 &self,
486 cx: &MatchCheckCtx,
487 constructor: &Constructor,
488 ) -> MatchCheckResult<PatStack> {
489 assert_eq!(
490 Pat::Wild,
491 self.get_head().expect("expand_wildcard called on empty PatStack").as_pat(cx),
492 "expand_wildcard must only be called on PatStack with wild at head",
493 );
494
495 let mut patterns: PatStackInner = smallvec![];
496
497 for _ in 0..constructor.arity(cx)? {
498 patterns.push(PatIdOrWild::Wild);
499 }
500
501 for pat in &self.0[1..] {
502 patterns.push(*pat);
503 }
504
505 Ok(PatStack::from_vec(patterns))
506 }
507}
508
509/// A collection of PatStack.
510///
511/// This type is modeled from the struct of the same name in `rustc`.
512pub(crate) struct Matrix(Vec<PatStack>);
513
514impl Matrix {
515 pub(crate) fn empty() -> Self {
516 Self(vec![])
517 }
518
519 pub(crate) fn push(&mut self, cx: &MatchCheckCtx, row: PatStack) {
520 if let Some(Pat::Or(pat_ids)) = row.get_head().map(|pat_id| pat_id.as_pat(cx)) {
521 // Or patterns are expanded here
522 for pat_id in pat_ids {
523 self.0.push(PatStack::from_pattern(pat_id));
524 }
525 } else {
526 self.0.push(row);
527 }
528 }
529
530 fn is_empty(&self) -> bool {
531 self.0.is_empty()
532 }
533
534 fn heads(&self) -> Vec<PatIdOrWild> {
535 self.0.iter().flat_map(|p| p.get_head()).collect()
536 }
537
538 /// Computes `D(self)` for each contained PatStack.
539 ///
540 /// See the module docs and the associated documentation in rustc for details.
541 fn specialize_wildcard(&self, cx: &MatchCheckCtx) -> Self {
542 Self::collect(cx, self.0.iter().filter_map(|r| r.specialize_wildcard(cx)))
543 }
544
545 /// Computes `S(constructor, self)` for each contained PatStack.
546 ///
547 /// See the module docs and the associated documentation in rustc for details.
548 fn specialize_constructor(
549 &self,
550 cx: &MatchCheckCtx,
551 constructor: &Constructor,
552 ) -> MatchCheckResult<Self> {
553 let mut new_matrix = Matrix::empty();
554 for pat in &self.0 {
555 if let Some(pat) = pat.specialize_constructor(cx, constructor)? {
556 new_matrix.push(cx, pat);
557 }
558 }
559
560 Ok(new_matrix)
561 }
562
563 fn collect<T: IntoIterator<Item = PatStack>>(cx: &MatchCheckCtx, iter: T) -> Self {
564 let mut matrix = Matrix::empty();
565
566 for pat in iter {
567 // using push ensures we expand or-patterns
568 matrix.push(cx, pat);
569 }
570
571 matrix
572 }
573}
574
575#[derive(Clone, Debug, PartialEq)]
576/// An indication of the usefulness of a given match arm, where
577/// usefulness is defined as matching some patterns which were
578/// not matched by an prior match arms.
579///
580/// We may eventually need an `Unknown` variant here.
581pub enum Usefulness {
582 Useful,
583 NotUseful,
584}
585
586pub struct MatchCheckCtx<'a> {
587 pub match_expr: Idx<Expr>,
588 pub body: Arc<Body>,
589 pub infer: Arc<InferenceResult>,
590 pub db: &'a dyn HirDatabase,
591}
592
593/// Given a set of patterns `matrix`, and pattern to consider `v`, determines
594/// whether `v` is useful. A pattern is useful if it covers cases which were
595/// not previously covered.
596///
597/// When calling this function externally (that is, not the recursive calls) it
598/// expected that you have already type checked the match arms. All patterns in
599/// matrix should be the same type as v, as well as they should all be the same
600/// type as the match expression.
601pub(crate) fn is_useful(
602 cx: &MatchCheckCtx,
603 matrix: &Matrix,
604 v: &PatStack,
605) -> MatchCheckResult<Usefulness> {
606 // Handle two special cases:
607 // - enum with no variants
608 // - `!` type
609 // In those cases, no match arm is useful.
610 match cx.infer[cx.match_expr].strip_references() {
611 Ty::Apply(ApplicationTy { ctor: TypeCtor::Adt(AdtId::EnumId(enum_id)), .. }) => {
612 if cx.db.enum_data(*enum_id).variants.is_empty() {
613 return Ok(Usefulness::NotUseful);
614 }
615 }
616 Ty::Apply(ApplicationTy { ctor: TypeCtor::Never, .. }) => {
617 return Ok(Usefulness::NotUseful);
618 }
619 _ => (),
620 }
621
622 let head = match v.get_head() {
623 Some(head) => head,
624 None => {
625 let result = if matrix.is_empty() { Usefulness::Useful } else { Usefulness::NotUseful };
626
627 return Ok(result);
628 }
629 };
630
631 if let Pat::Or(pat_ids) = head.as_pat(cx) {
632 let mut found_unimplemented = false;
633 let any_useful = pat_ids.iter().any(|&pat_id| {
634 let v = PatStack::from_pattern(pat_id);
635
636 match is_useful(cx, matrix, &v) {
637 Ok(Usefulness::Useful) => true,
638 Ok(Usefulness::NotUseful) => false,
639 _ => {
640 found_unimplemented = true;
641 false
642 }
643 }
644 });
645
646 return if any_useful {
647 Ok(Usefulness::Useful)
648 } else if found_unimplemented {
649 Err(MatchCheckErr::NotImplemented)
650 } else {
651 Ok(Usefulness::NotUseful)
652 };
653 }
654
655 if let Some(constructor) = pat_constructor(cx, head)? {
656 let matrix = matrix.specialize_constructor(&cx, &constructor)?;
657 let v = v
658 .specialize_constructor(&cx, &constructor)?
659 .expect("we know this can't fail because we get the constructor from `v.head()` above");
660
661 is_useful(&cx, &matrix, &v)
662 } else {
663 // expanding wildcard
664 let mut used_constructors: Vec<Constructor> = vec![];
665 for pat in matrix.heads() {
666 if let Some(constructor) = pat_constructor(cx, pat)? {
667 used_constructors.push(constructor);
668 }
669 }
670
671 // We assume here that the first constructor is the "correct" type. Since we
672 // only care about the "type" of the constructor (i.e. if it is a bool we
673 // don't care about the value), this assumption should be valid as long as
674 // the match statement is well formed. We currently uphold this invariant by
675 // filtering match arms before calling `is_useful`, only passing in match arms
676 // whose type matches the type of the match expression.
677 match &used_constructors.first() {
678 Some(constructor) if all_constructors_covered(&cx, constructor, &used_constructors) => {
679 // If all constructors are covered, then we need to consider whether
680 // any values are covered by this wildcard.
681 //
682 // For example, with matrix '[[Some(true)], [None]]', all
683 // constructors are covered (`Some`/`None`), so we need
684 // to perform specialization to see that our wildcard will cover
685 // the `Some(false)` case.
686 //
687 // Here we create a constructor for each variant and then check
688 // usefulness after specializing for that constructor.
689 let mut found_unimplemented = false;
690 for constructor in constructor.all_constructors(cx) {
691 let matrix = matrix.specialize_constructor(&cx, &constructor)?;
692 let v = v.expand_wildcard(&cx, &constructor)?;
693
694 match is_useful(&cx, &matrix, &v) {
695 Ok(Usefulness::Useful) => return Ok(Usefulness::Useful),
696 Ok(Usefulness::NotUseful) => continue,
697 _ => found_unimplemented = true,
698 };
699 }
700
701 if found_unimplemented {
702 Err(MatchCheckErr::NotImplemented)
703 } else {
704 Ok(Usefulness::NotUseful)
705 }
706 }
707 _ => {
708 // Either not all constructors are covered, or the only other arms
709 // are wildcards. Either way, this pattern is useful if it is useful
710 // when compared to those arms with wildcards.
711 let matrix = matrix.specialize_wildcard(&cx);
712 let v = v.to_tail();
713
714 is_useful(&cx, &matrix, &v)
715 }
716 }
717 }
718}
719
720#[derive(Debug, Clone, Copy)]
721/// Similar to TypeCtor, but includes additional information about the specific
722/// value being instantiated. For example, TypeCtor::Bool doesn't contain the
723/// boolean value.
724enum Constructor {
725 Bool(bool),
726 Tuple { arity: usize },
727 Enum(EnumVariantId),
728}
729
730impl Constructor {
731 fn arity(&self, cx: &MatchCheckCtx) -> MatchCheckResult<usize> {
732 let arity = match self {
733 Constructor::Bool(_) => 0,
734 Constructor::Tuple { arity } => *arity,
735 Constructor::Enum(e) => {
736 match cx.db.enum_data(e.parent).variants[e.local_id].variant_data.as_ref() {
737 VariantData::Tuple(struct_field_data) => struct_field_data.len(),
738 VariantData::Record(struct_field_data) => struct_field_data.len(),
739 VariantData::Unit => 0,
740 }
741 }
742 };
743
744 Ok(arity)
745 }
746
747 fn all_constructors(&self, cx: &MatchCheckCtx) -> Vec<Constructor> {
748 match self {
749 Constructor::Bool(_) => vec![Constructor::Bool(true), Constructor::Bool(false)],
750 Constructor::Tuple { .. } => vec![*self],
751 Constructor::Enum(e) => cx
752 .db
753 .enum_data(e.parent)
754 .variants
755 .iter()
756 .map(|(local_id, _)| {
757 Constructor::Enum(EnumVariantId { parent: e.parent, local_id })
758 })
759 .collect(),
760 }
761 }
762}
763
764/// Returns the constructor for the given pattern. Should only return None
765/// in the case of a Wild pattern.
766fn pat_constructor(cx: &MatchCheckCtx, pat: PatIdOrWild) -> MatchCheckResult<Option<Constructor>> {
767 let res = match pat.as_pat(cx) {
768 Pat::Wild => None,
769 // FIXME somehow create the Tuple constructor with the proper arity. If there are
770 // ellipsis, the arity is not equal to the number of patterns.
771 Pat::Tuple { args: pats, ellipsis } if ellipsis.is_none() => {
772 Some(Constructor::Tuple { arity: pats.len() })
773 }
774 Pat::Lit(lit_expr) => match cx.body.exprs[lit_expr] {
775 Expr::Literal(Literal::Bool(val)) => Some(Constructor::Bool(val)),
776 _ => return Err(MatchCheckErr::NotImplemented),
777 },
778 Pat::TupleStruct { .. } | Pat::Path(_) | Pat::Record { .. } => {
779 let pat_id = pat.as_id().expect("we already know this pattern is not a wild");
780 let variant_id =
781 cx.infer.variant_resolution_for_pat(pat_id).ok_or(MatchCheckErr::Unknown)?;
782 match variant_id {
783 VariantId::EnumVariantId(enum_variant_id) => {
784 Some(Constructor::Enum(enum_variant_id))
785 }
786 _ => return Err(MatchCheckErr::NotImplemented),
787 }
788 }
789 _ => return Err(MatchCheckErr::NotImplemented),
790 };
791
792 Ok(res)
793}
794
795fn all_constructors_covered(
796 cx: &MatchCheckCtx,
797 constructor: &Constructor,
798 used_constructors: &[Constructor],
799) -> bool {
800 match constructor {
801 Constructor::Tuple { arity } => {
802 used_constructors.iter().any(|constructor| match constructor {
803 Constructor::Tuple { arity: used_arity } => arity == used_arity,
804 _ => false,
805 })
806 }
807 Constructor::Bool(_) => {
808 if used_constructors.is_empty() {
809 return false;
810 }
811
812 let covers_true =
813 used_constructors.iter().any(|c| matches!(c, Constructor::Bool(true)));
814 let covers_false =
815 used_constructors.iter().any(|c| matches!(c, Constructor::Bool(false)));
816
817 covers_true && covers_false
818 }
819 Constructor::Enum(e) => cx.db.enum_data(e.parent).variants.iter().all(|(id, _)| {
820 for constructor in used_constructors {
821 if let Constructor::Enum(e) = constructor {
822 if id == e.local_id {
823 return true;
824 }
825 }
826 }
827
828 false
829 }),
830 }
831}
832
833fn enum_variant_matches(cx: &MatchCheckCtx, pat_id: PatId, enum_variant_id: EnumVariantId) -> bool {
834 Some(enum_variant_id.into()) == cx.infer.variant_resolution_for_pat(pat_id)
835}
836
837#[cfg(test)]
838mod tests {
839 pub(super) use insta::assert_snapshot;
840 pub(super) use ra_db::fixture::WithFixture;
841
842 pub(super) use crate::{diagnostics::MissingMatchArms, test_db::TestDB};
843
844 pub(super) fn check_diagnostic_message(ra_fixture: &str) -> String {
845 TestDB::with_single_file(ra_fixture).0.diagnostic::<MissingMatchArms>().0
846 }
847
848 pub(super) fn check_diagnostic(ra_fixture: &str) {
849 let diagnostic_count =
850 TestDB::with_single_file(ra_fixture).0.diagnostic::<MissingMatchArms>().1;
851
852 assert_eq!(1, diagnostic_count, "no diagnostic reported");
853 }
854
855 pub(super) fn check_no_diagnostic(ra_fixture: &str) {
856 let (s, diagnostic_count) =
857 TestDB::with_single_file(ra_fixture).0.diagnostic::<MissingMatchArms>();
858
859 assert_eq!(0, diagnostic_count, "expected no diagnostic, found one: {}", s);
860 }
861
862 #[test]
863 fn empty_tuple_no_arms_diagnostic_message() {
864 assert_snapshot!(
865 check_diagnostic_message(r"
866 fn test_fn() {
867 match () {
868 }
869 }
870 "),
871 @"\"()\": Missing match arm\n"
872 );
873 }
874
875 #[test]
876 fn empty_tuple_no_arms() {
877 check_diagnostic(
878 r"
879 fn test_fn() {
880 match () {
881 }
882 }
883 ",
884 );
885 }
886
887 #[test]
888 fn empty_tuple_wild() {
889 check_no_diagnostic(
890 r"
891 fn test_fn() {
892 match () {
893 _ => {}
894 }
895 }
896 ",
897 );
898 }
899
900 #[test]
901 fn empty_tuple_no_diagnostic() {
902 check_no_diagnostic(
903 r"
904 fn test_fn() {
905 match () {
906 () => {}
907 }
908 }
909 ",
910 );
911 }
912
913 #[test]
914 fn tuple_of_empty_tuple_no_arms() {
915 check_diagnostic(
916 r"
917 fn test_fn() {
918 match (()) {
919 }
920 }
921 ",
922 );
923 }
924
925 #[test]
926 fn tuple_of_empty_tuple_no_diagnostic() {
927 check_no_diagnostic(
928 r"
929 fn test_fn() {
930 match (()) {
931 (()) => {}
932 }
933 }
934 ",
935 );
936 }
937
938 #[test]
939 fn tuple_of_two_empty_tuple_no_arms() {
940 check_diagnostic(
941 r"
942 fn test_fn() {
943 match ((), ()) {
944 }
945 }
946 ",
947 );
948 }
949
950 #[test]
951 fn tuple_of_two_empty_tuple_no_diagnostic() {
952 check_no_diagnostic(
953 r"
954 fn test_fn() {
955 match ((), ()) {
956 ((), ()) => {}
957 }
958 }
959 ",
960 );
961 }
962
963 #[test]
964 fn bool_no_arms() {
965 check_diagnostic(
966 r"
967 fn test_fn() {
968 match false {
969 }
970 }
971 ",
972 );
973 }
974
975 #[test]
976 fn bool_missing_arm() {
977 check_diagnostic(
978 r"
979 fn test_fn() {
980 match false {
981 true => {}
982 }
983 }
984 ",
985 );
986 }
987
988 #[test]
989 fn bool_no_diagnostic() {
990 check_no_diagnostic(
991 r"
992 fn test_fn() {
993 match false {
994 true => {}
995 false => {}
996 }
997 }
998 ",
999 );
1000 }
1001
1002 #[test]
1003 fn tuple_of_bools_no_arms() {
1004 check_diagnostic(
1005 r"
1006 fn test_fn() {
1007 match (false, true) {
1008 }
1009 }
1010 ",
1011 );
1012 }
1013
1014 #[test]
1015 fn tuple_of_bools_missing_arms() {
1016 check_diagnostic(
1017 r"
1018 fn test_fn() {
1019 match (false, true) {
1020 (true, true) => {},
1021 }
1022 }
1023 ",
1024 );
1025 }
1026
1027 #[test]
1028 fn tuple_of_bools_missing_arm() {
1029 check_diagnostic(
1030 r"
1031 fn test_fn() {
1032 match (false, true) {
1033 (false, true) => {},
1034 (false, false) => {},
1035 (true, false) => {},
1036 }
1037 }
1038 ",
1039 );
1040 }
1041
1042 #[test]
1043 fn tuple_of_bools_with_wilds() {
1044 check_no_diagnostic(
1045 r"
1046 fn test_fn() {
1047 match (false, true) {
1048 (false, _) => {},
1049 (true, false) => {},
1050 (_, true) => {},
1051 }
1052 }
1053 ",
1054 );
1055 }
1056
1057 #[test]
1058 fn tuple_of_bools_no_diagnostic() {
1059 check_no_diagnostic(
1060 r"
1061 fn test_fn() {
1062 match (false, true) {
1063 (true, true) => {},
1064 (true, false) => {},
1065 (false, true) => {},
1066 (false, false) => {},
1067 }
1068 }
1069 ",
1070 );
1071 }
1072
1073 #[test]
1074 fn tuple_of_bools_binding_missing_arms() {
1075 check_diagnostic(
1076 r"
1077 fn test_fn() {
1078 match (false, true) {
1079 (true, _x) => {},
1080 }
1081 }
1082 ",
1083 );
1084 }
1085
1086 #[test]
1087 fn tuple_of_bools_binding_no_diagnostic() {
1088 check_no_diagnostic(
1089 r"
1090 fn test_fn() {
1091 match (false, true) {
1092 (true, _x) => {},
1093 (false, true) => {},
1094 (false, false) => {},
1095 }
1096 }
1097 ",
1098 );
1099 }
1100
1101 #[test]
1102 fn tuple_of_bools_with_ellipsis_at_end_no_diagnostic() {
1103 check_no_diagnostic(
1104 r"
1105 fn test_fn() {
1106 match (false, true, false) {
1107 (false, ..) => {},
1108 (true, ..) => {},
1109 }
1110 }
1111 ",
1112 );
1113 }
1114
1115 #[test]
1116 fn tuple_of_bools_with_ellipsis_at_beginning_no_diagnostic() {
1117 check_no_diagnostic(
1118 r"
1119 fn test_fn() {
1120 match (false, true, false) {
1121 (.., false) => {},
1122 (.., true) => {},
1123 }
1124 }
1125 ",
1126 );
1127 }
1128
1129 #[test]
1130 fn tuple_of_bools_with_ellipsis_no_diagnostic() {
1131 check_no_diagnostic(
1132 r"
1133 fn test_fn() {
1134 match (false, true, false) {
1135 (..) => {},
1136 }
1137 }
1138 ",
1139 );
1140 }
1141
1142 #[test]
1143 fn tuple_of_tuple_and_bools_no_arms() {
1144 check_diagnostic(
1145 r"
1146 fn test_fn() {
1147 match (false, ((), false)) {
1148 }
1149 }
1150 ",
1151 );
1152 }
1153
1154 #[test]
1155 fn tuple_of_tuple_and_bools_missing_arms() {
1156 check_diagnostic(
1157 r"
1158 fn test_fn() {
1159 match (false, ((), false)) {
1160 (true, ((), true)) => {},
1161 }
1162 }
1163 ",
1164 );
1165 }
1166
1167 #[test]
1168 fn tuple_of_tuple_and_bools_no_diagnostic() {
1169 check_no_diagnostic(
1170 r"
1171 fn test_fn() {
1172 match (false, ((), false)) {
1173 (true, ((), true)) => {},
1174 (true, ((), false)) => {},
1175 (false, ((), true)) => {},
1176 (false, ((), false)) => {},
1177 }
1178 }
1179 ",
1180 );
1181 }
1182
1183 #[test]
1184 fn tuple_of_tuple_and_bools_wildcard_missing_arms() {
1185 check_diagnostic(
1186 r"
1187 fn test_fn() {
1188 match (false, ((), false)) {
1189 (true, _) => {},
1190 }
1191 }
1192 ",
1193 );
1194 }
1195
1196 #[test]
1197 fn tuple_of_tuple_and_bools_wildcard_no_diagnostic() {
1198 check_no_diagnostic(
1199 r"
1200 fn test_fn() {
1201 match (false, ((), false)) {
1202 (true, ((), true)) => {},
1203 (true, ((), false)) => {},
1204 (false, _) => {},
1205 }
1206 }
1207 ",
1208 );
1209 }
1210
1211 #[test]
1212 fn enum_no_arms() {
1213 check_diagnostic(
1214 r"
1215 enum Either {
1216 A,
1217 B,
1218 }
1219 fn test_fn() {
1220 match Either::A {
1221 }
1222 }
1223 ",
1224 );
1225 }
1226
1227 #[test]
1228 fn enum_missing_arms() {
1229 check_diagnostic(
1230 r"
1231 enum Either {
1232 A,
1233 B,
1234 }
1235 fn test_fn() {
1236 match Either::B {
1237 Either::A => {},
1238 }
1239 }
1240 ",
1241 );
1242 }
1243
1244 #[test]
1245 fn enum_no_diagnostic() {
1246 check_no_diagnostic(
1247 r"
1248 enum Either {
1249 A,
1250 B,
1251 }
1252 fn test_fn() {
1253 match Either::B {
1254 Either::A => {},
1255 Either::B => {},
1256 }
1257 }
1258 ",
1259 );
1260 }
1261
1262 #[test]
1263 fn enum_ref_missing_arms() {
1264 check_diagnostic(
1265 r"
1266 enum Either {
1267 A,
1268 B,
1269 }
1270 fn test_fn() {
1271 match &Either::B {
1272 Either::A => {},
1273 }
1274 }
1275 ",
1276 );
1277 }
1278
1279 #[test]
1280 fn enum_ref_no_diagnostic() {
1281 check_no_diagnostic(
1282 r"
1283 enum Either {
1284 A,
1285 B,
1286 }
1287 fn test_fn() {
1288 match &Either::B {
1289 Either::A => {},
1290 Either::B => {},
1291 }
1292 }
1293 ",
1294 );
1295 }
1296
1297 #[test]
1298 fn enum_containing_bool_no_arms() {
1299 check_diagnostic(
1300 r"
1301 enum Either {
1302 A(bool),
1303 B,
1304 }
1305 fn test_fn() {
1306 match Either::B {
1307 }
1308 }
1309 ",
1310 );
1311 }
1312
1313 #[test]
1314 fn enum_containing_bool_missing_arms() {
1315 check_diagnostic(
1316 r"
1317 enum Either {
1318 A(bool),
1319 B,
1320 }
1321 fn test_fn() {
1322 match Either::B {
1323 Either::A(true) => (),
1324 Either::B => (),
1325 }
1326 }
1327 ",
1328 );
1329 }
1330
1331 #[test]
1332 fn enum_containing_bool_no_diagnostic() {
1333 check_no_diagnostic(
1334 r"
1335 enum Either {
1336 A(bool),
1337 B,
1338 }
1339 fn test_fn() {
1340 match Either::B {
1341 Either::A(true) => (),
1342 Either::A(false) => (),
1343 Either::B => (),
1344 }
1345 }
1346 ",
1347 );
1348 }
1349
1350 #[test]
1351 fn enum_containing_bool_with_wild_no_diagnostic() {
1352 check_no_diagnostic(
1353 r"
1354 enum Either {
1355 A(bool),
1356 B,
1357 }
1358 fn test_fn() {
1359 match Either::B {
1360 Either::B => (),
1361 _ => (),
1362 }
1363 }
1364 ",
1365 );
1366 }
1367
1368 #[test]
1369 fn enum_containing_bool_with_wild_2_no_diagnostic() {
1370 check_no_diagnostic(
1371 r"
1372 enum Either {
1373 A(bool),
1374 B,
1375 }
1376 fn test_fn() {
1377 match Either::B {
1378 Either::A(_) => (),
1379 Either::B => (),
1380 }
1381 }
1382 ",
1383 );
1384 }
1385
1386 #[test]
1387 fn enum_different_sizes_missing_arms() {
1388 check_diagnostic(
1389 r"
1390 enum Either {
1391 A(bool),
1392 B(bool, bool),
1393 }
1394 fn test_fn() {
1395 match Either::A(false) {
1396 Either::A(_) => (),
1397 Either::B(false, _) => (),
1398 }
1399 }
1400 ",
1401 );
1402 }
1403
1404 #[test]
1405 fn enum_different_sizes_no_diagnostic() {
1406 check_no_diagnostic(
1407 r"
1408 enum Either {
1409 A(bool),
1410 B(bool, bool),
1411 }
1412 fn test_fn() {
1413 match Either::A(false) {
1414 Either::A(_) => (),
1415 Either::B(true, _) => (),
1416 Either::B(false, _) => (),
1417 }
1418 }
1419 ",
1420 );
1421 }
1422
1423 #[test]
1424 fn or_no_diagnostic() {
1425 check_no_diagnostic(
1426 r"
1427 enum Either {
1428 A(bool),
1429 B(bool, bool),
1430 }
1431 fn test_fn() {
1432 match Either::A(false) {
1433 Either::A(true) | Either::A(false) => (),
1434 Either::B(true, _) => (),
1435 Either::B(false, _) => (),
1436 }
1437 }
1438 ",
1439 );
1440 }
1441
1442 #[test]
1443 fn tuple_of_enum_no_diagnostic() {
1444 check_no_diagnostic(
1445 r"
1446 enum Either {
1447 A(bool),
1448 B(bool, bool),
1449 }
1450 enum Either2 {
1451 C,
1452 D,
1453 }
1454 fn test_fn() {
1455 match (Either::A(false), Either2::C) {
1456 (Either::A(true), _) | (Either::A(false), _) => (),
1457 (Either::B(true, _), Either2::C) => (),
1458 (Either::B(false, _), Either2::C) => (),
1459 (Either::B(_, _), Either2::D) => (),
1460 }
1461 }
1462 ",
1463 );
1464 }
1465
1466 #[test]
1467 fn mismatched_types() {
1468 // Match statements with arms that don't match the
1469 // expression pattern do not fire this diagnostic.
1470 check_no_diagnostic(
1471 r"
1472 enum Either {
1473 A,
1474 B,
1475 }
1476 enum Either2 {
1477 C,
1478 D,
1479 }
1480 fn test_fn() {
1481 match Either::A {
1482 Either2::C => (),
1483 Either2::D => (),
1484 }
1485 }
1486 ",
1487 );
1488 }
1489
1490 #[test]
1491 fn mismatched_types_with_different_arity() {
1492 // Match statements with arms that don't match the
1493 // expression pattern do not fire this diagnostic.
1494 check_no_diagnostic(
1495 r"
1496 fn test_fn() {
1497 match (true, false) {
1498 (true, false, true) => (),
1499 (true) => (),
1500 }
1501 }
1502 ",
1503 );
1504 }
1505
1506 #[test]
1507 fn malformed_match_arm_tuple_missing_pattern() {
1508 // Match statements with arms that don't match the
1509 // expression pattern do not fire this diagnostic.
1510 check_no_diagnostic(
1511 r"
1512 fn test_fn() {
1513 match (0) {
1514 () => (),
1515 }
1516 }
1517 ",
1518 );
1519 }
1520
1521 #[test]
1522 fn malformed_match_arm_tuple_enum_missing_pattern() {
1523 // We are testing to be sure we don't panic here when the match
1524 // arm `Either::B` is missing its pattern.
1525 check_no_diagnostic(
1526 r"
1527 enum Either {
1528 A,
1529 B(u32),
1530 }
1531 fn test_fn() {
1532 match Either::A {
1533 Either::A => (),
1534 Either::B() => (),
1535 }
1536 }
1537 ",
1538 );
1539 }
1540
1541 #[test]
1542 fn enum_not_in_scope() {
1543 // The enum is not in scope so we don't perform exhaustiveness
1544 // checking, but we want to be sure we don't panic here (and
1545 // we don't create a diagnostic).
1546 check_no_diagnostic(
1547 r"
1548 fn test_fn() {
1549 match Foo::Bar {
1550 Foo::Baz => (),
1551 }
1552 }
1553 ",
1554 );
1555 }
1556
1557 #[test]
1558 fn expr_diverges() {
1559 check_no_diagnostic(
1560 r"
1561 enum Either {
1562 A,
1563 B,
1564 }
1565 fn test_fn() {
1566 match loop {} {
1567 Either::A => (),
1568 Either::B => (),
1569 }
1570 }
1571 ",
1572 );
1573 }
1574
1575 #[test]
1576 fn expr_loop_with_break() {
1577 check_no_diagnostic(
1578 r"
1579 enum Either {
1580 A,
1581 B,
1582 }
1583 fn test_fn() {
1584 match loop { break Foo::A } {
1585 Either::A => (),
1586 Either::B => (),
1587 }
1588 }
1589 ",
1590 );
1591 }
1592
1593 #[test]
1594 fn expr_partially_diverges() {
1595 check_no_diagnostic(
1596 r"
1597 enum Either<T> {
1598 A(T),
1599 B,
1600 }
1601 fn foo() -> Either<!> {
1602 Either::B
1603 }
1604 fn test_fn() -> u32 {
1605 match foo() {
1606 Either::A(val) => val,
1607 Either::B => 0,
1608 }
1609 }
1610 ",
1611 );
1612 }
1613
1614 #[test]
1615 fn enum_record_no_arms() {
1616 check_diagnostic(
1617 r"
1618 enum Either {
1619 A { foo: bool },
1620 B,
1621 }
1622 fn test_fn() {
1623 let a = Either::A { foo: true };
1624 match a {
1625 }
1626 }
1627 ",
1628 );
1629 }
1630
1631 #[test]
1632 fn enum_record_missing_arms() {
1633 check_diagnostic(
1634 r"
1635 enum Either {
1636 A { foo: bool },
1637 B,
1638 }
1639 fn test_fn() {
1640 let a = Either::A { foo: true };
1641 match a {
1642 Either::A { foo: true } => (),
1643 }
1644 }
1645 ",
1646 );
1647 }
1648
1649 #[test]
1650 fn enum_record_no_diagnostic() {
1651 check_no_diagnostic(
1652 r"
1653 enum Either {
1654 A { foo: bool },
1655 B,
1656 }
1657 fn test_fn() {
1658 let a = Either::A { foo: true };
1659 match a {
1660 Either::A { foo: true } => (),
1661 Either::A { foo: false } => (),
1662 Either::B => (),
1663 }
1664 }
1665 ",
1666 );
1667 }
1668
1669 #[test]
1670 fn enum_record_missing_field_no_diagnostic() {
1671 // When `Either::A` is missing a struct member, we don't want
1672 // to fire the missing match arm diagnostic. This should fire
1673 // some other diagnostic.
1674 check_no_diagnostic(
1675 r"
1676 enum Either {
1677 A { foo: bool },
1678 B,
1679 }
1680 fn test_fn() {
1681 let a = Either::B;
1682 match a {
1683 Either::A { } => (),
1684 Either::B => (),
1685 }
1686 }
1687 ",
1688 );
1689 }
1690
1691 #[test]
1692 fn enum_record_missing_field_missing_match_arm() {
1693 // Even though `Either::A` is missing fields, we still want to fire
1694 // the missing arm diagnostic here, since we know `Either::B` is missing.
1695 check_diagnostic(
1696 r"
1697 enum Either {
1698 A { foo: bool },
1699 B,
1700 }
1701 fn test_fn() {
1702 let a = Either::B;
1703 match a {
1704 Either::A { } => (),
1705 }
1706 }
1707 ",
1708 );
1709 }
1710
1711 #[test]
1712 fn enum_record_no_diagnostic_wild() {
1713 check_no_diagnostic(
1714 r"
1715 enum Either {
1716 A { foo: bool },
1717 B,
1718 }
1719 fn test_fn() {
1720 let a = Either::A { foo: true };
1721 match a {
1722 Either::A { foo: _ } => (),
1723 Either::B => (),
1724 }
1725 }
1726 ",
1727 );
1728 }
1729
1730 #[test]
1731 fn enum_record_fields_out_of_order_missing_arm() {
1732 check_diagnostic(
1733 r"
1734 enum Either {
1735 A { foo: bool, bar: () },
1736 B,
1737 }
1738 fn test_fn() {
1739 let a = Either::A { foo: true };
1740 match a {
1741 Either::A { bar: (), foo: false } => (),
1742 Either::A { foo: true, bar: () } => (),
1743 }
1744 }
1745 ",
1746 );
1747 }
1748
1749 #[test]
1750 fn enum_record_fields_out_of_order_no_diagnostic() {
1751 check_no_diagnostic(
1752 r"
1753 enum Either {
1754 A { foo: bool, bar: () },
1755 B,
1756 }
1757 fn test_fn() {
1758 let a = Either::A { foo: true };
1759 match a {
1760 Either::A { bar: (), foo: false } => (),
1761 Either::A { foo: true, bar: () } => (),
1762 Either::B => (),
1763 }
1764 }
1765 ",
1766 );
1767 }
1768
1769 #[test]
1770 fn enum_record_ellipsis_missing_arm() {
1771 check_diagnostic(
1772 r"
1773 enum Either {
1774 A { foo: bool, bar: bool },
1775 B,
1776 }
1777 fn test_fn() {
1778 match Either::B {
1779 Either::A { foo: true, .. } => (),
1780 Either::B => (),
1781 }
1782 }
1783 ",
1784 );
1785 }
1786
1787 #[test]
1788 fn enum_record_ellipsis_no_diagnostic() {
1789 check_no_diagnostic(
1790 r"
1791 enum Either {
1792 A { foo: bool, bar: bool },
1793 B,
1794 }
1795 fn test_fn() {
1796 let a = Either::A { foo: true };
1797 match a {
1798 Either::A { foo: true, .. } => (),
1799 Either::A { foo: false, .. } => (),
1800 Either::B => (),
1801 }
1802 }
1803 ",
1804 );
1805 }
1806
1807 #[test]
1808 fn enum_record_ellipsis_all_fields_missing_arm() {
1809 check_diagnostic(
1810 r"
1811 enum Either {
1812 A { foo: bool, bar: bool },
1813 B,
1814 }
1815 fn test_fn() {
1816 let a = Either::B;
1817 match a {
1818 Either::A { .. } => (),
1819 }
1820 }
1821 ",
1822 );
1823 }
1824
1825 #[test]
1826 fn enum_record_ellipsis_all_fields_no_diagnostic() {
1827 check_no_diagnostic(
1828 r"
1829 enum Either {
1830 A { foo: bool, bar: bool },
1831 B,
1832 }
1833 fn test_fn() {
1834 let a = Either::B;
1835 match a {
1836 Either::A { .. } => (),
1837 Either::B => (),
1838 }
1839 }
1840 ",
1841 );
1842 }
1843
1844 #[test]
1845 fn enum_tuple_partial_ellipsis_no_diagnostic() {
1846 check_no_diagnostic(
1847 r"
1848 enum Either {
1849 A(bool, bool, bool, bool),
1850 B,
1851 }
1852 fn test_fn() {
1853 match Either::B {
1854 Either::A(true, .., true) => {},
1855 Either::A(true, .., false) => {},
1856 Either::A(false, .., true) => {},
1857 Either::A(false, .., false) => {},
1858 Either::B => {},
1859 }
1860 }
1861 ",
1862 );
1863 }
1864
1865 #[test]
1866 fn enum_tuple_partial_ellipsis_2_no_diagnostic() {
1867 check_no_diagnostic(
1868 r"
1869 enum Either {
1870 A(bool, bool, bool, bool),
1871 B,
1872 }
1873 fn test_fn() {
1874 match Either::B {
1875 Either::A(true, .., true) => {},
1876 Either::A(true, .., false) => {},
1877 Either::A(.., true) => {},
1878 Either::A(.., false) => {},
1879 Either::B => {},
1880 }
1881 }
1882 ",
1883 );
1884 }
1885
1886 #[test]
1887 fn enum_tuple_partial_ellipsis_missing_arm() {
1888 check_diagnostic(
1889 r"
1890 enum Either {
1891 A(bool, bool, bool, bool),
1892 B,
1893 }
1894 fn test_fn() {
1895 match Either::B {
1896 Either::A(true, .., true) => {},
1897 Either::A(true, .., false) => {},
1898 Either::A(false, .., false) => {},
1899 Either::B => {},
1900 }
1901 }
1902 ",
1903 );
1904 }
1905
1906 #[test]
1907 fn enum_tuple_partial_ellipsis_2_missing_arm() {
1908 check_diagnostic(
1909 r"
1910 enum Either {
1911 A(bool, bool, bool, bool),
1912 B,
1913 }
1914 fn test_fn() {
1915 match Either::B {
1916 Either::A(true, .., true) => {},
1917 Either::A(true, .., false) => {},
1918 Either::A(.., true) => {},
1919 Either::B => {},
1920 }
1921 }
1922 ",
1923 );
1924 }
1925
1926 #[test]
1927 fn enum_tuple_ellipsis_no_diagnostic() {
1928 check_no_diagnostic(
1929 r"
1930 enum Either {
1931 A(bool, bool, bool, bool),
1932 B,
1933 }
1934 fn test_fn() {
1935 match Either::B {
1936 Either::A(..) => {},
1937 Either::B => {},
1938 }
1939 }
1940 ",
1941 );
1942 }
1943
1944 #[test]
1945 fn enum_never() {
1946 check_no_diagnostic(
1947 r"
1948 enum Never {}
1949
1950 fn test_fn(never: Never) {
1951 match never {}
1952 }
1953 ",
1954 );
1955 }
1956
1957 #[test]
1958 fn type_never() {
1959 check_no_diagnostic(
1960 r"
1961 fn test_fn(never: !) {
1962 match never {}
1963 }
1964 ",
1965 );
1966 }
1967
1968 #[test]
1969 fn enum_never_ref() {
1970 check_no_diagnostic(
1971 r"
1972 enum Never {}
1973
1974 fn test_fn(never: &Never) {
1975 match never {}
1976 }
1977 ",
1978 );
1979 }
1980
1981 #[test]
1982 fn expr_diverges_missing_arm() {
1983 check_no_diagnostic(
1984 r"
1985 enum Either {
1986 A,
1987 B,
1988 }
1989 fn test_fn() {
1990 match loop {} {
1991 Either::A => (),
1992 }
1993 }
1994 ",
1995 );
1996 }
1997
1998 #[test]
1999 fn or_pattern_panic() {
2000 check_no_diagnostic(
2001 r"
2002 pub enum Category {
2003 Infinity,
2004 Zero,
2005 }
2006
2007 fn panic(a: Category, b: Category) {
2008 match (a, b) {
2009 (Category::Zero | Category::Infinity, _) => {}
2010 (_, Category::Zero | Category::Infinity) => {}
2011 }
2012 }
2013 ",
2014 );
2015 }
2016
2017 #[test]
2018 fn or_pattern_panic_2() {
2019 // FIXME: This is a false positive, but the code used to cause a panic in the match checker,
2020 // so this acts as a regression test for that.
2021 check_diagnostic(
2022 r"
2023 pub enum Category {
2024 Infinity,
2025 Zero,
2026 }
2027
2028 fn panic(a: Category, b: Category) {
2029 match (a, b) {
2030 (Category::Infinity, Category::Infinity) | (Category::Zero, Category::Zero) => {}
2031
2032 (Category::Infinity | Category::Zero, _) => {}
2033 }
2034 }
2035 ",
2036 );
2037 }
2038}
2039
2040#[cfg(test)]
2041mod false_negatives {
2042 //! The implementation of match checking here is a work in progress. As we roll this out, we
2043 //! prefer false negatives to false positives (ideally there would be no false positives). This
2044 //! test module should document known false negatives. Eventually we will have a complete
2045 //! implementation of match checking and this module will be empty.
2046 //!
2047 //! The reasons for documenting known false negatives:
2048 //!
2049 //! 1. It acts as a backlog of work that can be done to improve the behavior of the system.
2050 //! 2. It ensures the code doesn't panic when handling these cases.
2051
2052 use super::tests::*;
2053
2054 #[test]
2055 fn integers() {
2056 // This is a false negative.
2057 // We don't currently check integer exhaustiveness.
2058 check_no_diagnostic(
2059 r"
2060 fn test_fn() {
2061 match 5 {
2062 10 => (),
2063 11..20 => (),
2064 }
2065 }
2066 ",
2067 );
2068 }
2069
2070 #[test]
2071 fn internal_or() {
2072 // This is a false negative.
2073 // We do not currently handle patterns with internal `or`s.
2074 check_no_diagnostic(
2075 r"
2076 fn test_fn() {
2077 enum Either {
2078 A(bool),
2079 B,
2080 }
2081 match Either::B {
2082 Either::A(true | false) => (),
2083 }
2084 }
2085 ",
2086 );
2087 }
2088
2089 #[test]
2090 fn expr_loop_missing_arm() {
2091 // This is a false negative.
2092 // We currently infer the type of `loop { break Foo::A }` to `!`, which
2093 // causes us to skip the diagnostic since `Either::A` doesn't type check
2094 // with `!`.
2095 check_diagnostic(
2096 r"
2097 enum Either {
2098 A,
2099 B,
2100 }
2101 fn test_fn() {
2102 match loop { break Foo::A } {
2103 Either::A => (),
2104 }
2105 }
2106 ",
2107 );
2108 }
2109
2110 #[test]
2111 fn tuple_of_bools_with_ellipsis_at_end_missing_arm() {
2112 // This is a false negative.
2113 // We don't currently handle tuple patterns with ellipsis.
2114 check_no_diagnostic(
2115 r"
2116 fn test_fn() {
2117 match (false, true, false) {
2118 (false, ..) => {},
2119 }
2120 }
2121 ",
2122 );
2123 }
2124
2125 #[test]
2126 fn tuple_of_bools_with_ellipsis_at_beginning_missing_arm() {
2127 // This is a false negative.
2128 // We don't currently handle tuple patterns with ellipsis.
2129 check_no_diagnostic(
2130 r"
2131 fn test_fn() {
2132 match (false, true, false) {
2133 (.., false) => {},
2134 }
2135 }
2136 ",
2137 );
2138 }
2139
2140 #[test]
2141 fn struct_missing_arm() {
2142 // This is a false negative.
2143 // We don't currently handle structs.
2144 check_no_diagnostic(
2145 r"
2146 struct Foo {
2147 a: bool,
2148 }
2149 fn test_fn(f: Foo) {
2150 match f {
2151 Foo { a: true } => {},
2152 }
2153 }
2154 ",
2155 );
2156 }
2157}
generated by cgit v1.2.3 (git 2.25.1) at 2024-09-13 20:48:57 +0100