summaryrefslogtreecommitdiffstats
path: root/src/tools/rust-analyzer/crates/hir-ty/src/diagnostics/match_check/deconstruct_pat.rs
diff options
context:
space:
mode:
Diffstat (limited to 'src/tools/rust-analyzer/crates/hir-ty/src/diagnostics/match_check/deconstruct_pat.rs')
-rw-r--r--src/tools/rust-analyzer/crates/hir-ty/src/diagnostics/match_check/deconstruct_pat.rs1094
1 files changed, 1094 insertions, 0 deletions
diff --git a/src/tools/rust-analyzer/crates/hir-ty/src/diagnostics/match_check/deconstruct_pat.rs b/src/tools/rust-analyzer/crates/hir-ty/src/diagnostics/match_check/deconstruct_pat.rs
new file mode 100644
index 000000000..bbbe539c1
--- /dev/null
+++ b/src/tools/rust-analyzer/crates/hir-ty/src/diagnostics/match_check/deconstruct_pat.rs
@@ -0,0 +1,1094 @@
+//! [`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:
+//!
+//! ```
+//! 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`].
+
+use std::{
+ cell::Cell,
+ cmp::{max, min},
+ iter::once,
+ ops::RangeInclusive,
+};
+
+use hir_def::{EnumVariantId, HasModule, LocalFieldId, VariantId};
+use smallvec::{smallvec, SmallVec};
+use stdx::never;
+
+use crate::{infer::normalize, AdtId, Interner, Scalar, Ty, TyExt, TyKind};
+
+use super::{
+ is_box,
+ usefulness::{helper::Captures, MatchCheckCtx, PatCtxt},
+ FieldPat, Pat, PatKind,
+};
+
+use self::Constructor::*;
+
+/// Recursively expand this pattern into its subpatterns. Only useful for or-patterns.
+fn expand_or_pat(pat: &Pat) -> Vec<&Pat> {
+ fn expand<'p>(pat: &'p Pat, vec: &mut Vec<&'p Pat>) {
+ if let PatKind::Or { pats } = pat.kind.as_ref() {
+ for pat in pats {
+ expand(pat, vec);
+ }
+ } else {
+ vec.push(pat)
+ }
+ }
+
+ let mut pats = Vec::new();
+ expand(pat, &mut pats);
+ pats
+}
+
+/// [Constructor] uses this in umimplemented variants.
+/// It allows porting match expressions from upstream algorithm without losing semantics.
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub(super) enum Void {}
+
+/// 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, Debug, PartialEq, Eq)]
+pub(super) struct IntRange {
+ range: RangeInclusive<u128>,
+}
+
+impl IntRange {
+ #[inline]
+ fn is_integral(ty: &Ty) -> bool {
+ matches!(
+ ty.kind(Interner),
+ TyKind::Scalar(Scalar::Char | Scalar::Int(_) | Scalar::Uint(_) | Scalar::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 from_bool(value: bool) -> IntRange {
+ let val = value as u128;
+ IntRange { range: val..=val }
+ }
+
+ #[inline]
+ fn from_range(lo: u128, hi: u128, scalar_ty: Scalar) -> IntRange {
+ match scalar_ty {
+ Scalar::Bool => IntRange { range: lo..=hi },
+ _ => unimplemented!(),
+ }
+ }
+
+ 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) })
+ } else {
+ None
+ }
+ }
+
+ fn to_pat(&self, _cx: &MatchCheckCtx<'_, '_>, ty: Ty) -> Pat {
+ match ty.kind(Interner) {
+ TyKind::Scalar(Scalar::Bool) => {
+ let kind = match self.boundaries() {
+ (0, 0) => PatKind::LiteralBool { value: false },
+ (1, 1) => PatKind::LiteralBool { value: true },
+ (0, 1) => PatKind::Wild,
+ (lo, hi) => {
+ never!("bad range for bool pattern: {}..={}", lo, hi);
+ PatKind::Wild
+ }
+ };
+ Pat { ty, kind: kind.into() }
+ }
+ _ => unimplemented!(),
+ }
+ }
+
+ /// 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
+ }
+ }
+}
+
+/// 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:
+/// ```
+/// |-------------------------| // `self`
+/// |------| |----------| |----|
+/// |-------| |-------|
+/// ```
+/// would be iterated over as follows:
+/// ```
+/// ||---|--||-|---|---|---|--|
+/// ```
+#[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> + '_ {
+ 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(|(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 }
+ })
+ }
+}
+
+/// A constructor for array and slice patterns.
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub(super) struct Slice {
+ _unimplemented: Void,
+}
+
+impl Slice {
+ fn arity(self) -> usize {
+ match self._unimplemented {}
+ }
+
+ /// See `Constructor::is_covered_by`
+ fn is_covered_by(self, _other: Self) -> bool {
+ match self._unimplemented {}
+ }
+}
+
+/// 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`.
+#[allow(dead_code)]
+#[derive(Clone, Debug, PartialEq)]
+pub(super) enum Constructor {
+ /// The constructor for patterns that have a single constructor, like tuples, struct patterns
+ /// and fixed-length arrays.
+ Single,
+ /// Enum variants.
+ Variant(EnumVariantId),
+ /// Ranges of integer literal values (`2`, `2..=5` or `2..5`).
+ IntRange(IntRange),
+ /// Ranges of floating-point literal values (`2.0..=5.2`).
+ FloatRange(Void),
+ /// String literals. Strings are not quite the same as `&[u8]` so we treat them separately.
+ Str(Void),
+ /// 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 Constructor {
+ 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,
+ }
+ }
+
+ pub(super) fn is_unstable_variant(&self, _pcx: PatCtxt<'_, '_>) -> bool {
+ false //FIXME: implement this
+ }
+
+ pub(super) fn is_doc_hidden_variant(&self, _pcx: PatCtxt<'_, '_>) -> bool {
+ false //FIXME: implement this
+ }
+
+ fn variant_id_for_adt(&self, adt: hir_def::AdtId) -> VariantId {
+ match *self {
+ Variant(id) => id.into(),
+ Single => {
+ assert!(!matches!(adt, hir_def::AdtId::EnumId(_)));
+ match adt {
+ hir_def::AdtId::EnumId(_) => unreachable!(),
+ hir_def::AdtId::StructId(id) => id.into(),
+ hir_def::AdtId::UnionId(id) => id.into(),
+ }
+ }
+ _ => panic!("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<'_, '_>) -> usize {
+ match self {
+ Single | Variant(_) => match *pcx.ty.kind(Interner) {
+ TyKind::Tuple(arity, ..) => arity,
+ TyKind::Ref(..) => 1,
+ TyKind::Adt(adt, ..) => {
+ if is_box(adt.0, pcx.cx.db) {
+ // 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 = self.variant_id_for_adt(adt.0);
+ Fields::list_variant_nonhidden_fields(pcx.cx, pcx.ty, variant).count()
+ }
+ }
+ _ => {
+ never!("Unexpected type for `Single` constructor: {:?}", pcx.ty);
+ 0
+ }
+ },
+ Slice(slice) => slice.arity(),
+ Str(..)
+ | FloatRange(..)
+ | IntRange(..)
+ | NonExhaustive
+ | Opaque
+ | Missing { .. }
+ | Wildcard => 0,
+ Or => {
+ never!("The `Or` constructor doesn't have a fixed arity");
+ 0
+ }
+ }
+ }
+
+ /// 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<'_, '_>,
+ ctors: impl Iterator<Item = &'a Constructor> + Clone,
+ ) -> SmallVec<[Self; 1]> {
+ 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) => match slice._unimplemented {},
+ // 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(&self, _pcx: PatCtxt<'_, '_>, 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(void), FloatRange(..)) => match *void {},
+ (Str(void), Str(..)) => match *void {},
+ (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,
+
+ _ => {
+ never!("trying to compare incompatible constructors {:?} and {:?}", self, other);
+ // Continue with 'whatever is covered' supposed to result in false no-error diagnostic.
+ true
+ }
+ }
+ }
+
+ /// Faster version of `is_covered_by` when applied to many constructors. `used_ctors` is
+ /// assumed to be built from `matrix.head_ctors()` with wildcards filtered out, and `self` is
+ /// assumed to have been split from a wildcard.
+ fn is_covered_by_any(&self, _pcx: PatCtxt<'_, '_>, used_ctors: &[Constructor]) -> 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(_) => used_ctors.iter().any(|c| c == self),
+ 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 => {
+ never!("found unexpected ctor in all_ctors: {:?}", self);
+ true
+ }
+ }
+ }
+}
+
+/// 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 {
+ /// Constructors seen in the matrix.
+ matrix_ctors: Vec<Constructor>,
+ /// All the constructors for this type
+ all_ctors: SmallVec<[Constructor; 1]>,
+}
+
+impl SplitWildcard {
+ pub(super) fn new(pcx: PatCtxt<'_, '_>) -> Self {
+ let cx = pcx.cx;
+ let make_range = |start, end, scalar| IntRange(IntRange::from_range(start, end, scalar));
+
+ // Unhandled types are treated as non-exhaustive. Being explicit here instead of falling
+ // to catchall arm to ease further implementation.
+ let unhandled = || smallvec![NonExhaustive];
+
+ // 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(Interner) {
+ TyKind::Scalar(Scalar::Bool) => smallvec![make_range(0, 1, Scalar::Bool)],
+ // TyKind::Array(..) if ... => unhandled(),
+ TyKind::Array(..) | TyKind::Slice(..) => unhandled(),
+ &TyKind::Adt(AdtId(hir_def::AdtId::EnumId(enum_id)), ..) => {
+ let enum_data = cx.db.enum_data(enum_id);
+
+ // 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.feature_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 = enum_data.variants.is_empty()
+ && !is_exhaustive_pat_feature
+ && !pcx.is_top_level;
+
+ let mut ctors: SmallVec<[_; 1]> = enum_data
+ .variants
+ .iter()
+ .filter(|&(_, _v)| {
+ // If `exhaustive_patterns` is enabled, we exclude variants known to be
+ // uninhabited.
+ let is_uninhabited = is_exhaustive_pat_feature
+ && unimplemented!("after MatchCheckCtx.feature_exhaustive_patterns()");
+ !is_uninhabited
+ })
+ .map(|(local_id, _)| Variant(EnumVariantId { parent: enum_id, local_id }))
+ .collect();
+
+ if is_secretly_empty || is_declared_nonexhaustive {
+ ctors.push(NonExhaustive);
+ }
+ ctors
+ }
+ TyKind::Scalar(Scalar::Char) => unhandled(),
+ TyKind::Scalar(Scalar::Int(..) | Scalar::Uint(..)) => unhandled(),
+ TyKind::Never if !cx.feature_exhaustive_patterns() && !pcx.is_top_level => {
+ smallvec![NonExhaustive]
+ }
+ TyKind::Never => SmallVec::new(),
+ _ if cx.is_uninhabited(pcx.ty) => SmallVec::new(),
+ TyKind::Adt(..) | TyKind::Tuple(..) | TyKind::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<'_, '_>,
+ ctors: impl Iterator<Item = &'a Constructor> + Clone,
+ ) {
+ // 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| !c.is_wildcard()).cloned().collect();
+ }
+
+ /// Whether there are any value constructors for this type that are not present in the matrix.
+ fn any_missing(&self, pcx: PatCtxt<'_, '_>) -> 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: PatCtxt<'a, 'p>,
+ ) -> impl Iterator<Item = &'a Constructor> + 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<'_, '_>) -> SmallVec<[Constructor; 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), _, _, _]`.
+/// ```rust
+/// 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 `mir::Field` you must use
+/// `index_with_declared_idx`.
+#[derive(Clone, Copy)]
+pub(super) struct Fields<'p> {
+ fields: &'p [DeconstructedPat<'p>],
+}
+
+impl<'p> Fields<'p> {
+ fn empty() -> Self {
+ Fields { fields: &[] }
+ }
+
+ fn singleton(cx: &MatchCheckCtx<'_, 'p>, field: DeconstructedPat<'p>) -> Self {
+ let field = cx.pattern_arena.alloc(field);
+ Fields { fields: std::slice::from_ref(field) }
+ }
+
+ pub(super) fn from_iter(
+ cx: &MatchCheckCtx<'_, 'p>,
+ fields: impl IntoIterator<Item = DeconstructedPat<'p>>,
+ ) -> Self {
+ let fields: &[_] = cx.pattern_arena.alloc_extend(fields);
+ Fields { fields }
+ }
+
+ fn wildcards_from_tys(cx: &MatchCheckCtx<'_, 'p>, tys: impl IntoIterator<Item = Ty>) -> Self {
+ Fields::from_iter(cx, tys.into_iter().map(DeconstructedPat::wildcard))
+ }
+
+ // 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 MatchCheckCtx<'a, 'p>,
+ ty: &'a Ty,
+ variant: VariantId,
+ ) -> impl Iterator<Item = (LocalFieldId, Ty)> + Captures<'a> + Captures<'p> {
+ let (adt, substs) = ty.as_adt().unwrap();
+
+ let adt_is_local = variant.module(cx.db.upcast()).krate() == cx.module.krate();
+ // Whether we must not match the fields of this variant exhaustively.
+ let is_non_exhaustive = is_field_list_non_exhaustive(variant, cx) && !adt_is_local;
+
+ let visibility = cx.db.field_visibilities(variant);
+ let field_ty = cx.db.field_types(variant);
+ let fields_len = variant.variant_data(cx.db.upcast()).fields().len() as u32;
+
+ (0..fields_len).map(|idx| LocalFieldId::from_raw(idx.into())).filter_map(move |fid| {
+ let ty = field_ty[fid].clone().substitute(Interner, substs);
+ let ty = normalize(cx.db, cx.body, ty);
+ let is_visible = matches!(adt, hir_def::AdtId::EnumId(..))
+ || visibility[fid].is_visible_from(cx.db.upcast(), cx.module);
+ let is_uninhabited = cx.is_uninhabited(&ty);
+
+ if is_uninhabited && (!is_visible || is_non_exhaustive) {
+ None
+ } else {
+ Some((fid, ty))
+ }
+ })
+ }
+
+ /// Creates a new list of wildcard fields for a given constructor. The result must have a
+ /// length of `constructor.arity()`.
+ pub(crate) fn wildcards(
+ cx: &MatchCheckCtx<'_, 'p>,
+ ty: &Ty,
+ constructor: &Constructor,
+ ) -> Self {
+ let ret = match constructor {
+ Single | Variant(_) => match ty.kind(Interner) {
+ TyKind::Tuple(_, substs) => {
+ let tys = substs.iter(Interner).map(|ty| ty.assert_ty_ref(Interner));
+ Fields::wildcards_from_tys(cx, tys.cloned())
+ }
+ TyKind::Ref(.., rty) => Fields::wildcards_from_tys(cx, once(rty.clone())),
+ &TyKind::Adt(AdtId(adt), ref substs) => {
+ if is_box(adt, cx.db) {
+ // 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.
+ let subst_ty = substs.at(Interner, 0).assert_ty_ref(Interner).clone();
+ Fields::wildcards_from_tys(cx, once(subst_ty))
+ } else {
+ let variant = constructor.variant_id_for_adt(adt);
+ let tys = Fields::list_variant_nonhidden_fields(cx, ty, variant)
+ .map(|(_, ty)| ty);
+ Fields::wildcards_from_tys(cx, tys)
+ }
+ }
+ ty_kind => {
+ never!("Unexpected type for `Single` constructor: {:?}", ty_kind);
+ Fields::wildcards_from_tys(cx, once(ty.clone()))
+ }
+ },
+ Slice(slice) => match slice._unimplemented {},
+ Str(..)
+ | FloatRange(..)
+ | IntRange(..)
+ | NonExhaustive
+ | Opaque
+ | Missing { .. }
+ | Wildcard => Fields::empty(),
+ Or => {
+ never!("called `Fields::wildcards` on an `Or` ctor");
+ Fields::empty()
+ }
+ };
+ ret
+ }
+
+ /// Returns the list of patterns.
+ pub(super) fn iter_patterns<'a>(
+ &'a self,
+ ) -> impl Iterator<Item = &'p DeconstructedPat<'p>> + 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> {
+ ctor: Constructor,
+ fields: Fields<'p>,
+ ty: Ty,
+ reachable: Cell<bool>,
+}
+
+impl<'p> DeconstructedPat<'p> {
+ pub(super) fn wildcard(ty: Ty) -> Self {
+ Self::new(Wildcard, Fields::empty(), ty)
+ }
+
+ pub(super) fn new(ctor: Constructor, fields: Fields<'p>, ty: Ty) -> Self {
+ DeconstructedPat { ctor, fields, ty, 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>, ctor: Constructor) -> Self {
+ let fields = Fields::wildcards(pcx.cx, pcx.ty, &ctor);
+ DeconstructedPat::new(ctor, fields, pcx.ty.clone())
+ }
+
+ /// 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.clone())
+ }
+
+ pub(crate) fn from_pat(cx: &MatchCheckCtx<'_, 'p>, pat: &Pat) -> Self {
+ let mkpat = |pat| DeconstructedPat::from_pat(cx, pat);
+ let ctor;
+ let fields;
+ match pat.kind.as_ref() {
+ 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(Interner) {
+ TyKind::Tuple(_, substs) => {
+ ctor = Single;
+ let mut wilds: SmallVec<[_; 2]> = substs
+ .iter(Interner)
+ .map(|arg| arg.assert_ty_ref(Interner).clone())
+ .map(DeconstructedPat::wildcard)
+ .collect();
+ for pat in subpatterns {
+ let idx: u32 = pat.field.into_raw().into();
+ wilds[idx as usize] = mkpat(&pat.pattern);
+ }
+ fields = Fields::from_iter(cx, wilds)
+ }
+ TyKind::Adt(adt, substs) if is_box(adt.0, cx.db) => {
+ // 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 pat =
+ subpatterns.iter().find(|pat| pat.field.into_raw() == 0u32.into());
+ let field = if let Some(pat) = pat {
+ mkpat(&pat.pattern)
+ } else {
+ let ty = substs.at(Interner, 0).assert_ty_ref(Interner).clone();
+ DeconstructedPat::wildcard(ty)
+ };
+ ctor = Single;
+ fields = Fields::singleton(cx, field)
+ }
+ &TyKind::Adt(adt, _) => {
+ ctor = match pat.kind.as_ref() {
+ PatKind::Leaf { .. } => Single,
+ PatKind::Variant { enum_variant, .. } => Variant(*enum_variant),
+ _ => {
+ never!();
+ Wildcard
+ }
+ };
+ let variant = ctor.variant_id_for_adt(adt.0);
+ let fields_len = variant.variant_data(cx.db.upcast()).fields().len();
+ // 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>> = vec![None; fields_len];
+ let tys = Fields::list_variant_nonhidden_fields(cx, &pat.ty, variant)
+ .enumerate()
+ .map(|(i, (fid, ty))| {
+ let field_idx: u32 = fid.into_raw().into();
+ field_id_to_id[field_idx as usize] = Some(i);
+ ty
+ });
+ let mut wilds: SmallVec<[_; 2]> =
+ tys.map(DeconstructedPat::wildcard).collect();
+ for pat in subpatterns {
+ let field_idx: u32 = pat.field.into_raw().into();
+ if let Some(i) = field_id_to_id[field_idx as usize] {
+ wilds[i] = mkpat(&pat.pattern);
+ }
+ }
+ fields = Fields::from_iter(cx, wilds);
+ }
+ _ => {
+ never!("pattern has unexpected type: pat: {:?}, ty: {:?}", pat, &pat.ty);
+ ctor = Wildcard;
+ fields = Fields::empty();
+ }
+ }
+ }
+ &PatKind::LiteralBool { value } => {
+ ctor = IntRange(IntRange::from_bool(value));
+ fields = Fields::empty();
+ }
+ PatKind::Or { .. } => {
+ ctor = Or;
+ let pats: SmallVec<[_; 2]> = expand_or_pat(pat).into_iter().map(mkpat).collect();
+ fields = Fields::from_iter(cx, pats)
+ }
+ }
+ DeconstructedPat::new(ctor, fields, pat.ty.clone())
+ }
+
+ pub(crate) fn to_pat(&self, cx: &MatchCheckCtx<'_, 'p>) -> Pat {
+ let mut subpatterns = self.iter_fields().map(|p| p.to_pat(cx));
+ let pat = match &self.ctor {
+ Single | Variant(_) => match self.ty.kind(Interner) {
+ TyKind::Tuple(..) => PatKind::Leaf {
+ subpatterns: subpatterns
+ .zip(0u32..)
+ .map(|(p, i)| FieldPat {
+ field: LocalFieldId::from_raw(i.into()),
+ pattern: p,
+ })
+ .collect(),
+ },
+ TyKind::Adt(adt, _) if is_box(adt.0, cx.db) => {
+ // 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() }
+ }
+ TyKind::Adt(adt, substs) => {
+ let variant = self.ctor.variant_id_for_adt(adt.0);
+ let subpatterns = Fields::list_variant_nonhidden_fields(cx, self.ty(), variant)
+ .zip(subpatterns)
+ .map(|((field, _ty), pattern)| FieldPat { field, pattern })
+ .collect();
+
+ if let VariantId::EnumVariantId(enum_variant) = variant {
+ PatKind::Variant { substs: substs.clone(), enum_variant, 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.
+ TyKind::Ref(..) => PatKind::Deref { subpattern: subpatterns.next().unwrap() },
+ _ => {
+ never!("unexpected ctor for type {:?} {:?}", self.ctor, self.ty);
+ PatKind::Wild
+ }
+ },
+ &Slice(slice) => match slice._unimplemented {},
+ &Str(void) => match void {},
+ &FloatRange(void) => match void {},
+ IntRange(range) => return range.to_pat(cx, self.ty.clone()),
+ Wildcard | NonExhaustive => PatKind::Wild,
+ Missing { .. } => {
+ never!(
+ "trying to convert a `Missing` constructor into a `Pat`; this is a bug, \
+ `Missing` should have been processed in `apply_constructors`"
+ );
+ PatKind::Wild
+ }
+ Opaque | Or => {
+ never!("can't convert to pattern: {:?}", self.ctor);
+ PatKind::Wild
+ }
+ };
+ Pat { ty: self.ty.clone(), kind: Box::new(pat) }
+ }
+
+ pub(super) fn is_or_pat(&self) -> bool {
+ matches!(self.ctor, Or)
+ }
+
+ pub(super) fn ctor(&self) -> &Constructor {
+ &self.ctor
+ }
+
+ pub(super) fn ty(&self) -> &Ty {
+ &self.ty
+ }
+
+ pub(super) fn iter_fields<'a>(&'a self) -> impl Iterator<Item = &'p DeconstructedPat<'p>> + '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,
+ cx: &MatchCheckCtx<'_, 'p>,
+ other_ctor: &Constructor,
+ ) -> SmallVec<[&'p DeconstructedPat<'p>; 2]> {
+ match (&self.ctor, other_ctor) {
+ (Wildcard, _) => {
+ // We return a wildcard for each field of `other_ctor`.
+ Fields::wildcards(cx, &self.ty, other_ctor).iter_patterns().collect()
+ }
+ (Slice(self_slice), Slice(other_slice))
+ if self_slice.arity() != other_slice.arity() =>
+ {
+ match self_slice._unimplemented {}
+ }
+ _ => 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()
+ }
+}
+
+fn is_field_list_non_exhaustive(variant_id: VariantId, cx: &MatchCheckCtx<'_, '_>) -> bool {
+ let attr_def_id = match variant_id {
+ VariantId::EnumVariantId(id) => id.into(),
+ VariantId::StructId(id) => id.into(),
+ VariantId::UnionId(id) => id.into(),
+ };
+ cx.db.attrs(attr_def_id).by_key("non_exhaustive").exists()
+}
generated by cgit v1.2.3 (git 2.39.1) at 2024-06-21 16:40:11 +0000