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
.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)),
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(PatRange { lo: lo_const, hi: hi_const, end: RangeEnd::Included }
)
258 Pat { ty, span: DUMMY_SP, kind: Box::new(kind) }
261 /// Lint on likely incorrect range patterns (#63987)
262 pub(super) fn lint_overlapping_range_endpoints
<'a
, 'p
: 'a
, 'tcx
: 'a
>(
264 pcx
: PatCtxt
<'_
, 'p
, 'tcx
>,
265 pats
: impl Iterator
<Item
= &'a DeconstructedPat
<'p
, 'tcx
>>,
269 if self.is_singleton() {
273 if column_count
!= 1 {
274 // FIXME: for now, only check for overlapping ranges on simple range
275 // patterns. Otherwise with the current logic the following is detected
278 // match (0u8, true) {
279 // (0 ..= 125, false) => {}
280 // (125 ..= 255, true) => {}
287 let overlaps
: Vec
<_
> = pats
288 .filter_map(|pat
| Some((pat
.ctor().as_int_range()?
, pat
.span())))
289 .filter(|(range
, _
)| self.suspicious_intersection(range
))
290 .map(|(range
, span
)| (self.intersection(&range
).unwrap(), span
))
293 if !overlaps
.is_empty() {
294 pcx
.cx
.tcx
.struct_span_lint_hir(
295 lint
::builtin
::OVERLAPPING_RANGE_ENDPOINTS
,
299 let mut err
= lint
.build("multiple patterns overlap on their endpoints");
300 for (int_range
, span
) in overlaps
{
304 "this range overlaps on `{}`...",
305 int_range
.to_pat(pcx
.cx
.tcx
, pcx
.ty
)
309 err
.span_label(pcx
.span
, "... with this range");
310 err
.note("you likely meant to write mutually exclusive ranges");
317 /// See `Constructor::is_covered_by`
318 fn is_covered_by(&self, other
: &Self) -> bool
{
319 if self.intersection(other
).is_some() {
320 // Constructor splitting should ensure that all intersections we encounter are actually
322 assert
!(self.is_subrange(other
));
330 /// Note: this is often not what we want: e.g. `false` is converted into the range `0..=0` and
331 /// would be displayed as such. To render properly, convert to a pattern first.
332 impl fmt
::Debug
for IntRange
{
333 fn fmt(&self, f
: &mut fmt
::Formatter
<'_
>) -> fmt
::Result
{
334 let (lo
, hi
) = self.boundaries();
335 let bias
= self.bias
;
336 let (lo
, hi
) = (lo ^ bias
, hi ^ bias
);
337 write
!(f
, "{}", lo
)?
;
338 write
!(f
, "{}", RangeEnd
::Included
)?
;
343 /// Represents a border between 2 integers. Because the intervals spanning borders must be able to
344 /// cover every integer, we need to be able to represent 2^128 + 1 such borders.
345 #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
351 /// A range of integers that is partitioned into disjoint subranges. This does constructor
352 /// splitting for integer ranges as explained at the top of the file.
354 /// This is fed multiple ranges, and returns an output that covers the input, but is split so that
355 /// the only intersections between an output range and a seen range are inclusions. No output range
356 /// straddles the boundary of one of the inputs.
358 /// The following input:
360 /// |-------------------------| // `self`
361 /// |------| |----------| |----|
362 /// |-------| |-------|
364 /// would be iterated over as follows:
366 /// ||---|--||-|---|---|---|--|
368 #[derive(Debug, Clone)]
369 struct SplitIntRange
{
370 /// The range we are splitting
372 /// The borders of ranges we have seen. They are all contained within `range`. This is kept
374 borders
: Vec
<IntBorder
>,
378 fn new(range
: IntRange
) -> Self {
379 SplitIntRange { range, borders: Vec::new() }
383 fn to_borders(r
: IntRange
) -> [IntBorder
; 2] {
385 let (lo
, hi
) = r
.boundaries();
386 let lo
= JustBefore(lo
);
387 let hi
= match hi
.checked_add(1) {
388 Some(m
) => JustBefore(m
),
394 /// Add ranges relative to which we split.
395 fn split(&mut self, ranges
: impl Iterator
<Item
= IntRange
>) {
396 let this_range
= &self.range
;
397 let included_ranges
= ranges
.filter_map(|r
| this_range
.intersection(&r
));
398 let included_borders
= included_ranges
.flat_map(|r
| {
399 let borders
= Self::to_borders(r
);
400 once(borders
[0]).chain(once(borders
[1]))
402 self.borders
.extend(included_borders
);
403 self.borders
.sort_unstable();
406 /// Iterate over the contained ranges.
407 fn iter
<'a
>(&'a
self) -> impl Iterator
<Item
= IntRange
> + Captures
<'a
> {
410 let self_range
= Self::to_borders(self.range
.clone());
411 // Start with the start of the range.
412 let mut prev_border
= self_range
[0];
416 // End with the end of the range.
417 .chain(once(self_range
[1]))
418 // List pairs of adjacent borders.
420 let ret
= (prev_border
, border
);
421 prev_border
= border
;
425 .filter(|(prev_border
, border
)| prev_border
!= border
)
426 // Finally, convert to ranges.
427 .map(move |(prev_border
, border
)| {
428 let range
= match (prev_border
, border
) {
429 (JustBefore(n
), JustBefore(m
)) if n
< m
=> n
..=(m
- 1),
430 (JustBefore(n
), AfterMax
) => n
..=u128
::MAX
,
431 _
=> unreachable
!(), // Ruled out by the sorting and filtering we did
433 IntRange { range, bias: self.range.bias }
438 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
440 /// Patterns of length `n` (`[x, y]`).
442 /// Patterns using the `..` notation (`[x, .., y]`).
443 /// Captures any array constructor of `length >= i + j`.
444 /// In the case where `array_len` is `Some(_)`,
445 /// this indicates that we only care about the first `i` and the last `j` values of the array,
446 /// and everything in between is a wildcard `_`.
447 VarLen(usize, usize),
451 fn arity(self) -> usize {
453 FixedLen(length
) => length
,
454 VarLen(prefix
, suffix
) => prefix
+ suffix
,
458 /// Whether this pattern includes patterns of length `other_len`.
459 fn covers_length(self, other_len
: usize) -> bool
{
461 FixedLen(len
) => len
== other_len
,
462 VarLen(prefix
, suffix
) => prefix
+ suffix
<= other_len
,
467 /// A constructor for array and slice patterns.
468 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
469 pub(super) struct Slice
{
470 /// `None` if the matched value is a slice, `Some(n)` if it is an array of size `n`.
471 array_len
: Option
<usize>,
472 /// The kind of pattern it is: fixed-length `[x, y]` or variable length `[x, .., y]`.
477 fn new(array_len
: Option
<usize>, kind
: SliceKind
) -> Self {
478 let kind
= match (array_len
, kind
) {
479 // If the middle `..` is empty, we effectively have a fixed-length pattern.
480 (Some(len
), VarLen(prefix
, suffix
)) if prefix
+ suffix
>= len
=> FixedLen(len
),
483 Slice { array_len, kind }
486 fn arity(self) -> usize {
490 /// See `Constructor::is_covered_by`
491 fn is_covered_by(self, other
: Self) -> bool
{
492 other
.kind
.covers_length(self.arity())
496 /// This computes constructor splitting for variable-length slices, as explained at the top of the
499 /// A slice pattern `[x, .., y]` behaves like the infinite or-pattern `[x, y] | [x, _, y] | [x, _,
500 /// _, y] | ...`. The corresponding value constructors are fixed-length array constructors above a
501 /// given minimum length. We obviously can't list this infinitude of constructors. Thankfully,
502 /// it turns out that for each finite set of slice patterns, all sufficiently large array lengths
505 /// Let's look at an example, where we are trying to split the last pattern:
507 /// # fn foo(x: &[bool]) {
509 /// [true, true, ..] => {}
510 /// [.., false, false] => {}
515 /// Here are the results of specialization for the first few lengths:
517 /// # fn foo(x: &[bool]) { match x {
523 /// [true, true] => {}
524 /// [false, false] => {}
527 /// [true, true, _ ] => {}
528 /// [_, false, false] => {}
531 /// [true, true, _, _ ] => {}
532 /// [_, _, false, false] => {}
533 /// [_, _, _, _ ] => {}
535 /// [true, true, _, _, _ ] => {}
536 /// [_, _, _, false, false] => {}
537 /// [_, _, _, _, _ ] => {}
542 /// If we went above length 5, we would simply be inserting more columns full of wildcards in the
543 /// middle. This means that the set of witnesses for length `l >= 5` if equivalent to the set for
544 /// any other `l' >= 5`: simply add or remove wildcards in the middle to convert between them.
546 /// This applies to any set of slice patterns: there will be a length `L` above which all lengths
547 /// behave the same. This is exactly what we need for constructor splitting. Therefore a
548 /// variable-length slice can be split into a variable-length slice of minimal length `L`, and many
549 /// fixed-length slices of lengths `< L`.
551 /// For each variable-length pattern `p` with a prefix of length `plâ‚š` and suffix of length `slâ‚š`,
552 /// only the first `plâ‚š` and the last `slâ‚š` elements are examined. Therefore, as long as `L` is
553 /// positive (to avoid concerns about empty types), all elements after the maximum prefix length
554 /// and before the maximum suffix length are not examined by any variable-length pattern, and
555 /// therefore can be added/removed without affecting them - creating equivalent patterns from any
556 /// sufficiently-large length.
558 /// Of course, if fixed-length patterns exist, we must be sure that our length is large enough to
559 /// miss them all, so we can pick `L = max(max(FIXED_LEN)+1, max(PREFIX_LEN) + max(SUFFIX_LEN))`
561 /// `max_slice` below will be made to have arity `L`.
563 struct SplitVarLenSlice
{
564 /// If the type is an array, this is its size.
565 array_len
: Option
<usize>,
566 /// The arity of the input slice.
568 /// The smallest slice bigger than any slice seen. `max_slice.arity()` is the length `L`
570 max_slice
: SliceKind
,
573 impl SplitVarLenSlice
{
574 fn new(prefix
: usize, suffix
: usize, array_len
: Option
<usize>) -> Self {
575 SplitVarLenSlice { array_len, arity: prefix + suffix, max_slice: VarLen(prefix, suffix) }
578 /// Pass a set of slices relative to which to split this one.
579 fn split(&mut self, slices
: impl Iterator
<Item
= SliceKind
>) {
580 let VarLen(max_prefix_len
, max_suffix_len
) = &mut self.max_slice
else {
584 // We grow `self.max_slice` to be larger than all slices encountered, as described above.
585 // For diagnostics, we keep the prefix and suffix lengths separate, but grow them so that
586 // `L = max_prefix_len + max_suffix_len`.
587 let mut max_fixed_len
= 0;
588 for slice
in slices
{
591 max_fixed_len
= cmp
::max(max_fixed_len
, len
);
593 VarLen(prefix
, suffix
) => {
594 *max_prefix_len
= cmp
::max(*max_prefix_len
, prefix
);
595 *max_suffix_len
= cmp
::max(*max_suffix_len
, suffix
);
599 // We want `L = max(L, max_fixed_len + 1)`, modulo the fact that we keep prefix and
601 if max_fixed_len
+ 1 >= *max_prefix_len
+ *max_suffix_len
{
602 // The subtraction can't overflow thanks to the above check.
603 // The new `max_prefix_len` is larger than its previous value.
604 *max_prefix_len
= max_fixed_len
+ 1 - *max_suffix_len
;
607 // We cap the arity of `max_slice` at the array size.
608 match self.array_len
{
609 Some(len
) if self.max_slice
.arity() >= len
=> self.max_slice
= FixedLen(len
),
614 /// Iterate over the partition of this slice.
615 fn iter
<'a
>(&'a
self) -> impl Iterator
<Item
= Slice
> + Captures
<'a
> {
616 let smaller_lengths
= match self.array_len
{
617 // The only admissible fixed-length slice is one of the array size. Whether `max_slice`
618 // is fixed-length or variable-length, it will be the only relevant slice to output
620 Some(_
) => (0..0), // empty range
621 // We cover all arities in the range `(self.arity..infinity)`. We split that range into
622 // two: lengths smaller than `max_slice.arity()` are treated independently as
623 // fixed-lengths slices, and lengths above are captured by `max_slice`.
624 None
=> self.arity
..self.max_slice
.arity(),
628 .chain(once(self.max_slice
))
629 .map(move |kind
| Slice
::new(self.array_len
, kind
))
633 /// A value can be decomposed into a constructor applied to some fields. This struct represents
634 /// the constructor. See also `Fields`.
636 /// `pat_constructor` retrieves the constructor corresponding to a pattern.
637 /// `specialize_constructor` returns the list of fields corresponding to a pattern, given a
638 /// constructor. `Constructor::apply` reconstructs the pattern from a pair of `Constructor` and
640 #[derive(Clone, Debug, PartialEq)]
641 pub(super) enum Constructor
<'tcx
> {
642 /// The constructor for patterns that have a single constructor, like tuples, struct patterns
643 /// and fixed-length arrays.
647 /// Ranges of integer literal values (`2`, `2..=5` or `2..5`).
649 /// Ranges of floating-point literal values (`2.0..=5.2`).
650 FloatRange(mir
::ConstantKind
<'tcx
>, mir
::ConstantKind
<'tcx
>, RangeEnd
),
651 /// String literals. Strings are not quite the same as `&[u8]` so we treat them separately.
652 Str(mir
::ConstantKind
<'tcx
>),
653 /// Array and slice patterns.
655 /// Constants that must not be matched structurally. They are treated as black
656 /// boxes for the purposes of exhaustiveness: we must not inspect them, and they
657 /// don't count towards making a match exhaustive.
659 /// Fake extra constructor for enums that aren't allowed to be matched exhaustively. Also used
660 /// for those types for which we cannot list constructors explicitly, like `f64` and `str`.
662 /// Stands for constructors that are not seen in the matrix, as explained in the documentation
663 /// for [`SplitWildcard`]. The carried `bool` is used for the `non_exhaustive_omitted_patterns`
665 Missing { nonexhaustive_enum_missing_real_variants: bool }
,
666 /// Wildcard pattern.
672 impl<'tcx
> Constructor
<'tcx
> {
673 pub(super) fn is_wildcard(&self) -> bool
{
674 matches
!(self, Wildcard
)
677 pub(super) fn is_non_exhaustive(&self) -> bool
{
678 matches
!(self, NonExhaustive
)
681 fn as_int_range(&self) -> Option
<&IntRange
> {
683 IntRange(range
) => Some(range
),
688 fn as_slice(&self) -> Option
<Slice
> {
690 Slice(slice
) => Some(*slice
),
695 /// Checks if the `Constructor` is a variant and `TyCtxt::eval_stability` returns
696 /// `EvalResult::Deny { .. }`.
698 /// This means that the variant has a stdlib unstable feature marking it.
699 pub(super) fn is_unstable_variant(&self, pcx
: PatCtxt
<'_
, '_
, 'tcx
>) -> bool
{
700 if let Constructor
::Variant(idx
) = self && let ty
::Adt(adt
, _
) = pcx
.ty
.kind() {
701 let variant_def_id
= adt
.variant(*idx
).def_id
;
702 // Filter variants that depend on a disabled unstable feature.
704 pcx
.cx
.tcx
.eval_stability(variant_def_id
, None
, DUMMY_SP
, None
),
705 EvalResult
::Deny { .. }
711 /// Checks if the `Constructor` is a `Constructor::Variant` with a `#[doc(hidden)]`
712 /// attribute from a type not local to the current crate.
713 pub(super) fn is_doc_hidden_variant(&self, pcx
: PatCtxt
<'_
, '_
, 'tcx
>) -> bool
{
714 if let Constructor
::Variant(idx
) = self && let ty
::Adt(adt
, _
) = pcx
.ty
.kind() {
715 let variant_def_id
= adt
.variants()[*idx
].def_id
;
716 return pcx
.cx
.tcx
.is_doc_hidden(variant_def_id
) && !variant_def_id
.is_local();
721 fn variant_index_for_adt(&self, adt
: ty
::AdtDef
<'tcx
>) -> VariantIdx
{
725 assert
!(!adt
.is_enum());
728 _
=> bug
!("bad constructor {:?} for adt {:?}", self, adt
),
732 /// The number of fields for this constructor. This must be kept in sync with
733 /// `Fields::wildcards`.
734 pub(super) fn arity(&self, pcx
: PatCtxt
<'_
, '_
, 'tcx
>) -> usize {
736 Single
| Variant(_
) => match pcx
.ty
.kind() {
737 ty
::Tuple(fs
) => fs
.len(),
739 ty
::Adt(adt
, ..) => {
741 // The only legal patterns of type `Box` (outside `std`) are `_` and box
742 // patterns. If we're here we can assume this is a box pattern.
745 let variant
= &adt
.variant(self.variant_index_for_adt(*adt
));
746 Fields
::list_variant_nonhidden_fields(pcx
.cx
, pcx
.ty
, variant
).count()
749 _
=> bug
!("Unexpected type for `Single` constructor: {:?}", pcx
.ty
),
751 Slice(slice
) => slice
.arity(),
759 Or
=> bug
!("The `Or` constructor doesn't have a fixed arity"),
763 /// Some constructors (namely `Wildcard`, `IntRange` and `Slice`) actually stand for a set of actual
764 /// constructors (like variants, integers or fixed-sized slices). When specializing for these
765 /// constructors, we want to be specialising for the actual underlying constructors.
766 /// Naively, we would simply return the list of constructors they correspond to. We instead are
767 /// more clever: if there are constructors that we know will behave the same wrt the current
768 /// matrix, we keep them grouped. For example, all slices of a sufficiently large length
769 /// will either be all useful or all non-useful with a given matrix.
771 /// See the branches for details on how the splitting is done.
773 /// This function may discard some irrelevant constructors if this preserves behavior and
774 /// diagnostics. Eg. for the `_` case, we ignore the constructors already present in the
775 /// matrix, unless all of them are.
776 pub(super) fn split
<'a
>(
778 pcx
: PatCtxt
<'_
, '_
, 'tcx
>,
779 ctors
: impl Iterator
<Item
= &'a Constructor
<'tcx
>> + Clone
,
780 ) -> SmallVec
<[Self; 1]>
786 let mut split_wildcard
= SplitWildcard
::new(pcx
);
787 split_wildcard
.split(pcx
, ctors
);
788 split_wildcard
.into_ctors(pcx
)
790 // Fast-track if the range is trivial. In particular, we don't do the overlapping
792 IntRange(ctor_range
) if !ctor_range
.is_singleton() => {
793 let mut split_range
= SplitIntRange
::new(ctor_range
.clone());
794 let int_ranges
= ctors
.filter_map(|ctor
| ctor
.as_int_range());
795 split_range
.split(int_ranges
.cloned());
796 split_range
.iter().map(IntRange
).collect()
798 &Slice(Slice { kind: VarLen(self_prefix, self_suffix), array_len }
) => {
799 let mut split_self
= SplitVarLenSlice
::new(self_prefix
, self_suffix
, array_len
);
800 let slices
= ctors
.filter_map(|c
| c
.as_slice()).map(|s
| s
.kind
);
801 split_self
.split(slices
);
802 split_self
.iter().map(Slice
).collect()
804 // Any other constructor can be used unchanged.
805 _
=> smallvec
![self.clone()],
809 /// Returns whether `self` is covered by `other`, i.e. whether `self` is a subset of `other`.
810 /// For the simple cases, this is simply checking for equality. For the "grouped" constructors,
811 /// this checks for inclusion.
812 // We inline because this has a single call site in `Matrix::specialize_constructor`.
814 pub(super) fn is_covered_by
<'p
>(&self, pcx
: PatCtxt
<'_
, 'p
, 'tcx
>, other
: &Self) -> bool
{
815 // This must be kept in sync with `is_covered_by_any`.
816 match (self, other
) {
817 // Wildcards cover anything
818 (_
, Wildcard
) => true,
819 // The missing ctors are not covered by anything in the matrix except wildcards.
820 (Missing { .. }
| Wildcard
, _
) => false,
822 (Single
, Single
) => true,
823 (Variant(self_id
), Variant(other_id
)) => self_id
== other_id
,
825 (IntRange(self_range
), IntRange(other_range
)) => self_range
.is_covered_by(other_range
),
827 FloatRange(self_from
, self_to
, self_end
),
828 FloatRange(other_from
, other_to
, other_end
),
831 compare_const_vals(pcx
.cx
.tcx
, *self_to
, *other_to
, pcx
.cx
.param_env
),
832 compare_const_vals(pcx
.cx
.tcx
, *self_from
, *other_from
, pcx
.cx
.param_env
),
834 (Some(to
), Some(from
)) => {
835 (from
== Ordering
::Greater
|| from
== Ordering
::Equal
)
836 && (to
== Ordering
::Less
837 || (other_end
== self_end
&& to
== Ordering
::Equal
))
842 (Str(self_val
), Str(other_val
)) => {
843 // FIXME Once valtrees are available we can directly use the bytes
844 // in the `Str` variant of the valtree for the comparison here.
845 self_val
== other_val
847 (Slice(self_slice
), Slice(other_slice
)) => self_slice
.is_covered_by(*other_slice
),
849 // We are trying to inspect an opaque constant. Thus we skip the row.
850 (Opaque
, _
) | (_
, Opaque
) => false,
851 // Only a wildcard pattern can match the special extra constructor.
852 (NonExhaustive
, _
) => false,
856 "trying to compare incompatible constructors {:?} and {:?}",
863 /// Faster version of `is_covered_by` when applied to many constructors. `used_ctors` is
864 /// assumed to be built from `matrix.head_ctors()` with wildcards filtered out, and `self` is
865 /// assumed to have been split from a wildcard.
866 fn is_covered_by_any
<'p
>(
868 pcx
: PatCtxt
<'_
, 'p
, 'tcx
>,
869 used_ctors
: &[Constructor
<'tcx
>],
871 if used_ctors
.is_empty() {
875 // This must be kept in sync with `is_covered_by`.
877 // If `self` is `Single`, `used_ctors` cannot contain anything else than `Single`s.
878 Single
=> !used_ctors
.is_empty(),
879 Variant(vid
) => used_ctors
.iter().any(|c
| matches
!(c
, Variant(i
) if i
== vid
)),
880 IntRange(range
) => used_ctors
882 .filter_map(|c
| c
.as_int_range())
883 .any(|other
| range
.is_covered_by(other
)),
884 Slice(slice
) => used_ctors
886 .filter_map(|c
| c
.as_slice())
887 .any(|other
| slice
.is_covered_by(other
)),
888 // This constructor is never covered by anything else
889 NonExhaustive
=> false,
890 Str(..) | FloatRange(..) | Opaque
| Missing { .. }
| Wildcard
| Or
=> {
891 span_bug
!(pcx
.span
, "found unexpected ctor in all_ctors: {:?}", self)
897 /// A wildcard constructor that we split relative to the constructors in the matrix, as explained
898 /// at the top of the file.
900 /// A constructor that is not present in the matrix rows will only be covered by the rows that have
901 /// wildcards. Thus we can group all of those constructors together; we call them "missing
902 /// constructors". Splitting a wildcard would therefore list all present constructors individually
903 /// (or grouped if they are integers or slices), and then all missing constructors together as a
906 /// However we can go further: since any constructor will match the wildcard rows, and having more
907 /// rows can only reduce the amount of usefulness witnesses, we can skip the present constructors
908 /// and only try the missing ones.
909 /// This will not preserve the whole list of witnesses, but will preserve whether the list is empty
910 /// or not. In fact this is quite natural from the point of view of diagnostics too. This is done
911 /// in `to_ctors`: in some cases we only return `Missing`.
913 pub(super) struct SplitWildcard
<'tcx
> {
914 /// Constructors seen in the matrix.
915 matrix_ctors
: Vec
<Constructor
<'tcx
>>,
916 /// All the constructors for this type
917 all_ctors
: SmallVec
<[Constructor
<'tcx
>; 1]>,
920 impl<'tcx
> SplitWildcard
<'tcx
> {
921 pub(super) fn new
<'p
>(pcx
: PatCtxt
<'_
, 'p
, 'tcx
>) -> Self {
922 debug
!("SplitWildcard::new({:?})", pcx
.ty
);
924 let make_range
= |start
, end
| {
926 // `unwrap()` is ok because we know the type is an integer.
927 IntRange
::from_range(cx
.tcx
, start
, end
, pcx
.ty
, &RangeEnd
::Included
).unwrap(),
930 // This determines the set of all possible constructors for the type `pcx.ty`. For numbers,
931 // arrays and slices we use ranges and variable-length slices when appropriate.
933 // If the `exhaustive_patterns` feature is enabled, we make sure to omit constructors that
934 // are statically impossible. E.g., for `Option<!>`, we do not include `Some(_)` in the
935 // returned list of constructors.
936 // Invariant: this is empty if and only if the type is uninhabited (as determined by
937 // `cx.is_uninhabited()`).
938 let all_ctors
= match pcx
.ty
.kind() {
939 ty
::Bool
=> smallvec
![make_range(0, 1)],
940 ty
::Array(sub_ty
, len
) if len
.try_eval_usize(cx
.tcx
, cx
.param_env
).is_some() => {
941 let len
= len
.eval_usize(cx
.tcx
, cx
.param_env
) as usize;
942 if len
!= 0 && cx
.is_uninhabited(*sub_ty
) {
945 smallvec
![Slice(Slice
::new(Some(len
), VarLen(0, 0)))]
948 // Treat arrays of a constant but unknown length like slices.
949 ty
::Array(sub_ty
, _
) | ty
::Slice(sub_ty
) => {
950 let kind
= if cx
.is_uninhabited(*sub_ty
) { FixedLen(0) }
else { VarLen(0, 0) }
;
951 smallvec
![Slice(Slice
::new(None
, kind
))]
953 ty
::Adt(def
, substs
) if def
.is_enum() => {
954 // If the enum is declared as `#[non_exhaustive]`, we treat it as if it had an
955 // additional "unknown" constructor.
956 // There is no point in enumerating all possible variants, because the user can't
957 // actually match against them all themselves. So we always return only the fictitious
959 // E.g., in an example like:
962 // let err: io::ErrorKind = ...;
964 // io::ErrorKind::NotFound => {},
968 // we don't want to show every possible IO error, but instead have only `_` as the
970 let is_declared_nonexhaustive
= cx
.is_foreign_non_exhaustive_enum(pcx
.ty
);
972 let is_exhaustive_pat_feature
= cx
.tcx
.features().exhaustive_patterns
;
974 // If `exhaustive_patterns` is disabled and our scrutinee is an empty enum, we treat it
975 // as though it had an "unknown" constructor to avoid exposing its emptiness. The
976 // exception is if the pattern is at the top level, because we want empty matches to be
977 // considered exhaustive.
978 let is_secretly_empty
=
979 def
.variants().is_empty() && !is_exhaustive_pat_feature
&& !pcx
.is_top_level
;
981 let mut ctors
: SmallVec
<[_
; 1]> = def
985 // If `exhaustive_patterns` is enabled, we exclude variants known to be
987 let is_uninhabited
= is_exhaustive_pat_feature
988 && v
.uninhabited_from(cx
.tcx
, substs
, def
.adt_kind(), cx
.param_env
)
989 .contains(cx
.tcx
, cx
.module
);
992 .map(|(idx
, _
)| Variant(idx
))
995 if is_secretly_empty
|| is_declared_nonexhaustive
{
996 ctors
.push(NonExhaustive
);
1002 // The valid Unicode Scalar Value ranges.
1003 make_range('
\u{0000}'
as u128
, '
\u{D7FF}'
as u128
),
1004 make_range('
\u{E000}'
as u128
, '
\u{10FFFF}'
as u128
),
1007 ty
::Int(_
) | ty
::Uint(_
)
1008 if pcx
.ty
.is_ptr_sized_integral()
1009 && !cx
.tcx
.features().precise_pointer_size_matching
=>
1011 // `usize`/`isize` are not allowed to be matched exhaustively unless the
1012 // `precise_pointer_size_matching` feature is enabled. So we treat those types like
1013 // `#[non_exhaustive]` enums by returning a special unmatchable constructor.
1014 smallvec
![NonExhaustive
]
1017 let bits
= Integer
::from_int_ty(&cx
.tcx
, ity
).size().bits() as u128
;
1018 let min
= 1u128 << (bits
- 1);
1020 smallvec
![make_range(min
, max
)]
1023 let size
= Integer
::from_uint_ty(&cx
.tcx
, uty
).size();
1024 let max
= size
.truncate(u128
::MAX
);
1025 smallvec
![make_range(0, max
)]
1027 // If `exhaustive_patterns` is disabled and our scrutinee is the never type, we cannot
1028 // expose its emptiness. The exception is if the pattern is at the top level, because we
1029 // want empty matches to be considered exhaustive.
1030 ty
::Never
if !cx
.tcx
.features().exhaustive_patterns
&& !pcx
.is_top_level
=> {
1031 smallvec
![NonExhaustive
]
1033 ty
::Never
=> smallvec
![],
1034 _
if cx
.is_uninhabited(pcx
.ty
) => smallvec
![],
1035 ty
::Adt(..) | ty
::Tuple(..) | ty
::Ref(..) => smallvec
![Single
],
1036 // This type is one for which we cannot list constructors, like `str` or `f64`.
1037 _
=> smallvec
![NonExhaustive
],
1040 SplitWildcard { matrix_ctors: Vec::new(), all_ctors }
1043 /// Pass a set of constructors relative to which to split this one. Don't call twice, it won't
1044 /// do what you want.
1045 pub(super) fn split
<'a
>(
1047 pcx
: PatCtxt
<'_
, '_
, 'tcx
>,
1048 ctors
: impl Iterator
<Item
= &'a Constructor
<'tcx
>> + Clone
,
1052 // Since `all_ctors` never contains wildcards, this won't recurse further.
1054 self.all_ctors
.iter().flat_map(|ctor
| ctor
.split(pcx
, ctors
.clone())).collect();
1055 self.matrix_ctors
= ctors
.filter(|c
| !c
.is_wildcard()).cloned().collect();
1058 /// Whether there are any value constructors for this type that are not present in the matrix.
1059 fn any_missing(&self, pcx
: PatCtxt
<'_
, '_
, 'tcx
>) -> bool
{
1060 self.iter_missing(pcx
).next().is_some()
1063 /// Iterate over the constructors for this type that are not present in the matrix.
1064 pub(super) fn iter_missing
<'a
, 'p
>(
1066 pcx
: PatCtxt
<'a
, 'p
, 'tcx
>,
1067 ) -> impl Iterator
<Item
= &'a Constructor
<'tcx
>> + Captures
<'p
> {
1068 self.all_ctors
.iter().filter(move |ctor
| !ctor
.is_covered_by_any(pcx
, &self.matrix_ctors
))
1071 /// Return the set of constructors resulting from splitting the wildcard. As explained at the
1072 /// top of the file, if any constructors are missing we can ignore the present ones.
1073 fn into_ctors(self, pcx
: PatCtxt
<'_
, '_
, 'tcx
>) -> SmallVec
<[Constructor
<'tcx
>; 1]> {
1074 if self.any_missing(pcx
) {
1075 // Some constructors are missing, thus we can specialize with the special `Missing`
1076 // constructor, which stands for those constructors that are not seen in the matrix,
1077 // and matches the same rows as any of them (namely the wildcard rows). See the top of
1078 // the file for details.
1079 // However, when all constructors are missing we can also specialize with the full
1080 // `Wildcard` constructor. The difference will depend on what we want in diagnostics.
1082 // If some constructors are missing, we typically want to report those constructors,
1085 // enum Direction { N, S, E, W }
1086 // let Direction::N = ...;
1088 // we can report 3 witnesses: `S`, `E`, and `W`.
1090 // However, if the user didn't actually specify a constructor
1091 // in this arm, e.g., in
1093 // let x: (Direction, Direction, bool) = ...;
1094 // let (_, _, false) = x;
1096 // we don't want to show all 16 possible witnesses `(<direction-1>, <direction-2>,
1097 // true)` - we are satisfied with `(_, _, true)`. So if all constructors are missing we
1098 // prefer to report just a wildcard `_`.
1100 // The exception is: if we are at the top-level, for example in an empty match, we
1101 // sometimes prefer reporting the list of constructors instead of just `_`.
1102 let report_when_all_missing
= pcx
.is_top_level
&& !IntRange
::is_integral(pcx
.ty
);
1103 let ctor
= if !self.matrix_ctors
.is_empty() || report_when_all_missing
{
1104 if pcx
.is_non_exhaustive
{
1106 nonexhaustive_enum_missing_real_variants
: self
1108 .any(|c
| !(c
.is_non_exhaustive() || c
.is_unstable_variant(pcx
))),
1111 Missing { nonexhaustive_enum_missing_real_variants: false }
1116 return smallvec
![ctor
];
1119 // All the constructors are present in the matrix, so we just go through them all.
1124 /// A value can be decomposed into a constructor applied to some fields. This struct represents
1125 /// those fields, generalized to allow patterns in each field. See also `Constructor`.
1127 /// This is constructed for a constructor using [`Fields::wildcards()`]. The idea is that
1128 /// [`Fields::wildcards()`] constructs a list of fields where all entries are wildcards, and then
1129 /// given a pattern we fill some of the fields with its subpatterns.
1130 /// In the following example `Fields::wildcards` returns `[_, _, _, _]`. Then in
1131 /// `extract_pattern_arguments` we fill some of the entries, and the result is
1132 /// `[Some(0), _, _, _]`.
1133 /// ```compile_fail,E0004
1134 /// # fn foo() -> [Option<u8>; 4] { [None; 4] }
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
.variant(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
.variant(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_constant(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
.variant(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: *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
, _
) => Some(adt
.variant(self.ctor
.variant_index_for_adt(*adt
))),
1648 ty
::Tuple(_
) => None
,
1649 _
=> unreachable
!(),
1652 if let Some(variant
) = variant
{
1653 write
!(f
, "{}", variant
.name
)?
;
1656 // Without `cx`, we can't know which field corresponds to which, so we can't
1657 // get the names of the fields. Instead we just display everything as a tuple
1658 // struct, which should be good enough.
1660 for p
in self.iter_fields() {
1661 write
!(f
, "{}", start_or_comma())?
;
1662 write
!(f
, "{:?}", p
)?
;
1666 // Note: given the expansion of `&str` patterns done in `expand_pattern`, we should
1667 // be careful to detect strings here. However a string literal pattern will never
1668 // be reported as a non-exhaustiveness witness, so we can ignore this issue.
1669 ty
::Ref(_
, _
, mutbl
) => {
1670 let subpattern
= self.iter_fields().next().unwrap();
1671 write
!(f
, "&{}{:?}", mutbl
.prefix_str(), subpattern
)
1673 _
=> write
!(f
, "_"),
1676 let mut subpatterns
= self.fields
.iter_patterns();
1680 for p
in subpatterns
{
1681 write
!(f
, "{}{:?}", start_or_comma(), p
)?
;
1684 VarLen(prefix_len
, _
) => {
1685 for p
in subpatterns
.by_ref().take(prefix_len
) {
1686 write
!(f
, "{}{:?}", start_or_comma(), p
)?
;
1688 write
!(f
, "{}", start_or_comma())?
;
1690 for p
in subpatterns
{
1691 write
!(f
, "{}{:?}", start_or_comma(), p
)?
;
1697 &FloatRange(lo
, hi
, end
) => {
1698 write
!(f
, "{}", lo
)?
;
1699 write
!(f
, "{}", end
)?
;
1702 IntRange(range
) => write
!(f
, "{:?}", range
), // Best-effort, will render e.g. `false` as `0..=0`
1703 Wildcard
| Missing { .. }
| NonExhaustive
=> write
!(f
, "_ : {:?}", self.ty
),
1705 for pat
in self.iter_fields() {
1706 write
!(f
, "{}{:?}", start_or_continue(" | "), pat
)?
;
1710 Str(value
) => write
!(f
, "{}", value
),
1711 Opaque
=> write
!(f
, "<constant pattern>"),