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:
16 //! ```compile_fail,E0004
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::{self, Field};
56 use rustc_middle::thir::{FieldPat, Pat, PatKind, PatRange};
57 use rustc_middle::ty::layout::IntegerExt;
58 use rustc_middle::ty::{self, 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 {
75 for pat in pats.iter() {
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)),
136 fn from_constant<'tcx>(
138 param_env: ty::ParamEnv<'tcx>,
139 value: mir::ConstantKind<'tcx>,
140 ) -> Option<IntRange> {
142 if let Some((target_size, bias)) = Self::integral_size_and_signed_bias(tcx, ty) {
145 mir::ConstantKind::Val(ConstValue::Scalar(scalar), _) => {
146 // For this specific pattern we can skip a lot of effort and go
147 // straight to the result, after doing a bit of checking. (We
148 // could remove this branch and just fall through, which
149 // is more general but much slower.)
150 if let Ok(Ok(bits)) = scalar.to_bits_or_ptr_internal(target_size) {
156 mir::ConstantKind::Ty(c) => match c.kind() {
157 ty::ConstKind::Value(_) => bug!(
158 "encountered ConstValue in mir::ConstantKind::Ty, whereas this is expected to be in ConstantKind::Val"
165 // This is a more general form of the previous case.
166 value.try_eval_bits(tcx, param_env, ty)
168 let val = val ^ bias;
169 Some(IntRange { range: val..=val, bias })
182 ) -> Option<IntRange> {
183 if Self::is_integral(ty) {
184 // Perform a shift if the underlying types are signed,
185 // which makes the interval arithmetic simpler.
186 let bias = IntRange::signed_bias(tcx, ty);
187 let (lo, hi) = (lo ^ bias, hi ^ bias);
188 let offset = (*end == RangeEnd::Excluded) as u128;
189 if lo > hi || (lo == hi && *end == RangeEnd::Excluded) {
190 // This should have been caught earlier by E0030.
191 bug!("malformed range pattern: {}..={}", lo, (hi - offset));
193 Some(IntRange { range: lo..=(hi - offset), bias })
199 // The return value of `signed_bias` should be XORed with an endpoint to encode/decode it.
200 fn signed_bias(tcx: TyCtxt<'_>, ty: Ty<'_>) -> u128 {
203 let bits = Integer::from_int_ty(&tcx, ity).size().bits() as u128;
210 fn is_subrange(&self, other: &Self) -> bool {
211 other.range.start() <= self.range.start() && self.range.end() <= other.range.end()
214 fn intersection(&self, other: &Self) -> Option<Self> {
215 let (lo, hi) = self.boundaries();
216 let (other_lo, other_hi) = other.boundaries();
217 if lo <= other_hi && other_lo <= hi {
218 Some(IntRange { range: max(lo, other_lo)..=min(hi, other_hi), bias: self.bias })
224 fn suspicious_intersection(&self, other: &Self) -> bool {
225 // `false` in the following cases:
226 // 1 ---- // 1 ---------- // 1 ---- // 1 ----
227 // 2 ---------- // 2 ---- // 2 ---- // 2 ----
229 // The following are currently `false`, but could be `true` in the future (#64007):
230 // 1 --------- // 1 ---------
231 // 2 ---------- // 2 ----------
233 // `true` in the following cases:
234 // 1 ------- // 1 -------
235 // 2 -------- // 2 -------
236 let (lo, hi) = self.boundaries();
237 let (other_lo, other_hi) = other.boundaries();
238 (lo == other_hi || hi == other_lo) && !self.is_singleton() && !other.is_singleton()
241 /// Only used for displaying the range properly.
242 fn to_pat<'tcx>(&self, tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> Pat<'tcx> {
243 let (lo, hi) = self.boundaries();
245 let bias = self.bias;
246 let (lo, hi) = (lo ^ bias, hi ^ bias);
248 let env = ty::ParamEnv::empty().and(ty);
249 let lo_const = mir::ConstantKind::from_bits(tcx, lo, env);
250 let hi_const = mir::ConstantKind::from_bits(tcx, hi, env);
252 let kind = if lo == hi {
253 PatKind::Constant { value: lo_const }
255 PatKind::Range(Box::new(PatRange {
258 end: RangeEnd::Included,
262 Pat { ty, span: DUMMY_SP, kind }
265 /// Lint on likely incorrect range patterns (#63987)
266 pub(super) fn lint_overlapping_range_endpoints<'a, 'p: 'a, 'tcx: 'a>(
268 pcx: &PatCtxt<'_, 'p, 'tcx>,
269 pats: impl Iterator<Item = &'a DeconstructedPat<'p, 'tcx>>,
273 if self.is_singleton() {
277 if column_count != 1 {
278 // FIXME: for now, only check for overlapping ranges on simple range
279 // patterns. Otherwise with the current logic the following is detected
282 // match (0u8, true) {
283 // (0 ..= 125, false) => {}
284 // (125 ..= 255, true) => {}
291 let overlaps: Vec<_> = pats
292 .filter_map(|pat| Some((pat.ctor().as_int_range()?, pat.span())))
293 .filter(|(range, _)| self.suspicious_intersection(range))
294 .map(|(range, span)| (self.intersection(&range).unwrap(), span))
297 if !overlaps.is_empty() {
298 pcx.cx.tcx.struct_span_lint_hir(
299 lint::builtin::OVERLAPPING_RANGE_ENDPOINTS,
303 let mut err = lint.build("multiple patterns overlap on their endpoints");
304 for (int_range, span) in overlaps {
308 "this range overlaps on `{}`...",
309 int_range.to_pat(pcx.cx.tcx, pcx.ty)
313 err.span_label(pcx.span, "... with this range");
314 err.note("you likely meant to write mutually exclusive ranges");
321 /// See `Constructor::is_covered_by`
322 fn is_covered_by(&self, other: &Self) -> bool {
323 if self.intersection(other).is_some() {
324 // Constructor splitting should ensure that all intersections we encounter are actually
326 assert!(self.is_subrange(other));
334 /// Note: this is often not what we want: e.g. `false` is converted into the range `0..=0` and
335 /// would be displayed as such. To render properly, convert to a pattern first.
336 impl fmt::Debug for IntRange {
337 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
338 let (lo, hi) = self.boundaries();
339 let bias = self.bias;
340 let (lo, hi) = (lo ^ bias, hi ^ bias);
341 write!(f, "{}", lo)?;
342 write!(f, "{}", RangeEnd::Included)?;
347 /// Represents a border between 2 integers. Because the intervals spanning borders must be able to
348 /// cover every integer, we need to be able to represent 2^128 + 1 such borders.
349 #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
355 /// A range of integers that is partitioned into disjoint subranges. This does constructor
356 /// splitting for integer ranges as explained at the top of the file.
358 /// This is fed multiple ranges, and returns an output that covers the input, but is split so that
359 /// the only intersections between an output range and a seen range are inclusions. No output range
360 /// straddles the boundary of one of the inputs.
362 /// The following input:
364 /// |-------------------------| // `self`
365 /// |------| |----------| |----|
366 /// |-------| |-------|
368 /// would be iterated over as follows:
370 /// ||---|--||-|---|---|---|--|
372 #[derive(Debug, Clone)]
373 struct SplitIntRange {
374 /// The range we are splitting
376 /// The borders of ranges we have seen. They are all contained within `range`. This is kept
378 borders: Vec<IntBorder>,
382 fn new(range: IntRange) -> Self {
383 SplitIntRange { range, borders: Vec::new() }
387 fn to_borders(r: IntRange) -> [IntBorder; 2] {
389 let (lo, hi) = r.boundaries();
390 let lo = JustBefore(lo);
391 let hi = match hi.checked_add(1) {
392 Some(m) => JustBefore(m),
398 /// Add ranges relative to which we split.
399 fn split(&mut self, ranges: impl Iterator<Item = IntRange>) {
400 let this_range = &self.range;
401 let included_ranges = ranges.filter_map(|r| this_range.intersection(&r));
402 let included_borders = included_ranges.flat_map(|r| {
403 let borders = Self::to_borders(r);
404 once(borders[0]).chain(once(borders[1]))
406 self.borders.extend(included_borders);
407 self.borders.sort_unstable();
410 /// Iterate over the contained ranges.
411 fn iter<'a>(&'a self) -> impl Iterator<Item = IntRange> + Captures<'a> {
414 let self_range = Self::to_borders(self.range.clone());
415 // Start with the start of the range.
416 let mut prev_border = self_range[0];
420 // End with the end of the range.
421 .chain(once(self_range[1]))
422 // List pairs of adjacent borders.
424 let ret = (prev_border, border);
425 prev_border = border;
429 .filter(|(prev_border, border)| prev_border != border)
430 // Finally, convert to ranges.
431 .map(move |(prev_border, border)| {
432 let range = match (prev_border, border) {
433 (JustBefore(n), JustBefore(m)) if n < m => n..=(m - 1),
434 (JustBefore(n), AfterMax) => n..=u128::MAX,
435 _ => unreachable!(), // Ruled out by the sorting and filtering we did
437 IntRange { range, bias: self.range.bias }
442 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
444 /// Patterns of length `n` (`[x, y]`).
446 /// Patterns using the `..` notation (`[x, .., y]`).
447 /// Captures any array constructor of `length >= i + j`.
448 /// In the case where `array_len` is `Some(_)`,
449 /// this indicates that we only care about the first `i` and the last `j` values of the array,
450 /// and everything in between is a wildcard `_`.
451 VarLen(usize, usize),
455 fn arity(self) -> usize {
457 FixedLen(length) => length,
458 VarLen(prefix, suffix) => prefix + suffix,
462 /// Whether this pattern includes patterns of length `other_len`.
463 fn covers_length(self, other_len: usize) -> bool {
465 FixedLen(len) => len == other_len,
466 VarLen(prefix, suffix) => prefix + suffix <= other_len,
471 /// A constructor for array and slice patterns.
472 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
473 pub(super) struct Slice {
474 /// `None` if the matched value is a slice, `Some(n)` if it is an array of size `n`.
475 array_len: Option<usize>,
476 /// The kind of pattern it is: fixed-length `[x, y]` or variable length `[x, .., y]`.
481 fn new(array_len: Option<usize>, kind: SliceKind) -> Self {
482 let kind = match (array_len, kind) {
483 // If the middle `..` is empty, we effectively have a fixed-length pattern.
484 (Some(len), VarLen(prefix, suffix)) if prefix + suffix >= len => FixedLen(len),
487 Slice { array_len, kind }
490 fn arity(self) -> usize {
494 /// See `Constructor::is_covered_by`
495 fn is_covered_by(self, other: Self) -> bool {
496 other.kind.covers_length(self.arity())
500 /// This computes constructor splitting for variable-length slices, as explained at the top of the
503 /// A slice pattern `[x, .., y]` behaves like the infinite or-pattern `[x, y] | [x, _, y] | [x, _,
504 /// _, y] | ...`. The corresponding value constructors are fixed-length array constructors above a
505 /// given minimum length. We obviously can't list this infinitude of constructors. Thankfully,
506 /// it turns out that for each finite set of slice patterns, all sufficiently large array lengths
509 /// Let's look at an example, where we are trying to split the last pattern:
511 /// # fn foo(x: &[bool]) {
513 /// [true, true, ..] => {}
514 /// [.., false, false] => {}
519 /// Here are the results of specialization for the first few lengths:
521 /// # fn foo(x: &[bool]) { match x {
527 /// [true, true] => {}
528 /// [false, false] => {}
531 /// [true, true, _ ] => {}
532 /// [_, false, false] => {}
535 /// [true, true, _, _ ] => {}
536 /// [_, _, false, false] => {}
537 /// [_, _, _, _ ] => {}
539 /// [true, true, _, _, _ ] => {}
540 /// [_, _, _, false, false] => {}
541 /// [_, _, _, _, _ ] => {}
546 /// If we went above length 5, we would simply be inserting more columns full of wildcards in the
547 /// middle. This means that the set of witnesses for length `l >= 5` if equivalent to the set for
548 /// any other `l' >= 5`: simply add or remove wildcards in the middle to convert between them.
550 /// This applies to any set of slice patterns: there will be a length `L` above which all lengths
551 /// behave the same. This is exactly what we need for constructor splitting. Therefore a
552 /// variable-length slice can be split into a variable-length slice of minimal length `L`, and many
553 /// fixed-length slices of lengths `< L`.
555 /// For each variable-length pattern `p` with a prefix of length `plâ‚š` and suffix of length `slâ‚š`,
556 /// only the first `plâ‚š` and the last `slâ‚š` elements are examined. Therefore, as long as `L` is
557 /// positive (to avoid concerns about empty types), all elements after the maximum prefix length
558 /// and before the maximum suffix length are not examined by any variable-length pattern, and
559 /// therefore can be added/removed without affecting them - creating equivalent patterns from any
560 /// sufficiently-large length.
562 /// Of course, if fixed-length patterns exist, we must be sure that our length is large enough to
563 /// miss them all, so we can pick `L = max(max(FIXED_LEN)+1, max(PREFIX_LEN) + max(SUFFIX_LEN))`
565 /// `max_slice` below will be made to have arity `L`.
567 struct SplitVarLenSlice {
568 /// If the type is an array, this is its size.
569 array_len: Option<usize>,
570 /// The arity of the input slice.
572 /// The smallest slice bigger than any slice seen. `max_slice.arity()` is the length `L`
574 max_slice: SliceKind,
577 impl SplitVarLenSlice {
578 fn new(prefix: usize, suffix: usize, array_len: Option<usize>) -> Self {
579 SplitVarLenSlice { array_len, arity: prefix + suffix, max_slice: VarLen(prefix, suffix) }
582 /// Pass a set of slices relative to which to split this one.
583 fn split(&mut self, slices: impl Iterator<Item = SliceKind>) {
584 let VarLen(max_prefix_len, max_suffix_len) = &mut self.max_slice else {
588 // We grow `self.max_slice` to be larger than all slices encountered, as described above.
589 // For diagnostics, we keep the prefix and suffix lengths separate, but grow them so that
590 // `L = max_prefix_len + max_suffix_len`.
591 let mut max_fixed_len = 0;
592 for slice in slices {
595 max_fixed_len = cmp::max(max_fixed_len, len);
597 VarLen(prefix, suffix) => {
598 *max_prefix_len = cmp::max(*max_prefix_len, prefix);
599 *max_suffix_len = cmp::max(*max_suffix_len, suffix);
603 // We want `L = max(L, max_fixed_len + 1)`, modulo the fact that we keep prefix and
605 if max_fixed_len + 1 >= *max_prefix_len + *max_suffix_len {
606 // The subtraction can't overflow thanks to the above check.
607 // The new `max_prefix_len` is larger than its previous value.
608 *max_prefix_len = max_fixed_len + 1 - *max_suffix_len;
611 // We cap the arity of `max_slice` at the array size.
612 match self.array_len {
613 Some(len) if self.max_slice.arity() >= len => self.max_slice = FixedLen(len),
618 /// Iterate over the partition of this slice.
619 fn iter<'a>(&'a self) -> impl Iterator<Item = Slice> + Captures<'a> {
620 let smaller_lengths = match self.array_len {
621 // The only admissible fixed-length slice is one of the array size. Whether `max_slice`
622 // is fixed-length or variable-length, it will be the only relevant slice to output
624 Some(_) => 0..0, // empty range
625 // We cover all arities in the range `(self.arity..infinity)`. We split that range into
626 // two: lengths smaller than `max_slice.arity()` are treated independently as
627 // fixed-lengths slices, and lengths above are captured by `max_slice`.
628 None => self.arity..self.max_slice.arity(),
632 .chain(once(self.max_slice))
633 .map(move |kind| Slice::new(self.array_len, kind))
637 /// A value can be decomposed into a constructor applied to some fields. This struct represents
638 /// the constructor. See also `Fields`.
640 /// `pat_constructor` retrieves the constructor corresponding to a pattern.
641 /// `specialize_constructor` returns the list of fields corresponding to a pattern, given a
642 /// constructor. `Constructor::apply` reconstructs the pattern from a pair of `Constructor` and
644 #[derive(Clone, Debug, PartialEq)]
645 pub(super) enum Constructor<'tcx> {
646 /// The constructor for patterns that have a single constructor, like tuples, struct patterns
647 /// and fixed-length arrays.
651 /// Ranges of integer literal values (`2`, `2..=5` or `2..5`).
653 /// Ranges of floating-point literal values (`2.0..=5.2`).
654 FloatRange(mir::ConstantKind<'tcx>, mir::ConstantKind<'tcx>, RangeEnd),
655 /// String literals. Strings are not quite the same as `&[u8]` so we treat them separately.
656 Str(mir::ConstantKind<'tcx>),
657 /// Array and slice patterns.
659 /// Constants that must not be matched structurally. They are treated as black
660 /// boxes for the purposes of exhaustiveness: we must not inspect them, and they
661 /// don't count towards making a match exhaustive.
663 /// Fake extra constructor for enums that aren't allowed to be matched exhaustively. Also used
664 /// for those types for which we cannot list constructors explicitly, like `f64` and `str`.
666 /// Stands for constructors that are not seen in the matrix, as explained in the documentation
667 /// for [`SplitWildcard`]. The carried `bool` is used for the `non_exhaustive_omitted_patterns`
669 Missing { nonexhaustive_enum_missing_real_variants: bool },
670 /// Wildcard pattern.
676 impl<'tcx> Constructor<'tcx> {
677 pub(super) fn is_wildcard(&self) -> bool {
678 matches!(self, Wildcard)
681 pub(super) fn is_non_exhaustive(&self) -> bool {
682 matches!(self, NonExhaustive)
685 fn as_int_range(&self) -> Option<&IntRange> {
687 IntRange(range) => Some(range),
692 fn as_slice(&self) -> Option<Slice> {
694 Slice(slice) => Some(*slice),
699 /// Checks if the `Constructor` is a variant and `TyCtxt::eval_stability` returns
700 /// `EvalResult::Deny { .. }`.
702 /// This means that the variant has a stdlib unstable feature marking it.
703 pub(super) fn is_unstable_variant(&self, pcx: &PatCtxt<'_, '_, 'tcx>) -> bool {
704 if let Constructor::Variant(idx) = self && let ty::Adt(adt, _) = pcx.ty.kind() {
705 let variant_def_id = adt.variant(*idx).def_id;
706 // Filter variants that depend on a disabled unstable feature.
708 pcx.cx.tcx.eval_stability(variant_def_id, None, DUMMY_SP, None),
709 EvalResult::Deny { .. }
715 /// Checks if the `Constructor` is a `Constructor::Variant` with a `#[doc(hidden)]`
716 /// attribute from a type not local to the current crate.
717 pub(super) fn is_doc_hidden_variant(&self, pcx: &PatCtxt<'_, '_, 'tcx>) -> bool {
718 if let Constructor::Variant(idx) = self && let ty::Adt(adt, _) = pcx.ty.kind() {
719 let variant_def_id = adt.variants()[*idx].def_id;
720 return pcx.cx.tcx.is_doc_hidden(variant_def_id) && !variant_def_id.is_local();
725 fn variant_index_for_adt(&self, adt: ty::AdtDef<'tcx>) -> VariantIdx {
729 assert!(!adt.is_enum());
732 _ => bug!("bad constructor {:?} for adt {:?}", self, adt),
736 /// The number of fields for this constructor. This must be kept in sync with
737 /// `Fields::wildcards`.
738 pub(super) fn arity(&self, pcx: &PatCtxt<'_, '_, 'tcx>) -> usize {
740 Single | Variant(_) => match pcx.ty.kind() {
741 ty::Tuple(fs) => fs.len(),
743 ty::Adt(adt, ..) => {
745 // The only legal patterns of type `Box` (outside `std`) are `_` and box
746 // patterns. If we're here we can assume this is a box pattern.
749 let variant = &adt.variant(self.variant_index_for_adt(*adt));
750 Fields::list_variant_nonhidden_fields(pcx.cx, pcx.ty, variant).count()
753 _ => bug!("Unexpected type for `Single` constructor: {:?}", pcx.ty),
755 Slice(slice) => slice.arity(),
763 Or => bug!("The `Or` constructor doesn't have a fixed arity"),
767 /// Some constructors (namely `Wildcard`, `IntRange` and `Slice`) actually stand for a set of actual
768 /// constructors (like variants, integers or fixed-sized slices). When specializing for these
769 /// constructors, we want to be specialising for the actual underlying constructors.
770 /// Naively, we would simply return the list of constructors they correspond to. We instead are
771 /// more clever: if there are constructors that we know will behave the same wrt the current
772 /// matrix, we keep them grouped. For example, all slices of a sufficiently large length
773 /// will either be all useful or all non-useful with a given matrix.
775 /// See the branches for details on how the splitting is done.
777 /// This function may discard some irrelevant constructors if this preserves behavior and
778 /// diagnostics. Eg. for the `_` case, we ignore the constructors already present in the
779 /// matrix, unless all of them are.
780 pub(super) fn split<'a>(
782 pcx: &PatCtxt<'_, '_, 'tcx>,
783 ctors: impl Iterator<Item = &'a Constructor<'tcx>> + Clone,
784 ) -> SmallVec<[Self; 1]>
790 let mut split_wildcard = SplitWildcard::new(pcx);
791 split_wildcard.split(pcx, ctors);
792 split_wildcard.into_ctors(pcx)
794 // Fast-track if the range is trivial. In particular, we don't do the overlapping
796 IntRange(ctor_range) if !ctor_range.is_singleton() => {
797 let mut split_range = SplitIntRange::new(ctor_range.clone());
798 let int_ranges = ctors.filter_map(|ctor| ctor.as_int_range());
799 split_range.split(int_ranges.cloned());
800 split_range.iter().map(IntRange).collect()
802 &Slice(Slice { kind: VarLen(self_prefix, self_suffix), array_len }) => {
803 let mut split_self = SplitVarLenSlice::new(self_prefix, self_suffix, array_len);
804 let slices = ctors.filter_map(|c| c.as_slice()).map(|s| s.kind);
805 split_self.split(slices);
806 split_self.iter().map(Slice).collect()
808 // Any other constructor can be used unchanged.
809 _ => smallvec![self.clone()],
813 /// Returns whether `self` is covered by `other`, i.e. whether `self` is a subset of `other`.
814 /// For the simple cases, this is simply checking for equality. For the "grouped" constructors,
815 /// this checks for inclusion.
816 // We inline because this has a single call site in `Matrix::specialize_constructor`.
818 pub(super) fn is_covered_by<'p>(&self, pcx: &PatCtxt<'_, 'p, 'tcx>, other: &Self) -> bool {
819 // This must be kept in sync with `is_covered_by_any`.
820 match (self, other) {
821 // Wildcards cover anything
822 (_, Wildcard) => true,
823 // The missing ctors are not covered by anything in the matrix except wildcards.
824 (Missing { .. } | Wildcard, _) => false,
826 (Single, Single) => true,
827 (Variant(self_id), Variant(other_id)) => self_id == other_id,
829 (IntRange(self_range), IntRange(other_range)) => self_range.is_covered_by(other_range),
831 FloatRange(self_from, self_to, self_end),
832 FloatRange(other_from, other_to, other_end),
835 compare_const_vals(pcx.cx.tcx, *self_to, *other_to, pcx.cx.param_env),
836 compare_const_vals(pcx.cx.tcx, *self_from, *other_from, pcx.cx.param_env),
838 (Some(to), Some(from)) => {
839 (from == Ordering::Greater || from == Ordering::Equal)
840 && (to == Ordering::Less
841 || (other_end == self_end && to == Ordering::Equal))
846 (Str(self_val), Str(other_val)) => {
847 // FIXME Once valtrees are available we can directly use the bytes
848 // in the `Str` variant of the valtree for the comparison here.
849 self_val == other_val
851 (Slice(self_slice), Slice(other_slice)) => self_slice.is_covered_by(*other_slice),
853 // We are trying to inspect an opaque constant. Thus we skip the row.
854 (Opaque, _) | (_, Opaque) => false,
855 // Only a wildcard pattern can match the special extra constructor.
856 (NonExhaustive, _) => false,
860 "trying to compare incompatible constructors {:?} and {:?}",
867 /// Faster version of `is_covered_by` when applied to many constructors. `used_ctors` is
868 /// assumed to be built from `matrix.head_ctors()` with wildcards filtered out, and `self` is
869 /// assumed to have been split from a wildcard.
870 fn is_covered_by_any<'p>(
872 pcx: &PatCtxt<'_, 'p, 'tcx>,
873 used_ctors: &[Constructor<'tcx>],
875 if used_ctors.is_empty() {
879 // This must be kept in sync with `is_covered_by`.
881 // If `self` is `Single`, `used_ctors` cannot contain anything else than `Single`s.
882 Single => !used_ctors.is_empty(),
883 Variant(vid) => used_ctors.iter().any(|c| matches!(c, Variant(i) if i == vid)),
884 IntRange(range) => used_ctors
886 .filter_map(|c| c.as_int_range())
887 .any(|other| range.is_covered_by(other)),
888 Slice(slice) => used_ctors
890 .filter_map(|c| c.as_slice())
891 .any(|other| slice.is_covered_by(other)),
892 // This constructor is never covered by anything else
893 NonExhaustive => false,
894 Str(..) | FloatRange(..) | Opaque | Missing { .. } | Wildcard | Or => {
895 span_bug!(pcx.span, "found unexpected ctor in all_ctors: {:?}", self)
901 /// A wildcard constructor that we split relative to the constructors in the matrix, as explained
902 /// at the top of the file.
904 /// A constructor that is not present in the matrix rows will only be covered by the rows that have
905 /// wildcards. Thus we can group all of those constructors together; we call them "missing
906 /// constructors". Splitting a wildcard would therefore list all present constructors individually
907 /// (or grouped if they are integers or slices), and then all missing constructors together as a
910 /// However we can go further: since any constructor will match the wildcard rows, and having more
911 /// rows can only reduce the amount of usefulness witnesses, we can skip the present constructors
912 /// and only try the missing ones.
913 /// This will not preserve the whole list of witnesses, but will preserve whether the list is empty
914 /// or not. In fact this is quite natural from the point of view of diagnostics too. This is done
915 /// in `to_ctors`: in some cases we only return `Missing`.
917 pub(super) struct SplitWildcard<'tcx> {
918 /// Constructors seen in the matrix.
919 matrix_ctors: Vec<Constructor<'tcx>>,
920 /// All the constructors for this type
921 all_ctors: SmallVec<[Constructor<'tcx>; 1]>,
924 impl<'tcx> SplitWildcard<'tcx> {
925 pub(super) fn new<'p>(pcx: &PatCtxt<'_, 'p, 'tcx>) -> Self {
926 debug!("SplitWildcard::new({:?})", pcx.ty);
928 let make_range = |start, end| {
930 // `unwrap()` is ok because we know the type is an integer.
931 IntRange::from_range(cx.tcx, start, end, pcx.ty, &RangeEnd::Included).unwrap(),
934 // This determines the set of all possible constructors for the type `pcx.ty`. For numbers,
935 // arrays and slices we use ranges and variable-length slices when appropriate.
937 // If the `exhaustive_patterns` feature is enabled, we make sure to omit constructors that
938 // are statically impossible. E.g., for `Option<!>`, we do not include `Some(_)` in the
939 // returned list of constructors.
940 // Invariant: this is empty if and only if the type is uninhabited (as determined by
941 // `cx.is_uninhabited()`).
942 let all_ctors = match pcx.ty.kind() {
943 ty::Bool => smallvec![make_range(0, 1)],
944 ty::Array(sub_ty, len) if len.try_eval_usize(cx.tcx, cx.param_env).is_some() => {
945 let len = len.eval_usize(cx.tcx, cx.param_env) as usize;
946 if len != 0 && cx.is_uninhabited(*sub_ty) {
949 smallvec![Slice(Slice::new(Some(len), VarLen(0, 0)))]
952 // Treat arrays of a constant but unknown length like slices.
953 ty::Array(sub_ty, _) | ty::Slice(sub_ty) => {
954 let kind = if cx.is_uninhabited(*sub_ty) { FixedLen(0) } else { VarLen(0, 0) };
955 smallvec![Slice(Slice::new(None, kind))]
957 ty::Adt(def, substs) if def.is_enum() => {
958 // If the enum is declared as `#[non_exhaustive]`, we treat it as if it had an
959 // additional "unknown" constructor.
960 // There is no point in enumerating all possible variants, because the user can't
961 // actually match against them all themselves. So we always return only the fictitious
963 // E.g., in an example like:
966 // let err: io::ErrorKind = ...;
968 // io::ErrorKind::NotFound => {},
972 // we don't want to show every possible IO error, but instead have only `_` as the
974 let is_declared_nonexhaustive = cx.is_foreign_non_exhaustive_enum(pcx.ty);
976 let is_exhaustive_pat_feature = cx.tcx.features().exhaustive_patterns;
978 // If `exhaustive_patterns` is disabled and our scrutinee is an empty enum, we treat it
979 // as though it had an "unknown" constructor to avoid exposing its emptiness. The
980 // exception is if the pattern is at the top level, because we want empty matches to be
981 // considered exhaustive.
982 let is_secretly_empty =
983 def.variants().is_empty() && !is_exhaustive_pat_feature && !pcx.is_top_level;
985 let mut ctors: SmallVec<[_; 1]> = def
989 // If `exhaustive_patterns` is enabled, we exclude variants known to be
991 let is_uninhabited = is_exhaustive_pat_feature
992 && v.uninhabited_from(cx.tcx, substs, def.adt_kind(), cx.param_env)
993 .contains(cx.tcx, cx.module);
996 .map(|(idx, _)| Variant(idx))
999 if is_secretly_empty || is_declared_nonexhaustive {
1000 ctors.push(NonExhaustive);
1006 // The valid Unicode Scalar Value ranges.
1007 make_range('\u{0000}' as u128, '\u{D7FF}' as u128),
1008 make_range('\u{E000}' as u128, '\u{10FFFF}' as u128),
1011 ty::Int(_) | ty::Uint(_)
1012 if pcx.ty.is_ptr_sized_integral()
1013 && !cx.tcx.features().precise_pointer_size_matching =>
1015 // `usize`/`isize` are not allowed to be matched exhaustively unless the
1016 // `precise_pointer_size_matching` feature is enabled. So we treat those types like
1017 // `#[non_exhaustive]` enums by returning a special unmatchable constructor.
1018 smallvec![NonExhaustive]
1021 let bits = Integer::from_int_ty(&cx.tcx, ity).size().bits() as u128;
1022 let min = 1u128 << (bits - 1);
1024 smallvec![make_range(min, max)]
1027 let size = Integer::from_uint_ty(&cx.tcx, uty).size();
1028 let max = size.truncate(u128::MAX);
1029 smallvec![make_range(0, max)]
1031 // If `exhaustive_patterns` is disabled and our scrutinee is the never type, we cannot
1032 // expose its emptiness. The exception is if the pattern is at the top level, because we
1033 // want empty matches to be considered exhaustive.
1034 ty::Never if !cx.tcx.features().exhaustive_patterns && !pcx.is_top_level => {
1035 smallvec![NonExhaustive]
1037 ty::Never => smallvec![],
1038 _ if cx.is_uninhabited(pcx.ty) => smallvec![],
1039 ty::Adt(..) | ty::Tuple(..) | ty::Ref(..) => smallvec![Single],
1040 // This type is one for which we cannot list constructors, like `str` or `f64`.
1041 _ => smallvec![NonExhaustive],
1044 SplitWildcard { matrix_ctors: Vec::new(), all_ctors }
1047 /// Pass a set of constructors relative to which to split this one. Don't call twice, it won't
1048 /// do what you want.
1049 pub(super) fn split<'a>(
1051 pcx: &PatCtxt<'_, '_, 'tcx>,
1052 ctors: impl Iterator<Item = &'a Constructor<'tcx>> + Clone,
1056 // Since `all_ctors` never contains wildcards, this won't recurse further.
1058 self.all_ctors.iter().flat_map(|ctor| ctor.split(pcx, ctors.clone())).collect();
1059 self.matrix_ctors = ctors.filter(|c| !c.is_wildcard()).cloned().collect();
1062 /// Whether there are any value constructors for this type that are not present in the matrix.
1063 fn any_missing(&self, pcx: &PatCtxt<'_, '_, 'tcx>) -> bool {
1064 self.iter_missing(pcx).next().is_some()
1067 /// Iterate over the constructors for this type that are not present in the matrix.
1068 pub(super) fn iter_missing<'a, 'p>(
1070 pcx: &'a PatCtxt<'a, 'p, 'tcx>,
1071 ) -> impl Iterator<Item = &'a Constructor<'tcx>> + Captures<'p> {
1072 self.all_ctors.iter().filter(move |ctor| !ctor.is_covered_by_any(pcx, &self.matrix_ctors))
1075 /// Return the set of constructors resulting from splitting the wildcard. As explained at the
1076 /// top of the file, if any constructors are missing we can ignore the present ones.
1077 fn into_ctors(self, pcx: &PatCtxt<'_, '_, 'tcx>) -> SmallVec<[Constructor<'tcx>; 1]> {
1078 if self.any_missing(pcx) {
1079 // Some constructors are missing, thus we can specialize with the special `Missing`
1080 // constructor, which stands for those constructors that are not seen in the matrix,
1081 // and matches the same rows as any of them (namely the wildcard rows). See the top of
1082 // the file for details.
1083 // However, when all constructors are missing we can also specialize with the full
1084 // `Wildcard` constructor. The difference will depend on what we want in diagnostics.
1086 // If some constructors are missing, we typically want to report those constructors,
1089 // enum Direction { N, S, E, W }
1090 // let Direction::N = ...;
1092 // we can report 3 witnesses: `S`, `E`, and `W`.
1094 // However, if the user didn't actually specify a constructor
1095 // in this arm, e.g., in
1097 // let x: (Direction, Direction, bool) = ...;
1098 // let (_, _, false) = x;
1100 // we don't want to show all 16 possible witnesses `(<direction-1>, <direction-2>,
1101 // true)` - we are satisfied with `(_, _, true)`. So if all constructors are missing we
1102 // prefer to report just a wildcard `_`.
1104 // The exception is: if we are at the top-level, for example in an empty match, we
1105 // sometimes prefer reporting the list of constructors instead of just `_`.
1106 let report_when_all_missing = pcx.is_top_level && !IntRange::is_integral(pcx.ty);
1107 let ctor = if !self.matrix_ctors.is_empty() || report_when_all_missing {
1108 if pcx.is_non_exhaustive {
1110 nonexhaustive_enum_missing_real_variants: self
1112 .any(|c| !(c.is_non_exhaustive() || c.is_unstable_variant(pcx))),
1115 Missing { nonexhaustive_enum_missing_real_variants: false }
1120 return smallvec![ctor];
1123 // All the constructors are present in the matrix, so we just go through them all.
1128 /// A value can be decomposed into a constructor applied to some fields. This struct represents
1129 /// those fields, generalized to allow patterns in each field. See also `Constructor`.
1131 /// This is constructed for a constructor using [`Fields::wildcards()`]. The idea is that
1132 /// [`Fields::wildcards()`] constructs a list of fields where all entries are wildcards, and then
1133 /// given a pattern we fill some of the fields with its subpatterns.
1134 /// In the following example `Fields::wildcards` returns `[_, _, _, _]`. Then in
1135 /// `extract_pattern_arguments` we fill some of the entries, and the result is
1136 /// `[Some(0), _, _, _]`.
1137 /// ```compile_fail,E0004
1138 /// # fn foo() -> [Option<u8>; 4] { [None; 4] }
1139 /// let x: [Option<u8>; 4] = foo();
1141 /// [Some(0), ..] => {}
1145 /// Note that the number of fields of a constructor may not match the fields declared in the
1146 /// original struct/variant. This happens if a private or `non_exhaustive` field is uninhabited,
1147 /// because the code mustn't observe that it is uninhabited. In that case that field is not
1148 /// included in `fields`. For that reason, when you have a `mir::Field` you must use
1149 /// `index_with_declared_idx`.
1150 #[derive(Debug, Clone, Copy)]
1151 pub(super) struct Fields<'p, 'tcx> {
1152 fields: &'p [DeconstructedPat<'p, 'tcx>],
1155 impl<'p, 'tcx> Fields<'p, 'tcx> {
1156 fn empty() -> Self {
1157 Fields { fields: &[] }
1160 fn singleton(cx: &MatchCheckCtxt<'p, 'tcx>, field: DeconstructedPat<'p, 'tcx>) -> Self {
1161 let field: &_ = cx.pattern_arena.alloc(field);
1162 Fields { fields: std::slice::from_ref(field) }
1165 pub(super) fn from_iter(
1166 cx: &MatchCheckCtxt<'p, 'tcx>,
1167 fields: impl IntoIterator<Item = DeconstructedPat<'p, 'tcx>>,
1169 let fields: &[_] = cx.pattern_arena.alloc_from_iter(fields);
1173 fn wildcards_from_tys(
1174 cx: &MatchCheckCtxt<'p, 'tcx>,
1175 tys: impl IntoIterator<Item = Ty<'tcx>>,
1177 Fields::from_iter(cx, tys.into_iter().map(DeconstructedPat::wildcard))
1180 // In the cases of either a `#[non_exhaustive]` field list or a non-public field, we hide
1181 // uninhabited fields in order not to reveal the uninhabitedness of the whole variant.
1182 // This lists the fields we keep along with their types.
1183 fn list_variant_nonhidden_fields<'a>(
1184 cx: &'a MatchCheckCtxt<'p, 'tcx>,
1186 variant: &'a VariantDef,
1187 ) -> impl Iterator<Item = (Field, Ty<'tcx>)> + Captures<'a> + Captures<'p> {
1188 let ty::Adt(adt, substs) = ty.kind() else { bug!() };
1189 // Whether we must not match the fields of this variant exhaustively.
1190 let is_non_exhaustive = variant.is_field_list_non_exhaustive() && !adt.did().is_local();
1192 variant.fields.iter().enumerate().filter_map(move |(i, field)| {
1193 let ty = field.ty(cx.tcx, substs);
1194 // `field.ty()` doesn't normalize after substituting.
1195 let ty = cx.tcx.normalize_erasing_regions(cx.param_env, ty);
1196 let is_visible = adt.is_enum() || field.vis.is_accessible_from(cx.module, cx.tcx);
1197 let is_uninhabited = cx.is_uninhabited(ty);
1199 if is_uninhabited && (!is_visible || is_non_exhaustive) {
1202 Some((Field::new(i), ty))
1207 /// Creates a new list of wildcard fields for a given constructor. The result must have a
1208 /// length of `constructor.arity()`.
1209 #[instrument(level = "trace")]
1210 pub(super) fn wildcards(pcx: &PatCtxt<'_, 'p, 'tcx>, constructor: &Constructor<'tcx>) -> Self {
1211 let ret = match constructor {
1212 Single | Variant(_) => match pcx.ty.kind() {
1213 ty::Tuple(fs) => Fields::wildcards_from_tys(pcx.cx, fs.iter()),
1214 ty::Ref(_, rty, _) => Fields::wildcards_from_tys(pcx.cx, once(*rty)),
1215 ty::Adt(adt, substs) => {
1217 // The only legal patterns of type `Box` (outside `std`) are `_` and box
1218 // patterns. If we're here we can assume this is a box pattern.
1219 Fields::wildcards_from_tys(pcx.cx, once(substs.type_at(0)))
1221 let variant = &adt.variant(constructor.variant_index_for_adt(*adt));
1222 let tys = Fields::list_variant_nonhidden_fields(pcx.cx, pcx.ty, variant)
1224 Fields::wildcards_from_tys(pcx.cx, tys)
1227 _ => bug!("Unexpected type for `Single` constructor: {:?}", pcx),
1229 Slice(slice) => match *pcx.ty.kind() {
1230 ty::Slice(ty) | ty::Array(ty, _) => {
1231 let arity = slice.arity();
1232 Fields::wildcards_from_tys(pcx.cx, (0..arity).map(|_| ty))
1234 _ => bug!("bad slice pattern {:?} {:?}", constructor, pcx),
1242 | Wildcard => Fields::empty(),
1244 bug!("called `Fields::wildcards` on an `Or` ctor")
1251 /// Returns the list of patterns.
1252 pub(super) fn iter_patterns<'a>(
1254 ) -> impl Iterator<Item = &'p DeconstructedPat<'p, 'tcx>> + Captures<'a> {
1259 /// Values and patterns can be represented as a constructor applied to some fields. This represents
1260 /// a pattern in this form.
1261 /// This also keeps track of whether the pattern has been found reachable during analysis. For this
1262 /// reason we should be careful not to clone patterns for which we care about that. Use
1263 /// `clone_and_forget_reachability` if you're sure.
1264 pub(crate) struct DeconstructedPat<'p, 'tcx> {
1265 ctor: Constructor<'tcx>,
1266 fields: Fields<'p, 'tcx>,
1269 reachable: Cell<bool>,
1272 impl<'p, 'tcx> DeconstructedPat<'p, 'tcx> {
1273 pub(super) fn wildcard(ty: Ty<'tcx>) -> Self {
1274 Self::new(Wildcard, Fields::empty(), ty, DUMMY_SP)
1278 ctor: Constructor<'tcx>,
1279 fields: Fields<'p, 'tcx>,
1283 DeconstructedPat { ctor, fields, ty, span, reachable: Cell::new(false) }
1286 /// Construct a pattern that matches everything that starts with this constructor.
1287 /// For example, if `ctor` is a `Constructor::Variant` for `Option::Some`, we get the pattern
1289 pub(super) fn wild_from_ctor(pcx: &PatCtxt<'_, 'p, 'tcx>, ctor: Constructor<'tcx>) -> Self {
1290 let fields = Fields::wildcards(pcx, &ctor);
1291 DeconstructedPat::new(ctor, fields, pcx.ty, DUMMY_SP)
1294 /// Clone this value. This method emphasizes that cloning loses reachability information and
1295 /// should be done carefully.
1296 pub(super) fn clone_and_forget_reachability(&self) -> Self {
1297 DeconstructedPat::new(self.ctor.clone(), self.fields, self.ty, self.span)
1300 pub(crate) fn from_pat(cx: &MatchCheckCtxt<'p, 'tcx>, pat: &Pat<'tcx>) -> Self {
1301 let mkpat = |pat| DeconstructedPat::from_pat(cx, pat);
1305 PatKind::AscribeUserType { subpattern, .. } => return mkpat(subpattern),
1306 PatKind::Binding { subpattern: Some(subpat), .. } => return mkpat(subpat),
1307 PatKind::Binding { subpattern: None, .. } | PatKind::Wild => {
1309 fields = Fields::empty();
1311 PatKind::Deref { subpattern } => {
1313 fields = Fields::singleton(cx, mkpat(subpattern));
1315 PatKind::Leaf { subpatterns } | PatKind::Variant { subpatterns, .. } => {
1316 match pat.ty.kind() {
1319 let mut wilds: SmallVec<[_; 2]> =
1320 fs.iter().map(DeconstructedPat::wildcard).collect();
1321 for pat in subpatterns {
1322 wilds[pat.field.index()] = mkpat(&pat.pattern);
1324 fields = Fields::from_iter(cx, wilds);
1326 ty::Adt(adt, substs) if adt.is_box() => {
1327 // The only legal patterns of type `Box` (outside `std`) are `_` and box
1328 // patterns. If we're here we can assume this is a box pattern.
1329 // FIXME(Nadrieril): A `Box` can in theory be matched either with `Box(_,
1330 // _)` or a box pattern. As a hack to avoid an ICE with the former, we
1331 // ignore other fields than the first one. This will trigger an error later
1333 // See https://github.com/rust-lang/rust/issues/82772 ,
1334 // explanation: https://github.com/rust-lang/rust/pull/82789#issuecomment-796921977
1335 // The problem is that we can't know from the type whether we'll match
1336 // normally or through box-patterns. We'll have to figure out a proper
1337 // solution when we introduce generalized deref patterns. Also need to
1338 // prevent mixing of those two options.
1339 let pat = subpatterns.into_iter().find(|pat| pat.field.index() == 0);
1340 let pat = if let Some(pat) = pat {
1343 DeconstructedPat::wildcard(substs.type_at(0))
1346 fields = Fields::singleton(cx, pat);
1348 ty::Adt(adt, _) => {
1349 ctor = match pat.kind {
1350 PatKind::Leaf { .. } => Single,
1351 PatKind::Variant { variant_index, .. } => Variant(variant_index),
1354 let variant = &adt.variant(ctor.variant_index_for_adt(*adt));
1355 // For each field in the variant, we store the relevant index into `self.fields` if any.
1356 let mut field_id_to_id: Vec<Option<usize>> =
1357 (0..variant.fields.len()).map(|_| None).collect();
1358 let tys = Fields::list_variant_nonhidden_fields(cx, pat.ty, variant)
1360 .map(|(i, (field, ty))| {
1361 field_id_to_id[field.index()] = Some(i);
1364 let mut wilds: SmallVec<[_; 2]> =
1365 tys.map(DeconstructedPat::wildcard).collect();
1366 for pat in subpatterns {
1367 if let Some(i) = field_id_to_id[pat.field.index()] {
1368 wilds[i] = mkpat(&pat.pattern);
1371 fields = Fields::from_iter(cx, wilds);
1373 _ => bug!("pattern has unexpected type: pat: {:?}, ty: {:?}", pat, pat.ty),
1376 PatKind::Constant { value } => {
1377 if let Some(int_range) = IntRange::from_constant(cx.tcx, cx.param_env, *value) {
1378 ctor = IntRange(int_range);
1379 fields = Fields::empty();
1381 match pat.ty.kind() {
1383 ctor = FloatRange(*value, *value, RangeEnd::Included);
1384 fields = Fields::empty();
1386 ty::Ref(_, t, _) if t.is_str() => {
1387 // We want a `&str` constant to behave like a `Deref` pattern, to be compatible
1388 // with other `Deref` patterns. This could have been done in `const_to_pat`,
1389 // but that causes issues with the rest of the matching code.
1390 // So here, the constructor for a `"foo"` pattern is `&` (represented by
1391 // `Single`), and has one field. That field has constructor `Str(value)` and no
1393 // Note: `t` is `str`, not `&str`.
1395 DeconstructedPat::new(Str(*value), Fields::empty(), *t, pat.span);
1397 fields = Fields::singleton(cx, subpattern)
1399 // All constants that can be structurally matched have already been expanded
1400 // into the corresponding `Pat`s by `const_to_pat`. Constants that remain are
1404 fields = Fields::empty();
1409 &PatKind::Range(box PatRange { lo, hi, end }) => {
1411 ctor = if let Some(int_range) = IntRange::from_range(
1413 lo.eval_bits(cx.tcx, cx.param_env, lo.ty()),
1414 hi.eval_bits(cx.tcx, cx.param_env, hi.ty()),
1420 FloatRange(lo, hi, end)
1422 fields = Fields::empty();
1424 PatKind::Array { prefix, slice, suffix } | PatKind::Slice { prefix, slice, suffix } => {
1425 let array_len = match pat.ty.kind() {
1426 ty::Array(_, length) => Some(length.eval_usize(cx.tcx, cx.param_env) as usize),
1427 ty::Slice(_) => None,
1428 _ => span_bug!(pat.span, "bad ty {:?} for slice pattern", pat.ty),
1430 let kind = if slice.is_some() {
1431 VarLen(prefix.len(), suffix.len())
1433 FixedLen(prefix.len() + suffix.len())
1435 ctor = Slice(Slice::new(array_len, kind));
1437 Fields::from_iter(cx, prefix.iter().chain(suffix.iter()).map(|p| mkpat(&*p)));
1439 PatKind::Or { .. } => {
1441 let pats = expand_or_pat(pat);
1442 fields = Fields::from_iter(cx, pats.into_iter().map(mkpat));
1445 DeconstructedPat::new(ctor, fields, pat.ty, pat.span)
1448 pub(crate) fn to_pat(&self, cx: &MatchCheckCtxt<'p, 'tcx>) -> Pat<'tcx> {
1449 let is_wildcard = |pat: &Pat<'_>| {
1450 matches!(pat.kind, PatKind::Binding { subpattern: None, .. } | PatKind::Wild)
1452 let mut subpatterns = self.iter_fields().map(|p| Box::new(p.to_pat(cx)));
1453 let kind = match &self.ctor {
1454 Single | Variant(_) => match self.ty.kind() {
1455 ty::Tuple(..) => PatKind::Leaf {
1456 subpatterns: subpatterns
1458 .map(|(i, pattern)| FieldPat { field: Field::new(i), pattern })
1461 ty::Adt(adt_def, _) if adt_def.is_box() => {
1462 // Without `box_patterns`, the only legal pattern of type `Box` is `_` (outside
1463 // of `std`). So this branch is only reachable when the feature is enabled and
1464 // the pattern is a box pattern.
1465 PatKind::Deref { subpattern: subpatterns.next().unwrap() }
1467 ty::Adt(adt_def, substs) => {
1468 let variant_index = self.ctor.variant_index_for_adt(*adt_def);
1469 let variant = &adt_def.variant(variant_index);
1470 let subpatterns = Fields::list_variant_nonhidden_fields(cx, self.ty, variant)
1472 .map(|((field, _ty), pattern)| FieldPat { field, pattern })
1475 if adt_def.is_enum() {
1476 PatKind::Variant { adt_def: *adt_def, substs, variant_index, subpatterns }
1478 PatKind::Leaf { subpatterns }
1481 // Note: given the expansion of `&str` patterns done in `expand_pattern`, we should
1482 // be careful to reconstruct the correct constant pattern here. However a string
1483 // literal pattern will never be reported as a non-exhaustiveness witness, so we
1484 // ignore this issue.
1485 ty::Ref(..) => PatKind::Deref { subpattern: subpatterns.next().unwrap() },
1486 _ => bug!("unexpected ctor for type {:?} {:?}", self.ctor, self.ty),
1490 FixedLen(_) => PatKind::Slice {
1491 prefix: subpatterns.collect(),
1493 suffix: Box::new([]),
1495 VarLen(prefix, _) => {
1496 let mut subpatterns = subpatterns.peekable();
1497 let mut prefix: Vec<_> = subpatterns.by_ref().take(prefix).collect();
1498 if slice.array_len.is_some() {
1499 // Improves diagnostics a bit: if the type is a known-size array, instead
1500 // of reporting `[x, _, .., _, y]`, we prefer to report `[x, .., y]`.
1501 // This is incorrect if the size is not known, since `[_, ..]` captures
1502 // arrays of lengths `>= 1` whereas `[..]` captures any length.
1503 while !prefix.is_empty() && is_wildcard(prefix.last().unwrap()) {
1506 while subpatterns.peek().is_some()
1507 && is_wildcard(subpatterns.peek().unwrap())
1512 let suffix: Box<[_]> = subpatterns.collect();
1513 let wild = Pat::wildcard_from_ty(self.ty);
1515 prefix: prefix.into_boxed_slice(),
1516 slice: Some(Box::new(wild)),
1522 &Str(value) => PatKind::Constant { value },
1523 &FloatRange(lo, hi, end) => PatKind::Range(Box::new(PatRange { lo, hi, end })),
1524 IntRange(range) => return range.to_pat(cx.tcx, self.ty),
1525 Wildcard | NonExhaustive => PatKind::Wild,
1526 Missing { .. } => bug!(
1527 "trying to convert a `Missing` constructor into a `Pat`; this is probably a bug,
1528 `Missing` should have been processed in `apply_constructors`"
1531 bug!("can't convert to pattern: {:?}", self)
1535 Pat { ty: self.ty, span: DUMMY_SP, kind }
1538 pub(super) fn is_or_pat(&self) -> bool {
1539 matches!(self.ctor, Or)
1542 pub(super) fn ctor(&self) -> &Constructor<'tcx> {
1545 pub(super) fn ty(&self) -> Ty<'tcx> {
1548 pub(super) fn span(&self) -> Span {
1552 pub(super) fn iter_fields<'a>(
1554 ) -> impl Iterator<Item = &'p DeconstructedPat<'p, 'tcx>> + Captures<'a> {
1555 self.fields.iter_patterns()
1558 /// Specialize this pattern with a constructor.
1559 /// `other_ctor` can be different from `self.ctor`, but must be covered by it.
1560 pub(super) fn specialize<'a>(
1562 pcx: &PatCtxt<'_, 'p, 'tcx>,
1563 other_ctor: &Constructor<'tcx>,
1564 ) -> SmallVec<[&'p DeconstructedPat<'p, 'tcx>; 2]> {
1565 match (&self.ctor, other_ctor) {
1567 // We return a wildcard for each field of `other_ctor`.
1568 Fields::wildcards(pcx, other_ctor).iter_patterns().collect()
1570 (Slice(self_slice), Slice(other_slice))
1571 if self_slice.arity() != other_slice.arity() =>
1573 // The only tricky case: two slices of different arity. Since `self_slice` covers
1574 // `other_slice`, `self_slice` must be `VarLen`, i.e. of the form
1575 // `[prefix, .., suffix]`. Moreover `other_slice` is guaranteed to have a larger
1576 // arity. So we fill the middle part with enough wildcards to reach the length of
1577 // the new, larger slice.
1578 match self_slice.kind {
1579 FixedLen(_) => bug!("{:?} doesn't cover {:?}", self_slice, other_slice),
1580 VarLen(prefix, suffix) => {
1581 let (ty::Slice(inner_ty) | ty::Array(inner_ty, _)) = *self.ty.kind() else {
1582 bug!("bad slice pattern {:?} {:?}", self.ctor, self.ty);
1584 let prefix = &self.fields.fields[..prefix];
1585 let suffix = &self.fields.fields[self_slice.arity() - suffix..];
1587 pcx.cx.pattern_arena.alloc(DeconstructedPat::wildcard(inner_ty));
1588 let extra_wildcards = other_slice.arity() - self_slice.arity();
1589 let extra_wildcards = (0..extra_wildcards).map(|_| wildcard);
1590 prefix.iter().chain(extra_wildcards).chain(suffix).collect()
1594 _ => self.fields.iter_patterns().collect(),
1598 /// We keep track for each pattern if it was ever reachable during the analysis. This is used
1599 /// with `unreachable_spans` to report unreachable subpatterns arising from or patterns.
1600 pub(super) fn set_reachable(&self) {
1601 self.reachable.set(true)
1603 pub(super) fn is_reachable(&self) -> bool {
1604 self.reachable.get()
1607 /// Report the spans of subpatterns that were not reachable, if any.
1608 pub(super) fn unreachable_spans(&self) -> Vec<Span> {
1609 let mut spans = Vec::new();
1610 self.collect_unreachable_spans(&mut spans);
1614 fn collect_unreachable_spans(&self, spans: &mut Vec<Span>) {
1615 // We don't look at subpatterns if we already reported the whole pattern as unreachable.
1616 if !self.is_reachable() {
1617 spans.push(self.span);
1619 for p in self.iter_fields() {
1620 p.collect_unreachable_spans(spans);
1626 /// This is mostly copied from the `Pat` impl. This is best effort and not good enough for a
1628 impl<'p, 'tcx> fmt::Debug for DeconstructedPat<'p, 'tcx> {
1629 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1630 // Printing lists is a chore.
1631 let mut first = true;
1632 let mut start_or_continue = |s| {
1640 let mut start_or_comma = || start_or_continue(", ");
1643 Single | Variant(_) => match self.ty.kind() {
1644 ty::Adt(def, _) if def.is_box() => {
1645 // Without `box_patterns`, the only legal pattern of type `Box` is `_` (outside
1646 // of `std`). So this branch is only reachable when the feature is enabled and
1647 // the pattern is a box pattern.
1648 let subpattern = self.iter_fields().next().unwrap();
1649 write!(f, "box {:?}", subpattern)
1651 ty::Adt(..) | ty::Tuple(..) => {
1652 let variant = match self.ty.kind() {
1653 ty::Adt(adt, _) => Some(adt.variant(self.ctor.variant_index_for_adt(*adt))),
1654 ty::Tuple(_) => None,
1655 _ => unreachable!(),
1658 if let Some(variant) = variant {
1659 write!(f, "{}", variant.name)?;
1662 // Without `cx`, we can't know which field corresponds to which, so we can't
1663 // get the names of the fields. Instead we just display everything as a tuple
1664 // struct, which should be good enough.
1666 for p in self.iter_fields() {
1667 write!(f, "{}", start_or_comma())?;
1668 write!(f, "{:?}", p)?;
1672 // Note: given the expansion of `&str` patterns done in `expand_pattern`, we should
1673 // be careful to detect strings here. However a string literal pattern will never
1674 // be reported as a non-exhaustiveness witness, so we can ignore this issue.
1675 ty::Ref(_, _, mutbl) => {
1676 let subpattern = self.iter_fields().next().unwrap();
1677 write!(f, "&{}{:?}", mutbl.prefix_str(), subpattern)
1679 _ => write!(f, "_"),
1682 let mut subpatterns = self.fields.iter_patterns();
1686 for p in subpatterns {
1687 write!(f, "{}{:?}", start_or_comma(), p)?;
1690 VarLen(prefix_len, _) => {
1691 for p in subpatterns.by_ref().take(prefix_len) {
1692 write!(f, "{}{:?}", start_or_comma(), p)?;
1694 write!(f, "{}", start_or_comma())?;
1696 for p in subpatterns {
1697 write!(f, "{}{:?}", start_or_comma(), p)?;
1703 &FloatRange(lo, hi, end) => {
1704 write!(f, "{}", lo)?;
1705 write!(f, "{}", end)?;
1708 IntRange(range) => write!(f, "{:?}", range), // Best-effort, will render e.g. `false` as `0..=0`
1709 Wildcard | Missing { .. } | NonExhaustive => write!(f, "_ : {:?}", self.ty),
1711 for pat in self.iter_fields() {
1712 write!(f, "{}{:?}", start_or_continue(" | "), pat)?;
1716 Str(value) => write!(f, "{}", value),
1717 Opaque => write!(f, "<constant pattern>"),