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`]; for slices, see
43 //! [`SplitVarLenSlice`].
51 use hir_def::{EnumVariantId, HasModule, LocalFieldId, VariantId};
52 use smallvec::{smallvec, SmallVec};
54 use crate::{AdtId, Interner, Scalar, Ty, TyExt, TyKind};
57 usefulness::{MatchCheckCtx, PatCtxt},
58 FieldPat, Pat, PatId, PatKind,
61 use self::Constructor::*;
63 /// [Constructor] uses this in umimplemented variants.
64 /// It allows porting match expressions from upstream algorithm without losing semantics.
65 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
66 pub(super) enum Void {}
68 /// An inclusive interval, used for precise integer exhaustiveness checking.
69 /// `IntRange`s always store a contiguous range. This means that values are
70 /// encoded such that `0` encodes the minimum value for the integer,
71 /// regardless of the signedness.
72 /// For example, the pattern `-128..=127i8` is encoded as `0..=255`.
73 /// This makes comparisons and arithmetic on interval endpoints much more
74 /// straightforward. See `signed_bias` for details.
76 /// `IntRange` is never used to encode an empty range or a "range" that wraps
77 /// around the (offset) space: i.e., `range.lo <= range.hi`.
78 #[derive(Clone, Debug, PartialEq, Eq)]
79 pub(super) struct IntRange {
80 range: RangeInclusive<u128>,
85 fn is_integral(ty: &Ty) -> bool {
86 match ty.kind(&Interner) {
87 TyKind::Scalar(Scalar::Char)
88 | TyKind::Scalar(Scalar::Int(_))
89 | TyKind::Scalar(Scalar::Uint(_))
90 | TyKind::Scalar(Scalar::Bool) => true,
95 fn is_singleton(&self) -> bool {
96 self.range.start() == self.range.end()
99 fn boundaries(&self) -> (u128, u128) {
100 (*self.range.start(), *self.range.end())
104 fn from_bool(value: bool) -> IntRange {
105 let val = value as u128;
106 IntRange { range: val..=val }
110 fn from_range(lo: u128, hi: u128, scalar_ty: Scalar) -> IntRange {
111 if let Scalar::Bool = scalar_ty {
112 IntRange { range: lo..=hi }
118 fn is_subrange(&self, other: &Self) -> bool {
119 other.range.start() <= self.range.start() && self.range.end() <= other.range.end()
122 fn intersection(&self, other: &Self) -> Option<Self> {
123 let (lo, hi) = self.boundaries();
124 let (other_lo, other_hi) = other.boundaries();
125 if lo <= other_hi && other_lo <= hi {
126 Some(IntRange { range: max(lo, other_lo)..=min(hi, other_hi) })
132 /// See `Constructor::is_covered_by`
133 fn is_covered_by(&self, other: &Self) -> bool {
134 if self.intersection(other).is_some() {
135 // Constructor splitting should ensure that all intersections we encounter are actually
137 assert!(self.is_subrange(other));
145 /// Represents a border between 2 integers. Because the intervals spanning borders must be able to
146 /// cover every integer, we need to be able to represent 2^128 + 1 such borders.
147 #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
153 /// A range of integers that is partitioned into disjoint subranges. This does constructor
154 /// splitting for integer ranges as explained at the top of the file.
156 /// This is fed multiple ranges, and returns an output that covers the input, but is split so that
157 /// the only intersections between an output range and a seen range are inclusions. No output range
158 /// straddles the boundary of one of the inputs.
160 /// The following input:
162 /// |-------------------------| // `self`
163 /// |------| |----------| |----|
164 /// |-------| |-------|
166 /// would be iterated over as follows:
168 /// ||---|--||-|---|---|---|--|
170 #[derive(Debug, Clone)]
171 struct SplitIntRange {
172 /// The range we are splitting
174 /// The borders of ranges we have seen. They are all contained within `range`. This is kept
176 borders: Vec<IntBorder>,
180 fn new(range: IntRange) -> Self {
181 SplitIntRange { range, borders: Vec::new() }
185 fn to_borders(r: IntRange) -> [IntBorder; 2] {
187 let (lo, hi) = r.boundaries();
188 let lo = JustBefore(lo);
189 let hi = match hi.checked_add(1) {
190 Some(m) => JustBefore(m),
196 /// Add ranges relative to which we split.
197 fn split(&mut self, ranges: impl Iterator<Item = IntRange>) {
198 let this_range = &self.range;
199 let included_ranges = ranges.filter_map(|r| this_range.intersection(&r));
200 let included_borders = included_ranges.flat_map(|r| {
201 let borders = Self::to_borders(r);
202 once(borders[0]).chain(once(borders[1]))
204 self.borders.extend(included_borders);
205 self.borders.sort_unstable();
208 /// Iterate over the contained ranges.
209 fn iter(&self) -> impl Iterator<Item = IntRange> + '_ {
212 let self_range = Self::to_borders(self.range.clone());
213 // Start with the start of the range.
214 let mut prev_border = self_range[0];
218 // End with the end of the range.
219 .chain(once(self_range[1]))
220 // List pairs of adjacent borders.
222 let ret = (prev_border, border);
223 prev_border = border;
227 .filter(|(prev_border, border)| prev_border != border)
228 // Finally, convert to ranges.
229 .map(|(prev_border, border)| {
230 let range = match (prev_border, border) {
231 (JustBefore(n), JustBefore(m)) if n < m => n..=(m - 1),
232 (JustBefore(n), AfterMax) => n..=u128::MAX,
233 _ => unreachable!(), // Ruled out by the sorting and filtering we did
240 /// A constructor for array and slice patterns.
241 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
242 pub(super) struct Slice {
243 _unimplemented: Void,
247 /// See `Constructor::is_covered_by`
248 fn is_covered_by(self, _other: Self) -> bool {
249 unimplemented!() // never called as Slice contains Void
253 /// A value can be decomposed into a constructor applied to some fields. This struct represents
254 /// the constructor. See also `Fields`.
256 /// `pat_constructor` retrieves the constructor corresponding to a pattern.
257 /// `specialize_constructor` returns the list of fields corresponding to a pattern, given a
258 /// constructor. `Constructor::apply` reconstructs the pattern from a pair of `Constructor` and
261 #[derive(Clone, Debug, PartialEq)]
262 pub(super) enum Constructor {
263 /// The constructor for patterns that have a single constructor, like tuples, struct patterns
264 /// and fixed-length arrays.
267 Variant(EnumVariantId),
268 /// Ranges of integer literal values (`2`, `2..=5` or `2..5`).
270 /// Ranges of floating-point literal values (`2.0..=5.2`).
272 /// String literals. Strings are not quite the same as `&[u8]` so we treat them separately.
274 /// Array and slice patterns.
276 /// Constants that must not be matched structurally. They are treated as black
277 /// boxes for the purposes of exhaustiveness: we must not inspect them, and they
278 /// don't count towards making a match exhaustive.
280 /// Fake extra constructor for enums that aren't allowed to be matched exhaustively. Also used
281 /// for those types for which we cannot list constructors explicitly, like `f64` and `str`.
283 /// Stands for constructors that are not seen in the matrix, as explained in the documentation
284 /// for [`SplitWildcard`].
286 /// Wildcard pattern.
291 pub(super) fn is_wildcard(&self) -> bool {
292 matches!(self, Wildcard)
295 fn as_int_range(&self) -> Option<&IntRange> {
297 IntRange(range) => Some(range),
302 fn as_slice(&self) -> Option<Slice> {
304 Slice(slice) => Some(*slice),
309 fn variant_id_for_adt(&self, adt: hir_def::AdtId) -> VariantId {
311 Variant(id) => id.into(),
313 assert!(!matches!(adt, hir_def::AdtId::EnumId(_)));
315 hir_def::AdtId::EnumId(_) => unreachable!(),
316 hir_def::AdtId::StructId(id) => id.into(),
317 hir_def::AdtId::UnionId(id) => id.into(),
320 _ => panic!("bad constructor {:?} for adt {:?}", self, adt),
324 /// Determines the constructor that the given pattern can be specialized to.
325 pub(super) fn from_pat(cx: &MatchCheckCtx<'_>, pat: PatId) -> Self {
326 match cx.pattern_arena.borrow()[pat].kind.as_ref() {
327 PatKind::Binding { .. } | PatKind::Wild => Wildcard,
328 PatKind::Leaf { .. } | PatKind::Deref { .. } => Single,
329 &PatKind::Variant { enum_variant, .. } => Variant(enum_variant),
330 &PatKind::LiteralBool { value } => IntRange(IntRange::from_bool(value)),
331 PatKind::Or { .. } => cx.bug("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,
403 _ => pcx.cx.bug(&format!(
404 "trying to compare incompatible constructors {:?} and {:?}",
410 /// Faster version of `is_covered_by` when applied to many constructors. `used_ctors` is
411 /// assumed to be built from `matrix.head_ctors()` with wildcards filtered out, and `self` is
412 /// assumed to have been split from a wildcard.
413 fn is_covered_by_any(&self, pcx: PatCtxt<'_>, used_ctors: &[Constructor]) -> bool {
414 if used_ctors.is_empty() {
418 // This must be kept in sync with `is_covered_by`.
420 // If `self` is `Single`, `used_ctors` cannot contain anything else than `Single`s.
421 Single => !used_ctors.is_empty(),
422 Variant(_) => used_ctors.iter().any(|c| c == self),
423 IntRange(range) => used_ctors
425 .filter_map(|c| c.as_int_range())
426 .any(|other| range.is_covered_by(other)),
427 Slice(slice) => used_ctors
429 .filter_map(|c| c.as_slice())
430 .any(|other| slice.is_covered_by(other)),
431 // This constructor is never covered by anything else
432 NonExhaustive => false,
433 Str(..) | FloatRange(..) | Opaque | Missing | Wildcard => {
434 pcx.cx.bug(&format!("found unexpected ctor in all_ctors: {:?}", self))
440 /// A wildcard constructor that we split relative to the constructors in the matrix, as explained
441 /// at the top of the file.
443 /// A constructor that is not present in the matrix rows will only be covered by the rows that have
444 /// wildcards. Thus we can group all of those constructors together; we call them "missing
445 /// constructors". Splitting a wildcard would therefore list all present constructors individually
446 /// (or grouped if they are integers or slices), and then all missing constructors together as a
449 /// However we can go further: since any constructor will match the wildcard rows, and having more
450 /// rows can only reduce the amount of usefulness witnesses, we can skip the present constructors
451 /// and only try the missing ones.
452 /// This will not preserve the whole list of witnesses, but will preserve whether the list is empty
453 /// or not. In fact this is quite natural from the point of view of diagnostics too. This is done
454 /// in `to_ctors`: in some cases we only return `Missing`.
456 pub(super) struct SplitWildcard {
457 /// Constructors seen in the matrix.
458 matrix_ctors: Vec<Constructor>,
459 /// All the constructors for this type
460 all_ctors: SmallVec<[Constructor; 1]>,
464 pub(super) fn new(pcx: PatCtxt<'_>) -> Self {
466 let make_range = |start, end, scalar| IntRange(IntRange::from_range(start, end, scalar));
468 // Unhandled types are treated as non-exhaustive. Being explicit here instead of falling
469 // to catchall arm to ease further implementation.
470 let unhandled = || smallvec![NonExhaustive];
472 // This determines the set of all possible constructors for the type `pcx.ty`. For numbers,
473 // arrays and slices we use ranges and variable-length slices when appropriate.
475 // If the `exhaustive_patterns` feature is enabled, we make sure to omit constructors that
476 // are statically impossible. E.g., for `Option<!>`, we do not include `Some(_)` in the
477 // returned list of constructors.
478 // Invariant: this is empty if and only if the type is uninhabited (as determined by
479 // `cx.is_uninhabited()`).
480 let all_ctors = match pcx.ty.kind(&Interner) {
481 TyKind::Scalar(Scalar::Bool) => smallvec![make_range(0, 1, Scalar::Bool)],
482 // TyKind::Array(..) if ... => unhandled(),
483 TyKind::Array(..) | TyKind::Slice(..) => unhandled(),
484 &TyKind::Adt(AdtId(hir_def::AdtId::EnumId(enum_id)), ref _substs) => {
485 let enum_data = cx.db.enum_data(enum_id);
487 // If the enum is declared as `#[non_exhaustive]`, we treat it as if it had an
488 // additional "unknown" constructor.
489 // There is no point in enumerating all possible variants, because the user can't
490 // actually match against them all themselves. So we always return only the fictitious
492 // E.g., in an example like:
495 // let err: io::ErrorKind = ...;
497 // io::ErrorKind::NotFound => {},
501 // we don't want to show every possible IO error, but instead have only `_` as the
503 let is_declared_nonexhaustive = cx.is_foreign_non_exhaustive_enum(enum_id);
505 // If `exhaustive_patterns` is disabled and our scrutinee is an empty enum, we treat it
506 // as though it had an "unknown" constructor to avoid exposing its emptiness. The
507 // exception is if the pattern is at the top level, because we want empty matches to be
508 // considered exhaustive.
509 let is_secretly_empty = enum_data.variants.is_empty()
510 && !cx.feature_exhaustive_patterns()
511 && !pcx.is_top_level;
513 if is_secretly_empty || is_declared_nonexhaustive {
514 smallvec![NonExhaustive]
515 } else if cx.feature_exhaustive_patterns() {
516 unimplemented!() // see MatchCheckCtx.feature_exhaustive_patterns()
521 .map(|(local_id, ..)| Variant(EnumVariantId { parent: enum_id, local_id }))
525 TyKind::Scalar(Scalar::Char) => unhandled(),
526 TyKind::Scalar(Scalar::Int(..)) | TyKind::Scalar(Scalar::Uint(..)) => unhandled(),
527 TyKind::Never if !cx.feature_exhaustive_patterns() && !pcx.is_top_level => {
528 smallvec![NonExhaustive]
530 TyKind::Never => SmallVec::new(),
531 _ if cx.is_uninhabited(&pcx.ty) => SmallVec::new(),
532 TyKind::Adt(..) | TyKind::Tuple(..) | TyKind::Ref(..) => smallvec![Single],
533 // This type is one for which we cannot list constructors, like `str` or `f64`.
534 _ => smallvec![NonExhaustive],
536 SplitWildcard { matrix_ctors: Vec::new(), all_ctors }
539 /// Pass a set of constructors relative to which to split this one. Don't call twice, it won't
540 /// do what you want.
541 pub(super) fn split<'a>(
544 ctors: impl Iterator<Item = &'a Constructor> + Clone,
546 // Since `all_ctors` never contains wildcards, this won't recurse further.
548 self.all_ctors.iter().flat_map(|ctor| ctor.split(pcx, ctors.clone())).collect();
549 self.matrix_ctors = ctors.filter(|c| !c.is_wildcard()).cloned().collect();
552 /// Whether there are any value constructors for this type that are not present in the matrix.
553 fn any_missing(&self, pcx: PatCtxt<'_>) -> bool {
554 self.iter_missing(pcx).next().is_some()
557 /// Iterate over the constructors for this type that are not present in the matrix.
558 pub(super) fn iter_missing<'a>(
561 ) -> impl Iterator<Item = &'a Constructor> {
562 self.all_ctors.iter().filter(move |ctor| !ctor.is_covered_by_any(pcx, &self.matrix_ctors))
565 /// Return the set of constructors resulting from splitting the wildcard. As explained at the
566 /// top of the file, if any constructors are missing we can ignore the present ones.
567 fn into_ctors(self, pcx: PatCtxt<'_>) -> SmallVec<[Constructor; 1]> {
568 if self.any_missing(pcx) {
569 // Some constructors are missing, thus we can specialize with the special `Missing`
570 // constructor, which stands for those constructors that are not seen in the matrix,
571 // and matches the same rows as any of them (namely the wildcard rows). See the top of
572 // the file for details.
573 // However, when all constructors are missing we can also specialize with the full
574 // `Wildcard` constructor. The difference will depend on what we want in diagnostics.
576 // If some constructors are missing, we typically want to report those constructors,
579 // enum Direction { N, S, E, W }
580 // let Direction::N = ...;
582 // we can report 3 witnesses: `S`, `E`, and `W`.
584 // However, if the user didn't actually specify a constructor
585 // in this arm, e.g., in
587 // let x: (Direction, Direction, bool) = ...;
588 // let (_, _, false) = x;
590 // we don't want to show all 16 possible witnesses `(<direction-1>, <direction-2>,
591 // true)` - we are satisfied with `(_, _, true)`. So if all constructors are missing we
592 // prefer to report just a wildcard `_`.
594 // The exception is: if we are at the top-level, for example in an empty match, we
595 // sometimes prefer reporting the list of constructors instead of just `_`.
596 let report_when_all_missing = pcx.is_top_level && !IntRange::is_integral(pcx.ty);
597 let ctor = if !self.matrix_ctors.is_empty() || report_when_all_missing {
602 return smallvec![ctor];
605 // All the constructors are present in the matrix, so we just go through them all.
610 /// A value can be decomposed into a constructor applied to some fields. This struct represents
611 /// those fields, generalized to allow patterns in each field. See also `Constructor`.
612 /// This is constructed from a constructor using [`Fields::wildcards()`].
614 /// If a private or `non_exhaustive` field is uninhabited, the code mustn't observe that it is
615 /// uninhabited. For that, we filter these fields out of the matrix. This is handled automatically
616 /// in `Fields`. This filtering is uncommon in practice, because uninhabited fields are rarely used,
617 /// so we avoid it when possible to preserve performance.
618 #[derive(Debug, Clone)]
619 pub(super) enum Fields {
620 /// Lists of patterns that don't contain any filtered fields.
621 /// `Slice` and `Vec` behave the same; the difference is only to avoid allocating and
622 /// triple-dereferences when possible. Frankly this is premature optimization, I (Nadrieril)
623 /// have not measured if it really made a difference.
624 Vec(SmallVec<[PatId; 2]>),
628 /// Internal use. Use `Fields::wildcards()` instead.
629 /// Must not be used if the pattern is a field of a struct/tuple/variant.
630 fn from_single_pattern(pat: PatId) -> Self {
631 Fields::Vec(smallvec![pat])
634 /// Convenience; internal use.
635 fn wildcards_from_tys(cx: &MatchCheckCtx<'_>, tys: impl IntoIterator<Item = Ty>) -> Self {
636 let wilds = tys.into_iter().map(Pat::wildcard_from_ty);
637 let pats = wilds.map(|pat| cx.alloc_pat(pat)).collect();
641 /// Creates a new list of wildcard fields for a given constructor.
642 pub(crate) fn wildcards(pcx: PatCtxt<'_>, constructor: &Constructor) -> Self {
645 let wildcard_from_ty = |ty: &Ty| cx.alloc_pat(Pat::wildcard_from_ty(ty.clone()));
647 let ret = match constructor {
648 Single | Variant(_) => match ty.kind(&Interner) {
649 TyKind::Tuple(_, substs) => {
650 let tys = substs.iter(&Interner).map(|ty| ty.assert_ty_ref(&Interner));
651 Fields::wildcards_from_tys(cx, tys.cloned())
653 TyKind::Ref(.., rty) => Fields::from_single_pattern(wildcard_from_ty(rty)),
654 &TyKind::Adt(AdtId(adt), ref substs) => {
655 if adt_is_box(adt, cx) {
656 // Use T as the sub pattern type of Box<T>.
657 let subst_ty = substs.at(&Interner, 0).assert_ty_ref(&Interner);
658 Fields::from_single_pattern(wildcard_from_ty(subst_ty))
660 let variant_id = constructor.variant_id_for_adt(adt);
662 variant_id.module(cx.db.upcast()).krate() == cx.module.krate();
663 // Whether we must not match the fields of this variant exhaustively.
664 let is_non_exhaustive =
665 is_field_list_non_exhaustive(variant_id, cx) && !adt_is_local;
667 let field_ty_data = cx.db.field_types(variant_id);
671 .map(|(_, binders)| binders.clone().substitute(&Interner, substs))
674 // In the following cases, we don't need to filter out any fields. This is
675 // the vast majority of real cases, since uninhabited fields are uncommon.
676 let has_no_hidden_fields = (matches!(adt, hir_def::AdtId::EnumId(_))
677 && !is_non_exhaustive)
678 || !field_tys().any(|ty| cx.is_uninhabited(&ty));
680 if has_no_hidden_fields {
681 Fields::wildcards_from_tys(cx, field_tys())
683 //FIXME(iDawer): see MatchCheckCtx::is_uninhabited, has_no_hidden_fields is always true
684 unimplemented!("exhaustive_patterns feature")
689 cx.bug(&format!("Unexpected type for `Single` constructor: {:?}", ty_kind))
695 Str(..) | FloatRange(..) | IntRange(..) | NonExhaustive | Opaque | Missing
696 | Wildcard => Fields::Vec(Default::default()),
701 /// Apply a constructor to a list of patterns, yielding a new pattern. `self`
702 /// must have as many elements as this constructor's arity.
704 /// This is roughly the inverse of `specialize_constructor`.
707 /// `ctor`: `Constructor::Single`
708 /// `ty`: `Foo(u32, u32, u32)`
709 /// `self`: `[10, 20, _]`
710 /// returns `Foo(10, 20, _)`
712 /// `ctor`: `Constructor::Variant(Option::Some)`
713 /// `ty`: `Option<bool>`
714 /// `self`: `[false]`
715 /// returns `Some(false)`
716 pub(super) fn apply(self, pcx: PatCtxt<'_>, ctor: &Constructor) -> Pat {
717 let subpatterns_and_indices = self.patterns_and_indices();
718 let mut subpatterns =
719 subpatterns_and_indices.iter().map(|&(_, p)| pcx.cx.pattern_arena.borrow()[p].clone());
720 // FIXME(iDawer) witnesses are not yet used
721 const UNHANDLED: PatKind = PatKind::Wild;
723 let pat = match ctor {
724 Single | Variant(_) => match pcx.ty.kind(&Interner) {
725 TyKind::Adt(..) | TyKind::Tuple(..) => {
726 // We want the real indices here.
727 let subpatterns = subpatterns_and_indices
729 .map(|&(field, pat)| FieldPat {
731 pattern: pcx.cx.pattern_arena.borrow()[pat].clone(),
735 if let Some((adt, substs)) = pcx.ty.as_adt() {
736 if let hir_def::AdtId::EnumId(_) = adt {
737 let enum_variant = match ctor {
741 PatKind::Variant { substs: substs.clone(), enum_variant, subpatterns }
743 PatKind::Leaf { 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 pcx.cx.bug(&format!("bad slice pattern {:?} {:?}", ctor, pcx.ty))
759 Constructor::Slice(_) => UNHANDLED,
761 FloatRange(..) => UNHANDLED,
762 Constructor::IntRange(_) => UNHANDLED,
763 NonExhaustive => PatKind::Wild,
764 Wildcard => return Pat::wildcard_from_ty(pcx.ty.clone()),
765 Opaque => pcx.cx.bug("we should not try to apply an opaque constructor"),
766 Missing => pcx.cx.bug(
767 "trying to apply the `Missing` constructor;\
768 this should have been done in `apply_constructors`",
772 Pat { ty: pcx.ty.clone(), kind: Box::new(pat) }
775 /// Returns the number of patterns. This is the same as the arity of the constructor used to
776 /// construct `self`.
777 pub(super) fn len(&self) -> usize {
779 Fields::Vec(pats) => pats.len(),
783 /// Returns the list of patterns along with the corresponding field indices.
784 fn patterns_and_indices(&self) -> SmallVec<[(LocalFieldId, PatId); 2]> {
786 Fields::Vec(pats) => pats
790 .map(|(i, p)| (LocalFieldId::from_raw((i as u32).into()), p))
795 pub(super) fn into_patterns(self) -> SmallVec<[PatId; 2]> {
797 Fields::Vec(pats) => pats,
801 /// Overrides some of the fields with the provided patterns. Exactly like
802 /// `replace_fields_indexed`, except that it takes `FieldPat`s as input.
803 fn replace_with_fieldpats(
805 new_pats: impl IntoIterator<Item = (LocalFieldId, PatId)>,
807 self.replace_fields_indexed(
808 new_pats.into_iter().map(|(field, pat)| (u32::from(field.into_raw()) as usize, pat)),
812 /// Overrides some of the fields with the provided patterns. This is used when a pattern
813 /// defines some fields but not all, for example `Foo { field1: Some(_), .. }`: here we start
814 /// with a `Fields` that is just one wildcard per field of the `Foo` struct, and override the
815 /// entry corresponding to `field1` with the pattern `Some(_)`. This is also used for slice
816 /// patterns for the same reason.
817 fn replace_fields_indexed(&self, new_pats: impl IntoIterator<Item = (usize, PatId)>) -> Self {
818 let mut fields = self.clone();
821 Fields::Vec(pats) => {
822 for (i, pat) in new_pats {
823 if let Some(p) = pats.get_mut(i) {
832 /// Replaces contained fields with the given list of patterns. There must be `len()` patterns
834 pub(super) fn replace_fields(
836 cx: &MatchCheckCtx<'_>,
837 pats: impl IntoIterator<Item = Pat>,
839 let pats = pats.into_iter().map(|pat| cx.alloc_pat(pat)).collect();
842 Fields::Vec(_) => Fields::Vec(pats),
846 /// Replaces contained fields with the arguments of the given pattern. Only use on a pattern
847 /// that is compatible with the constructor used to build `self`.
848 /// This is meant to be used on the result of `Fields::wildcards()`. The idea is that
849 /// `wildcards` constructs a list of fields where all entries are wildcards, and the pattern
850 /// provided to this function fills some of the fields with non-wildcards.
851 /// In the following example `Fields::wildcards` would return `[_, _, _, _]`. If we call
852 /// `replace_with_pattern_arguments` on it with the pattern, the result will be `[Some(0), _,
855 /// let x: [Option<u8>; 4] = foo();
857 /// [Some(0), ..] => {}
860 /// This is guaranteed to preserve the number of patterns in `self`.
861 pub(super) fn replace_with_pattern_arguments(
864 cx: &MatchCheckCtx<'_>,
866 // FIXME(iDawer): Factor out pattern deep cloning. See discussion:
867 // https://github.com/rust-analyzer/rust-analyzer/pull/8717#discussion_r633086640
868 let mut arena = cx.pattern_arena.borrow_mut();
869 match arena[pat].kind.as_ref() {
870 PatKind::Deref { subpattern } => {
871 assert_eq!(self.len(), 1);
872 let subpattern = subpattern.clone();
873 Fields::from_single_pattern(arena.alloc(subpattern))
875 PatKind::Leaf { subpatterns } | PatKind::Variant { subpatterns, .. } => {
876 let subpatterns = subpatterns.clone();
877 let subpatterns = subpatterns
879 .map(|field_pat| (field_pat.field, arena.alloc(field_pat.pattern.clone())));
880 self.replace_with_fieldpats(subpatterns)
884 | PatKind::Binding { .. }
885 | PatKind::LiteralBool { .. }
886 | PatKind::Or { .. } => self.clone(),
891 fn is_field_list_non_exhaustive(variant_id: VariantId, cx: &MatchCheckCtx<'_>) -> bool {
892 let attr_def_id = match variant_id {
893 VariantId::EnumVariantId(id) => id.into(),
894 VariantId::StructId(id) => id.into(),
895 VariantId::UnionId(id) => id.into(),
897 cx.db.attrs(attr_def_id).by_key("non_exhaustive").exists()
900 fn adt_is_box(adt: hir_def::AdtId, cx: &MatchCheckCtx<'_>) -> bool {
901 use hir_def::lang_item::LangItemTarget;
902 match cx.db.lang_item(cx.module.krate(), "owned_box".into()) {
903 Some(LangItemTarget::StructId(box_id)) => adt == box_id.into(),