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`].
45 use self::Constructor::*;
46 use self::SliceKind::*;
48 use super::compare_const_vals;
49 use super::usefulness::{MatchCheckCtxt, PatCtxt};
51 use rustc_data_structures::captures::Captures;
52 use rustc_index::vec::Idx;
54 use rustc_hir::{HirId, RangeEnd};
55 use rustc_middle::mir::Field;
56 use rustc_middle::thir::{FieldPat, Pat, PatKind, PatRange};
57 use rustc_middle::ty::layout::IntegerExt;
58 use rustc_middle::ty::{self, Const, Ty, TyCtxt, VariantDef};
59 use rustc_middle::{middle::stability::EvalResult, mir::interpret::ConstValue};
60 use rustc_session::lint;
61 use rustc_span::{Span, DUMMY_SP};
62 use rustc_target::abi::{Integer, Size, VariantIdx};
64 use smallvec::{smallvec, SmallVec};
66 use std::cmp::{self, max, min, Ordering};
68 use std::iter::{once, IntoIterator};
69 use std::ops::RangeInclusive;
71 /// Recursively expand this pattern into its subpatterns. Only useful for or-patterns.
72 fn expand_or_pat<'p, 'tcx>(pat: &'p Pat<'tcx>) -> Vec<&'p Pat<'tcx>> {
73 fn expand<'p, 'tcx>(pat: &'p Pat<'tcx>, vec: &mut Vec<&'p Pat<'tcx>>) {
74 if let PatKind::Or { pats } = pat.kind.as_ref() {
83 let mut pats = Vec::new();
84 expand(pat, &mut pats);
88 /// An inclusive interval, used for precise integer exhaustiveness checking.
89 /// `IntRange`s always store a contiguous range. This means that values are
90 /// encoded such that `0` encodes the minimum value for the integer,
91 /// regardless of the signedness.
92 /// For example, the pattern `-128..=127i8` is encoded as `0..=255`.
93 /// This makes comparisons and arithmetic on interval endpoints much more
94 /// straightforward. See `signed_bias` for details.
96 /// `IntRange` is never used to encode an empty range or a "range" that wraps
97 /// around the (offset) space: i.e., `range.lo <= range.hi`.
98 #[derive(Clone, PartialEq, Eq)]
99 pub(super) struct IntRange {
100 range: RangeInclusive<u128>,
101 /// Keeps the bias used for encoding the range. It depends on the type of the range and
102 /// possibly the pointer size of the current architecture. The algorithm ensures we never
103 /// compare `IntRange`s with different types/architectures.
109 fn is_integral(ty: Ty<'_>) -> bool {
110 matches!(ty.kind(), ty::Char | ty::Int(_) | ty::Uint(_) | ty::Bool)
113 fn is_singleton(&self) -> bool {
114 self.range.start() == self.range.end()
117 fn boundaries(&self) -> (u128, u128) {
118 (*self.range.start(), *self.range.end())
122 fn integral_size_and_signed_bias(tcx: TyCtxt<'_>, ty: Ty<'_>) -> Option<(Size, u128)> {
124 ty::Bool => Some((Size::from_bytes(1), 0)),
125 ty::Char => Some((Size::from_bytes(4), 0)),
127 let size = Integer::from_int_ty(&tcx, ity).size();
128 Some((size, 1u128 << (size.bits() as u128 - 1)))
130 ty::Uint(uty) => Some((Integer::from_uint_ty(&tcx, uty).size(), 0)),
138 param_env: ty::ParamEnv<'tcx>,
140 ) -> Option<IntRange> {
142 if let Some((target_size, bias)) = Self::integral_size_and_signed_bias(tcx, ty) {
144 if let ty::ConstKind::Value(ConstValue::Scalar(scalar)) = value.val() {
145 // For this specific pattern we can skip a lot of effort and go
146 // straight to the result, after doing a bit of checking. (We
147 // could remove this branch and just fall through, which
148 // is more general but much slower.)
149 if let Ok(bits) = scalar.to_bits_or_ptr_internal(target_size) {
153 // This is a more general form of the previous case.
154 value.try_eval_bits(tcx, param_env, ty)
156 let val = val ^ bias;
157 Some(IntRange { range: val..=val, bias })
170 ) -> Option<IntRange> {
171 if Self::is_integral(ty) {
172 // Perform a shift if the underlying types are signed,
173 // which makes the interval arithmetic simpler.
174 let bias = IntRange::signed_bias(tcx, ty);
175 let (lo, hi) = (lo ^ bias, hi ^ bias);
176 let offset = (*end == RangeEnd::Excluded) as u128;
177 if lo > hi || (lo == hi && *end == RangeEnd::Excluded) {
178 // This should have been caught earlier by E0030.
179 bug!("malformed range pattern: {}..={}", lo, (hi - offset));
181 Some(IntRange { range: lo..=(hi - offset), bias })
187 // The return value of `signed_bias` should be XORed with an endpoint to encode/decode it.
188 fn signed_bias(tcx: TyCtxt<'_>, ty: Ty<'_>) -> u128 {
191 let bits = Integer::from_int_ty(&tcx, ity).size().bits() as u128;
198 fn is_subrange(&self, other: &Self) -> bool {
199 other.range.start() <= self.range.start() && self.range.end() <= other.range.end()
202 fn intersection(&self, other: &Self) -> Option<Self> {
203 let (lo, hi) = self.boundaries();
204 let (other_lo, other_hi) = other.boundaries();
205 if lo <= other_hi && other_lo <= hi {
206 Some(IntRange { range: max(lo, other_lo)..=min(hi, other_hi), bias: self.bias })
212 fn suspicious_intersection(&self, other: &Self) -> bool {
213 // `false` in the following cases:
214 // 1 ---- // 1 ---------- // 1 ---- // 1 ----
215 // 2 ---------- // 2 ---- // 2 ---- // 2 ----
217 // The following are currently `false`, but could be `true` in the future (#64007):
218 // 1 --------- // 1 ---------
219 // 2 ---------- // 2 ----------
221 // `true` in the following cases:
222 // 1 ------- // 1 -------
223 // 2 -------- // 2 -------
224 let (lo, hi) = self.boundaries();
225 let (other_lo, other_hi) = other.boundaries();
226 (lo == other_hi || hi == other_lo) && !self.is_singleton() && !other.is_singleton()
229 /// Only used for displaying the range properly.
230 fn to_pat<'tcx>(&self, tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> Pat<'tcx> {
231 let (lo, hi) = self.boundaries();
233 let bias = self.bias;
234 let (lo, hi) = (lo ^ bias, hi ^ bias);
236 let env = ty::ParamEnv::empty().and(ty);
237 let lo_const = ty::Const::from_bits(tcx, lo, env);
238 let hi_const = ty::Const::from_bits(tcx, hi, env);
240 let kind = if lo == hi {
241 PatKind::Constant { value: lo_const }
243 PatKind::Range(PatRange { lo: lo_const, hi: hi_const, end: RangeEnd::Included })
246 Pat { ty, span: DUMMY_SP, kind: Box::new(kind) }
249 /// Lint on likely incorrect range patterns (#63987)
250 pub(super) fn lint_overlapping_range_endpoints<'a, 'p: 'a, 'tcx: 'a>(
252 pcx: PatCtxt<'_, 'p, 'tcx>,
253 pats: impl Iterator<Item = &'a DeconstructedPat<'p, 'tcx>>,
257 if self.is_singleton() {
261 if column_count != 1 {
262 // FIXME: for now, only check for overlapping ranges on simple range
263 // patterns. Otherwise with the current logic the following is detected
266 // match (0u8, true) {
267 // (0 ..= 125, false) => {}
268 // (125 ..= 255, true) => {}
275 let overlaps: Vec<_> = pats
276 .filter_map(|pat| Some((pat.ctor().as_int_range()?, pat.span())))
277 .filter(|(range, _)| self.suspicious_intersection(range))
278 .map(|(range, span)| (self.intersection(&range).unwrap(), span))
281 if !overlaps.is_empty() {
282 pcx.cx.tcx.struct_span_lint_hir(
283 lint::builtin::OVERLAPPING_RANGE_ENDPOINTS,
287 let mut err = lint.build("multiple patterns overlap on their endpoints");
288 for (int_range, span) in overlaps {
292 "this range overlaps on `{}`...",
293 int_range.to_pat(pcx.cx.tcx, pcx.ty)
297 err.span_label(pcx.span, "... with this range");
298 err.note("you likely meant to write mutually exclusive ranges");
305 /// See `Constructor::is_covered_by`
306 fn is_covered_by(&self, other: &Self) -> bool {
307 if self.intersection(other).is_some() {
308 // Constructor splitting should ensure that all intersections we encounter are actually
310 assert!(self.is_subrange(other));
318 /// Note: this is often not what we want: e.g. `false` is converted into the range `0..=0` and
319 /// would be displayed as such. To render properly, convert to a pattern first.
320 impl fmt::Debug for IntRange {
321 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
322 let (lo, hi) = self.boundaries();
323 let bias = self.bias;
324 let (lo, hi) = (lo ^ bias, hi ^ bias);
325 write!(f, "{}", lo)?;
326 write!(f, "{}", RangeEnd::Included)?;
331 /// Represents a border between 2 integers. Because the intervals spanning borders must be able to
332 /// cover every integer, we need to be able to represent 2^128 + 1 such borders.
333 #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
339 /// A range of integers that is partitioned into disjoint subranges. This does constructor
340 /// splitting for integer ranges as explained at the top of the file.
342 /// This is fed multiple ranges, and returns an output that covers the input, but is split so that
343 /// the only intersections between an output range and a seen range are inclusions. No output range
344 /// straddles the boundary of one of the inputs.
346 /// The following input:
348 /// |-------------------------| // `self`
349 /// |------| |----------| |----|
350 /// |-------| |-------|
352 /// would be iterated over as follows:
354 /// ||---|--||-|---|---|---|--|
356 #[derive(Debug, Clone)]
357 struct SplitIntRange {
358 /// The range we are splitting
360 /// The borders of ranges we have seen. They are all contained within `range`. This is kept
362 borders: Vec<IntBorder>,
366 fn new(range: IntRange) -> Self {
367 SplitIntRange { range, borders: Vec::new() }
371 fn to_borders(r: IntRange) -> [IntBorder; 2] {
373 let (lo, hi) = r.boundaries();
374 let lo = JustBefore(lo);
375 let hi = match hi.checked_add(1) {
376 Some(m) => JustBefore(m),
382 /// Add ranges relative to which we split.
383 fn split(&mut self, ranges: impl Iterator<Item = IntRange>) {
384 let this_range = &self.range;
385 let included_ranges = ranges.filter_map(|r| this_range.intersection(&r));
386 let included_borders = included_ranges.flat_map(|r| {
387 let borders = Self::to_borders(r);
388 once(borders[0]).chain(once(borders[1]))
390 self.borders.extend(included_borders);
391 self.borders.sort_unstable();
394 /// Iterate over the contained ranges.
395 fn iter<'a>(&'a self) -> impl Iterator<Item = IntRange> + Captures<'a> {
398 let self_range = Self::to_borders(self.range.clone());
399 // Start with the start of the range.
400 let mut prev_border = self_range[0];
404 // End with the end of the range.
405 .chain(once(self_range[1]))
406 // List pairs of adjacent borders.
408 let ret = (prev_border, border);
409 prev_border = border;
413 .filter(|(prev_border, border)| prev_border != border)
414 // Finally, convert to ranges.
415 .map(move |(prev_border, border)| {
416 let range = match (prev_border, border) {
417 (JustBefore(n), JustBefore(m)) if n < m => n..=(m - 1),
418 (JustBefore(n), AfterMax) => n..=u128::MAX,
419 _ => unreachable!(), // Ruled out by the sorting and filtering we did
421 IntRange { range, bias: self.range.bias }
426 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
428 /// Patterns of length `n` (`[x, y]`).
430 /// Patterns using the `..` notation (`[x, .., y]`).
431 /// Captures any array constructor of `length >= i + j`.
432 /// In the case where `array_len` is `Some(_)`,
433 /// this indicates that we only care about the first `i` and the last `j` values of the array,
434 /// and everything in between is a wildcard `_`.
435 VarLen(usize, usize),
439 fn arity(self) -> usize {
441 FixedLen(length) => length,
442 VarLen(prefix, suffix) => prefix + suffix,
446 /// Whether this pattern includes patterns of length `other_len`.
447 fn covers_length(self, other_len: usize) -> bool {
449 FixedLen(len) => len == other_len,
450 VarLen(prefix, suffix) => prefix + suffix <= other_len,
455 /// A constructor for array and slice patterns.
456 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
457 pub(super) struct Slice {
458 /// `None` if the matched value is a slice, `Some(n)` if it is an array of size `n`.
459 array_len: Option<usize>,
460 /// The kind of pattern it is: fixed-length `[x, y]` or variable length `[x, .., y]`.
465 fn new(array_len: Option<usize>, kind: SliceKind) -> Self {
466 let kind = match (array_len, kind) {
467 // If the middle `..` is empty, we effectively have a fixed-length pattern.
468 (Some(len), VarLen(prefix, suffix)) if prefix + suffix >= len => FixedLen(len),
471 Slice { array_len, kind }
474 fn arity(self) -> usize {
478 /// See `Constructor::is_covered_by`
479 fn is_covered_by(self, other: Self) -> bool {
480 other.kind.covers_length(self.arity())
484 /// This computes constructor splitting for variable-length slices, as explained at the top of the
487 /// A slice pattern `[x, .., y]` behaves like the infinite or-pattern `[x, y] | [x, _, y] | [x, _,
488 /// _, y] | ...`. The corresponding value constructors are fixed-length array constructors above a
489 /// given minimum length. We obviously can't list this infinitude of constructors. Thankfully,
490 /// it turns out that for each finite set of slice patterns, all sufficiently large array lengths
493 /// Let's look at an example, where we are trying to split the last pattern:
496 /// [true, true, ..] => {}
497 /// [.., false, false] => {}
501 /// Here are the results of specialization for the first few lengths:
508 /// [true, true] => {}
509 /// [false, false] => {}
512 /// [true, true, _ ] => {}
513 /// [_, false, false] => {}
516 /// [true, true, _, _ ] => {}
517 /// [_, _, false, false] => {}
518 /// [_, _, _, _ ] => {}
520 /// [true, true, _, _, _ ] => {}
521 /// [_, _, _, false, false] => {}
522 /// [_, _, _, _, _ ] => {}
525 /// If we went above length 5, we would simply be inserting more columns full of wildcards in the
526 /// middle. This means that the set of witnesses for length `l >= 5` if equivalent to the set for
527 /// any other `l' >= 5`: simply add or remove wildcards in the middle to convert between them.
529 /// This applies to any set of slice patterns: there will be a length `L` above which all lengths
530 /// behave the same. This is exactly what we need for constructor splitting. Therefore a
531 /// variable-length slice can be split into a variable-length slice of minimal length `L`, and many
532 /// fixed-length slices of lengths `< L`.
534 /// For each variable-length pattern `p` with a prefix of length `plâ‚š` and suffix of length `slâ‚š`,
535 /// only the first `plâ‚š` and the last `slâ‚š` elements are examined. Therefore, as long as `L` is
536 /// positive (to avoid concerns about empty types), all elements after the maximum prefix length
537 /// and before the maximum suffix length are not examined by any variable-length pattern, and
538 /// therefore can be added/removed without affecting them - creating equivalent patterns from any
539 /// sufficiently-large length.
541 /// Of course, if fixed-length patterns exist, we must be sure that our length is large enough to
542 /// miss them all, so we can pick `L = max(max(FIXED_LEN)+1, max(PREFIX_LEN) + max(SUFFIX_LEN))`
544 /// `max_slice` below will be made to have arity `L`.
546 struct SplitVarLenSlice {
547 /// If the type is an array, this is its size.
548 array_len: Option<usize>,
549 /// The arity of the input slice.
551 /// The smallest slice bigger than any slice seen. `max_slice.arity()` is the length `L`
553 max_slice: SliceKind,
556 impl SplitVarLenSlice {
557 fn new(prefix: usize, suffix: usize, array_len: Option<usize>) -> Self {
558 SplitVarLenSlice { array_len, arity: prefix + suffix, max_slice: VarLen(prefix, suffix) }
561 /// Pass a set of slices relative to which to split this one.
562 fn split(&mut self, slices: impl Iterator<Item = SliceKind>) {
563 let VarLen(max_prefix_len, max_suffix_len) = &mut self.max_slice else {
567 // We grow `self.max_slice` to be larger than all slices encountered, as described above.
568 // For diagnostics, we keep the prefix and suffix lengths separate, but grow them so that
569 // `L = max_prefix_len + max_suffix_len`.
570 let mut max_fixed_len = 0;
571 for slice in slices {
574 max_fixed_len = cmp::max(max_fixed_len, len);
576 VarLen(prefix, suffix) => {
577 *max_prefix_len = cmp::max(*max_prefix_len, prefix);
578 *max_suffix_len = cmp::max(*max_suffix_len, suffix);
582 // We want `L = max(L, max_fixed_len + 1)`, modulo the fact that we keep prefix and
584 if max_fixed_len + 1 >= *max_prefix_len + *max_suffix_len {
585 // The subtraction can't overflow thanks to the above check.
586 // The new `max_prefix_len` is larger than its previous value.
587 *max_prefix_len = max_fixed_len + 1 - *max_suffix_len;
590 // We cap the arity of `max_slice` at the array size.
591 match self.array_len {
592 Some(len) if self.max_slice.arity() >= len => self.max_slice = FixedLen(len),
597 /// Iterate over the partition of this slice.
598 fn iter<'a>(&'a self) -> impl Iterator<Item = Slice> + Captures<'a> {
599 let smaller_lengths = match self.array_len {
600 // The only admissible fixed-length slice is one of the array size. Whether `max_slice`
601 // is fixed-length or variable-length, it will be the only relevant slice to output
603 Some(_) => (0..0), // empty range
604 // We cover all arities in the range `(self.arity..infinity)`. We split that range into
605 // two: lengths smaller than `max_slice.arity()` are treated independently as
606 // fixed-lengths slices, and lengths above are captured by `max_slice`.
607 None => self.arity..self.max_slice.arity(),
611 .chain(once(self.max_slice))
612 .map(move |kind| Slice::new(self.array_len, kind))
616 /// A value can be decomposed into a constructor applied to some fields. This struct represents
617 /// the constructor. See also `Fields`.
619 /// `pat_constructor` retrieves the constructor corresponding to a pattern.
620 /// `specialize_constructor` returns the list of fields corresponding to a pattern, given a
621 /// constructor. `Constructor::apply` reconstructs the pattern from a pair of `Constructor` and
623 #[derive(Clone, Debug, PartialEq)]
624 pub(super) enum Constructor<'tcx> {
625 /// The constructor for patterns that have a single constructor, like tuples, struct patterns
626 /// and fixed-length arrays.
630 /// Ranges of integer literal values (`2`, `2..=5` or `2..5`).
632 /// Ranges of floating-point literal values (`2.0..=5.2`).
633 FloatRange(ty::Const<'tcx>, ty::Const<'tcx>, RangeEnd),
634 /// String literals. Strings are not quite the same as `&[u8]` so we treat them separately.
635 Str(ty::Const<'tcx>),
636 /// Array and slice patterns.
638 /// Constants that must not be matched structurally. They are treated as black
639 /// boxes for the purposes of exhaustiveness: we must not inspect them, and they
640 /// don't count towards making a match exhaustive.
642 /// Fake extra constructor for enums that aren't allowed to be matched exhaustively. Also used
643 /// for those types for which we cannot list constructors explicitly, like `f64` and `str`.
645 /// Stands for constructors that are not seen in the matrix, as explained in the documentation
646 /// for [`SplitWildcard`]. The carried `bool` is used for the `non_exhaustive_omitted_patterns`
648 Missing { nonexhaustive_enum_missing_real_variants: bool },
649 /// Wildcard pattern.
655 impl<'tcx> Constructor<'tcx> {
656 pub(super) fn is_wildcard(&self) -> bool {
657 matches!(self, Wildcard)
660 pub(super) fn is_non_exhaustive(&self) -> bool {
661 matches!(self, NonExhaustive)
664 fn as_int_range(&self) -> Option<&IntRange> {
666 IntRange(range) => Some(range),
671 fn as_slice(&self) -> Option<Slice> {
673 Slice(slice) => Some(*slice),
678 /// Checks if the `Constructor` is a variant and `TyCtxt::eval_stability` returns
679 /// `EvalResult::Deny { .. }`.
681 /// This means that the variant has a stdlib unstable feature marking it.
682 pub(super) fn is_unstable_variant(&self, pcx: PatCtxt<'_, '_, 'tcx>) -> bool {
683 if let Constructor::Variant(idx) = self {
684 if let ty::Adt(adt, _) = pcx.ty.kind() {
685 let variant_def_id = adt.variants[*idx].def_id;
686 // Filter variants that depend on a disabled unstable feature.
688 pcx.cx.tcx.eval_stability(variant_def_id, None, DUMMY_SP, None),
689 EvalResult::Deny { .. }
696 /// Checks if the `Constructor` is a `Constructor::Variant` with a `#[doc(hidden)]`
698 pub(super) fn is_doc_hidden_variant(&self, pcx: PatCtxt<'_, '_, 'tcx>) -> bool {
699 if let Constructor::Variant(idx) = self {
700 if let ty::Adt(adt, _) = pcx.ty.kind() {
701 let variant_def_id = adt.variants[*idx].def_id;
702 return pcx.cx.tcx.is_doc_hidden(variant_def_id);
708 fn variant_index_for_adt(&self, adt: &'tcx ty::AdtDef) -> VariantIdx {
712 assert!(!adt.is_enum());
715 _ => bug!("bad constructor {:?} for adt {:?}", self, adt),
719 /// The number of fields for this constructor. This must be kept in sync with
720 /// `Fields::wildcards`.
721 pub(super) fn arity(&self, pcx: PatCtxt<'_, '_, 'tcx>) -> usize {
723 Single | Variant(_) => match pcx.ty.kind() {
724 ty::Tuple(fs) => fs.len(),
726 ty::Adt(adt, ..) => {
728 // The only legal patterns of type `Box` (outside `std`) are `_` and box
729 // patterns. If we're here we can assume this is a box pattern.
732 let variant = &adt.variants[self.variant_index_for_adt(adt)];
733 Fields::list_variant_nonhidden_fields(pcx.cx, pcx.ty, variant).count()
736 _ => bug!("Unexpected type for `Single` constructor: {:?}", pcx.ty),
738 Slice(slice) => slice.arity(),
746 Or => bug!("The `Or` constructor doesn't have a fixed arity"),
750 /// Some constructors (namely `Wildcard`, `IntRange` and `Slice`) actually stand for a set of actual
751 /// constructors (like variants, integers or fixed-sized slices). When specializing for these
752 /// constructors, we want to be specialising for the actual underlying constructors.
753 /// Naively, we would simply return the list of constructors they correspond to. We instead are
754 /// more clever: if there are constructors that we know will behave the same wrt the current
755 /// matrix, we keep them grouped. For example, all slices of a sufficiently large length
756 /// will either be all useful or all non-useful with a given matrix.
758 /// See the branches for details on how the splitting is done.
760 /// This function may discard some irrelevant constructors if this preserves behavior and
761 /// diagnostics. Eg. for the `_` case, we ignore the constructors already present in the
762 /// matrix, unless all of them are.
763 pub(super) fn split<'a>(
765 pcx: PatCtxt<'_, '_, 'tcx>,
766 ctors: impl Iterator<Item = &'a Constructor<'tcx>> + Clone,
767 ) -> SmallVec<[Self; 1]>
773 let mut split_wildcard = SplitWildcard::new(pcx);
774 split_wildcard.split(pcx, ctors);
775 split_wildcard.into_ctors(pcx)
777 // Fast-track if the range is trivial. In particular, we don't do the overlapping
779 IntRange(ctor_range) if !ctor_range.is_singleton() => {
780 let mut split_range = SplitIntRange::new(ctor_range.clone());
781 let int_ranges = ctors.filter_map(|ctor| ctor.as_int_range());
782 split_range.split(int_ranges.cloned());
783 split_range.iter().map(IntRange).collect()
785 &Slice(Slice { kind: VarLen(self_prefix, self_suffix), array_len }) => {
786 let mut split_self = SplitVarLenSlice::new(self_prefix, self_suffix, array_len);
787 let slices = ctors.filter_map(|c| c.as_slice()).map(|s| s.kind);
788 split_self.split(slices);
789 split_self.iter().map(Slice).collect()
791 // Any other constructor can be used unchanged.
792 _ => smallvec![self.clone()],
796 /// Returns whether `self` is covered by `other`, i.e. whether `self` is a subset of `other`.
797 /// For the simple cases, this is simply checking for equality. For the "grouped" constructors,
798 /// this checks for inclusion.
799 // We inline because this has a single call site in `Matrix::specialize_constructor`.
801 pub(super) fn is_covered_by<'p>(&self, pcx: PatCtxt<'_, 'p, 'tcx>, other: &Self) -> bool {
802 // This must be kept in sync with `is_covered_by_any`.
803 match (self, other) {
804 // Wildcards cover anything
805 (_, Wildcard) => true,
806 // The missing ctors are not covered by anything in the matrix except wildcards.
807 (Missing { .. } | Wildcard, _) => false,
809 (Single, Single) => true,
810 (Variant(self_id), Variant(other_id)) => self_id == other_id,
812 (IntRange(self_range), IntRange(other_range)) => self_range.is_covered_by(other_range),
814 FloatRange(self_from, self_to, self_end),
815 FloatRange(other_from, other_to, other_end),
818 compare_const_vals(pcx.cx.tcx, *self_to, *other_to, pcx.cx.param_env, pcx.ty),
827 (Some(to), Some(from)) => {
828 (from == Ordering::Greater || from == Ordering::Equal)
829 && (to == Ordering::Less
830 || (other_end == self_end && to == Ordering::Equal))
835 (Str(self_val), Str(other_val)) => {
836 // FIXME: there's probably a more direct way of comparing for equality
837 match compare_const_vals(
844 Some(comparison) => comparison == Ordering::Equal,
848 (Slice(self_slice), Slice(other_slice)) => self_slice.is_covered_by(*other_slice),
850 // We are trying to inspect an opaque constant. Thus we skip the row.
851 (Opaque, _) | (_, Opaque) => false,
852 // Only a wildcard pattern can match the special extra constructor.
853 (NonExhaustive, _) => false,
857 "trying to compare incompatible constructors {:?} and {:?}",
864 /// Faster version of `is_covered_by` when applied to many constructors. `used_ctors` is
865 /// assumed to be built from `matrix.head_ctors()` with wildcards filtered out, and `self` is
866 /// assumed to have been split from a wildcard.
867 fn is_covered_by_any<'p>(
869 pcx: PatCtxt<'_, 'p, 'tcx>,
870 used_ctors: &[Constructor<'tcx>],
872 if used_ctors.is_empty() {
876 // This must be kept in sync with `is_covered_by`.
878 // If `self` is `Single`, `used_ctors` cannot contain anything else than `Single`s.
879 Single => !used_ctors.is_empty(),
880 Variant(vid) => used_ctors.iter().any(|c| matches!(c, Variant(i) if i == vid)),
881 IntRange(range) => used_ctors
883 .filter_map(|c| c.as_int_range())
884 .any(|other| range.is_covered_by(other)),
885 Slice(slice) => used_ctors
887 .filter_map(|c| c.as_slice())
888 .any(|other| slice.is_covered_by(other)),
889 // This constructor is never covered by anything else
890 NonExhaustive => false,
891 Str(..) | FloatRange(..) | Opaque | Missing { .. } | Wildcard | Or => {
892 span_bug!(pcx.span, "found unexpected ctor in all_ctors: {:?}", self)
898 /// A wildcard constructor that we split relative to the constructors in the matrix, as explained
899 /// at the top of the file.
901 /// A constructor that is not present in the matrix rows will only be covered by the rows that have
902 /// wildcards. Thus we can group all of those constructors together; we call them "missing
903 /// constructors". Splitting a wildcard would therefore list all present constructors individually
904 /// (or grouped if they are integers or slices), and then all missing constructors together as a
907 /// However we can go further: since any constructor will match the wildcard rows, and having more
908 /// rows can only reduce the amount of usefulness witnesses, we can skip the present constructors
909 /// and only try the missing ones.
910 /// This will not preserve the whole list of witnesses, but will preserve whether the list is empty
911 /// or not. In fact this is quite natural from the point of view of diagnostics too. This is done
912 /// in `to_ctors`: in some cases we only return `Missing`.
914 pub(super) struct SplitWildcard<'tcx> {
915 /// Constructors seen in the matrix.
916 matrix_ctors: Vec<Constructor<'tcx>>,
917 /// All the constructors for this type
918 all_ctors: SmallVec<[Constructor<'tcx>; 1]>,
921 impl<'tcx> SplitWildcard<'tcx> {
922 pub(super) fn new<'p>(pcx: PatCtxt<'_, 'p, 'tcx>) -> Self {
923 debug!("SplitWildcard::new({:?})", pcx.ty);
925 let make_range = |start, end| {
927 // `unwrap()` is ok because we know the type is an integer.
928 IntRange::from_range(cx.tcx, start, end, pcx.ty, &RangeEnd::Included).unwrap(),
931 // This determines the set of all possible constructors for the type `pcx.ty`. For numbers,
932 // arrays and slices we use ranges and variable-length slices when appropriate.
934 // If the `exhaustive_patterns` feature is enabled, we make sure to omit constructors that
935 // are statically impossible. E.g., for `Option<!>`, we do not include `Some(_)` in the
936 // returned list of constructors.
937 // Invariant: this is empty if and only if the type is uninhabited (as determined by
938 // `cx.is_uninhabited()`).
939 let all_ctors = match pcx.ty.kind() {
940 ty::Bool => smallvec![make_range(0, 1)],
941 ty::Array(sub_ty, len) if len.try_eval_usize(cx.tcx, cx.param_env).is_some() => {
942 let len = len.eval_usize(cx.tcx, cx.param_env) as usize;
943 if len != 0 && cx.is_uninhabited(*sub_ty) {
946 smallvec![Slice(Slice::new(Some(len), VarLen(0, 0)))]
949 // Treat arrays of a constant but unknown length like slices.
950 ty::Array(sub_ty, _) | ty::Slice(sub_ty) => {
951 let kind = if cx.is_uninhabited(*sub_ty) { FixedLen(0) } else { VarLen(0, 0) };
952 smallvec![Slice(Slice::new(None, kind))]
954 ty::Adt(def, substs) if def.is_enum() => {
955 // If the enum is declared as `#[non_exhaustive]`, we treat it as if it had an
956 // additional "unknown" constructor.
957 // There is no point in enumerating all possible variants, because the user can't
958 // actually match against them all themselves. So we always return only the fictitious
960 // E.g., in an example like:
963 // let err: io::ErrorKind = ...;
965 // io::ErrorKind::NotFound => {},
969 // we don't want to show every possible IO error, but instead have only `_` as the
971 let is_declared_nonexhaustive = cx.is_foreign_non_exhaustive_enum(pcx.ty);
973 let is_exhaustive_pat_feature = cx.tcx.features().exhaustive_patterns;
975 // If `exhaustive_patterns` is disabled and our scrutinee is an empty enum, we treat it
976 // as though it had an "unknown" constructor to avoid exposing its emptiness. The
977 // exception is if the pattern is at the top level, because we want empty matches to be
978 // considered exhaustive.
979 let is_secretly_empty =
980 def.variants.is_empty() && !is_exhaustive_pat_feature && !pcx.is_top_level;
982 let mut ctors: SmallVec<[_; 1]> = def
986 // If `exhaustive_patterns` is enabled, we exclude variants known to be
988 let is_uninhabited = is_exhaustive_pat_feature
989 && v.uninhabited_from(cx.tcx, substs, def.adt_kind(), cx.param_env)
990 .contains(cx.tcx, cx.module);
993 .map(|(idx, _)| Variant(idx))
996 if is_secretly_empty || is_declared_nonexhaustive {
997 ctors.push(NonExhaustive);
1003 // The valid Unicode Scalar Value ranges.
1004 make_range('\u{0000}' as u128, '\u{D7FF}' as u128),
1005 make_range('\u{E000}' as u128, '\u{10FFFF}' as u128),
1008 ty::Int(_) | ty::Uint(_)
1009 if pcx.ty.is_ptr_sized_integral()
1010 && !cx.tcx.features().precise_pointer_size_matching =>
1012 // `usize`/`isize` are not allowed to be matched exhaustively unless the
1013 // `precise_pointer_size_matching` feature is enabled. So we treat those types like
1014 // `#[non_exhaustive]` enums by returning a special unmatcheable constructor.
1015 smallvec![NonExhaustive]
1018 let bits = Integer::from_int_ty(&cx.tcx, ity).size().bits() as u128;
1019 let min = 1u128 << (bits - 1);
1021 smallvec![make_range(min, max)]
1024 let size = Integer::from_uint_ty(&cx.tcx, uty).size();
1025 let max = size.truncate(u128::MAX);
1026 smallvec![make_range(0, max)]
1028 // If `exhaustive_patterns` is disabled and our scrutinee is the never type, we cannot
1029 // expose its emptiness. The exception is if the pattern is at the top level, because we
1030 // want empty matches to be considered exhaustive.
1031 ty::Never if !cx.tcx.features().exhaustive_patterns && !pcx.is_top_level => {
1032 smallvec![NonExhaustive]
1034 ty::Never => smallvec![],
1035 _ if cx.is_uninhabited(pcx.ty) => smallvec![],
1036 ty::Adt(..) | ty::Tuple(..) | ty::Ref(..) => smallvec![Single],
1037 // This type is one for which we cannot list constructors, like `str` or `f64`.
1038 _ => smallvec![NonExhaustive],
1041 SplitWildcard { matrix_ctors: Vec::new(), all_ctors }
1044 /// Pass a set of constructors relative to which to split this one. Don't call twice, it won't
1045 /// do what you want.
1046 pub(super) fn split<'a>(
1048 pcx: PatCtxt<'_, '_, 'tcx>,
1049 ctors: impl Iterator<Item = &'a Constructor<'tcx>> + Clone,
1053 // Since `all_ctors` never contains wildcards, this won't recurse further.
1055 self.all_ctors.iter().flat_map(|ctor| ctor.split(pcx, ctors.clone())).collect();
1056 self.matrix_ctors = ctors.filter(|c| !c.is_wildcard()).cloned().collect();
1059 /// Whether there are any value constructors for this type that are not present in the matrix.
1060 fn any_missing(&self, pcx: PatCtxt<'_, '_, 'tcx>) -> bool {
1061 self.iter_missing(pcx).next().is_some()
1064 /// Iterate over the constructors for this type that are not present in the matrix.
1065 pub(super) fn iter_missing<'a, 'p>(
1067 pcx: PatCtxt<'a, 'p, 'tcx>,
1068 ) -> impl Iterator<Item = &'a Constructor<'tcx>> + Captures<'p> {
1069 self.all_ctors.iter().filter(move |ctor| !ctor.is_covered_by_any(pcx, &self.matrix_ctors))
1072 /// Return the set of constructors resulting from splitting the wildcard. As explained at the
1073 /// top of the file, if any constructors are missing we can ignore the present ones.
1074 fn into_ctors(self, pcx: PatCtxt<'_, '_, 'tcx>) -> SmallVec<[Constructor<'tcx>; 1]> {
1075 if self.any_missing(pcx) {
1076 // Some constructors are missing, thus we can specialize with the special `Missing`
1077 // constructor, which stands for those constructors that are not seen in the matrix,
1078 // and matches the same rows as any of them (namely the wildcard rows). See the top of
1079 // the file for details.
1080 // However, when all constructors are missing we can also specialize with the full
1081 // `Wildcard` constructor. The difference will depend on what we want in diagnostics.
1083 // If some constructors are missing, we typically want to report those constructors,
1086 // enum Direction { N, S, E, W }
1087 // let Direction::N = ...;
1089 // we can report 3 witnesses: `S`, `E`, and `W`.
1091 // However, if the user didn't actually specify a constructor
1092 // in this arm, e.g., in
1094 // let x: (Direction, Direction, bool) = ...;
1095 // let (_, _, false) = x;
1097 // we don't want to show all 16 possible witnesses `(<direction-1>, <direction-2>,
1098 // true)` - we are satisfied with `(_, _, true)`. So if all constructors are missing we
1099 // prefer to report just a wildcard `_`.
1101 // The exception is: if we are at the top-level, for example in an empty match, we
1102 // sometimes prefer reporting the list of constructors instead of just `_`.
1103 let report_when_all_missing = pcx.is_top_level && !IntRange::is_integral(pcx.ty);
1104 let ctor = if !self.matrix_ctors.is_empty() || report_when_all_missing {
1105 if pcx.is_non_exhaustive {
1107 nonexhaustive_enum_missing_real_variants: self
1109 .any(|c| !(c.is_non_exhaustive() || c.is_unstable_variant(pcx))),
1112 Missing { nonexhaustive_enum_missing_real_variants: false }
1117 return smallvec![ctor];
1120 // All the constructors are present in the matrix, so we just go through them all.
1125 /// A value can be decomposed into a constructor applied to some fields. This struct represents
1126 /// those fields, generalized to allow patterns in each field. See also `Constructor`.
1128 /// This is constructed for a constructor using [`Fields::wildcards()`]. The idea is that
1129 /// [`Fields::wildcards()`] constructs a list of fields where all entries are wildcards, and then
1130 /// given a pattern we fill some of the fields with its subpatterns.
1131 /// In the following example `Fields::wildcards` returns `[_, _, _, _]`. Then in
1132 /// `extract_pattern_arguments` we fill some of the entries, and the result is
1133 /// `[Some(0), _, _, _]`.
1135 /// let x: [Option<u8>; 4] = foo();
1137 /// [Some(0), ..] => {}
1141 /// Note that the number of fields of a constructor may not match the fields declared in the
1142 /// original struct/variant. This happens if a private or `non_exhaustive` field is uninhabited,
1143 /// because the code mustn't observe that it is uninhabited. In that case that field is not
1144 /// included in `fields`. For that reason, when you have a `mir::Field` you must use
1145 /// `index_with_declared_idx`.
1146 #[derive(Debug, Clone, Copy)]
1147 pub(super) struct Fields<'p, 'tcx> {
1148 fields: &'p [DeconstructedPat<'p, 'tcx>],
1151 impl<'p, 'tcx> Fields<'p, 'tcx> {
1152 fn empty() -> Self {
1153 Fields { fields: &[] }
1156 fn singleton(cx: &MatchCheckCtxt<'p, 'tcx>, field: DeconstructedPat<'p, 'tcx>) -> Self {
1157 let field: &_ = cx.pattern_arena.alloc(field);
1158 Fields { fields: std::slice::from_ref(field) }
1161 pub(super) fn from_iter(
1162 cx: &MatchCheckCtxt<'p, 'tcx>,
1163 fields: impl IntoIterator<Item = DeconstructedPat<'p, 'tcx>>,
1165 let fields: &[_] = cx.pattern_arena.alloc_from_iter(fields);
1169 fn wildcards_from_tys(
1170 cx: &MatchCheckCtxt<'p, 'tcx>,
1171 tys: impl IntoIterator<Item = Ty<'tcx>>,
1173 Fields::from_iter(cx, tys.into_iter().map(DeconstructedPat::wildcard))
1176 // In the cases of either a `#[non_exhaustive]` field list or a non-public field, we hide
1177 // uninhabited fields in order not to reveal the uninhabitedness of the whole variant.
1178 // This lists the fields we keep along with their types.
1179 fn list_variant_nonhidden_fields<'a>(
1180 cx: &'a MatchCheckCtxt<'p, 'tcx>,
1182 variant: &'a VariantDef,
1183 ) -> impl Iterator<Item = (Field, Ty<'tcx>)> + Captures<'a> + Captures<'p> {
1184 let ty::Adt(adt, substs) = ty.kind() else { bug!() };
1185 // Whether we must not match the fields of this variant exhaustively.
1186 let is_non_exhaustive = variant.is_field_list_non_exhaustive() && !adt.did.is_local();
1188 variant.fields.iter().enumerate().filter_map(move |(i, field)| {
1189 let ty = field.ty(cx.tcx, substs);
1190 // `field.ty()` doesn't normalize after substituting.
1191 let ty = cx.tcx.normalize_erasing_regions(cx.param_env, ty);
1192 let is_visible = adt.is_enum() || field.vis.is_accessible_from(cx.module, cx.tcx);
1193 let is_uninhabited = cx.is_uninhabited(ty);
1195 if is_uninhabited && (!is_visible || is_non_exhaustive) {
1198 Some((Field::new(i), ty))
1203 /// Creates a new list of wildcard fields for a given constructor. The result must have a
1204 /// length of `constructor.arity()`.
1205 pub(super) fn wildcards(
1206 cx: &MatchCheckCtxt<'p, 'tcx>,
1208 constructor: &Constructor<'tcx>,
1210 let ret = match constructor {
1211 Single | Variant(_) => match ty.kind() {
1212 ty::Tuple(fs) => Fields::wildcards_from_tys(cx, fs.iter()),
1213 ty::Ref(_, rty, _) => Fields::wildcards_from_tys(cx, once(*rty)),
1214 ty::Adt(adt, substs) => {
1216 // The only legal patterns of type `Box` (outside `std`) are `_` and box
1217 // patterns. If we're here we can assume this is a box pattern.
1218 Fields::wildcards_from_tys(cx, once(substs.type_at(0)))
1220 let variant = &adt.variants[constructor.variant_index_for_adt(adt)];
1221 let tys = Fields::list_variant_nonhidden_fields(cx, ty, variant)
1223 Fields::wildcards_from_tys(cx, tys)
1226 _ => bug!("Unexpected type for `Single` constructor: {:?}", ty),
1228 Slice(slice) => match *ty.kind() {
1229 ty::Slice(ty) | ty::Array(ty, _) => {
1230 let arity = slice.arity();
1231 Fields::wildcards_from_tys(cx, (0..arity).map(|_| ty))
1233 _ => bug!("bad slice pattern {:?} {:?}", constructor, ty),
1241 | Wildcard => Fields::empty(),
1243 bug!("called `Fields::wildcards` on an `Or` ctor")
1246 debug!("Fields::wildcards({:?}, {:?}) = {:#?}", constructor, ty, ret);
1250 /// Returns the list of patterns.
1251 pub(super) fn iter_patterns<'a>(
1253 ) -> impl Iterator<Item = &'p DeconstructedPat<'p, 'tcx>> + Captures<'a> {
1258 /// Values and patterns can be represented as a constructor applied to some fields. This represents
1259 /// a pattern in this form.
1260 /// This also keeps track of whether the pattern has been found reachable during analysis. For this
1261 /// reason we should be careful not to clone patterns for which we care about that. Use
1262 /// `clone_and_forget_reachability` if you're sure.
1263 pub(crate) struct DeconstructedPat<'p, 'tcx> {
1264 ctor: Constructor<'tcx>,
1265 fields: Fields<'p, 'tcx>,
1268 reachable: Cell<bool>,
1271 impl<'p, 'tcx> DeconstructedPat<'p, 'tcx> {
1272 pub(super) fn wildcard(ty: Ty<'tcx>) -> Self {
1273 Self::new(Wildcard, Fields::empty(), ty, DUMMY_SP)
1277 ctor: Constructor<'tcx>,
1278 fields: Fields<'p, 'tcx>,
1282 DeconstructedPat { ctor, fields, ty, span, reachable: Cell::new(false) }
1285 /// Construct a pattern that matches everything that starts with this constructor.
1286 /// For example, if `ctor` is a `Constructor::Variant` for `Option::Some`, we get the pattern
1288 pub(super) fn wild_from_ctor(pcx: PatCtxt<'_, 'p, 'tcx>, ctor: Constructor<'tcx>) -> Self {
1289 let fields = Fields::wildcards(pcx.cx, pcx.ty, &ctor);
1290 DeconstructedPat::new(ctor, fields, pcx.ty, DUMMY_SP)
1293 /// Clone this value. This method emphasizes that cloning loses reachability information and
1294 /// should be done carefully.
1295 pub(super) fn clone_and_forget_reachability(&self) -> Self {
1296 DeconstructedPat::new(self.ctor.clone(), self.fields, self.ty, self.span)
1299 pub(crate) fn from_pat(cx: &MatchCheckCtxt<'p, 'tcx>, pat: &Pat<'tcx>) -> Self {
1300 let mkpat = |pat| DeconstructedPat::from_pat(cx, pat);
1303 match pat.kind.as_ref() {
1304 PatKind::AscribeUserType { subpattern, .. } => return mkpat(subpattern),
1305 PatKind::Binding { subpattern: Some(subpat), .. } => return mkpat(subpat),
1306 PatKind::Binding { subpattern: None, .. } | PatKind::Wild => {
1308 fields = Fields::empty();
1310 PatKind::Deref { subpattern } => {
1312 fields = Fields::singleton(cx, mkpat(subpattern));
1314 PatKind::Leaf { subpatterns } | PatKind::Variant { subpatterns, .. } => {
1315 match pat.ty.kind() {
1318 let mut wilds: SmallVec<[_; 2]> =
1319 fs.iter().map(DeconstructedPat::wildcard).collect();
1320 for pat in subpatterns {
1321 wilds[pat.field.index()] = mkpat(&pat.pattern);
1323 fields = Fields::from_iter(cx, wilds);
1325 ty::Adt(adt, substs) if adt.is_box() => {
1326 // The only legal patterns of type `Box` (outside `std`) are `_` and box
1327 // patterns. If we're here we can assume this is a box pattern.
1328 // FIXME(Nadrieril): A `Box` can in theory be matched either with `Box(_,
1329 // _)` or a box pattern. As a hack to avoid an ICE with the former, we
1330 // ignore other fields than the first one. This will trigger an error later
1332 // See https://github.com/rust-lang/rust/issues/82772 ,
1333 // explanation: https://github.com/rust-lang/rust/pull/82789#issuecomment-796921977
1334 // The problem is that we can't know from the type whether we'll match
1335 // normally or through box-patterns. We'll have to figure out a proper
1336 // solution when we introduce generalized deref patterns. Also need to
1337 // prevent mixing of those two options.
1338 let pat = subpatterns.into_iter().find(|pat| pat.field.index() == 0);
1339 let pat = if let Some(pat) = pat {
1342 DeconstructedPat::wildcard(substs.type_at(0))
1345 fields = Fields::singleton(cx, pat);
1347 ty::Adt(adt, _) => {
1348 ctor = match pat.kind.as_ref() {
1349 PatKind::Leaf { .. } => Single,
1350 PatKind::Variant { variant_index, .. } => Variant(*variant_index),
1353 let variant = &adt.variants[ctor.variant_index_for_adt(adt)];
1354 // For each field in the variant, we store the relevant index into `self.fields` if any.
1355 let mut field_id_to_id: Vec<Option<usize>> =
1356 (0..variant.fields.len()).map(|_| None).collect();
1357 let tys = Fields::list_variant_nonhidden_fields(cx, pat.ty, variant)
1359 .map(|(i, (field, ty))| {
1360 field_id_to_id[field.index()] = Some(i);
1363 let mut wilds: SmallVec<[_; 2]> =
1364 tys.map(DeconstructedPat::wildcard).collect();
1365 for pat in subpatterns {
1366 if let Some(i) = field_id_to_id[pat.field.index()] {
1367 wilds[i] = mkpat(&pat.pattern);
1370 fields = Fields::from_iter(cx, wilds);
1372 _ => bug!("pattern has unexpected type: pat: {:?}, ty: {:?}", pat, pat.ty),
1375 PatKind::Constant { value } => {
1376 if let Some(int_range) = IntRange::from_const(cx.tcx, cx.param_env, *value) {
1377 ctor = IntRange(int_range);
1378 fields = Fields::empty();
1380 match pat.ty.kind() {
1382 ctor = FloatRange(*value, *value, RangeEnd::Included);
1383 fields = Fields::empty();
1385 ty::Ref(_, t, _) if t.is_str() => {
1386 // We want a `&str` constant to behave like a `Deref` pattern, to be compatible
1387 // with other `Deref` patterns. This could have been done in `const_to_pat`,
1388 // but that causes issues with the rest of the matching code.
1389 // So here, the constructor for a `"foo"` pattern is `&` (represented by
1390 // `Single`), and has one field. That field has constructor `Str(value)` and no
1392 // Note: `t` is `str`, not `&str`.
1394 DeconstructedPat::new(Str(*value), Fields::empty(), *t, pat.span);
1396 fields = Fields::singleton(cx, subpattern)
1398 // All constants that can be structurally matched have already been expanded
1399 // into the corresponding `Pat`s by `const_to_pat`. Constants that remain are
1403 fields = Fields::empty();
1408 &PatKind::Range(PatRange { lo, hi, end }) => {
1410 ctor = if let Some(int_range) = IntRange::from_range(
1412 lo.eval_bits(cx.tcx, cx.param_env, lo.ty()),
1413 hi.eval_bits(cx.tcx, cx.param_env, hi.ty()),
1419 FloatRange(lo, hi, end)
1421 fields = Fields::empty();
1423 PatKind::Array { prefix, slice, suffix } | PatKind::Slice { prefix, slice, suffix } => {
1424 let array_len = match pat.ty.kind() {
1425 ty::Array(_, length) => Some(length.eval_usize(cx.tcx, cx.param_env) as usize),
1426 ty::Slice(_) => None,
1427 _ => span_bug!(pat.span, "bad ty {:?} for slice pattern", pat.ty),
1429 let kind = if slice.is_some() {
1430 VarLen(prefix.len(), suffix.len())
1432 FixedLen(prefix.len() + suffix.len())
1434 ctor = Slice(Slice::new(array_len, kind));
1435 fields = Fields::from_iter(cx, prefix.iter().chain(suffix).map(mkpat));
1437 PatKind::Or { .. } => {
1439 let pats = expand_or_pat(pat);
1440 fields = Fields::from_iter(cx, pats.into_iter().map(mkpat));
1443 DeconstructedPat::new(ctor, fields, pat.ty, pat.span)
1446 pub(crate) fn to_pat(&self, cx: &MatchCheckCtxt<'p, 'tcx>) -> Pat<'tcx> {
1447 let is_wildcard = |pat: &Pat<'_>| {
1448 matches!(*pat.kind, PatKind::Binding { subpattern: None, .. } | PatKind::Wild)
1450 let mut subpatterns = self.iter_fields().map(|p| p.to_pat(cx));
1451 let pat = match &self.ctor {
1452 Single | Variant(_) => match self.ty.kind() {
1453 ty::Tuple(..) => PatKind::Leaf {
1454 subpatterns: subpatterns
1456 .map(|(i, p)| FieldPat { field: Field::new(i), pattern: p })
1459 ty::Adt(adt_def, _) if adt_def.is_box() => {
1460 // Without `box_patterns`, the only legal pattern of type `Box` is `_` (outside
1461 // of `std`). So this branch is only reachable when the feature is enabled and
1462 // the pattern is a box pattern.
1463 PatKind::Deref { subpattern: subpatterns.next().unwrap() }
1465 ty::Adt(adt_def, substs) => {
1466 let variant_index = self.ctor.variant_index_for_adt(adt_def);
1467 let variant = &adt_def.variants[variant_index];
1468 let subpatterns = Fields::list_variant_nonhidden_fields(cx, self.ty, variant)
1470 .map(|((field, _ty), pattern)| FieldPat { field, pattern })
1473 if adt_def.is_enum() {
1474 PatKind::Variant { adt_def, substs, variant_index, subpatterns }
1476 PatKind::Leaf { subpatterns }
1479 // Note: given the expansion of `&str` patterns done in `expand_pattern`, we should
1480 // be careful to reconstruct the correct constant pattern here. However a string
1481 // literal pattern will never be reported as a non-exhaustiveness witness, so we
1482 // ignore this issue.
1483 ty::Ref(..) => PatKind::Deref { subpattern: subpatterns.next().unwrap() },
1484 _ => bug!("unexpected ctor for type {:?} {:?}", self.ctor, self.ty),
1488 FixedLen(_) => PatKind::Slice {
1489 prefix: subpatterns.collect(),
1493 VarLen(prefix, _) => {
1494 let mut subpatterns = subpatterns.peekable();
1495 let mut prefix: Vec<_> = subpatterns.by_ref().take(prefix).collect();
1496 if slice.array_len.is_some() {
1497 // Improves diagnostics a bit: if the type is a known-size array, instead
1498 // of reporting `[x, _, .., _, y]`, we prefer to report `[x, .., y]`.
1499 // This is incorrect if the size is not known, since `[_, ..]` captures
1500 // arrays of lengths `>= 1` whereas `[..]` captures any length.
1501 while !prefix.is_empty() && is_wildcard(prefix.last().unwrap()) {
1504 while subpatterns.peek().is_some()
1505 && is_wildcard(subpatterns.peek().unwrap())
1510 let suffix: Vec<_> = subpatterns.collect();
1511 let wild = Pat::wildcard_from_ty(self.ty);
1512 PatKind::Slice { prefix, slice: Some(wild), suffix }
1516 &Str(value) => PatKind::Constant { value },
1517 &FloatRange(lo, hi, end) => PatKind::Range(PatRange { lo, hi, end }),
1518 IntRange(range) => return range.to_pat(cx.tcx, self.ty),
1519 Wildcard | NonExhaustive => PatKind::Wild,
1520 Missing { .. } => bug!(
1521 "trying to convert a `Missing` constructor into a `Pat`; this is probably a bug,
1522 `Missing` should have been processed in `apply_constructors`"
1525 bug!("can't convert to pattern: {:?}", self)
1529 Pat { ty: self.ty, span: DUMMY_SP, kind: Box::new(pat) }
1532 pub(super) fn is_or_pat(&self) -> bool {
1533 matches!(self.ctor, Or)
1536 pub(super) fn ctor(&self) -> &Constructor<'tcx> {
1539 pub(super) fn ty(&self) -> Ty<'tcx> {
1542 pub(super) fn span(&self) -> Span {
1546 pub(super) fn iter_fields<'a>(
1548 ) -> impl Iterator<Item = &'p DeconstructedPat<'p, 'tcx>> + Captures<'a> {
1549 self.fields.iter_patterns()
1552 /// Specialize this pattern with a constructor.
1553 /// `other_ctor` can be different from `self.ctor`, but must be covered by it.
1554 pub(super) fn specialize<'a>(
1556 cx: &MatchCheckCtxt<'p, 'tcx>,
1557 other_ctor: &Constructor<'tcx>,
1558 ) -> SmallVec<[&'p DeconstructedPat<'p, 'tcx>; 2]> {
1559 match (&self.ctor, other_ctor) {
1561 // We return a wildcard for each field of `other_ctor`.
1562 Fields::wildcards(cx, self.ty, other_ctor).iter_patterns().collect()
1564 (Slice(self_slice), Slice(other_slice))
1565 if self_slice.arity() != other_slice.arity() =>
1567 // The only tricky case: two slices of different arity. Since `self_slice` covers
1568 // `other_slice`, `self_slice` must be `VarLen`, i.e. of the form
1569 // `[prefix, .., suffix]`. Moreover `other_slice` is guaranteed to have a larger
1570 // arity. So we fill the middle part with enough wildcards to reach the length of
1571 // the new, larger slice.
1572 match self_slice.kind {
1573 FixedLen(_) => bug!("{:?} doesn't cover {:?}", self_slice, other_slice),
1574 VarLen(prefix, suffix) => {
1575 let (ty::Slice(inner_ty) | ty::Array(inner_ty, _)) = *self.ty.kind() else {
1576 bug!("bad slice pattern {:?} {:?}", self.ctor, self.ty);
1578 let prefix = &self.fields.fields[..prefix];
1579 let suffix = &self.fields.fields[self_slice.arity() - suffix..];
1581 cx.pattern_arena.alloc(DeconstructedPat::wildcard(inner_ty));
1582 let extra_wildcards = other_slice.arity() - self_slice.arity();
1583 let extra_wildcards = (0..extra_wildcards).map(|_| wildcard);
1584 prefix.iter().chain(extra_wildcards).chain(suffix).collect()
1588 _ => self.fields.iter_patterns().collect(),
1592 /// We keep track for each pattern if it was ever reachable during the analysis. This is used
1593 /// with `unreachable_spans` to report unreachable subpatterns arising from or patterns.
1594 pub(super) fn set_reachable(&self) {
1595 self.reachable.set(true)
1597 pub(super) fn is_reachable(&self) -> bool {
1598 self.reachable.get()
1601 /// Report the spans of subpatterns that were not reachable, if any.
1602 pub(super) fn unreachable_spans(&self) -> Vec<Span> {
1603 let mut spans = Vec::new();
1604 self.collect_unreachable_spans(&mut spans);
1608 fn collect_unreachable_spans(&self, spans: &mut Vec<Span>) {
1609 // We don't look at subpatterns if we already reported the whole pattern as unreachable.
1610 if !self.is_reachable() {
1611 spans.push(self.span);
1613 for p in self.iter_fields() {
1614 p.collect_unreachable_spans(spans);
1620 /// This is mostly copied from the `Pat` impl. This is best effort and not good enough for a
1622 impl<'p, 'tcx> fmt::Debug for DeconstructedPat<'p, 'tcx> {
1623 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1624 // Printing lists is a chore.
1625 let mut first = true;
1626 let mut start_or_continue = |s| {
1634 let mut start_or_comma = || start_or_continue(", ");
1637 Single | Variant(_) => match self.ty.kind() {
1638 ty::Adt(def, _) if def.is_box() => {
1639 // Without `box_patterns`, the only legal pattern of type `Box` is `_` (outside
1640 // of `std`). So this branch is only reachable when the feature is enabled and
1641 // the pattern is a box pattern.
1642 let subpattern = self.iter_fields().next().unwrap();
1643 write!(f, "box {:?}", subpattern)
1645 ty::Adt(..) | ty::Tuple(..) => {
1646 let variant = match self.ty.kind() {
1647 ty::Adt(adt, _) => {
1648 Some(&adt.variants[self.ctor.variant_index_for_adt(adt)])
1650 ty::Tuple(_) => None,
1651 _ => unreachable!(),
1654 if let Some(variant) = variant {
1655 write!(f, "{}", variant.name)?;
1658 // Without `cx`, we can't know which field corresponds to which, so we can't
1659 // get the names of the fields. Instead we just display everything as a suple
1660 // struct, which should be good enough.
1662 for p in self.iter_fields() {
1663 write!(f, "{}", start_or_comma())?;
1664 write!(f, "{:?}", p)?;
1668 // Note: given the expansion of `&str` patterns done in `expand_pattern`, we should
1669 // be careful to detect strings here. However a string literal pattern will never
1670 // be reported as a non-exhaustiveness witness, so we can ignore this issue.
1671 ty::Ref(_, _, mutbl) => {
1672 let subpattern = self.iter_fields().next().unwrap();
1673 write!(f, "&{}{:?}", mutbl.prefix_str(), subpattern)
1675 _ => write!(f, "_"),
1678 let mut subpatterns = self.fields.iter_patterns();
1682 for p in subpatterns {
1683 write!(f, "{}{:?}", start_or_comma(), p)?;
1686 VarLen(prefix_len, _) => {
1687 for p in subpatterns.by_ref().take(prefix_len) {
1688 write!(f, "{}{:?}", start_or_comma(), p)?;
1690 write!(f, "{}", start_or_comma())?;
1692 for p in subpatterns {
1693 write!(f, "{}{:?}", start_or_comma(), p)?;
1699 &FloatRange(lo, hi, end) => {
1700 write!(f, "{}", lo)?;
1701 write!(f, "{}", end)?;
1704 IntRange(range) => write!(f, "{:?}", range), // Best-effort, will render e.g. `false` as `0..=0`
1705 Wildcard | Missing { .. } | NonExhaustive => write!(f, "_ : {:?}", self.ty),
1707 for pat in self.iter_fields() {
1708 write!(f, "{}{:?}", start_or_continue(" | "), pat)?;
1712 Str(value) => write!(f, "{}", value),
1713 Opaque => write!(f, "<constant pattern>"),