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android / toolchain / rustc / cd1aefd586783f162dd848e314bd6991a5ffe033 / . / compiler / rustc_mir_build / src / thir / pattern / deconstruct_pat.rs
blob: 6a77146138bb582aa2df5cf59614c56598b379ab [file] [log] [blame]
//! [`super::usefulness`] explains most of what is happening in this file. As explained there,
//! values and patterns are made from constructors applied to fields. This file defines a
//! `Constructor` enum, a `Fields` struct, and various operations to manipulate them and convert
//! them from/to patterns.
//!
//! There's one idea that is not detailed in [`super::usefulness`] because the details are not
//! needed there: _constructor splitting_.
//!
//! # Constructor splitting
//!
//! The idea is as follows: given a constructor `c` and a matrix, we want to specialize in turn
//! with all the value constructors that are covered by `c`, and compute usefulness for each.
//! Instead of listing all those constructors (which is intractable), we group those value
//! constructors together as much as possible. Example:
//!
//! ```compile_fail,E0004
//! match (0, false) {
//! (0 ..=100, true) => {} // `p_1`
//! (50..=150, false) => {} // `p_2`
//! (0 ..=200, _) => {} // `q`
//! }
//! ```
//!
//! The naive approach would try all numbers in the range `0..=200`. But we can be a lot more
//! clever: `0` and `1` for example will match the exact same rows, and return equivalent
//! witnesses. In fact all of `0..50` would. We can thus restrict our exploration to 4
//! constructors: `0..50`, `50..=100`, `101..=150` and `151..=200`. That is enough and infinitely
//! more tractable.
//!
//! We capture this idea in a function `split(p_1 ... p_n, c)` which returns a list of constructors
//! `c'` covered by `c`. Given such a `c'`, we require that all value ctors `c''` covered by `c'`
//! return an equivalent set of witnesses after specializing and computing usefulness.
//! In the example above, witnesses for specializing by `c''` covered by `0..50` will only differ
//! in their first element.
//!
//! We usually also ask that the `c'` together cover all of the original `c`. However we allow
//! skipping some constructors as long as it doesn't change whether the resulting list of witnesses
//! is empty of not. We use this in the wildcard `_` case.
//!
//! Splitting is implemented in the [`Constructor::split`] function. We don't do splitting for
//! or-patterns; instead we just try the alternatives one-by-one. For details on splitting
//! wildcards, see [`SplitWildcard`]; for integer ranges, see [`SplitIntRange`]; for slices, see
//! [`SplitVarLenSlice`].
use std::cell::Cell;
use std::cmp::{self, max, min, Ordering};
use std::fmt;
use std::iter::once;
use std::ops::RangeInclusive;
use smallvec::{smallvec, SmallVec};
use rustc_data_structures::captures::Captures;
use rustc_hir::{HirId, RangeEnd};
use rustc_index::Idx;
use rustc_middle::mir;
use rustc_middle::thir::{FieldPat, Pat, PatKind, PatRange};
use rustc_middle::ty::layout::IntegerExt;
use rustc_middle::ty::{self, Ty, TyCtxt, VariantDef};
use rustc_middle::{middle::stability::EvalResult, mir::interpret::ConstValue};
use rustc_session::lint;
use rustc_span::{Span, DUMMY_SP};
use rustc_target::abi::{FieldIdx, Integer, Size, VariantIdx, FIRST_VARIANT};
use self::Constructor::*;
use self::SliceKind::*;
use super::compare_const_vals;
use super::usefulness::{MatchCheckCtxt, PatCtxt};
use crate::errors::{Overlap, OverlappingRangeEndpoints};
/// Recursively expand this pattern into its subpatterns. Only useful for or-patterns.
fn expand_or_pat<'p, 'tcx>(pat: &'p Pat<'tcx>) -> Vec<&'p Pat<'tcx>> {
fn expand<'p, 'tcx>(pat: &'p Pat<'tcx>, vec: &mut Vec<&'p Pat<'tcx>>) {
if let PatKind::Or { pats } = &pat.kind {
for pat in pats.iter() {
expand(&pat, vec);
}
} else {
vec.push(pat)
}
}
let mut pats = Vec::new();
expand(pat, &mut pats);
pats
}
/// An inclusive interval, used for precise integer exhaustiveness checking.
/// `IntRange`s always store a contiguous range. This means that values are
/// encoded such that `0` encodes the minimum value for the integer,
/// regardless of the signedness.
/// For example, the pattern `-128..=127i8` is encoded as `0..=255`.
/// This makes comparisons and arithmetic on interval endpoints much more
/// straightforward. See `signed_bias` for details.
///
/// `IntRange` is never used to encode an empty range or a "range" that wraps
/// around the (offset) space: i.e., `range.lo <= range.hi`.
#[derive(Clone, PartialEq, Eq)]
pub(crate) struct IntRange {
range: RangeInclusive<u128>,
/// Keeps the bias used for encoding the range. It depends on the type of the range and
/// possibly the pointer size of the current architecture. The algorithm ensures we never
/// compare `IntRange`s with different types/architectures.
bias: u128,
}
impl IntRange {
#[inline]
fn is_integral(ty: Ty<'_>) -> bool {
matches!(ty.kind(), ty::Char | ty::Int(_) | ty::Uint(_) | ty::Bool)
}
fn is_singleton(&self) -> bool {
self.range.start() == self.range.end()
}
fn boundaries(&self) -> (u128, u128) {
(*self.range.start(), *self.range.end())
}
#[inline]
fn integral_size_and_signed_bias(tcx: TyCtxt<'_>, ty: Ty<'_>) -> Option<(Size, u128)> {
match *ty.kind() {
ty::Bool => Some((Size::from_bytes(1), 0)),
ty::Char => Some((Size::from_bytes(4), 0)),
ty::Int(ity) => {
let size = Integer::from_int_ty(&tcx, ity).size();
Some((size, 1u128 << (size.bits() as u128 - 1)))
}
ty::Uint(uty) => Some((Integer::from_uint_ty(&tcx, uty).size(), 0)),
_ => None,
}
}
#[inline]
fn from_constant<'tcx>(
tcx: TyCtxt<'tcx>,
param_env: ty::ParamEnv<'tcx>,
value: mir::ConstantKind<'tcx>,
) -> Option<IntRange> {
let ty = value.ty();
if let Some((target_size, bias)) = Self::integral_size_and_signed_bias(tcx, ty) {
let val = if let mir::ConstantKind::Val(ConstValue::Scalar(scalar), _) = value {
// For this specific pattern we can skip a lot of effort and go
// straight to the result, after doing a bit of checking. (We
// could remove this branch and just fall through, which
// is more general but much slower.)
scalar.to_bits_or_ptr_internal(target_size).unwrap().left()?
} else {
if let mir::ConstantKind::Ty(c) = value
&& let ty::ConstKind::Value(_) = c.kind()
{
bug!("encountered ConstValue in mir::ConstantKind::Ty, whereas this is expected to be in ConstantKind::Val");
}
// This is a more general form of the previous case.
value.try_eval_bits(tcx, param_env, ty)?
};
let val = val ^ bias;
Some(IntRange { range: val..=val, bias })
} else {
None
}
}
#[inline]
fn from_range<'tcx>(
tcx: TyCtxt<'tcx>,
lo: u128,
hi: u128,
ty: Ty<'tcx>,
end: &RangeEnd,
) -> Option<IntRange> {
Self::is_integral(ty).then(|| {
// Perform a shift if the underlying types are signed,
// which makes the interval arithmetic simpler.
let bias = IntRange::signed_bias(tcx, ty);
let (lo, hi) = (lo ^ bias, hi ^ bias);
let offset = (*end == RangeEnd::Excluded) as u128;
if lo > hi || (lo == hi && *end == RangeEnd::Excluded) {
// This should have been caught earlier by E0030.
bug!("malformed range pattern: {}..={}", lo, (hi - offset));
}
IntRange { range: lo..=(hi - offset), bias }
})
}
// The return value of `signed_bias` should be XORed with an endpoint to encode/decode it.
fn signed_bias(tcx: TyCtxt<'_>, ty: Ty<'_>) -> u128 {
match *ty.kind() {
ty::Int(ity) => {
let bits = Integer::from_int_ty(&tcx, ity).size().bits() as u128;
1u128 << (bits - 1)
}
_ => 0,
}
}
fn is_subrange(&self, other: &Self) -> bool {
other.range.start() <= self.range.start() && self.range.end() <= other.range.end()
}
fn intersection(&self, other: &Self) -> Option<Self> {
let (lo, hi) = self.boundaries();
let (other_lo, other_hi) = other.boundaries();
if lo <= other_hi && other_lo <= hi {
Some(IntRange { range: max(lo, other_lo)..=min(hi, other_hi), bias: self.bias })
} else {
None
}
}
fn suspicious_intersection(&self, other: &Self) -> bool {
// `false` in the following cases:
// 1 ---- // 1 ---------- // 1 ---- // 1 ----
// 2 ---------- // 2 ---- // 2 ---- // 2 ----
//
// The following are currently `false`, but could be `true` in the future (#64007):
// 1 --------- // 1 ---------
// 2 ---------- // 2 ----------
//
// `true` in the following cases:
// 1 ------- // 1 -------
// 2 -------- // 2 -------
let (lo, hi) = self.boundaries();
let (other_lo, other_hi) = other.boundaries();
(lo == other_hi || hi == other_lo) && !self.is_singleton() && !other.is_singleton()
}
/// Only used for displaying the range properly.
fn to_pat<'tcx>(&self, tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> Pat<'tcx> {
let (lo, hi) = self.boundaries();
let bias = self.bias;
let (lo, hi) = (lo ^ bias, hi ^ bias);
let env = ty::ParamEnv::empty().and(ty);
let lo_const = mir::ConstantKind::from_bits(tcx, lo, env);
let hi_const = mir::ConstantKind::from_bits(tcx, hi, env);
let kind = if lo == hi {
PatKind::Constant { value: lo_const }
} else {
PatKind::Range(Box::new(PatRange {
lo: lo_const,
hi: hi_const,
end: RangeEnd::Included,
}))
};
Pat { ty, span: DUMMY_SP, kind }
}
/// Lint on likely incorrect range patterns (#63987)
pub(super) fn lint_overlapping_range_endpoints<'a, 'p: 'a, 'tcx: 'a>(
&self,
pcx: &PatCtxt<'_, 'p, 'tcx>,
pats: impl Iterator<Item = &'a DeconstructedPat<'p, 'tcx>>,
column_count: usize,
lint_root: HirId,
) {
if self.is_singleton() {
return;
}
if column_count != 1 {
// FIXME: for now, only check for overlapping ranges on simple range
// patterns. Otherwise with the current logic the following is detected
// as overlapping:
// ```
// match (0u8, true) {
// (0 ..= 125, false) => {}
// (125 ..= 255, true) => {}
// _ => {}
// }
// ```
return;
}
let overlap: Vec<_> = pats
.filter_map(|pat| Some((pat.ctor().as_int_range()?, pat.span())))
.filter(|(range, _)| self.suspicious_intersection(range))
.map(|(range, span)| Overlap {
range: self.intersection(&range).unwrap().to_pat(pcx.cx.tcx, pcx.ty),
span,
})
.collect();
if !overlap.is_empty() {
pcx.cx.tcx.emit_spanned_lint(
lint::builtin::OVERLAPPING_RANGE_ENDPOINTS,
lint_root,
pcx.span,
OverlappingRangeEndpoints { overlap, range: pcx.span },
);
}
}
/// See `Constructor::is_covered_by`
fn is_covered_by(&self, other: &Self) -> bool {
if self.intersection(other).is_some() {
// Constructor splitting should ensure that all intersections we encounter are actually
// inclusions.
assert!(self.is_subrange(other));
true
} else {
false
}
}
}
/// Note: this is often not what we want: e.g. `false` is converted into the range `0..=0` and
/// would be displayed as such. To render properly, convert to a pattern first.
impl fmt::Debug for IntRange {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
let (lo, hi) = self.boundaries();
let bias = self.bias;
let (lo, hi) = (lo ^ bias, hi ^ bias);
write!(f, "{}", lo)?;
write!(f, "{}", RangeEnd::Included)?;
write!(f, "{}", hi)
}
}
/// Represents a border between 2 integers. Because the intervals spanning borders must be able to
/// cover every integer, we need to be able to represent 2^128 + 1 such borders.
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
enum IntBorder {
JustBefore(u128),
AfterMax,
}
/// A range of integers that is partitioned into disjoint subranges. This does constructor
/// splitting for integer ranges as explained at the top of the file.
///
/// This is fed multiple ranges, and returns an output that covers the input, but is split so that
/// the only intersections between an output range and a seen range are inclusions. No output range
/// straddles the boundary of one of the inputs.
///
/// The following input:
/// ```text
/// |-------------------------| // `self`
/// |------| |----------| |----|
/// |-------| |-------|
/// ```
/// would be iterated over as follows:
/// ```text
/// ||---|--||-|---|---|---|--|
/// ```
#[derive(Debug, Clone)]
struct SplitIntRange {
/// The range we are splitting
range: IntRange,
/// The borders of ranges we have seen. They are all contained within `range`. This is kept
/// sorted.
borders: Vec<IntBorder>,
}
impl SplitIntRange {
fn new(range: IntRange) -> Self {
SplitIntRange { range, borders: Vec::new() }
}
/// Internal use
fn to_borders(r: IntRange) -> [IntBorder; 2] {
use IntBorder::*;
let (lo, hi) = r.boundaries();
let lo = JustBefore(lo);
let hi = match hi.checked_add(1) {
Some(m) => JustBefore(m),
None => AfterMax,
};
[lo, hi]
}
/// Add ranges relative to which we split.
fn split(&mut self, ranges: impl Iterator<Item = IntRange>) {
let this_range = &self.range;
let included_ranges = ranges.filter_map(|r| this_range.intersection(&r));
let included_borders = included_ranges.flat_map(|r| {
let borders = Self::to_borders(r);
once(borders[0]).chain(once(borders[1]))
});
self.borders.extend(included_borders);
self.borders.sort_unstable();
}
/// Iterate over the contained ranges.
fn iter(&self) -> impl Iterator<Item = IntRange> + Captures<'_> {
use IntBorder::*;
let self_range = Self::to_borders(self.range.clone());
// Start with the start of the range.
let mut prev_border = self_range[0];
self.borders
.iter()
.copied()
// End with the end of the range.
.chain(once(self_range[1]))
// List pairs of adjacent borders.
.map(move |border| {
let ret = (prev_border, border);
prev_border = border;
ret
})
// Skip duplicates.
.filter(|(prev_border, border)| prev_border != border)
// Finally, convert to ranges.
.map(move |(prev_border, border)| {
let range = match (prev_border, border) {
(JustBefore(n), JustBefore(m)) if n < m => n..=(m - 1),
(JustBefore(n), AfterMax) => n..=u128::MAX,
_ => unreachable!(), // Ruled out by the sorting and filtering we did
};
IntRange { range, bias: self.range.bias }
})
}
}
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
enum SliceKind {
/// Patterns of length `n` (`[x, y]`).
FixedLen(usize),
/// Patterns using the `..` notation (`[x, .., y]`).
/// Captures any array constructor of `length >= i + j`.
/// In the case where `array_len` is `Some(_)`,
/// this indicates that we only care about the first `i` and the last `j` values of the array,
/// and everything in between is a wildcard `_`.
VarLen(usize, usize),
}
impl SliceKind {
fn arity(self) -> usize {
match self {
FixedLen(length) => length,
VarLen(prefix, suffix) => prefix + suffix,
}
}
/// Whether this pattern includes patterns of length `other_len`.
fn covers_length(self, other_len: usize) -> bool {
match self {
FixedLen(len) => len == other_len,
VarLen(prefix, suffix) => prefix + suffix <= other_len,
}
}
}
/// A constructor for array and slice patterns.
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
pub(super) struct Slice {
/// `None` if the matched value is a slice, `Some(n)` if it is an array of size `n`.
array_len: Option<usize>,
/// The kind of pattern it is: fixed-length `[x, y]` or variable length `[x, .., y]`.
kind: SliceKind,
}
impl Slice {
fn new(array_len: Option<usize>, kind: SliceKind) -> Self {
let kind = match (array_len, kind) {
// If the middle `..` is empty, we effectively have a fixed-length pattern.
(Some(len), VarLen(prefix, suffix)) if prefix + suffix >= len => FixedLen(len),
_ => kind,
};
Slice { array_len, kind }
}
fn arity(self) -> usize {
self.kind.arity()
}
/// See `Constructor::is_covered_by`
fn is_covered_by(self, other: Self) -> bool {
other.kind.covers_length(self.arity())
}
}
/// This computes constructor splitting for variable-length slices, as explained at the top of the
/// file.
///
/// A slice pattern `[x, .., y]` behaves like the infinite or-pattern `[x, y] | [x, _, y] | [x, _,
/// _, y] | ...`. The corresponding value constructors are fixed-length array constructors above a
/// given minimum length. We obviously can't list this infinitude of constructors. Thankfully,
/// it turns out that for each finite set of slice patterns, all sufficiently large array lengths
/// are equivalent.
///
/// Let's look at an example, where we are trying to split the last pattern:
/// ```
/// # fn foo(x: &[bool]) {
/// match x {
/// [true, true, ..] => {}
/// [.., false, false] => {}
/// [..] => {}
/// }
/// # }
/// ```
/// Here are the results of specialization for the first few lengths:
/// ```
/// # fn foo(x: &[bool]) { match x {
/// // length 0
/// [] => {}
/// // length 1
/// [_] => {}
/// // length 2
/// [true, true] => {}
/// [false, false] => {}
/// [_, _] => {}
/// // length 3
/// [true, true, _ ] => {}
/// [_, false, false] => {}
/// [_, _, _ ] => {}
/// // length 4
/// [true, true, _, _ ] => {}
/// [_, _, false, false] => {}
/// [_, _, _, _ ] => {}
/// // length 5
/// [true, true, _, _, _ ] => {}
/// [_, _, _, false, false] => {}
/// [_, _, _, _, _ ] => {}
/// # _ => {}
/// # }}
/// ```
///
/// If we went above length 5, we would simply be inserting more columns full of wildcards in the
/// middle. This means that the set of witnesses for length `l >= 5` if equivalent to the set for
/// any other `l' >= 5`: simply add or remove wildcards in the middle to convert between them.
///
/// This applies to any set of slice patterns: there will be a length `L` above which all lengths
/// behave the same. This is exactly what we need for constructor splitting. Therefore a
/// variable-length slice can be split into a variable-length slice of minimal length `L`, and many
/// fixed-length slices of lengths `< L`.
///
/// For each variable-length pattern `p` with a prefix of length `plâ‚š` and suffix of length `slâ‚š`,
/// only the first `plâ‚š` and the last `slâ‚š` elements are examined. Therefore, as long as `L` is
/// positive (to avoid concerns about empty types), all elements after the maximum prefix length
/// and before the maximum suffix length are not examined by any variable-length pattern, and
/// therefore can be added/removed without affecting them - creating equivalent patterns from any
/// sufficiently-large length.
///
/// Of course, if fixed-length patterns exist, we must be sure that our length is large enough to
/// miss them all, so we can pick `L = max(max(FIXED_LEN)+1, max(PREFIX_LEN) + max(SUFFIX_LEN))`
///
/// `max_slice` below will be made to have arity `L`.
#[derive(Debug)]
struct SplitVarLenSlice {
/// If the type is an array, this is its size.
array_len: Option<usize>,
/// The arity of the input slice.
arity: usize,
/// The smallest slice bigger than any slice seen. `max_slice.arity()` is the length `L`
/// described above.
max_slice: SliceKind,
}
impl SplitVarLenSlice {
fn new(prefix: usize, suffix: usize, array_len: Option<usize>) -> Self {
SplitVarLenSlice { array_len, arity: prefix + suffix, max_slice: VarLen(prefix, suffix) }
}
/// Pass a set of slices relative to which to split this one.
fn split(&mut self, slices: impl Iterator<Item = SliceKind>) {
let VarLen(max_prefix_len, max_suffix_len) = &mut self.max_slice else {
// No need to split
return;
};
// We grow `self.max_slice` to be larger than all slices encountered, as described above.
// For diagnostics, we keep the prefix and suffix lengths separate, but grow them so that
// `L = max_prefix_len + max_suffix_len`.
let mut max_fixed_len = 0;
for slice in slices {
match slice {
FixedLen(len) => {
max_fixed_len = cmp::max(max_fixed_len, len);
}
VarLen(prefix, suffix) => {
*max_prefix_len = cmp::max(*max_prefix_len, prefix);
*max_suffix_len = cmp::max(*max_suffix_len, suffix);
}
}
}
// We want `L = max(L, max_fixed_len + 1)`, modulo the fact that we keep prefix and
// suffix separate.
if max_fixed_len + 1 >= *max_prefix_len + *max_suffix_len {
// The subtraction can't overflow thanks to the above check.
// The new `max_prefix_len` is larger than its previous value.
*max_prefix_len = max_fixed_len + 1 - *max_suffix_len;
}
// We cap the arity of `max_slice` at the array size.
match self.array_len {
Some(len) if self.max_slice.arity() >= len => self.max_slice = FixedLen(len),
_ => {}
}
}
/// Iterate over the partition of this slice.
fn iter(&self) -> impl Iterator<Item = Slice> + Captures<'_> {
let smaller_lengths = match self.array_len {
// The only admissible fixed-length slice is one of the array size. Whether `max_slice`
// is fixed-length or variable-length, it will be the only relevant slice to output
// here.
Some(_) => 0..0, // empty range
// We cover all arities in the range `(self.arity..infinity)`. We split that range into
// two: lengths smaller than `max_slice.arity()` are treated independently as
// fixed-lengths slices, and lengths above are captured by `max_slice`.
None => self.arity..self.max_slice.arity(),
};
smaller_lengths
.map(FixedLen)
.chain(once(self.max_slice))
.map(move |kind| Slice::new(self.array_len, kind))
}
}
/// A value can be decomposed into a constructor applied to some fields. This struct represents
/// the constructor. See also `Fields`.
///
/// `pat_constructor` retrieves the constructor corresponding to a pattern.
/// `specialize_constructor` returns the list of fields corresponding to a pattern, given a
/// constructor. `Constructor::apply` reconstructs the pattern from a pair of `Constructor` and
/// `Fields`.
#[derive(Clone, Debug, PartialEq)]
pub(super) enum Constructor<'tcx> {
/// The constructor for patterns that have a single constructor, like tuples, struct patterns
/// and fixed-length arrays.
Single,
/// Enum variants.
Variant(VariantIdx),
/// Ranges of integer literal values (`2`, `2..=5` or `2..5`).
IntRange(IntRange),
/// Ranges of floating-point literal values (`2.0..=5.2`).
FloatRange(mir::ConstantKind<'tcx>, mir::ConstantKind<'tcx>, RangeEnd),
/// String literals. Strings are not quite the same as `&[u8]` so we treat them separately.
Str(mir::ConstantKind<'tcx>),
/// Array and slice patterns.
Slice(Slice),
/// Constants that must not be matched structurally. They are treated as black
/// boxes for the purposes of exhaustiveness: we must not inspect them, and they
/// don't count towards making a match exhaustive.
Opaque,
/// Fake extra constructor for enums that aren't allowed to be matched exhaustively. Also used
/// for those types for which we cannot list constructors explicitly, like `f64` and `str`.
NonExhaustive,
/// Stands for constructors that are not seen in the matrix, as explained in the documentation
/// for [`SplitWildcard`]. The carried `bool` is used for the `non_exhaustive_omitted_patterns`
/// lint.
Missing { nonexhaustive_enum_missing_real_variants: bool },
/// Wildcard pattern.
Wildcard,
/// Or-pattern.
Or,
}
impl<'tcx> Constructor<'tcx> {
pub(super) fn is_wildcard(&self) -> bool {
matches!(self, Wildcard)
}
pub(super) fn is_non_exhaustive(&self) -> bool {
matches!(self, NonExhaustive)
}
fn as_int_range(&self) -> Option<&IntRange> {
match self {
IntRange(range) => Some(range),
_ => None,
}
}
fn as_slice(&self) -> Option<Slice> {
match self {
Slice(slice) => Some(*slice),
_ => None,
}
}
/// Checks if the `Constructor` is a variant and `TyCtxt::eval_stability` returns
/// `EvalResult::Deny { .. }`.
///
/// This means that the variant has a stdlib unstable feature marking it.
pub(super) fn is_unstable_variant(&self, pcx: &PatCtxt<'_, '_, 'tcx>) -> bool {
if let Constructor::Variant(idx) = self && let ty::Adt(adt, _) = pcx.ty.kind() {
let variant_def_id = adt.variant(*idx).def_id;
// Filter variants that depend on a disabled unstable feature.
return matches!(
pcx.cx.tcx.eval_stability(variant_def_id, None, DUMMY_SP, None),
EvalResult::Deny { .. }
);
}
false
}
/// Checks if the `Constructor` is a `Constructor::Variant` with a `#[doc(hidden)]`
/// attribute from a type not local to the current crate.
pub(super) fn is_doc_hidden_variant(&self, pcx: &PatCtxt<'_, '_, 'tcx>) -> bool {
if let Constructor::Variant(idx) = self && let ty::Adt(adt, _) = pcx.ty.kind() {
let variant_def_id = adt.variants()[*idx].def_id;
return pcx.cx.tcx.is_doc_hidden(variant_def_id) && !variant_def_id.is_local();
}
false
}
fn variant_index_for_adt(&self, adt: ty::AdtDef<'tcx>) -> VariantIdx {
match *self {
Variant(idx) => idx,
Single => {
assert!(!adt.is_enum());
FIRST_VARIANT
}
_ => bug!("bad constructor {:?} for adt {:?}", self, adt),
}
}
/// The number of fields for this constructor. This must be kept in sync with
/// `Fields::wildcards`.
pub(super) fn arity(&self, pcx: &PatCtxt<'_, '_, 'tcx>) -> usize {
match self {
Single | Variant(_) => match pcx.ty.kind() {
ty::Tuple(fs) => fs.len(),
ty::Ref(..) => 1,
ty::Adt(adt, ..) => {
if adt.is_box() {
// The only legal patterns of type `Box` (outside `std`) are `_` and box
// patterns. If we're here we can assume this is a box pattern.
1
} else {
let variant = &adt.variant(self.variant_index_for_adt(*adt));
Fields::list_variant_nonhidden_fields(pcx.cx, pcx.ty, variant).count()
}
}
_ => bug!("Unexpected type for `Single` constructor: {:?}", pcx.ty),
},
Slice(slice) => slice.arity(),
Str(..)
| FloatRange(..)
| IntRange(..)
| NonExhaustive
| Opaque
| Missing { .. }
| Wildcard => 0,
Or => bug!("The `Or` constructor doesn't have a fixed arity"),
}
}
/// Some constructors (namely `Wildcard`, `IntRange` and `Slice`) actually stand for a set of actual
/// constructors (like variants, integers or fixed-sized slices). When specializing for these
/// constructors, we want to be specialising for the actual underlying constructors.
/// Naively, we would simply return the list of constructors they correspond to. We instead are
/// more clever: if there are constructors that we know will behave the same wrt the current
/// matrix, we keep them grouped. For example, all slices of a sufficiently large length
/// will either be all useful or all non-useful with a given matrix.
///
/// See the branches for details on how the splitting is done.
///
/// This function may discard some irrelevant constructors if this preserves behavior and
/// diagnostics. Eg. for the `_` case, we ignore the constructors already present in the
/// matrix, unless all of them are.
pub(super) fn split<'a>(
&self,
pcx: &PatCtxt<'_, '_, 'tcx>,
ctors: impl Iterator<Item = &'a Constructor<'tcx>> + Clone,
) -> SmallVec<[Self; 1]>
where
'tcx: 'a,
{
match self {
Wildcard => {
let mut split_wildcard = SplitWildcard::new(pcx);
split_wildcard.split(pcx, ctors);
split_wildcard.into_ctors(pcx)
}
// Fast-track if the range is trivial. In particular, we don't do the overlapping
// ranges check.
IntRange(ctor_range) if !ctor_range.is_singleton() => {
let mut split_range = SplitIntRange::new(ctor_range.clone());
let int_ranges = ctors.filter_map(|ctor| ctor.as_int_range());
split_range.split(int_ranges.cloned());
split_range.iter().map(IntRange).collect()
}
&Slice(Slice { kind: VarLen(self_prefix, self_suffix), array_len }) => {
let mut split_self = SplitVarLenSlice::new(self_prefix, self_suffix, array_len);
let slices = ctors.filter_map(|c| c.as_slice()).map(|s| s.kind);
split_self.split(slices);
split_self.iter().map(Slice).collect()
}
// Any other constructor can be used unchanged.
_ => smallvec![self.clone()],
}
}
/// Returns whether `self` is covered by `other`, i.e. whether `self` is a subset of `other`.
/// For the simple cases, this is simply checking for equality. For the "grouped" constructors,
/// this checks for inclusion.
// We inline because this has a single call site in `Matrix::specialize_constructor`.
#[inline]
pub(super) fn is_covered_by<'p>(&self, pcx: &PatCtxt<'_, 'p, 'tcx>, other: &Self) -> bool {
// This must be kept in sync with `is_covered_by_any`.
match (self, other) {
// Wildcards cover anything
(_, Wildcard) => true,
// The missing ctors are not covered by anything in the matrix except wildcards.
(Missing { .. } | Wildcard, _) => false,
(Single, Single) => true,
(Variant(self_id), Variant(other_id)) => self_id == other_id,
(IntRange(self_range), IntRange(other_range)) => self_range.is_covered_by(other_range),
(
FloatRange(self_from, self_to, self_end),
FloatRange(other_from, other_to, other_end),
) => {
match (
compare_const_vals(pcx.cx.tcx, *self_to, *other_to, pcx.cx.param_env),
compare_const_vals(pcx.cx.tcx, *self_from, *other_from, pcx.cx.param_env),
) {
(Some(to), Some(from)) => {
(from == Ordering::Greater || from == Ordering::Equal)
&& (to == Ordering::Less
|| (other_end == self_end && to == Ordering::Equal))
}
_ => false,
}
}
(Str(self_val), Str(other_val)) => {
// FIXME Once valtrees are available we can directly use the bytes
// in the `Str` variant of the valtree for the comparison here.
self_val == other_val
}
(Slice(self_slice), Slice(other_slice)) => self_slice.is_covered_by(*other_slice),
// We are trying to inspect an opaque constant. Thus we skip the row.
(Opaque, _) | (_, Opaque) => false,
// Only a wildcard pattern can match the special extra constructor.
(NonExhaustive, _) => false,
_ => span_bug!(
pcx.span,
"trying to compare incompatible constructors {:?} and {:?}",
self,
other
),
}
}
/// Faster version of `is_covered_by` when applied to many constructors. `used_ctors` is
/// assumed to be built from `matrix.head_ctors()` with wildcards and opaques filtered out,
/// and `self` is assumed to have been split from a wildcard.
fn is_covered_by_any<'p>(
&self,
pcx: &PatCtxt<'_, 'p, 'tcx>,
used_ctors: &[Constructor<'tcx>],
) -> bool {
if used_ctors.is_empty() {
return false;
}
// This must be kept in sync with `is_covered_by`.
match self {
// If `self` is `Single`, `used_ctors` cannot contain anything else than `Single`s.
Single => !used_ctors.is_empty(),
Variant(vid) => used_ctors.iter().any(|c| matches!(c, Variant(i) if i == vid)),
IntRange(range) => used_ctors
.iter()
.filter_map(|c| c.as_int_range())
.any(|other| range.is_covered_by(other)),
Slice(slice) => used_ctors
.iter()
.filter_map(|c| c.as_slice())
.any(|other| slice.is_covered_by(other)),
// This constructor is never covered by anything else
NonExhaustive => false,
Str(..) | FloatRange(..) | Opaque | Missing { .. } | Wildcard | Or => {
span_bug!(pcx.span, "found unexpected ctor in all_ctors: {:?}", self)
}
}
}
}
/// A wildcard constructor that we split relative to the constructors in the matrix, as explained
/// at the top of the file.
///
/// A constructor that is not present in the matrix rows will only be covered by the rows that have
/// wildcards. Thus we can group all of those constructors together; we call them "missing
/// constructors". Splitting a wildcard would therefore list all present constructors individually
/// (or grouped if they are integers or slices), and then all missing constructors together as a
/// group.
///
/// However we can go further: since any constructor will match the wildcard rows, and having more
/// rows can only reduce the amount of usefulness witnesses, we can skip the present constructors
/// and only try the missing ones.
/// This will not preserve the whole list of witnesses, but will preserve whether the list is empty
/// or not. In fact this is quite natural from the point of view of diagnostics too. This is done
/// in `to_ctors`: in some cases we only return `Missing`.
#[derive(Debug)]
pub(super) struct SplitWildcard<'tcx> {
/// Constructors (other than wildcards and opaques) seen in the matrix.
matrix_ctors: Vec<Constructor<'tcx>>,
/// All the constructors for this type
all_ctors: SmallVec<[Constructor<'tcx>; 1]>,
}
impl<'tcx> SplitWildcard<'tcx> {
pub(super) fn new<'p>(pcx: &PatCtxt<'_, 'p, 'tcx>) -> Self {
debug!("SplitWildcard::new({:?})", pcx.ty);
let cx = pcx.cx;
let make_range = |start, end| {
IntRange(
// `unwrap()` is ok because we know the type is an integer.
IntRange::from_range(cx.tcx, start, end, pcx.ty, &RangeEnd::Included).unwrap(),
)
};
// This determines the set of all possible constructors for the type `pcx.ty`. For numbers,
// arrays and slices we use ranges and variable-length slices when appropriate.
//
// If the `exhaustive_patterns` feature is enabled, we make sure to omit constructors that
// are statically impossible. E.g., for `Option<!>`, we do not include `Some(_)` in the
// returned list of constructors.
// Invariant: this is empty if and only if the type is uninhabited (as determined by
// `cx.is_uninhabited()`).
let all_ctors = match pcx.ty.kind() {
ty::Bool => smallvec![make_range(0, 1)],
ty::Array(sub_ty, len) if len.try_eval_target_usize(cx.tcx, cx.param_env).is_some() => {
let len = len.eval_target_usize(cx.tcx, cx.param_env) as usize;
if len != 0 && cx.is_uninhabited(*sub_ty) {
smallvec![]
} else {
smallvec![Slice(Slice::new(Some(len), VarLen(0, 0)))]
}
}
// Treat arrays of a constant but unknown length like slices.
ty::Array(sub_ty, _) | ty::Slice(sub_ty) => {
let kind = if cx.is_uninhabited(*sub_ty) { FixedLen(0) } else { VarLen(0, 0) };
smallvec![Slice(Slice::new(None, kind))]
}
ty::Adt(def, substs) if def.is_enum() => {
// If the enum is declared as `#[non_exhaustive]`, we treat it as if it had an
// additional "unknown" constructor.
// There is no point in enumerating all possible variants, because the user can't
// actually match against them all themselves. So we always return only the fictitious
// constructor.
// E.g., in an example like:
//
// ```
// let err: io::ErrorKind = ...;
// match err {
// io::ErrorKind::NotFound => {},
// }
// ```
//
// we don't want to show every possible IO error, but instead have only `_` as the
// witness.
let is_declared_nonexhaustive = cx.is_foreign_non_exhaustive_enum(pcx.ty);
let is_exhaustive_pat_feature = cx.tcx.features().exhaustive_patterns;
// If `exhaustive_patterns` is disabled and our scrutinee is an empty enum, we treat it
// as though it had an "unknown" constructor to avoid exposing its emptiness. The
// exception is if the pattern is at the top level, because we want empty matches to be
// considered exhaustive.
let is_secretly_empty =
def.variants().is_empty() && !is_exhaustive_pat_feature && !pcx.is_top_level;
let mut ctors: SmallVec<[_; 1]> = def
.variants()
.iter_enumerated()
.filter(|(_, v)| {
// If `exhaustive_patterns` is enabled, we exclude variants known to be
// uninhabited.
!is_exhaustive_pat_feature
|| v.inhabited_predicate(cx.tcx, *def).subst(cx.tcx, substs).apply(
cx.tcx,
cx.param_env,
cx.module,
)
})
.map(|(idx, _)| Variant(idx))
.collect();
if is_secretly_empty || is_declared_nonexhaustive {
ctors.push(NonExhaustive);
}
ctors
}
ty::Char => {
smallvec![
// The valid Unicode Scalar Value ranges.
make_range('\u{0000}' as u128, '\u{D7FF}' as u128),
make_range('\u{E000}' as u128, '\u{10FFFF}' as u128),
]
}
ty::Int(_) | ty::Uint(_)
if pcx.ty.is_ptr_sized_integral()
&& !cx.tcx.features().precise_pointer_size_matching =>
{
// `usize`/`isize` are not allowed to be matched exhaustively unless the
// `precise_pointer_size_matching` feature is enabled. So we treat those types like
// `#[non_exhaustive]` enums by returning a special unmatchable constructor.
smallvec![NonExhaustive]
}
&ty::Int(ity) => {
let bits = Integer::from_int_ty(&cx.tcx, ity).size().bits() as u128;
let min = 1u128 << (bits - 1);
let max = min - 1;
smallvec![make_range(min, max)]
}
&ty::Uint(uty) => {
let size = Integer::from_uint_ty(&cx.tcx, uty).size();
let max = size.truncate(u128::MAX);
smallvec![make_range(0, max)]
}
// If `exhaustive_patterns` is disabled and our scrutinee is the never type, we cannot
// expose its emptiness. The exception is if the pattern is at the top level, because we
// want empty matches to be considered exhaustive.
ty::Never if !cx.tcx.features().exhaustive_patterns && !pcx.is_top_level => {
smallvec![NonExhaustive]
}
ty::Never => smallvec![],
_ if cx.is_uninhabited(pcx.ty) => smallvec![],
ty::Adt(..) | ty::Tuple(..) | ty::Ref(..) => smallvec![Single],
// This type is one for which we cannot list constructors, like `str` or `f64`.
_ => smallvec![NonExhaustive],
};
SplitWildcard { matrix_ctors: Vec::new(), all_ctors }
}
/// Pass a set of constructors relative to which to split this one. Don't call twice, it won't
/// do what you want.
pub(super) fn split<'a>(
&mut self,
pcx: &PatCtxt<'_, '_, 'tcx>,
ctors: impl Iterator<Item = &'a Constructor<'tcx>> + Clone,
) where
'tcx: 'a,
{
// Since `all_ctors` never contains wildcards, this won't recurse further.
self.all_ctors =
self.all_ctors.iter().flat_map(|ctor| ctor.split(pcx, ctors.clone())).collect();
self.matrix_ctors = ctors.filter(|c| !matches!(c, Wildcard | Opaque)).cloned().collect();
}
/// Whether there are any value constructors for this type that are not present in the matrix.
fn any_missing(&self, pcx: &PatCtxt<'_, '_, 'tcx>) -> bool {
self.iter_missing(pcx).next().is_some()
}
/// Iterate over the constructors for this type that are not present in the matrix.
pub(super) fn iter_missing<'a, 'p>(
&'a self,
pcx: &'a PatCtxt<'a, 'p, 'tcx>,
) -> impl Iterator<Item = &'a Constructor<'tcx>> + Captures<'p> {
self.all_ctors.iter().filter(move |ctor| !ctor.is_covered_by_any(pcx, &self.matrix_ctors))
}
/// Return the set of constructors resulting from splitting the wildcard. As explained at the
/// top of the file, if any constructors are missing we can ignore the present ones.
fn into_ctors(self, pcx: &PatCtxt<'_, '_, 'tcx>) -> SmallVec<[Constructor<'tcx>; 1]> {
if self.any_missing(pcx) {
// Some constructors are missing, thus we can specialize with the special `Missing`
// constructor, which stands for those constructors that are not seen in the matrix,
// and matches the same rows as any of them (namely the wildcard rows). See the top of
// the file for details.
// However, when all constructors are missing we can also specialize with the full
// `Wildcard` constructor. The difference will depend on what we want in diagnostics.
// If some constructors are missing, we typically want to report those constructors,
// e.g.:
// ```
// enum Direction { N, S, E, W }
// let Direction::N = ...;
// ```
// we can report 3 witnesses: `S`, `E`, and `W`.
//
// However, if the user didn't actually specify a constructor
// in this arm, e.g., in
// ```
// let x: (Direction, Direction, bool) = ...;
// let (_, _, false) = x;
// ```
// we don't want to show all 16 possible witnesses `(<direction-1>, <direction-2>,
// true)` - we are satisfied with `(_, _, true)`. So if all constructors are missing we
// prefer to report just a wildcard `_`.
//
// The exception is: if we are at the top-level, for example in an empty match, we
// sometimes prefer reporting the list of constructors instead of just `_`.
let report_when_all_missing = pcx.is_top_level && !IntRange::is_integral(pcx.ty);
let ctor = if !self.matrix_ctors.is_empty() || report_when_all_missing {
if pcx.is_non_exhaustive {
Missing {
nonexhaustive_enum_missing_real_variants: self
.iter_missing(pcx)
.any(|c| !(c.is_non_exhaustive() || c.is_unstable_variant(pcx))),
}
} else {
Missing { nonexhaustive_enum_missing_real_variants: false }
}
} else {
Wildcard
};
return smallvec![ctor];
}
// All the constructors are present in the matrix, so we just go through them all.
self.all_ctors
}
}
/// A value can be decomposed into a constructor applied to some fields. This struct represents
/// those fields, generalized to allow patterns in each field. See also `Constructor`.
///
/// This is constructed for a constructor using [`Fields::wildcards()`]. The idea is that
/// [`Fields::wildcards()`] constructs a list of fields where all entries are wildcards, and then
/// given a pattern we fill some of the fields with its subpatterns.
/// In the following example `Fields::wildcards` returns `[_, _, _, _]`. Then in
/// `extract_pattern_arguments` we fill some of the entries, and the result is
/// `[Some(0), _, _, _]`.
/// ```compile_fail,E0004
/// # fn foo() -> [Option<u8>; 4] { [None; 4] }
/// let x: [Option<u8>; 4] = foo();
/// match x {
/// [Some(0), ..] => {}
/// }
/// ```
///
/// Note that the number of fields of a constructor may not match the fields declared in the
/// original struct/variant. This happens if a private or `non_exhaustive` field is uninhabited,
/// because the code mustn't observe that it is uninhabited. In that case that field is not
/// included in `fields`. For that reason, when you have a `FieldIdx` you must use
/// `index_with_declared_idx`.
#[derive(Debug, Clone, Copy)]
pub(super) struct Fields<'p, 'tcx> {
fields: &'p [DeconstructedPat<'p, 'tcx>],
}
impl<'p, 'tcx> Fields<'p, 'tcx> {
fn empty() -> Self {
Fields { fields: &[] }
}
fn singleton(cx: &MatchCheckCtxt<'p, 'tcx>, field: DeconstructedPat<'p, 'tcx>) -> Self {
let field: &_ = cx.pattern_arena.alloc(field);
Fields { fields: std::slice::from_ref(field) }
}
pub(super) fn from_iter(
cx: &MatchCheckCtxt<'p, 'tcx>,
fields: impl IntoIterator<Item = DeconstructedPat<'p, 'tcx>>,
) -> Self {
let fields: &[_] = cx.pattern_arena.alloc_from_iter(fields);
Fields { fields }
}
fn wildcards_from_tys(
cx: &MatchCheckCtxt<'p, 'tcx>,
tys: impl IntoIterator<Item = Ty<'tcx>>,
span: Span,
) -> Self {
Fields::from_iter(cx, tys.into_iter().map(|ty| DeconstructedPat::wildcard(ty, span)))
}
// In the cases of either a `#[non_exhaustive]` field list or a non-public field, we hide
// uninhabited fields in order not to reveal the uninhabitedness of the whole variant.
// This lists the fields we keep along with their types.
fn list_variant_nonhidden_fields<'a>(
cx: &'a MatchCheckCtxt<'p, 'tcx>,
ty: Ty<'tcx>,
variant: &'a VariantDef,
) -> impl Iterator<Item = (FieldIdx, Ty<'tcx>)> + Captures<'a> + Captures<'p> {
let ty::Adt(adt, substs) = ty.kind() else { bug!() };
// Whether we must not match the fields of this variant exhaustively.
let is_non_exhaustive = variant.is_field_list_non_exhaustive() && !adt.did().is_local();
variant.fields.iter().enumerate().filter_map(move |(i, field)| {
let ty = field.ty(cx.tcx, substs);
// `field.ty()` doesn't normalize after substituting.
let ty = cx.tcx.normalize_erasing_regions(cx.param_env, ty);
let is_visible = adt.is_enum() || field.vis.is_accessible_from(cx.module, cx.tcx);
let is_uninhabited = cx.is_uninhabited(ty);
if is_uninhabited && (!is_visible || is_non_exhaustive) {
None
} else {
Some((FieldIdx::new(i), ty))
}
})
}
/// Creates a new list of wildcard fields for a given constructor. The result must have a
/// length of `constructor.arity()`.
#[instrument(level = "trace")]
pub(super) fn wildcards(pcx: &PatCtxt<'_, 'p, 'tcx>, constructor: &Constructor<'tcx>) -> Self {
let ret = match constructor {
Single | Variant(_) => match pcx.ty.kind() {
ty::Tuple(fs) => Fields::wildcards_from_tys(pcx.cx, fs.iter(), pcx.span),
ty::Ref(_, rty, _) => Fields::wildcards_from_tys(pcx.cx, once(*rty), pcx.span),
ty::Adt(adt, substs) => {
if adt.is_box() {
// The only legal patterns of type `Box` (outside `std`) are `_` and box
// patterns. If we're here we can assume this is a box pattern.
Fields::wildcards_from_tys(pcx.cx, once(substs.type_at(0)), pcx.span)
} else {
let variant = &adt.variant(constructor.variant_index_for_adt(*adt));
let tys = Fields::list_variant_nonhidden_fields(pcx.cx, pcx.ty, variant)
.map(|(_, ty)| ty);
Fields::wildcards_from_tys(pcx.cx, tys, pcx.span)
}
}
_ => bug!("Unexpected type for `Single` constructor: {:?}", pcx),
},
Slice(slice) => match *pcx.ty.kind() {
ty::Slice(ty) | ty::Array(ty, _) => {
let arity = slice.arity();
Fields::wildcards_from_tys(pcx.cx, (0..arity).map(|_| ty), pcx.span)
}
_ => bug!("bad slice pattern {:?} {:?}", constructor, pcx),
},
Str(..)
| FloatRange(..)
| IntRange(..)
| NonExhaustive
| Opaque
| Missing { .. }
| Wildcard => Fields::empty(),
Or => {
bug!("called `Fields::wildcards` on an `Or` ctor")
}
};
debug!(?ret);
ret
}
/// Returns the list of patterns.
pub(super) fn iter_patterns<'a>(
&'a self,
) -> impl Iterator<Item = &'p DeconstructedPat<'p, 'tcx>> + Captures<'a> {
self.fields.iter()
}
}
/// Values and patterns can be represented as a constructor applied to some fields. This represents
/// a pattern in this form.
/// This also keeps track of whether the pattern has been found reachable during analysis. For this
/// reason we should be careful not to clone patterns for which we care about that. Use
/// `clone_and_forget_reachability` if you're sure.
pub(crate) struct DeconstructedPat<'p, 'tcx> {
ctor: Constructor<'tcx>,
fields: Fields<'p, 'tcx>,
ty: Ty<'tcx>,
span: Span,
reachable: Cell<bool>,
}
impl<'p, 'tcx> DeconstructedPat<'p, 'tcx> {
pub(super) fn wildcard(ty: Ty<'tcx>, span: Span) -> Self {
Self::new(Wildcard, Fields::empty(), ty, span)
}
pub(super) fn new(
ctor: Constructor<'tcx>,
fields: Fields<'p, 'tcx>,
ty: Ty<'tcx>,
span: Span,
) -> Self {
DeconstructedPat { ctor, fields, ty, span, reachable: Cell::new(false) }
}
/// Construct a pattern that matches everything that starts with this constructor.
/// For example, if `ctor` is a `Constructor::Variant` for `Option::Some`, we get the pattern
/// `Some(_)`.
pub(super) fn wild_from_ctor(pcx: &PatCtxt<'_, 'p, 'tcx>, ctor: Constructor<'tcx>) -> Self {
let fields = Fields::wildcards(pcx, &ctor);
DeconstructedPat::new(ctor, fields, pcx.ty, pcx.span)
}
/// Clone this value. This method emphasizes that cloning loses reachability information and
/// should be done carefully.
pub(super) fn clone_and_forget_reachability(&self) -> Self {
DeconstructedPat::new(self.ctor.clone(), self.fields, self.ty, self.span)
}
pub(crate) fn from_pat(cx: &MatchCheckCtxt<'p, 'tcx>, pat: &Pat<'tcx>) -> Self {
let mkpat = |pat| DeconstructedPat::from_pat(cx, pat);
let ctor;
let fields;
match &pat.kind {
PatKind::AscribeUserType { subpattern, .. } => return mkpat(subpattern),
PatKind::Binding { subpattern: Some(subpat), .. } => return mkpat(subpat),
PatKind::Binding { subpattern: None, .. } | PatKind::Wild => {
ctor = Wildcard;
fields = Fields::empty();
}
PatKind::Deref { subpattern } => {
ctor = Single;
fields = Fields::singleton(cx, mkpat(subpattern));
}
PatKind::Leaf { subpatterns } | PatKind::Variant { subpatterns, .. } => {
match pat.ty.kind() {
ty::Tuple(fs) => {
ctor = Single;
let mut wilds: SmallVec<[_; 2]> =
fs.iter().map(|ty| DeconstructedPat::wildcard(ty, pat.span)).collect();
for pat in subpatterns {
wilds[pat.field.index()] = mkpat(&pat.pattern);
}
fields = Fields::from_iter(cx, wilds);
}
ty::Adt(adt, substs) if adt.is_box() => {
// The only legal patterns of type `Box` (outside `std`) are `_` and box
// patterns. If we're here we can assume this is a box pattern.
// FIXME(Nadrieril): A `Box` can in theory be matched either with `Box(_,
// _)` or a box pattern. As a hack to avoid an ICE with the former, we
// ignore other fields than the first one. This will trigger an error later
// anyway.
// See https://github.com/rust-lang/rust/issues/82772 ,
// explanation: https://github.com/rust-lang/rust/pull/82789#issuecomment-796921977
// The problem is that we can't know from the type whether we'll match
// normally or through box-patterns. We'll have to figure out a proper
// solution when we introduce generalized deref patterns. Also need to
// prevent mixing of those two options.
let pattern = subpatterns.into_iter().find(|pat| pat.field.index() == 0);
let pat = if let Some(pat) = pattern {
mkpat(&pat.pattern)
} else {
DeconstructedPat::wildcard(substs.type_at(0), pat.span)
};
ctor = Single;
fields = Fields::singleton(cx, pat);
}
ty::Adt(adt, _) => {
ctor = match pat.kind {
PatKind::Leaf { .. } => Single,
PatKind::Variant { variant_index, .. } => Variant(variant_index),
_ => bug!(),
};
let variant = &adt.variant(ctor.variant_index_for_adt(*adt));
// For each field in the variant, we store the relevant index into `self.fields` if any.
let mut field_id_to_id: Vec<Option<usize>> =
(0..variant.fields.len()).map(|_| None).collect();
let tys = Fields::list_variant_nonhidden_fields(cx, pat.ty, variant)
.enumerate()
.map(|(i, (field, ty))| {
field_id_to_id[field.index()] = Some(i);
ty
});
let mut wilds: SmallVec<[_; 2]> =
tys.map(|ty| DeconstructedPat::wildcard(ty, pat.span)).collect();
for pat in subpatterns {
if let Some(i) = field_id_to_id[pat.field.index()] {
wilds[i] = mkpat(&pat.pattern);
}
}
fields = Fields::from_iter(cx, wilds);
}
_ => bug!("pattern has unexpected type: pat: {:?}, ty: {:?}", pat, pat.ty),
}
}
PatKind::Constant { value } => {
if let Some(int_range) = IntRange::from_constant(cx.tcx, cx.param_env, *value) {
ctor = IntRange(int_range);
fields = Fields::empty();
} else {
match pat.ty.kind() {
ty::Float(_) => {
ctor = FloatRange(*value, *value, RangeEnd::Included);
fields = Fields::empty();
}
ty::Ref(_, t, _) if t.is_str() => {
// We want a `&str` constant to behave like a `Deref` pattern, to be compatible
// with other `Deref` patterns. This could have been done in `const_to_pat`,
// but that causes issues with the rest of the matching code.
// So here, the constructor for a `"foo"` pattern is `&` (represented by
// `Single`), and has one field. That field has constructor `Str(value)` and no
// fields.
// Note: `t` is `str`, not `&str`.
let subpattern =
DeconstructedPat::new(Str(*value), Fields::empty(), *t, pat.span);
ctor = Single;
fields = Fields::singleton(cx, subpattern)
}
// All constants that can be structurally matched have already been expanded
// into the corresponding `Pat`s by `const_to_pat`. Constants that remain are
// opaque.
_ => {
ctor = Opaque;
fields = Fields::empty();
}
}
}
}
&PatKind::Range(box PatRange { lo, hi, end }) => {
let ty = lo.ty();
ctor = if let Some(int_range) = IntRange::from_range(
cx.tcx,
lo.eval_bits(cx.tcx, cx.param_env, lo.ty()),
hi.eval_bits(cx.tcx, cx.param_env, hi.ty()),
ty,
&end,
) {
IntRange(int_range)
} else {
FloatRange(lo, hi, end)
};
fields = Fields::empty();
}
PatKind::Array { prefix, slice, suffix } | PatKind::Slice { prefix, slice, suffix } => {
let array_len = match pat.ty.kind() {
ty::Array(_, length) => {
Some(length.eval_target_usize(cx.tcx, cx.param_env) as usize)
}
ty::Slice(_) => None,
_ => span_bug!(pat.span, "bad ty {:?} for slice pattern", pat.ty),
};
let kind = if slice.is_some() {
VarLen(prefix.len(), suffix.len())
} else {
FixedLen(prefix.len() + suffix.len())
};
ctor = Slice(Slice::new(array_len, kind));
fields =
Fields::from_iter(cx, prefix.iter().chain(suffix.iter()).map(|p| mkpat(&*p)));
}
PatKind::Or { .. } => {
ctor = Or;
let pats = expand_or_pat(pat);
fields = Fields::from_iter(cx, pats.into_iter().map(mkpat));
}
}
DeconstructedPat::new(ctor, fields, pat.ty, pat.span)
}
pub(crate) fn to_pat(&self, cx: &MatchCheckCtxt<'p, 'tcx>) -> Pat<'tcx> {
let is_wildcard = |pat: &Pat<'_>| {
matches!(pat.kind, PatKind::Binding { subpattern: None, .. } | PatKind::Wild)
};
let mut subpatterns = self.iter_fields().map(|p| Box::new(p.to_pat(cx)));
let kind = match &self.ctor {
Single | Variant(_) => match self.ty.kind() {
ty::Tuple(..) => PatKind::Leaf {
subpatterns: subpatterns
.enumerate()
.map(|(i, pattern)| FieldPat { field: FieldIdx::new(i), pattern })
.collect(),
},
ty::Adt(adt_def, _) if adt_def.is_box() => {
// Without `box_patterns`, the only legal pattern of type `Box` is `_` (outside
// of `std`). So this branch is only reachable when the feature is enabled and
// the pattern is a box pattern.
PatKind::Deref { subpattern: subpatterns.next().unwrap() }
}
ty::Adt(adt_def, substs) => {
let variant_index = self.ctor.variant_index_for_adt(*adt_def);
let variant = &adt_def.variant(variant_index);
let subpatterns = Fields::list_variant_nonhidden_fields(cx, self.ty, variant)
.zip(subpatterns)
.map(|((field, _ty), pattern)| FieldPat { field, pattern })
.collect();
if adt_def.is_enum() {
PatKind::Variant { adt_def: *adt_def, substs, variant_index, subpatterns }
} else {
PatKind::Leaf { subpatterns }
}
}
// Note: given the expansion of `&str` patterns done in `expand_pattern`, we should
// be careful to reconstruct the correct constant pattern here. However a string
// literal pattern will never be reported as a non-exhaustiveness witness, so we
// ignore this issue.
ty::Ref(..) => PatKind::Deref { subpattern: subpatterns.next().unwrap() },
_ => bug!("unexpected ctor for type {:?} {:?}", self.ctor, self.ty),
},
Slice(slice) => {
match slice.kind {
FixedLen(_) => PatKind::Slice {
prefix: subpatterns.collect(),
slice: None,
suffix: Box::new([]),
},
VarLen(prefix, _) => {
let mut subpatterns = subpatterns.peekable();
let mut prefix: Vec<_> = subpatterns.by_ref().take(prefix).collect();
if slice.array_len.is_some() {
// Improves diagnostics a bit: if the type is a known-size array, instead
// of reporting `[x, _, .., _, y]`, we prefer to report `[x, .., y]`.
// This is incorrect if the size is not known, since `[_, ..]` captures
// arrays of lengths `>= 1` whereas `[..]` captures any length.
while !prefix.is_empty() && is_wildcard(prefix.last().unwrap()) {
prefix.pop();
}
while subpatterns.peek().is_some()
&& is_wildcard(subpatterns.peek().unwrap())
{
subpatterns.next();
}
}
let suffix: Box<[_]> = subpatterns.collect();
let wild = Pat::wildcard_from_ty(self.ty);
PatKind::Slice {
prefix: prefix.into_boxed_slice(),
slice: Some(Box::new(wild)),
suffix,
}
}
}
}
&Str(value) => PatKind::Constant { value },
&FloatRange(lo, hi, end) => PatKind::Range(Box::new(PatRange { lo, hi, end })),
IntRange(range) => return range.to_pat(cx.tcx, self.ty),
Wildcard | NonExhaustive => PatKind::Wild,
Missing { .. } => bug!(
"trying to convert a `Missing` constructor into a `Pat`; this is probably a bug,
`Missing` should have been processed in `apply_constructors`"
),
Opaque | Or => {
bug!("can't convert to pattern: {:?}", self)
}
};
Pat { ty: self.ty, span: DUMMY_SP, kind }
}
pub(super) fn is_or_pat(&self) -> bool {
matches!(self.ctor, Or)
}
pub(super) fn ctor(&self) -> &Constructor<'tcx> {
&self.ctor
}
pub(super) fn ty(&self) -> Ty<'tcx> {
self.ty
}
pub(super) fn span(&self) -> Span {
self.span
}
pub(super) fn iter_fields<'a>(
&'a self,
) -> impl Iterator<Item = &'p DeconstructedPat<'p, 'tcx>> + Captures<'a> {
self.fields.iter_patterns()
}
/// Specialize this pattern with a constructor.
/// `other_ctor` can be different from `self.ctor`, but must be covered by it.
pub(super) fn specialize<'a>(
&'a self,
pcx: &PatCtxt<'_, 'p, 'tcx>,
other_ctor: &Constructor<'tcx>,
) -> SmallVec<[&'p DeconstructedPat<'p, 'tcx>; 2]> {
match (&self.ctor, other_ctor) {
(Wildcard, _) => {
// We return a wildcard for each field of `other_ctor`.
Fields::wildcards(pcx, other_ctor).iter_patterns().collect()
}
(Slice(self_slice), Slice(other_slice))
if self_slice.arity() != other_slice.arity() =>
{
// The only tricky case: two slices of different arity. Since `self_slice` covers
// `other_slice`, `self_slice` must be `VarLen`, i.e. of the form
// `[prefix, .., suffix]`. Moreover `other_slice` is guaranteed to have a larger
// arity. So we fill the middle part with enough wildcards to reach the length of
// the new, larger slice.
match self_slice.kind {
FixedLen(_) => bug!("{:?} doesn't cover {:?}", self_slice, other_slice),
VarLen(prefix, suffix) => {
let (ty::Slice(inner_ty) | ty::Array(inner_ty, _)) = *self.ty.kind() else {
bug!("bad slice pattern {:?} {:?}", self.ctor, self.ty);
};
let prefix = &self.fields.fields[..prefix];
let suffix = &self.fields.fields[self_slice.arity() - suffix..];
let wildcard: &_ = pcx
.cx
.pattern_arena
.alloc(DeconstructedPat::wildcard(inner_ty, pcx.span));
let extra_wildcards = other_slice.arity() - self_slice.arity();
let extra_wildcards = (0..extra_wildcards).map(|_| wildcard);
prefix.iter().chain(extra_wildcards).chain(suffix).collect()
}
}
}
_ => self.fields.iter_patterns().collect(),
}
}
/// We keep track for each pattern if it was ever reachable during the analysis. This is used
/// with `unreachable_spans` to report unreachable subpatterns arising from or patterns.
pub(super) fn set_reachable(&self) {
self.reachable.set(true)
}
pub(super) fn is_reachable(&self) -> bool {
self.reachable.get()
}
/// Report the spans of subpatterns that were not reachable, if any.
pub(super) fn unreachable_spans(&self) -> Vec<Span> {
let mut spans = Vec::new();
self.collect_unreachable_spans(&mut spans);
spans
}
fn collect_unreachable_spans(&self, spans: &mut Vec<Span>) {
// We don't look at subpatterns if we already reported the whole pattern as unreachable.
if !self.is_reachable() {
spans.push(self.span);
} else {
for p in self.iter_fields() {
p.collect_unreachable_spans(spans);
}
}
}
}
/// This is mostly copied from the `Pat` impl. This is best effort and not good enough for a
/// `Display` impl.
impl<'p, 'tcx> fmt::Debug for DeconstructedPat<'p, 'tcx> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
// Printing lists is a chore.
let mut first = true;
let mut start_or_continue = |s| {
if first {
first = false;
""
} else {
s
}
};
let mut start_or_comma = || start_or_continue(", ");
match &self.ctor {
Single | Variant(_) => match self.ty.kind() {
ty::Adt(def, _) if def.is_box() => {
// Without `box_patterns`, the only legal pattern of type `Box` is `_` (outside
// of `std`). So this branch is only reachable when the feature is enabled and
// the pattern is a box pattern.
let subpattern = self.iter_fields().next().unwrap();
write!(f, "box {:?}", subpattern)
}
ty::Adt(..) | ty::Tuple(..) => {
let variant = match self.ty.kind() {
ty::Adt(adt, _) => Some(adt.variant(self.ctor.variant_index_for_adt(*adt))),
ty::Tuple(_) => None,
_ => unreachable!(),
};
if let Some(variant) = variant {
write!(f, "{}", variant.name)?;
}
// Without `cx`, we can't know which field corresponds to which, so we can't
// get the names of the fields. Instead we just display everything as a tuple
// struct, which should be good enough.
write!(f, "(")?;
for p in self.iter_fields() {
write!(f, "{}", start_or_comma())?;
write!(f, "{:?}", p)?;
}
write!(f, ")")
}
// Note: given the expansion of `&str` patterns done in `expand_pattern`, we should
// be careful to detect strings here. However a string literal pattern will never
// be reported as a non-exhaustiveness witness, so we can ignore this issue.
ty::Ref(_, _, mutbl) => {
let subpattern = self.iter_fields().next().unwrap();
write!(f, "&{}{:?}", mutbl.prefix_str(), subpattern)
}
_ => write!(f, "_"),
},
Slice(slice) => {
let mut subpatterns = self.fields.iter_patterns();
write!(f, "[")?;
match slice.kind {
FixedLen(_) => {
for p in subpatterns {
write!(f, "{}{:?}", start_or_comma(), p)?;
}
}
VarLen(prefix_len, _) => {
for p in subpatterns.by_ref().take(prefix_len) {
write!(f, "{}{:?}", start_or_comma(), p)?;
}
write!(f, "{}", start_or_comma())?;
write!(f, "..")?;
for p in subpatterns {
write!(f, "{}{:?}", start_or_comma(), p)?;
}
}
}
write!(f, "]")
}
&FloatRange(lo, hi, end) => {
write!(f, "{}", lo)?;
write!(f, "{}", end)?;
write!(f, "{}", hi)
}
IntRange(range) => write!(f, "{:?}", range), // Best-effort, will render e.g. `false` as `0..=0`
Wildcard | Missing { .. } | NonExhaustive => write!(f, "_ : {:?}", self.ty),
Or => {
for pat in self.iter_fields() {
write!(f, "{}{:?}", start_or_continue(" | "), pat)?;
}
Ok(())
}
Str(value) => write!(f, "{}", value),
Opaque => write!(f, "<constant pattern>"),
}
}
}