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Diffstat (limited to 'crates/hir-ty/src/diagnostics/match_check/deconstruct_pat.rs')
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diff --git a/crates/hir-ty/src/diagnostics/match_check/deconstruct_pat.rs b/crates/hir-ty/src/diagnostics/match_check/deconstruct_pat.rs deleted file mode 100644 index f066f8b798..0000000000 --- a/crates/hir-ty/src/diagnostics/match_check/deconstruct_pat.rs +++ /dev/null @@ -1,1098 +0,0 @@ -//! [`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, inhabitedness::is_enum_variant_uninhabited_from, 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 unimplemented 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 {self:?} for adt {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(pcx.cx.db, adt.0) { - // 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)), subst) => { - 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() - .map(|&(variant, _)| variant) - .filter(|&variant| { - // If `exhaustive_patterns` is enabled, we exclude variants known to be - // uninhabited. - let is_uninhabited = is_exhaustive_pat_feature - && is_enum_variant_uninhabited_from(variant, subst, cx.module, cx.db); - !is_uninhabited - }) - .map(Variant) - .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.db.trait_environment_for_body(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(cx.db, adt) { - // 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(cx.db, adt.0) => { - // 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(cx.db, adt.0) => { - // 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() -} |