1 //! [`super::usefulness`] explains most of what is happening in this file. As explained there,
2 //! values and patterns are made from constructors applied to fields. This file defines a
3 //! `Constructor` enum, a `Fields` struct, and various operations to manipulate them and convert
4 //! them from/to patterns.
6 //! There's one idea that is not detailed in [`super::usefulness`] because the details are not
7 //! needed there: _constructor splitting_.
9 //! # Constructor splitting
11 //! The idea is as follows: given a constructor `c` and a matrix, we want to specialize in turn
12 //! with all the value constructors that are covered by `c`, and compute usefulness for each.
13 //! Instead of listing all those constructors (which is intractable), we group those value
14 //! constructors together as much as possible. Example:
17 //! match (0, false) {
18 //! (0 ..=100, true) => {} // `p_1`
19 //! (50..=150, false) => {} // `p_2`
20 //! (0 ..=200, _) => {} // `q`
24 //! The naive approach would try all numbers in the range `0..=200`. But we can be a lot more
25 //! clever: `0` and `1` for example will match the exact same rows, and return equivalent
26 //! witnesses. In fact all of `0..50` would. We can thus restrict our exploration to 4
27 //! constructors: `0..50`, `50..=100`, `101..=150` and `151..=200`. That is enough and infinitely
30 //! We capture this idea in a function `split(p_1 ... p_n, c)` which returns a list of constructors
31 //! `c'` covered by `c`. Given such a `c'`, we require that all value ctors `c''` covered by `c'`
32 //! return an equivalent set of witnesses after specializing and computing usefulness.
33 //! In the example above, witnesses for specializing by `c''` covered by `0..50` will only differ
34 //! in their first element.
36 //! We usually also ask that the `c'` together cover all of the original `c`. However we allow
37 //! skipping some constructors as long as it doesn't change whether the resulting list of witnesses
38 //! is empty of not. We use this in the wildcard `_` case.
40 //! Splitting is implemented in the [`Constructor::split`] function. We don't do splitting for
41 //! or-patterns; instead we just try the alternatives one-by-one. For details on splitting
42 //! wildcards, see [`SplitWildcard`]; for integer ranges, see [`SplitIntRange`].
50 use hir_def::{EnumVariantId, HasModule, LocalFieldId, VariantId};
51 use smallvec::{smallvec, SmallVec};
55 use crate::{AdtId, Interner, Scalar, Ty, TyExt, TyKind};
58 usefulness::{MatchCheckCtx, PatCtxt},
59 FieldPat, Pat, PatId, PatKind,
62 use self::Constructor::*;
64 /// [Constructor] uses this in umimplemented variants.
65 /// It allows porting match expressions from upstream algorithm without losing semantics.
66 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
67 pub(super) enum Void {}
69 /// An inclusive interval, used for precise integer exhaustiveness checking.
70 /// `IntRange`s always store a contiguous range. This means that values are
71 /// encoded such that `0` encodes the minimum value for the integer,
72 /// regardless of the signedness.
73 /// For example, the pattern `-128..=127i8` is encoded as `0..=255`.
74 /// This makes comparisons and arithmetic on interval endpoints much more
75 /// straightforward. See `signed_bias` for details.
77 /// `IntRange` is never used to encode an empty range or a "range" that wraps
78 /// around the (offset) space: i.e., `range.lo <= range.hi`.
79 #[derive(Clone, Debug, PartialEq, Eq)]
80 pub(super) struct IntRange {
81 range: RangeInclusive<u128>,
86 fn is_integral(ty: &Ty) -> bool {
89 TyKind::Scalar(Scalar::Char | Scalar::Int(_) | Scalar::Uint(_) | Scalar::Bool)
93 fn is_singleton(&self) -> bool {
94 self.range.start() == self.range.end()
97 fn boundaries(&self) -> (u128, u128) {
98 (*self.range.start(), *self.range.end())
102 fn from_bool(value: bool) -> IntRange {
103 let val = value as u128;
104 IntRange { range: val..=val }
108 fn from_range(lo: u128, hi: u128, scalar_ty: Scalar) -> IntRange {
110 Scalar::Bool => IntRange { range: lo..=hi },
111 _ => unimplemented!(),
115 fn is_subrange(&self, other: &Self) -> bool {
116 other.range.start() <= self.range.start() && self.range.end() <= other.range.end()
119 fn intersection(&self, other: &Self) -> Option<Self> {
120 let (lo, hi) = self.boundaries();
121 let (other_lo, other_hi) = other.boundaries();
122 if lo <= other_hi && other_lo <= hi {
123 Some(IntRange { range: max(lo, other_lo)..=min(hi, other_hi) })
129 /// See `Constructor::is_covered_by`
130 fn is_covered_by(&self, other: &Self) -> bool {
131 if self.intersection(other).is_some() {
132 // Constructor splitting should ensure that all intersections we encounter are actually
134 assert!(self.is_subrange(other));
142 /// Represents a border between 2 integers. Because the intervals spanning borders must be able to
143 /// cover every integer, we need to be able to represent 2^128 + 1 such borders.
144 #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
150 /// A range of integers that is partitioned into disjoint subranges. This does constructor
151 /// splitting for integer ranges as explained at the top of the file.
153 /// This is fed multiple ranges, and returns an output that covers the input, but is split so that
154 /// the only intersections between an output range and a seen range are inclusions. No output range
155 /// straddles the boundary of one of the inputs.
157 /// The following input:
159 /// |-------------------------| // `self`
160 /// |------| |----------| |----|
161 /// |-------| |-------|
163 /// would be iterated over as follows:
165 /// ||---|--||-|---|---|---|--|
167 #[derive(Debug, Clone)]
168 struct SplitIntRange {
169 /// The range we are splitting
171 /// The borders of ranges we have seen. They are all contained within `range`. This is kept
173 borders: Vec<IntBorder>,
177 fn new(range: IntRange) -> Self {
178 SplitIntRange { range, borders: Vec::new() }
182 fn to_borders(r: IntRange) -> [IntBorder; 2] {
184 let (lo, hi) = r.boundaries();
185 let lo = JustBefore(lo);
186 let hi = match hi.checked_add(1) {
187 Some(m) => JustBefore(m),
193 /// Add ranges relative to which we split.
194 fn split(&mut self, ranges: impl Iterator<Item = IntRange>) {
195 let this_range = &self.range;
196 let included_ranges = ranges.filter_map(|r| this_range.intersection(&r));
197 let included_borders = included_ranges.flat_map(|r| {
198 let borders = Self::to_borders(r);
199 once(borders[0]).chain(once(borders[1]))
201 self.borders.extend(included_borders);
202 self.borders.sort_unstable();
205 /// Iterate over the contained ranges.
206 fn iter(&self) -> impl Iterator<Item = IntRange> + '_ {
209 let self_range = Self::to_borders(self.range.clone());
210 // Start with the start of the range.
211 let mut prev_border = self_range[0];
215 // End with the end of the range.
216 .chain(once(self_range[1]))
217 // List pairs of adjacent borders.
219 let ret = (prev_border, border);
220 prev_border = border;
224 .filter(|(prev_border, border)| prev_border != border)
225 // Finally, convert to ranges.
226 .map(|(prev_border, border)| {
227 let range = match (prev_border, border) {
228 (JustBefore(n), JustBefore(m)) if n < m => n..=(m - 1),
229 (JustBefore(n), AfterMax) => n..=u128::MAX,
230 _ => unreachable!(), // Ruled out by the sorting and filtering we did
237 /// A constructor for array and slice patterns.
238 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
239 pub(super) struct Slice {
240 _unimplemented: Void,
244 /// See `Constructor::is_covered_by`
245 fn is_covered_by(self, _other: Self) -> bool {
246 unimplemented!() // never called as Slice contains Void
250 /// A value can be decomposed into a constructor applied to some fields. This struct represents
251 /// the constructor. See also `Fields`.
253 /// `pat_constructor` retrieves the constructor corresponding to a pattern.
254 /// `specialize_constructor` returns the list of fields corresponding to a pattern, given a
255 /// constructor. `Constructor::apply` reconstructs the pattern from a pair of `Constructor` and
258 #[derive(Clone, Debug, PartialEq)]
259 pub(super) enum Constructor {
260 /// The constructor for patterns that have a single constructor, like tuples, struct patterns
261 /// and fixed-length arrays.
264 Variant(EnumVariantId),
265 /// Ranges of integer literal values (`2`, `2..=5` or `2..5`).
267 /// Ranges of floating-point literal values (`2.0..=5.2`).
269 /// String literals. Strings are not quite the same as `&[u8]` so we treat them separately.
271 /// Array and slice patterns.
273 /// Constants that must not be matched structurally. They are treated as black
274 /// boxes for the purposes of exhaustiveness: we must not inspect them, and they
275 /// don't count towards making a match exhaustive.
277 /// Fake extra constructor for enums that aren't allowed to be matched exhaustively. Also used
278 /// for those types for which we cannot list constructors explicitly, like `f64` and `str`.
280 /// Stands for constructors that are not seen in the matrix, as explained in the documentation
281 /// for [`SplitWildcard`].
283 /// Wildcard pattern.
288 pub(super) fn is_wildcard(&self) -> bool {
289 matches!(self, Wildcard)
292 fn as_int_range(&self) -> Option<&IntRange> {
294 IntRange(range) => Some(range),
299 fn as_slice(&self) -> Option<Slice> {
301 Slice(slice) => Some(*slice),
306 fn variant_id_for_adt(&self, adt: hir_def::AdtId) -> VariantId {
308 Variant(id) => id.into(),
310 assert!(!matches!(adt, hir_def::AdtId::EnumId(_)));
312 hir_def::AdtId::EnumId(_) => unreachable!(),
313 hir_def::AdtId::StructId(id) => id.into(),
314 hir_def::AdtId::UnionId(id) => id.into(),
317 _ => panic!("bad constructor {:?} for adt {:?}", self, adt),
321 /// Determines the constructor that the given pattern can be specialized to.
322 pub(super) fn from_pat(cx: &MatchCheckCtx<'_>, pat: PatId) -> Self {
323 match cx.pattern_arena.borrow()[pat].kind.as_ref() {
324 PatKind::Binding { .. } | PatKind::Wild => Wildcard,
325 PatKind::Leaf { .. } | PatKind::Deref { .. } => Single,
326 &PatKind::Variant { enum_variant, .. } => Variant(enum_variant),
327 &PatKind::LiteralBool { value } => IntRange(IntRange::from_bool(value)),
328 PatKind::Or { .. } => {
329 never!("Or-pattern should have been expanded earlier on.");
335 /// Some constructors (namely `Wildcard`, `IntRange` and `Slice`) actually stand for a set of actual
336 /// constructors (like variants, integers or fixed-sized slices). When specializing for these
337 /// constructors, we want to be specialising for the actual underlying constructors.
338 /// Naively, we would simply return the list of constructors they correspond to. We instead are
339 /// more clever: if there are constructors that we know will behave the same wrt the current
340 /// matrix, we keep them grouped. For example, all slices of a sufficiently large length
341 /// will either be all useful or all non-useful with a given matrix.
343 /// See the branches for details on how the splitting is done.
345 /// This function may discard some irrelevant constructors if this preserves behavior and
346 /// diagnostics. Eg. for the `_` case, we ignore the constructors already present in the
347 /// matrix, unless all of them are.
348 pub(super) fn split<'a>(
351 ctors: impl Iterator<Item = &'a Constructor> + Clone,
352 ) -> SmallVec<[Self; 1]> {
355 let mut split_wildcard = SplitWildcard::new(pcx);
356 split_wildcard.split(pcx, ctors);
357 split_wildcard.into_ctors(pcx)
359 // Fast-track if the range is trivial. In particular, we don't do the overlapping
361 IntRange(ctor_range) if !ctor_range.is_singleton() => {
362 let mut split_range = SplitIntRange::new(ctor_range.clone());
363 let int_ranges = ctors.filter_map(|ctor| ctor.as_int_range());
364 split_range.split(int_ranges.cloned());
365 split_range.iter().map(IntRange).collect()
367 Slice(_) => unimplemented!(),
368 // Any other constructor can be used unchanged.
369 _ => smallvec![self.clone()],
373 /// Returns whether `self` is covered by `other`, i.e. whether `self` is a subset of `other`.
374 /// For the simple cases, this is simply checking for equality. For the "grouped" constructors,
375 /// this checks for inclusion.
376 // We inline because this has a single call site in `Matrix::specialize_constructor`.
378 pub(super) fn is_covered_by(&self, _pcx: PatCtxt<'_>, other: &Self) -> bool {
379 // This must be kept in sync with `is_covered_by_any`.
380 match (self, other) {
381 // Wildcards cover anything
382 (_, Wildcard) => true,
383 // The missing ctors are not covered by anything in the matrix except wildcards.
384 (Missing | Wildcard, _) => false,
386 (Single, Single) => true,
387 (Variant(self_id), Variant(other_id)) => self_id == other_id,
389 (IntRange(self_range), IntRange(other_range)) => self_range.is_covered_by(other_range),
390 (FloatRange(..), FloatRange(..)) => {
393 (Str(..), Str(..)) => {
396 (Slice(self_slice), Slice(other_slice)) => self_slice.is_covered_by(*other_slice),
398 // We are trying to inspect an opaque constant. Thus we skip the row.
399 (Opaque, _) | (_, Opaque) => false,
400 // Only a wildcard pattern can match the special extra constructor.
401 (NonExhaustive, _) => false,
404 never!("trying to compare incompatible constructors {:?} and {:?}", self, other);
405 // Continue with 'whatever is covered' supposed to result in false no-error diagnostic.
411 /// Faster version of `is_covered_by` when applied to many constructors. `used_ctors` is
412 /// assumed to be built from `matrix.head_ctors()` with wildcards filtered out, and `self` is
413 /// assumed to have been split from a wildcard.
414 fn is_covered_by_any(&self, _pcx: PatCtxt<'_>, used_ctors: &[Constructor]) -> bool {
415 if used_ctors.is_empty() {
419 // This must be kept in sync with `is_covered_by`.
421 // If `self` is `Single`, `used_ctors` cannot contain anything else than `Single`s.
422 Single => !used_ctors.is_empty(),
423 Variant(_) => used_ctors.iter().any(|c| c == self),
424 IntRange(range) => used_ctors
426 .filter_map(|c| c.as_int_range())
427 .any(|other| range.is_covered_by(other)),
428 Slice(slice) => used_ctors
430 .filter_map(|c| c.as_slice())
431 .any(|other| slice.is_covered_by(other)),
432 // This constructor is never covered by anything else
433 NonExhaustive => false,
434 Str(..) | FloatRange(..) | Opaque | Missing | Wildcard => {
435 never!("found unexpected ctor in all_ctors: {:?}", self);
442 /// A wildcard constructor that we split relative to the constructors in the matrix, as explained
443 /// at the top of the file.
445 /// A constructor that is not present in the matrix rows will only be covered by the rows that have
446 /// wildcards. Thus we can group all of those constructors together; we call them "missing
447 /// constructors". Splitting a wildcard would therefore list all present constructors individually
448 /// (or grouped if they are integers or slices), and then all missing constructors together as a
451 /// However we can go further: since any constructor will match the wildcard rows, and having more
452 /// rows can only reduce the amount of usefulness witnesses, we can skip the present constructors
453 /// and only try the missing ones.
454 /// This will not preserve the whole list of witnesses, but will preserve whether the list is empty
455 /// or not. In fact this is quite natural from the point of view of diagnostics too. This is done
456 /// in `to_ctors`: in some cases we only return `Missing`.
458 pub(super) struct SplitWildcard {
459 /// Constructors seen in the matrix.
460 matrix_ctors: Vec<Constructor>,
461 /// All the constructors for this type
462 all_ctors: SmallVec<[Constructor; 1]>,
466 pub(super) fn new(pcx: PatCtxt<'_>) -> Self {
468 let make_range = |start, end, scalar| IntRange(IntRange::from_range(start, end, scalar));
470 // Unhandled types are treated as non-exhaustive. Being explicit here instead of falling
471 // to catchall arm to ease further implementation.
472 let unhandled = || smallvec![NonExhaustive];
474 // This determines the set of all possible constructors for the type `pcx.ty`. For numbers,
475 // arrays and slices we use ranges and variable-length slices when appropriate.
477 // If the `exhaustive_patterns` feature is enabled, we make sure to omit constructors that
478 // are statically impossible. E.g., for `Option<!>`, we do not include `Some(_)` in the
479 // returned list of constructors.
480 // Invariant: this is empty if and only if the type is uninhabited (as determined by
481 // `cx.is_uninhabited()`).
482 let all_ctors = match pcx.ty.kind(&Interner) {
483 TyKind::Scalar(Scalar::Bool) => smallvec![make_range(0, 1, Scalar::Bool)],
484 // TyKind::Array(..) if ... => unhandled(),
485 TyKind::Array(..) | TyKind::Slice(..) => unhandled(),
486 &TyKind::Adt(AdtId(hir_def::AdtId::EnumId(enum_id)), ref _substs) => {
487 let enum_data = cx.db.enum_data(enum_id);
489 // If the enum is declared as `#[non_exhaustive]`, we treat it as if it had an
490 // additional "unknown" constructor.
491 // There is no point in enumerating all possible variants, because the user can't
492 // actually match against them all themselves. So we always return only the fictitious
494 // E.g., in an example like:
497 // let err: io::ErrorKind = ...;
499 // io::ErrorKind::NotFound => {},
503 // we don't want to show every possible IO error, but instead have only `_` as the
505 let is_declared_nonexhaustive = cx.is_foreign_non_exhaustive_enum(enum_id);
507 // If `exhaustive_patterns` is disabled and our scrutinee is an empty enum, we treat it
508 // as though it had an "unknown" constructor to avoid exposing its emptiness. The
509 // exception is if the pattern is at the top level, because we want empty matches to be
510 // considered exhaustive.
511 let is_secretly_empty = enum_data.variants.is_empty()
512 && !cx.feature_exhaustive_patterns()
513 && !pcx.is_top_level;
515 if is_secretly_empty || is_declared_nonexhaustive {
516 smallvec![NonExhaustive]
517 } else if cx.feature_exhaustive_patterns() {
518 unimplemented!() // see MatchCheckCtx.feature_exhaustive_patterns()
523 .map(|(local_id, ..)| Variant(EnumVariantId { parent: enum_id, local_id }))
527 TyKind::Scalar(Scalar::Char) => unhandled(),
528 TyKind::Scalar(Scalar::Int(..) | Scalar::Uint(..)) => unhandled(),
529 TyKind::Never if !cx.feature_exhaustive_patterns() && !pcx.is_top_level => {
530 smallvec![NonExhaustive]
532 TyKind::Never => SmallVec::new(),
533 _ if cx.is_uninhabited(pcx.ty) => SmallVec::new(),
534 TyKind::Adt(..) | TyKind::Tuple(..) | TyKind::Ref(..) => smallvec![Single],
535 // This type is one for which we cannot list constructors, like `str` or `f64`.
536 _ => smallvec![NonExhaustive],
538 SplitWildcard { matrix_ctors: Vec::new(), all_ctors }
541 /// Pass a set of constructors relative to which to split this one. Don't call twice, it won't
542 /// do what you want.
543 pub(super) fn split<'a>(
546 ctors: impl Iterator<Item = &'a Constructor> + Clone,
548 // Since `all_ctors` never contains wildcards, this won't recurse further.
550 self.all_ctors.iter().flat_map(|ctor| ctor.split(pcx, ctors.clone())).collect();
551 self.matrix_ctors = ctors.filter(|c| !c.is_wildcard()).cloned().collect();
554 /// Whether there are any value constructors for this type that are not present in the matrix.
555 fn any_missing(&self, pcx: PatCtxt<'_>) -> bool {
556 self.iter_missing(pcx).next().is_some()
559 /// Iterate over the constructors for this type that are not present in the matrix.
560 pub(super) fn iter_missing<'a>(
563 ) -> impl Iterator<Item = &'a Constructor> {
564 self.all_ctors.iter().filter(move |ctor| !ctor.is_covered_by_any(pcx, &self.matrix_ctors))
567 /// Return the set of constructors resulting from splitting the wildcard. As explained at the
568 /// top of the file, if any constructors are missing we can ignore the present ones.
569 fn into_ctors(self, pcx: PatCtxt<'_>) -> SmallVec<[Constructor; 1]> {
570 if self.any_missing(pcx) {
571 // Some constructors are missing, thus we can specialize with the special `Missing`
572 // constructor, which stands for those constructors that are not seen in the matrix,
573 // and matches the same rows as any of them (namely the wildcard rows). See the top of
574 // the file for details.
575 // However, when all constructors are missing we can also specialize with the full
576 // `Wildcard` constructor. The difference will depend on what we want in diagnostics.
578 // If some constructors are missing, we typically want to report those constructors,
581 // enum Direction { N, S, E, W }
582 // let Direction::N = ...;
584 // we can report 3 witnesses: `S`, `E`, and `W`.
586 // However, if the user didn't actually specify a constructor
587 // in this arm, e.g., in
589 // let x: (Direction, Direction, bool) = ...;
590 // let (_, _, false) = x;
592 // we don't want to show all 16 possible witnesses `(<direction-1>, <direction-2>,
593 // true)` - we are satisfied with `(_, _, true)`. So if all constructors are missing we
594 // prefer to report just a wildcard `_`.
596 // The exception is: if we are at the top-level, for example in an empty match, we
597 // sometimes prefer reporting the list of constructors instead of just `_`.
598 let report_when_all_missing = pcx.is_top_level && !IntRange::is_integral(pcx.ty);
599 let ctor = if !self.matrix_ctors.is_empty() || report_when_all_missing {
604 return smallvec![ctor];
607 // All the constructors are present in the matrix, so we just go through them all.
612 /// A value can be decomposed into a constructor applied to some fields. This struct represents
613 /// those fields, generalized to allow patterns in each field. See also `Constructor`.
614 /// This is constructed from a constructor using [`Fields::wildcards()`].
616 /// If a private or `non_exhaustive` field is uninhabited, the code mustn't observe that it is
617 /// uninhabited. For that, we filter these fields out of the matrix. This is handled automatically
618 /// in `Fields`. This filtering is uncommon in practice, because uninhabited fields are rarely used,
619 /// so we avoid it when possible to preserve performance.
620 #[derive(Debug, Clone)]
621 pub(super) enum Fields {
622 /// Lists of patterns that don't contain any filtered fields.
623 /// `Slice` and `Vec` behave the same; the difference is only to avoid allocating and
624 /// triple-dereferences when possible. Frankly this is premature optimization, I (Nadrieril)
625 /// have not measured if it really made a difference.
626 Vec(SmallVec<[PatId; 2]>),
630 /// Internal use. Use `Fields::wildcards()` instead.
631 /// Must not be used if the pattern is a field of a struct/tuple/variant.
632 fn from_single_pattern(pat: PatId) -> Self {
633 Fields::Vec(smallvec![pat])
636 /// Convenience; internal use.
637 fn wildcards_from_tys(cx: &MatchCheckCtx<'_>, tys: impl IntoIterator<Item = Ty>) -> Self {
638 let wilds = tys.into_iter().map(Pat::wildcard_from_ty);
639 let pats = wilds.map(|pat| cx.alloc_pat(pat)).collect();
643 /// Creates a new list of wildcard fields for a given constructor.
644 pub(crate) fn wildcards(pcx: PatCtxt<'_>, constructor: &Constructor) -> Self {
647 let wildcard_from_ty = |ty: &Ty| cx.alloc_pat(Pat::wildcard_from_ty(ty.clone()));
649 let ret = match constructor {
650 Single | Variant(_) => match ty.kind(&Interner) {
651 TyKind::Tuple(_, substs) => {
652 let tys = substs.iter(&Interner).map(|ty| ty.assert_ty_ref(&Interner));
653 Fields::wildcards_from_tys(cx, tys.cloned())
655 TyKind::Ref(.., rty) => Fields::from_single_pattern(wildcard_from_ty(rty)),
656 &TyKind::Adt(AdtId(adt), ref substs) => {
657 if adt_is_box(adt, cx) {
658 // Use T as the sub pattern type of Box<T>.
659 let subst_ty = substs.at(&Interner, 0).assert_ty_ref(&Interner);
660 Fields::from_single_pattern(wildcard_from_ty(subst_ty))
662 let variant_id = constructor.variant_id_for_adt(adt);
664 variant_id.module(cx.db.upcast()).krate() == cx.module.krate();
665 // Whether we must not match the fields of this variant exhaustively.
666 let is_non_exhaustive =
667 is_field_list_non_exhaustive(variant_id, cx) && !adt_is_local;
669 cov_mark::hit!(match_check_wildcard_expanded_to_substitutions);
670 let field_ty_data = cx.db.field_types(variant_id);
674 .map(|(_, binders)| binders.clone().substitute(&Interner, substs))
677 // In the following cases, we don't need to filter out any fields. This is
678 // the vast majority of real cases, since uninhabited fields are uncommon.
679 let has_no_hidden_fields = (matches!(adt, hir_def::AdtId::EnumId(_))
680 && !is_non_exhaustive)
681 || !field_tys().any(|ty| cx.is_uninhabited(&ty));
683 if has_no_hidden_fields {
684 Fields::wildcards_from_tys(cx, field_tys())
686 //FIXME(iDawer): see MatchCheckCtx::is_uninhabited, has_no_hidden_fields is always true
687 unimplemented!("exhaustive_patterns feature")
692 never!("Unexpected type for `Single` constructor: {:?}", ty_kind);
693 Fields::from_single_pattern(wildcard_from_ty(ty))
699 Str(..) | FloatRange(..) | IntRange(..) | NonExhaustive | Opaque | Missing
700 | Wildcard => Fields::Vec(Default::default()),
705 /// Apply a constructor to a list of patterns, yielding a new pattern. `self`
706 /// must have as many elements as this constructor's arity.
708 /// This is roughly the inverse of `specialize_constructor`.
711 /// `ctor`: `Constructor::Single`
712 /// `ty`: `Foo(u32, u32, u32)`
713 /// `self`: `[10, 20, _]`
714 /// returns `Foo(10, 20, _)`
716 /// `ctor`: `Constructor::Variant(Option::Some)`
717 /// `ty`: `Option<bool>`
718 /// `self`: `[false]`
719 /// returns `Some(false)`
720 pub(super) fn apply(self, pcx: PatCtxt<'_>, ctor: &Constructor) -> Pat {
721 let subpatterns_and_indices = self.patterns_and_indices();
722 let mut subpatterns =
723 subpatterns_and_indices.iter().map(|&(_, p)| pcx.cx.pattern_arena.borrow()[p].clone());
724 // FIXME(iDawer) witnesses are not yet used
725 const UNHANDLED: PatKind = PatKind::Wild;
727 let pat = match ctor {
728 Single | Variant(_) => match pcx.ty.kind(&Interner) {
729 TyKind::Adt(..) | TyKind::Tuple(..) => {
730 // We want the real indices here.
731 let subpatterns = subpatterns_and_indices
733 .map(|&(field, pat)| FieldPat {
735 pattern: pcx.cx.pattern_arena.borrow()[pat].clone(),
739 if let Some((hir_def::AdtId::EnumId(_), substs)) = pcx.ty.as_adt() {
740 let enum_variant = match ctor {
744 PatKind::Variant { substs: substs.clone(), enum_variant, subpatterns }
746 PatKind::Leaf { subpatterns }
749 // Note: given the expansion of `&str` patterns done in `expand_pattern`, we should
750 // be careful to reconstruct the correct constant pattern here. However a string
751 // literal pattern will never be reported as a non-exhaustiveness witness, so we
752 // can ignore this issue.
753 TyKind::Ref(..) => PatKind::Deref { subpattern: subpatterns.next().unwrap() },
754 TyKind::Slice(..) | TyKind::Array(..) => {
755 never!("bad slice pattern {:?} {:?}", ctor, pcx.ty);
760 Constructor::Slice(_) => UNHANDLED,
762 FloatRange(..) => UNHANDLED,
763 Constructor::IntRange(_) => UNHANDLED,
764 NonExhaustive => PatKind::Wild,
765 Wildcard => return Pat::wildcard_from_ty(pcx.ty.clone()),
767 never!("we should not try to apply an opaque constructor");
772 "trying to apply the `Missing` constructor; \
773 this should have been done in `apply_constructors`",
779 Pat { ty: pcx.ty.clone(), kind: Box::new(pat) }
782 /// Returns the number of patterns. This is the same as the arity of the constructor used to
783 /// construct `self`.
784 pub(super) fn len(&self) -> usize {
786 Fields::Vec(pats) => pats.len(),
790 /// Returns the list of patterns along with the corresponding field indices.
791 fn patterns_and_indices(&self) -> SmallVec<[(LocalFieldId, PatId); 2]> {
793 Fields::Vec(pats) => pats
797 .map(|(i, p)| (LocalFieldId::from_raw((i as u32).into()), p))
802 pub(super) fn into_patterns(self) -> SmallVec<[PatId; 2]> {
804 Fields::Vec(pats) => pats,
808 /// Overrides some of the fields with the provided patterns. Exactly like
809 /// `replace_fields_indexed`, except that it takes `FieldPat`s as input.
810 fn replace_with_fieldpats(
812 new_pats: impl IntoIterator<Item = (LocalFieldId, PatId)>,
814 self.replace_fields_indexed(
815 new_pats.into_iter().map(|(field, pat)| (u32::from(field.into_raw()) as usize, pat)),
819 /// Overrides some of the fields with the provided patterns. This is used when a pattern
820 /// defines some fields but not all, for example `Foo { field1: Some(_), .. }`: here we start
821 /// with a `Fields` that is just one wildcard per field of the `Foo` struct, and override the
822 /// entry corresponding to `field1` with the pattern `Some(_)`. This is also used for slice
823 /// patterns for the same reason.
824 fn replace_fields_indexed(&self, new_pats: impl IntoIterator<Item = (usize, PatId)>) -> Self {
825 let mut fields = self.clone();
828 Fields::Vec(pats) => {
829 for (i, pat) in new_pats {
830 if let Some(p) = pats.get_mut(i) {
839 /// Replaces contained fields with the given list of patterns. There must be `len()` patterns
841 pub(super) fn replace_fields(
843 cx: &MatchCheckCtx<'_>,
844 pats: impl IntoIterator<Item = Pat>,
846 let pats = pats.into_iter().map(|pat| cx.alloc_pat(pat)).collect();
849 Fields::Vec(_) => Fields::Vec(pats),
853 /// Replaces contained fields with the arguments of the given pattern. Only use on a pattern
854 /// that is compatible with the constructor used to build `self`.
855 /// This is meant to be used on the result of `Fields::wildcards()`. The idea is that
856 /// `wildcards` constructs a list of fields where all entries are wildcards, and the pattern
857 /// provided to this function fills some of the fields with non-wildcards.
858 /// In the following example `Fields::wildcards` would return `[_, _, _, _]`. If we call
859 /// `replace_with_pattern_arguments` on it with the pattern, the result will be `[Some(0), _,
862 /// let x: [Option<u8>; 4] = foo();
864 /// [Some(0), ..] => {}
867 /// This is guaranteed to preserve the number of patterns in `self`.
868 pub(super) fn replace_with_pattern_arguments(
871 cx: &MatchCheckCtx<'_>,
873 // FIXME(iDawer): Factor out pattern deep cloning. See discussion:
874 // https://github.com/rust-analyzer/rust-analyzer/pull/8717#discussion_r633086640
875 let mut arena = cx.pattern_arena.borrow_mut();
876 match arena[pat].kind.as_ref() {
877 PatKind::Deref { subpattern } => {
878 assert_eq!(self.len(), 1);
879 let subpattern = subpattern.clone();
880 Fields::from_single_pattern(arena.alloc(subpattern))
882 PatKind::Leaf { subpatterns } | PatKind::Variant { subpatterns, .. } => {
883 let subpatterns = subpatterns.clone();
884 let subpatterns = subpatterns
886 .map(|field_pat| (field_pat.field, arena.alloc(field_pat.pattern.clone())));
887 self.replace_with_fieldpats(subpatterns)
891 | PatKind::Binding { .. }
892 | PatKind::LiteralBool { .. }
893 | PatKind::Or { .. } => self.clone(),
898 fn is_field_list_non_exhaustive(variant_id: VariantId, cx: &MatchCheckCtx<'_>) -> bool {
899 let attr_def_id = match variant_id {
900 VariantId::EnumVariantId(id) => id.into(),
901 VariantId::StructId(id) => id.into(),
902 VariantId::UnionId(id) => id.into(),
904 cx.db.attrs(attr_def_id).by_key("non_exhaustive").exists()
907 fn adt_is_box(adt: hir_def::AdtId, cx: &MatchCheckCtx<'_>) -> bool {
908 use hir_def::lang_item::LangItemTarget;
909 match cx.db.lang_item(cx.module.krate(), SmolStr::new_inline("owned_box")) {
910 Some(LangItemTarget::StructId(box_id)) => adt == box_id.into(),