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};
53 use crate::{AdtId, Interner, Scalar, Ty, TyExt, TyKind};
56 usefulness::{MatchCheckCtx, PatCtxt},
57 FieldPat, Pat, PatId, PatKind,
60 use self::Constructor::*;
62 /// [Constructor] uses this in umimplemented variants.
63 /// It allows porting match expressions from upstream algorithm without losing semantics.
64 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
65 pub(super) enum Void {}
67 /// An inclusive interval, used for precise integer exhaustiveness checking.
68 /// `IntRange`s always store a contiguous range. This means that values are
69 /// encoded such that `0` encodes the minimum value for the integer,
70 /// regardless of the signedness.
71 /// For example, the pattern `-128..=127i8` is encoded as `0..=255`.
72 /// This makes comparisons and arithmetic on interval endpoints much more
73 /// straightforward. See `signed_bias` for details.
75 /// `IntRange` is never used to encode an empty range or a "range" that wraps
76 /// around the (offset) space: i.e., `range.lo <= range.hi`.
77 #[derive(Clone, Debug, PartialEq, Eq)]
78 pub(super) struct IntRange {
79 range: RangeInclusive<u128>,
84 fn is_integral(ty: &Ty) -> bool {
85 match ty.kind(&Interner) {
86 TyKind::Scalar(Scalar::Char | Scalar::Int(_) | Scalar::Uint(_) | Scalar::Bool) => true,
91 fn is_singleton(&self) -> bool {
92 self.range.start() == self.range.end()
95 fn boundaries(&self) -> (u128, u128) {
96 (*self.range.start(), *self.range.end())
100 fn from_bool(value: bool) -> IntRange {
101 let val = value as u128;
102 IntRange { range: val..=val }
106 fn from_range(lo: u128, hi: u128, scalar_ty: Scalar) -> IntRange {
107 if let Scalar::Bool = scalar_ty {
108 IntRange { range: lo..=hi }
114 fn is_subrange(&self, other: &Self) -> bool {
115 other.range.start() <= self.range.start() && self.range.end() <= other.range.end()
118 fn intersection(&self, other: &Self) -> Option<Self> {
119 let (lo, hi) = self.boundaries();
120 let (other_lo, other_hi) = other.boundaries();
121 if lo <= other_hi && other_lo <= hi {
122 Some(IntRange { range: max(lo, other_lo)..=min(hi, other_hi) })
128 /// See `Constructor::is_covered_by`
129 fn is_covered_by(&self, other: &Self) -> bool {
130 if self.intersection(other).is_some() {
131 // Constructor splitting should ensure that all intersections we encounter are actually
133 assert!(self.is_subrange(other));
141 /// Represents a border between 2 integers. Because the intervals spanning borders must be able to
142 /// cover every integer, we need to be able to represent 2^128 + 1 such borders.
143 #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
149 /// A range of integers that is partitioned into disjoint subranges. This does constructor
150 /// splitting for integer ranges as explained at the top of the file.
152 /// This is fed multiple ranges, and returns an output that covers the input, but is split so that
153 /// the only intersections between an output range and a seen range are inclusions. No output range
154 /// straddles the boundary of one of the inputs.
156 /// The following input:
158 /// |-------------------------| // `self`
159 /// |------| |----------| |----|
160 /// |-------| |-------|
162 /// would be iterated over as follows:
164 /// ||---|--||-|---|---|---|--|
166 #[derive(Debug, Clone)]
167 struct SplitIntRange {
168 /// The range we are splitting
170 /// The borders of ranges we have seen. They are all contained within `range`. This is kept
172 borders: Vec<IntBorder>,
176 fn new(range: IntRange) -> Self {
177 SplitIntRange { range, borders: Vec::new() }
181 fn to_borders(r: IntRange) -> [IntBorder; 2] {
183 let (lo, hi) = r.boundaries();
184 let lo = JustBefore(lo);
185 let hi = match hi.checked_add(1) {
186 Some(m) => JustBefore(m),
192 /// Add ranges relative to which we split.
193 fn split(&mut self, ranges: impl Iterator<Item = IntRange>) {
194 let this_range = &self.range;
195 let included_ranges = ranges.filter_map(|r| this_range.intersection(&r));
196 let included_borders = included_ranges.flat_map(|r| {
197 let borders = Self::to_borders(r);
198 once(borders[0]).chain(once(borders[1]))
200 self.borders.extend(included_borders);
201 self.borders.sort_unstable();
204 /// Iterate over the contained ranges.
205 fn iter(&self) -> impl Iterator<Item = IntRange> + '_ {
208 let self_range = Self::to_borders(self.range.clone());
209 // Start with the start of the range.
210 let mut prev_border = self_range[0];
214 // End with the end of the range.
215 .chain(once(self_range[1]))
216 // List pairs of adjacent borders.
218 let ret = (prev_border, border);
219 prev_border = border;
223 .filter(|(prev_border, border)| prev_border != border)
224 // Finally, convert to ranges.
225 .map(|(prev_border, border)| {
226 let range = match (prev_border, border) {
227 (JustBefore(n), JustBefore(m)) if n < m => n..=(m - 1),
228 (JustBefore(n), AfterMax) => n..=u128::MAX,
229 _ => unreachable!(), // Ruled out by the sorting and filtering we did
236 /// A constructor for array and slice patterns.
237 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
238 pub(super) struct Slice {
239 _unimplemented: Void,
243 /// See `Constructor::is_covered_by`
244 fn is_covered_by(self, _other: Self) -> bool {
245 unimplemented!() // never called as Slice contains Void
249 /// A value can be decomposed into a constructor applied to some fields. This struct represents
250 /// the constructor. See also `Fields`.
252 /// `pat_constructor` retrieves the constructor corresponding to a pattern.
253 /// `specialize_constructor` returns the list of fields corresponding to a pattern, given a
254 /// constructor. `Constructor::apply` reconstructs the pattern from a pair of `Constructor` and
257 #[derive(Clone, Debug, PartialEq)]
258 pub(super) enum Constructor {
259 /// The constructor for patterns that have a single constructor, like tuples, struct patterns
260 /// and fixed-length arrays.
263 Variant(EnumVariantId),
264 /// Ranges of integer literal values (`2`, `2..=5` or `2..5`).
266 /// Ranges of floating-point literal values (`2.0..=5.2`).
268 /// String literals. Strings are not quite the same as `&[u8]` so we treat them separately.
270 /// Array and slice patterns.
272 /// Constants that must not be matched structurally. They are treated as black
273 /// boxes for the purposes of exhaustiveness: we must not inspect them, and they
274 /// don't count towards making a match exhaustive.
276 /// Fake extra constructor for enums that aren't allowed to be matched exhaustively. Also used
277 /// for those types for which we cannot list constructors explicitly, like `f64` and `str`.
279 /// Stands for constructors that are not seen in the matrix, as explained in the documentation
280 /// for [`SplitWildcard`].
282 /// Wildcard pattern.
287 pub(super) fn is_wildcard(&self) -> bool {
288 matches!(self, Wildcard)
291 fn as_int_range(&self) -> Option<&IntRange> {
293 IntRange(range) => Some(range),
298 fn as_slice(&self) -> Option<Slice> {
300 Slice(slice) => Some(*slice),
305 fn variant_id_for_adt(&self, adt: hir_def::AdtId) -> VariantId {
307 Variant(id) => id.into(),
309 assert!(!matches!(adt, hir_def::AdtId::EnumId(_)));
311 hir_def::AdtId::EnumId(_) => unreachable!(),
312 hir_def::AdtId::StructId(id) => id.into(),
313 hir_def::AdtId::UnionId(id) => id.into(),
316 _ => panic!("bad constructor {:?} for adt {:?}", self, adt),
320 /// Determines the constructor that the given pattern can be specialized to.
321 pub(super) fn from_pat(cx: &MatchCheckCtx<'_>, pat: PatId) -> Self {
322 match cx.pattern_arena.borrow()[pat].kind.as_ref() {
323 PatKind::Binding { .. } | PatKind::Wild => Wildcard,
324 PatKind::Leaf { .. } | PatKind::Deref { .. } => Single,
325 &PatKind::Variant { enum_variant, .. } => Variant(enum_variant),
326 &PatKind::LiteralBool { value } => IntRange(IntRange::from_bool(value)),
327 PatKind::Or { .. } => cx.bug("Or-pattern should have been expanded earlier on."),
331 /// Some constructors (namely `Wildcard`, `IntRange` and `Slice`) actually stand for a set of actual
332 /// constructors (like variants, integers or fixed-sized slices). When specializing for these
333 /// constructors, we want to be specialising for the actual underlying constructors.
334 /// Naively, we would simply return the list of constructors they correspond to. We instead are
335 /// more clever: if there are constructors that we know will behave the same wrt the current
336 /// matrix, we keep them grouped. For example, all slices of a sufficiently large length
337 /// will either be all useful or all non-useful with a given matrix.
339 /// See the branches for details on how the splitting is done.
341 /// This function may discard some irrelevant constructors if this preserves behavior and
342 /// diagnostics. Eg. for the `_` case, we ignore the constructors already present in the
343 /// matrix, unless all of them are.
344 pub(super) fn split<'a>(
347 ctors: impl Iterator<Item = &'a Constructor> + Clone,
348 ) -> SmallVec<[Self; 1]> {
351 let mut split_wildcard = SplitWildcard::new(pcx);
352 split_wildcard.split(pcx, ctors);
353 split_wildcard.into_ctors(pcx)
355 // Fast-track if the range is trivial. In particular, we don't do the overlapping
357 IntRange(ctor_range) if !ctor_range.is_singleton() => {
358 let mut split_range = SplitIntRange::new(ctor_range.clone());
359 let int_ranges = ctors.filter_map(|ctor| ctor.as_int_range());
360 split_range.split(int_ranges.cloned());
361 split_range.iter().map(IntRange).collect()
363 Slice(_) => unimplemented!(),
364 // Any other constructor can be used unchanged.
365 _ => smallvec![self.clone()],
369 /// Returns whether `self` is covered by `other`, i.e. whether `self` is a subset of `other`.
370 /// For the simple cases, this is simply checking for equality. For the "grouped" constructors,
371 /// this checks for inclusion.
372 // We inline because this has a single call site in `Matrix::specialize_constructor`.
374 pub(super) fn is_covered_by(&self, pcx: PatCtxt<'_>, other: &Self) -> bool {
375 // This must be kept in sync with `is_covered_by_any`.
376 match (self, other) {
377 // Wildcards cover anything
378 (_, Wildcard) => true,
379 // The missing ctors are not covered by anything in the matrix except wildcards.
380 (Missing | Wildcard, _) => false,
382 (Single, Single) => true,
383 (Variant(self_id), Variant(other_id)) => self_id == other_id,
385 (IntRange(self_range), IntRange(other_range)) => self_range.is_covered_by(other_range),
386 (FloatRange(..), FloatRange(..)) => {
389 (Str(..), Str(..)) => {
392 (Slice(self_slice), Slice(other_slice)) => self_slice.is_covered_by(*other_slice),
394 // We are trying to inspect an opaque constant. Thus we skip the row.
395 (Opaque, _) | (_, Opaque) => false,
396 // Only a wildcard pattern can match the special extra constructor.
397 (NonExhaustive, _) => false,
399 _ => pcx.cx.bug(&format!(
400 "trying to compare incompatible constructors {:?} and {:?}",
406 /// Faster version of `is_covered_by` when applied to many constructors. `used_ctors` is
407 /// assumed to be built from `matrix.head_ctors()` with wildcards filtered out, and `self` is
408 /// assumed to have been split from a wildcard.
409 fn is_covered_by_any(&self, pcx: PatCtxt<'_>, used_ctors: &[Constructor]) -> bool {
410 if used_ctors.is_empty() {
414 // This must be kept in sync with `is_covered_by`.
416 // If `self` is `Single`, `used_ctors` cannot contain anything else than `Single`s.
417 Single => !used_ctors.is_empty(),
418 Variant(_) => used_ctors.iter().any(|c| c == self),
419 IntRange(range) => used_ctors
421 .filter_map(|c| c.as_int_range())
422 .any(|other| range.is_covered_by(other)),
423 Slice(slice) => used_ctors
425 .filter_map(|c| c.as_slice())
426 .any(|other| slice.is_covered_by(other)),
427 // This constructor is never covered by anything else
428 NonExhaustive => false,
429 Str(..) | FloatRange(..) | Opaque | Missing | Wildcard => {
430 pcx.cx.bug(&format!("found unexpected ctor in all_ctors: {:?}", self))
436 /// A wildcard constructor that we split relative to the constructors in the matrix, as explained
437 /// at the top of the file.
439 /// A constructor that is not present in the matrix rows will only be covered by the rows that have
440 /// wildcards. Thus we can group all of those constructors together; we call them "missing
441 /// constructors". Splitting a wildcard would therefore list all present constructors individually
442 /// (or grouped if they are integers or slices), and then all missing constructors together as a
445 /// However we can go further: since any constructor will match the wildcard rows, and having more
446 /// rows can only reduce the amount of usefulness witnesses, we can skip the present constructors
447 /// and only try the missing ones.
448 /// This will not preserve the whole list of witnesses, but will preserve whether the list is empty
449 /// or not. In fact this is quite natural from the point of view of diagnostics too. This is done
450 /// in `to_ctors`: in some cases we only return `Missing`.
452 pub(super) struct SplitWildcard {
453 /// Constructors seen in the matrix.
454 matrix_ctors: Vec<Constructor>,
455 /// All the constructors for this type
456 all_ctors: SmallVec<[Constructor; 1]>,
460 pub(super) fn new(pcx: PatCtxt<'_>) -> Self {
462 let make_range = |start, end, scalar| IntRange(IntRange::from_range(start, end, scalar));
464 // Unhandled types are treated as non-exhaustive. Being explicit here instead of falling
465 // to catchall arm to ease further implementation.
466 let unhandled = || smallvec![NonExhaustive];
468 // This determines the set of all possible constructors for the type `pcx.ty`. For numbers,
469 // arrays and slices we use ranges and variable-length slices when appropriate.
471 // If the `exhaustive_patterns` feature is enabled, we make sure to omit constructors that
472 // are statically impossible. E.g., for `Option<!>`, we do not include `Some(_)` in the
473 // returned list of constructors.
474 // Invariant: this is empty if and only if the type is uninhabited (as determined by
475 // `cx.is_uninhabited()`).
476 let all_ctors = match pcx.ty.kind(&Interner) {
477 TyKind::Scalar(Scalar::Bool) => smallvec![make_range(0, 1, Scalar::Bool)],
478 // TyKind::Array(..) if ... => unhandled(),
479 TyKind::Array(..) | TyKind::Slice(..) => unhandled(),
480 &TyKind::Adt(AdtId(hir_def::AdtId::EnumId(enum_id)), ref _substs) => {
481 let enum_data = cx.db.enum_data(enum_id);
483 // If the enum is declared as `#[non_exhaustive]`, we treat it as if it had an
484 // additional "unknown" constructor.
485 // There is no point in enumerating all possible variants, because the user can't
486 // actually match against them all themselves. So we always return only the fictitious
488 // E.g., in an example like:
491 // let err: io::ErrorKind = ...;
493 // io::ErrorKind::NotFound => {},
497 // we don't want to show every possible IO error, but instead have only `_` as the
499 let is_declared_nonexhaustive = cx.is_foreign_non_exhaustive_enum(enum_id);
501 // If `exhaustive_patterns` is disabled and our scrutinee is an empty enum, we treat it
502 // as though it had an "unknown" constructor to avoid exposing its emptiness. The
503 // exception is if the pattern is at the top level, because we want empty matches to be
504 // considered exhaustive.
505 let is_secretly_empty = enum_data.variants.is_empty()
506 && !cx.feature_exhaustive_patterns()
507 && !pcx.is_top_level;
509 if is_secretly_empty || is_declared_nonexhaustive {
510 smallvec![NonExhaustive]
511 } else if cx.feature_exhaustive_patterns() {
512 unimplemented!() // see MatchCheckCtx.feature_exhaustive_patterns()
517 .map(|(local_id, ..)| Variant(EnumVariantId { parent: enum_id, local_id }))
521 TyKind::Scalar(Scalar::Char) => unhandled(),
522 TyKind::Scalar(Scalar::Int(..) | Scalar::Uint(..)) => unhandled(),
523 TyKind::Never if !cx.feature_exhaustive_patterns() && !pcx.is_top_level => {
524 smallvec![NonExhaustive]
526 TyKind::Never => SmallVec::new(),
527 _ if cx.is_uninhabited(pcx.ty) => SmallVec::new(),
528 TyKind::Adt(..) | TyKind::Tuple(..) | TyKind::Ref(..) => smallvec![Single],
529 // This type is one for which we cannot list constructors, like `str` or `f64`.
530 _ => smallvec![NonExhaustive],
532 SplitWildcard { matrix_ctors: Vec::new(), all_ctors }
535 /// Pass a set of constructors relative to which to split this one. Don't call twice, it won't
536 /// do what you want.
537 pub(super) fn split<'a>(
540 ctors: impl Iterator<Item = &'a Constructor> + Clone,
542 // Since `all_ctors` never contains wildcards, this won't recurse further.
544 self.all_ctors.iter().flat_map(|ctor| ctor.split(pcx, ctors.clone())).collect();
545 self.matrix_ctors = ctors.filter(|c| !c.is_wildcard()).cloned().collect();
548 /// Whether there are any value constructors for this type that are not present in the matrix.
549 fn any_missing(&self, pcx: PatCtxt<'_>) -> bool {
550 self.iter_missing(pcx).next().is_some()
553 /// Iterate over the constructors for this type that are not present in the matrix.
554 pub(super) fn iter_missing<'a>(
557 ) -> impl Iterator<Item = &'a Constructor> {
558 self.all_ctors.iter().filter(move |ctor| !ctor.is_covered_by_any(pcx, &self.matrix_ctors))
561 /// Return the set of constructors resulting from splitting the wildcard. As explained at the
562 /// top of the file, if any constructors are missing we can ignore the present ones.
563 fn into_ctors(self, pcx: PatCtxt<'_>) -> SmallVec<[Constructor; 1]> {
564 if self.any_missing(pcx) {
565 // Some constructors are missing, thus we can specialize with the special `Missing`
566 // constructor, which stands for those constructors that are not seen in the matrix,
567 // and matches the same rows as any of them (namely the wildcard rows). See the top of
568 // the file for details.
569 // However, when all constructors are missing we can also specialize with the full
570 // `Wildcard` constructor. The difference will depend on what we want in diagnostics.
572 // If some constructors are missing, we typically want to report those constructors,
575 // enum Direction { N, S, E, W }
576 // let Direction::N = ...;
578 // we can report 3 witnesses: `S`, `E`, and `W`.
580 // However, if the user didn't actually specify a constructor
581 // in this arm, e.g., in
583 // let x: (Direction, Direction, bool) = ...;
584 // let (_, _, false) = x;
586 // we don't want to show all 16 possible witnesses `(<direction-1>, <direction-2>,
587 // true)` - we are satisfied with `(_, _, true)`. So if all constructors are missing we
588 // prefer to report just a wildcard `_`.
590 // The exception is: if we are at the top-level, for example in an empty match, we
591 // sometimes prefer reporting the list of constructors instead of just `_`.
592 let report_when_all_missing = pcx.is_top_level && !IntRange::is_integral(pcx.ty);
593 let ctor = if !self.matrix_ctors.is_empty() || report_when_all_missing {
598 return smallvec![ctor];
601 // All the constructors are present in the matrix, so we just go through them all.
606 /// A value can be decomposed into a constructor applied to some fields. This struct represents
607 /// those fields, generalized to allow patterns in each field. See also `Constructor`.
608 /// This is constructed from a constructor using [`Fields::wildcards()`].
610 /// If a private or `non_exhaustive` field is uninhabited, the code mustn't observe that it is
611 /// uninhabited. For that, we filter these fields out of the matrix. This is handled automatically
612 /// in `Fields`. This filtering is uncommon in practice, because uninhabited fields are rarely used,
613 /// so we avoid it when possible to preserve performance.
614 #[derive(Debug, Clone)]
615 pub(super) enum Fields {
616 /// Lists of patterns that don't contain any filtered fields.
617 /// `Slice` and `Vec` behave the same; the difference is only to avoid allocating and
618 /// triple-dereferences when possible. Frankly this is premature optimization, I (Nadrieril)
619 /// have not measured if it really made a difference.
620 Vec(SmallVec<[PatId; 2]>),
624 /// Internal use. Use `Fields::wildcards()` instead.
625 /// Must not be used if the pattern is a field of a struct/tuple/variant.
626 fn from_single_pattern(pat: PatId) -> Self {
627 Fields::Vec(smallvec![pat])
630 /// Convenience; internal use.
631 fn wildcards_from_tys(cx: &MatchCheckCtx<'_>, tys: impl IntoIterator<Item = Ty>) -> Self {
632 let wilds = tys.into_iter().map(Pat::wildcard_from_ty);
633 let pats = wilds.map(|pat| cx.alloc_pat(pat)).collect();
637 /// Creates a new list of wildcard fields for a given constructor.
638 pub(crate) fn wildcards(pcx: PatCtxt<'_>, constructor: &Constructor) -> Self {
641 let wildcard_from_ty = |ty: &Ty| cx.alloc_pat(Pat::wildcard_from_ty(ty.clone()));
643 let ret = match constructor {
644 Single | Variant(_) => match ty.kind(&Interner) {
645 TyKind::Tuple(_, substs) => {
646 let tys = substs.iter(&Interner).map(|ty| ty.assert_ty_ref(&Interner));
647 Fields::wildcards_from_tys(cx, tys.cloned())
649 TyKind::Ref(.., rty) => Fields::from_single_pattern(wildcard_from_ty(rty)),
650 &TyKind::Adt(AdtId(adt), ref substs) => {
651 if adt_is_box(adt, cx) {
652 // Use T as the sub pattern type of Box<T>.
653 let subst_ty = substs.at(&Interner, 0).assert_ty_ref(&Interner);
654 Fields::from_single_pattern(wildcard_from_ty(subst_ty))
656 let variant_id = constructor.variant_id_for_adt(adt);
658 variant_id.module(cx.db.upcast()).krate() == cx.module.krate();
659 // Whether we must not match the fields of this variant exhaustively.
660 let is_non_exhaustive =
661 is_field_list_non_exhaustive(variant_id, cx) && !adt_is_local;
663 cov_mark::hit!(match_check_wildcard_expanded_to_substitutions);
664 let field_ty_data = cx.db.field_types(variant_id);
668 .map(|(_, binders)| binders.clone().substitute(&Interner, substs))
671 // In the following cases, we don't need to filter out any fields. This is
672 // the vast majority of real cases, since uninhabited fields are uncommon.
673 let has_no_hidden_fields = (matches!(adt, hir_def::AdtId::EnumId(_))
674 && !is_non_exhaustive)
675 || !field_tys().any(|ty| cx.is_uninhabited(&ty));
677 if has_no_hidden_fields {
678 Fields::wildcards_from_tys(cx, field_tys())
680 //FIXME(iDawer): see MatchCheckCtx::is_uninhabited, has_no_hidden_fields is always true
681 unimplemented!("exhaustive_patterns feature")
686 cx.bug(&format!("Unexpected type for `Single` constructor: {:?}", ty_kind))
692 Str(..) | FloatRange(..) | IntRange(..) | NonExhaustive | Opaque | Missing
693 | Wildcard => Fields::Vec(Default::default()),
698 /// Apply a constructor to a list of patterns, yielding a new pattern. `self`
699 /// must have as many elements as this constructor's arity.
701 /// This is roughly the inverse of `specialize_constructor`.
704 /// `ctor`: `Constructor::Single`
705 /// `ty`: `Foo(u32, u32, u32)`
706 /// `self`: `[10, 20, _]`
707 /// returns `Foo(10, 20, _)`
709 /// `ctor`: `Constructor::Variant(Option::Some)`
710 /// `ty`: `Option<bool>`
711 /// `self`: `[false]`
712 /// returns `Some(false)`
713 pub(super) fn apply(self, pcx: PatCtxt<'_>, ctor: &Constructor) -> Pat {
714 let subpatterns_and_indices = self.patterns_and_indices();
715 let mut subpatterns =
716 subpatterns_and_indices.iter().map(|&(_, p)| pcx.cx.pattern_arena.borrow()[p].clone());
717 // FIXME(iDawer) witnesses are not yet used
718 const UNHANDLED: PatKind = PatKind::Wild;
720 let pat = match ctor {
721 Single | Variant(_) => match pcx.ty.kind(&Interner) {
722 TyKind::Adt(..) | TyKind::Tuple(..) => {
723 // We want the real indices here.
724 let subpatterns = subpatterns_and_indices
726 .map(|&(field, pat)| FieldPat {
728 pattern: pcx.cx.pattern_arena.borrow()[pat].clone(),
732 if let Some((adt, substs)) = pcx.ty.as_adt() {
733 if let hir_def::AdtId::EnumId(_) = adt {
734 let enum_variant = match ctor {
738 PatKind::Variant { substs: substs.clone(), enum_variant, subpatterns }
740 PatKind::Leaf { subpatterns }
743 PatKind::Leaf { subpatterns }
746 // Note: given the expansion of `&str` patterns done in `expand_pattern`, we should
747 // be careful to reconstruct the correct constant pattern here. However a string
748 // literal pattern will never be reported as a non-exhaustiveness witness, so we
749 // can ignore this issue.
750 TyKind::Ref(..) => PatKind::Deref { subpattern: subpatterns.next().unwrap() },
751 TyKind::Slice(..) | TyKind::Array(..) => {
752 pcx.cx.bug(&format!("bad slice pattern {:?} {:?}", ctor, pcx.ty))
756 Constructor::Slice(_) => UNHANDLED,
758 FloatRange(..) => UNHANDLED,
759 Constructor::IntRange(_) => UNHANDLED,
760 NonExhaustive => PatKind::Wild,
761 Wildcard => return Pat::wildcard_from_ty(pcx.ty.clone()),
762 Opaque => pcx.cx.bug("we should not try to apply an opaque constructor"),
763 Missing => pcx.cx.bug(
764 "trying to apply the `Missing` constructor;\
765 this should have been done in `apply_constructors`",
769 Pat { ty: pcx.ty.clone(), kind: Box::new(pat) }
772 /// Returns the number of patterns. This is the same as the arity of the constructor used to
773 /// construct `self`.
774 pub(super) fn len(&self) -> usize {
776 Fields::Vec(pats) => pats.len(),
780 /// Returns the list of patterns along with the corresponding field indices.
781 fn patterns_and_indices(&self) -> SmallVec<[(LocalFieldId, PatId); 2]> {
783 Fields::Vec(pats) => pats
787 .map(|(i, p)| (LocalFieldId::from_raw((i as u32).into()), p))
792 pub(super) fn into_patterns(self) -> SmallVec<[PatId; 2]> {
794 Fields::Vec(pats) => pats,
798 /// Overrides some of the fields with the provided patterns. Exactly like
799 /// `replace_fields_indexed`, except that it takes `FieldPat`s as input.
800 fn replace_with_fieldpats(
802 new_pats: impl IntoIterator<Item = (LocalFieldId, PatId)>,
804 self.replace_fields_indexed(
805 new_pats.into_iter().map(|(field, pat)| (u32::from(field.into_raw()) as usize, pat)),
809 /// Overrides some of the fields with the provided patterns. This is used when a pattern
810 /// defines some fields but not all, for example `Foo { field1: Some(_), .. }`: here we start
811 /// with a `Fields` that is just one wildcard per field of the `Foo` struct, and override the
812 /// entry corresponding to `field1` with the pattern `Some(_)`. This is also used for slice
813 /// patterns for the same reason.
814 fn replace_fields_indexed(&self, new_pats: impl IntoIterator<Item = (usize, PatId)>) -> Self {
815 let mut fields = self.clone();
818 Fields::Vec(pats) => {
819 for (i, pat) in new_pats {
820 if let Some(p) = pats.get_mut(i) {
829 /// Replaces contained fields with the given list of patterns. There must be `len()` patterns
831 pub(super) fn replace_fields(
833 cx: &MatchCheckCtx<'_>,
834 pats: impl IntoIterator<Item = Pat>,
836 let pats = pats.into_iter().map(|pat| cx.alloc_pat(pat)).collect();
839 Fields::Vec(_) => Fields::Vec(pats),
843 /// Replaces contained fields with the arguments of the given pattern. Only use on a pattern
844 /// that is compatible with the constructor used to build `self`.
845 /// This is meant to be used on the result of `Fields::wildcards()`. The idea is that
846 /// `wildcards` constructs a list of fields where all entries are wildcards, and the pattern
847 /// provided to this function fills some of the fields with non-wildcards.
848 /// In the following example `Fields::wildcards` would return `[_, _, _, _]`. If we call
849 /// `replace_with_pattern_arguments` on it with the pattern, the result will be `[Some(0), _,
852 /// let x: [Option<u8>; 4] = foo();
854 /// [Some(0), ..] => {}
857 /// This is guaranteed to preserve the number of patterns in `self`.
858 pub(super) fn replace_with_pattern_arguments(
861 cx: &MatchCheckCtx<'_>,
863 // FIXME(iDawer): Factor out pattern deep cloning. See discussion:
864 // https://github.com/rust-analyzer/rust-analyzer/pull/8717#discussion_r633086640
865 let mut arena = cx.pattern_arena.borrow_mut();
866 match arena[pat].kind.as_ref() {
867 PatKind::Deref { subpattern } => {
868 assert_eq!(self.len(), 1);
869 let subpattern = subpattern.clone();
870 Fields::from_single_pattern(arena.alloc(subpattern))
872 PatKind::Leaf { subpatterns } | PatKind::Variant { subpatterns, .. } => {
873 let subpatterns = subpatterns.clone();
874 let subpatterns = subpatterns
876 .map(|field_pat| (field_pat.field, arena.alloc(field_pat.pattern.clone())));
877 self.replace_with_fieldpats(subpatterns)
881 | PatKind::Binding { .. }
882 | PatKind::LiteralBool { .. }
883 | PatKind::Or { .. } => self.clone(),
888 fn is_field_list_non_exhaustive(variant_id: VariantId, cx: &MatchCheckCtx<'_>) -> bool {
889 let attr_def_id = match variant_id {
890 VariantId::EnumVariantId(id) => id.into(),
891 VariantId::StructId(id) => id.into(),
892 VariantId::UnionId(id) => id.into(),
894 cx.db.attrs(attr_def_id).by_key("non_exhaustive").exists()
897 fn adt_is_box(adt: hir_def::AdtId, cx: &MatchCheckCtx<'_>) -> bool {
898 use hir_def::lang_item::LangItemTarget;
899 match cx.db.lang_item(cx.module.krate(), "owned_box".into()) {
900 Some(LangItemTarget::StructId(box_id)) => adt == box_id.into(),