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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.rs | 1094 |
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() +} |