From c3c2893f302d087ff3c1ddd3a1d4e88c03c4356b Mon Sep 17 00:00:00 2001 From: Dawer <7803845+iDawer@users.noreply.github.com> Date: Thu, 22 Apr 2021 20:17:27 +0500 Subject: Update match checking. fn is_useful , more skeletons Specify a lifetime on pattern references impl PatStack fill impl Matrix PatStack::pop_head_constructor Index-based approach struct PatCtxt fields construction fn Fields::wildcards split wildcard fn Constructor::is_covered_by_any(..) fn Matrix::specialize_constructor(..) impl Usefulness Initial work on witness construction Reorganize files Replace match checking diagnostic Handle types of expanded patterns unit match checking go brrr --- .../src/diagnostics/pattern/deconstruct_pat.rs | 627 ++++++++++++++++++ .../hir_ty/src/diagnostics/pattern/usefulness.rs | 736 +++++++++++++++++++++ 2 files changed, 1363 insertions(+) create mode 100644 crates/hir_ty/src/diagnostics/pattern/deconstruct_pat.rs create mode 100644 crates/hir_ty/src/diagnostics/pattern/usefulness.rs (limited to 'crates/hir_ty/src/diagnostics/pattern') diff --git a/crates/hir_ty/src/diagnostics/pattern/deconstruct_pat.rs b/crates/hir_ty/src/diagnostics/pattern/deconstruct_pat.rs new file mode 100644 index 000000000..cde04409e --- /dev/null +++ b/crates/hir_ty/src/diagnostics/pattern/deconstruct_pat.rs @@ -0,0 +1,627 @@ +use hir_def::{ + expr::{Pat, PatId}, + AttrDefId, EnumVariantId, HasModule, VariantId, +}; + +use smallvec::{smallvec, SmallVec}; + +use crate::{AdtId, Interner, Scalar, Ty, TyExt, TyKind}; + +use super::usefulness::{MatchCheckCtx, PatCtxt}; + +use self::Constructor::*; + +#[derive(Copy, Clone, Debug, PartialEq, Eq)] +pub(super) enum ToDo {} + +#[derive(Clone, Debug, PartialEq, Eq)] +pub(super) struct IntRange { + range: ToDo, +} + +impl IntRange { + #[inline] + fn is_integral(ty: &Ty) -> bool { + match ty.kind(&Interner) { + TyKind::Scalar(Scalar::Char) + | TyKind::Scalar(Scalar::Int(_)) + | TyKind::Scalar(Scalar::Uint(_)) + | TyKind::Scalar(Scalar::Bool) => true, + _ => false, + } + } + + /// See `Constructor::is_covered_by` + fn is_covered_by(&self, other: &Self) -> bool { + todo!() + } +} + +/// A constructor for array and slice patterns. +#[derive(Copy, Clone, Debug, PartialEq, Eq)] +pub(super) struct Slice { + todo: ToDo, +} + +impl Slice { + /// See `Constructor::is_covered_by` + fn is_covered_by(self, other: Self) -> bool { + todo!() + } +} + +/// A value can be decomposed into a constructor applied to some fields. This struct represents +/// the constructor. See also `Fields`. +/// +/// `pat_constructor` retrieves the constructor corresponding to a pattern. +/// `specialize_constructor` returns the list of fields corresponding to a pattern, given a +/// constructor. `Constructor::apply` reconstructs the pattern from a pair of `Constructor` and +/// `Fields`. +#[derive(Clone, Debug, PartialEq)] +pub(super) enum Constructor { + /// 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), + /// Array and slice patterns. + Slice(Slice), + /// Stands for constructors that are not seen in the matrix, as explained in the documentation + /// for [`SplitWildcard`]. + Missing, + /// Wildcard pattern. + Wildcard, +} + +impl Constructor { + pub(super) fn is_wildcard(&self) -> bool { + matches!(self, Wildcard) + } + + fn as_int_range(&self) -> Option<&IntRange> { + match self { + IntRange(range) => Some(range), + _ => None, + } + } + + fn as_slice(&self) -> Option { + match self { + Slice(slice) => Some(*slice), + _ => None, + } + } + + fn variant_id_for_adt(&self, adt: hir_def::AdtId, cx: &MatchCheckCtx<'_>) -> 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), + } + } + + pub(super) fn from_pat(cx: &MatchCheckCtx<'_>, pat: PatId) -> Self { + match &cx.pattern_arena.borrow()[pat] { + Pat::Bind { .. } | Pat::Wild => Wildcard, + Pat::Tuple { .. } | Pat::Ref { .. } | Pat::Box { .. } => Single, + + pat => todo!("Constructor::from_pat {:?}", pat), + // Pat::Missing => {} + // Pat::Or(_) => {} + // Pat::Record { path, args, ellipsis } => {} + // Pat::Range { start, end } => {} + // Pat::Slice { prefix, slice, suffix } => {} + // Pat::Path(_) => {} + // Pat::Lit(_) => {} + // Pat::TupleStruct { path, args, ellipsis } => {} + // Pat::ConstBlock(_) => {} + } + } + + /// 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 + 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(_) => todo!("Constructor::split IntRange"), + Slice(_) => todo!("Constructor::split Slice"), + // 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, + + (Constructor::IntRange(_), Constructor::IntRange(_)) => todo!(), + + (Constructor::Slice(_), Constructor::Slice(_)) => todo!(), + + _ => panic!("bug"), + } + } + + /// 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)), + + _ => todo!(), + } + } +} + +/// 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, + /// 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| IntRange(todo!()); + + // 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::Adt(AdtId(hir_def::AdtId::EnumId(_)), _) => todo!(), + TyKind::Adt(..) | TyKind::Tuple(..) | TyKind::Ref(..) => smallvec![Single], + _ => todo!(), + }; + 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 + 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>( + &'a self, + pcx: &'a PatCtxt<'_>, + ) -> impl Iterator { + 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 `(, , + // 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 { + Missing + } else { + Wildcard + }; + return smallvec![ctor]; + } + + // All the constructors are present in the matrix, so we just go through them all. + self.all_ctors + } +} + +#[test] +fn it_works2() {} + +/// Some fields need to be explicitly hidden away in certain cases; see the comment above the +/// `Fields` struct. This struct represents such a potentially-hidden field. +#[derive(Debug, Copy, Clone)] +pub(super) enum FilteredField { + Kept(PatId), + Hidden, +} + +impl FilteredField { + fn kept(self) -> Option { + match self { + FilteredField::Kept(p) => Some(p), + FilteredField::Hidden => None, + } + } +} + +/// 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 from a constructor using [`Fields::wildcards()`]. +/// +/// If a private or `non_exhaustive` field is uninhabited, the code mustn't observe that it is +/// uninhabited. For that, we filter these fields out of the matrix. This is handled automatically +/// in `Fields`. This filtering is uncommon in practice, because uninhabited fields are rarely used, +/// so we avoid it when possible to preserve performance. +#[derive(Debug, Clone)] +pub(super) enum Fields { + /// Lists of patterns that don't contain any filtered fields. + /// `Slice` and `Vec` behave the same; the difference is only to avoid allocating and + /// triple-dereferences when possible. Frankly this is premature optimization, I (Nadrieril) + /// have not measured if it really made a difference. + Vec(SmallVec<[PatId; 2]>), +} + +impl Fields { + /// Internal use. Use `Fields::wildcards()` instead. + /// Must not be used if the pattern is a field of a struct/tuple/variant. + fn from_single_pattern(pat: PatId) -> Self { + Fields::Vec(smallvec![pat]) + } + + /// Convenience; internal use. + fn wildcards_from_tys<'a>( + cx: &MatchCheckCtx<'_>, + tys: impl IntoIterator, + ) -> Self { + let wilds = tys.into_iter().map(|ty| (Pat::Wild, ty)); + let pats = wilds.map(|(pat, ty)| cx.alloc_pat(pat, ty)).collect(); + Fields::Vec(pats) + } + + pub(crate) fn wildcards(pcx: &PatCtxt<'_>, constructor: &Constructor) -> Self { + let ty = &pcx.ty; + let cx = pcx.cx; + let wildcard_from_ty = |ty| cx.alloc_pat(Pat::Wild, ty); + + 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) + } + TyKind::Ref(.., rty) => Fields::from_single_pattern(wildcard_from_ty(rty)), + TyKind::Adt(AdtId(adt), substs) => { + let adt_is_box = false; // TODO(iDawer): handle box patterns + if adt_is_box { + // Use T as the sub pattern type of Box. + let ty = substs.at(&Interner, 0).assert_ty_ref(&Interner); + Fields::from_single_pattern(wildcard_from_ty(ty)) + } else { + let variant_id = constructor.variant_id_for_adt(*adt, cx); + let variant = variant_id.variant_data(cx.db.upcast()); + let adt_is_local = variant_id.module(cx.db.upcast()).krate() == cx.krate; + // Whether we must not match the fields of this variant exhaustively. + let is_non_exhaustive = + is_field_list_non_exhaustive(variant_id, cx) && !adt_is_local; + let field_ty_arena = cx.db.field_types(variant_id); + let field_tys = + || field_ty_arena.iter().map(|(_, binders)| binders.skip_binders()); + // In the following cases, we don't need to filter out any fields. This is + // the vast majority of real cases, since uninhabited fields are uncommon. + let has_no_hidden_fields = (matches!(adt, hir_def::AdtId::EnumId(_)) + && !is_non_exhaustive) + || !field_tys().any(|ty| cx.is_uninhabited(ty)); + + if has_no_hidden_fields { + Fields::wildcards_from_tys(cx, field_tys()) + } else { + //FIXME(iDawer): see MatchCheckCtx::is_uninhabited + unimplemented!("exhaustive_patterns feature") + } + } + } + _ => panic!("Unexpected type for `Single` constructor: {:?}", ty), + }, + Missing | Wildcard => Fields::Vec(Default::default()), + _ => todo!(), + }; + ret + } + + /// Apply a constructor to a list of patterns, yielding a new pattern. `self` + /// must have as many elements as this constructor's arity. + /// + /// This is roughly the inverse of `specialize_constructor`. + /// + /// Examples: + /// `ctor`: `Constructor::Single` + /// `ty`: `Foo(u32, u32, u32)` + /// `self`: `[10, 20, _]` + /// returns `Foo(10, 20, _)` + /// + /// `ctor`: `Constructor::Variant(Option::Some)` + /// `ty`: `Option` + /// `self`: `[false]` + /// returns `Some(false)` + pub(super) fn apply(self, pcx: &PatCtxt<'_>, ctor: &Constructor) -> Pat { + let subpatterns_and_indices = self.patterns_and_indices(); + let mut subpatterns = subpatterns_and_indices.iter().map(|&(_, p)| p); + + match ctor { + Single | Variant(_) => match pcx.ty.kind(&Interner) { + TyKind::Adt(..) | TyKind::Tuple(..) => { + // We want the real indices here. + // TODO indices + let subpatterns = subpatterns_and_indices.iter().map(|&(_, pat)| pat).collect(); + + if let Some((adt, substs)) = pcx.ty.as_adt() { + if let hir_def::AdtId::EnumId(_) = adt { + todo!() + } else { + todo!() + } + } else { + // TODO ellipsis + Pat::Tuple { args: subpatterns, ellipsis: None } + } + } + + _ => todo!(), + // TyKind::AssociatedType(_, _) => {} + // TyKind::Scalar(_) => {} + // TyKind::Array(_, _) => {} + // TyKind::Slice(_) => {} + // TyKind::Raw(_, _) => {} + // TyKind::Ref(_, _, _) => {} + // TyKind::OpaqueType(_, _) => {} + // TyKind::FnDef(_, _) => {} + // TyKind::Str => {} + // TyKind::Never => {} + // TyKind::Closure(_, _) => {} + // TyKind::Generator(_, _) => {} + // TyKind::GeneratorWitness(_, _) => {} + // TyKind::Foreign(_) => {} + // TyKind::Error => {} + // TyKind::Placeholder(_) => {} + // TyKind::Dyn(_) => {} + // TyKind::Alias(_) => {} + // TyKind::Function(_) => {} + // TyKind::BoundVar(_) => {} + // TyKind::InferenceVar(_, _) => {} + }, + + _ => todo!(), + // Constructor::IntRange(_) => {} + // Constructor::Slice(_) => {} + // Missing => {} + // Wildcard => {} + } + } + + /// Returns the number of patterns. This is the same as the arity of the constructor used to + /// construct `self`. + pub(super) fn len(&self) -> usize { + match self { + Fields::Vec(pats) => pats.len(), + } + } + + /// Returns the list of patterns along with the corresponding field indices. + fn patterns_and_indices(&self) -> SmallVec<[(usize, PatId); 2]> { + match self { + Fields::Vec(pats) => pats.iter().copied().enumerate().collect(), + } + } + + pub(super) fn into_patterns(self) -> SmallVec<[PatId; 2]> { + match self { + Fields::Vec(pats) => pats, + } + } + + /// Overrides some of the fields with the provided patterns. Exactly like + /// `replace_fields_indexed`, except that it takes `FieldPat`s as input. + fn replace_with_fieldpats(&self, new_pats: impl IntoIterator) -> Self { + self.replace_fields_indexed(new_pats.into_iter().enumerate()) + } + + /// Overrides some of the fields with the provided patterns. This is used when a pattern + /// defines some fields but not all, for example `Foo { field1: Some(_), .. }`: here we start + /// with a `Fields` that is just one wildcard per field of the `Foo` struct, and override the + /// entry corresponding to `field1` with the pattern `Some(_)`. This is also used for slice + /// patterns for the same reason. + fn replace_fields_indexed(&self, new_pats: impl IntoIterator) -> Self { + let mut fields = self.clone(); + + match &mut fields { + Fields::Vec(pats) => { + for (i, pat) in new_pats { + if let Some(p) = pats.get_mut(i) { + *p = pat; + } + } + } + } + fields + } + + /// Replaces contained fields with the given list of patterns. There must be `len()` patterns + /// in `pats`. + pub(super) fn replace_fields( + &self, + cx: &MatchCheckCtx<'_>, + pats: impl IntoIterator, + ) -> Self { + let pats = { + let mut arena = cx.pattern_arena.borrow_mut(); + pats.into_iter().map(move |pat| /* arena.alloc(pat) */ todo!()).collect() + }; + + match self { + Fields::Vec(_) => Fields::Vec(pats), + } + } + + /// Replaces contained fields with the arguments of the given pattern. Only use on a pattern + /// that is compatible with the constructor used to build `self`. + /// This is meant to be used on the result of `Fields::wildcards()`. The idea is that + /// `wildcards` constructs a list of fields where all entries are wildcards, and the pattern + /// provided to this function fills some of the fields with non-wildcards. + /// In the following example `Fields::wildcards` would return `[_, _, _, _]`. If we call + /// `replace_with_pattern_arguments` on it with the pattern, the result will be `[Some(0), _, + /// _, _]`. + /// ```rust + /// let x: [Option; 4] = foo(); + /// match x { + /// [Some(0), ..] => {} + /// } + /// ``` + /// This is guaranteed to preserve the number of patterns in `self`. + pub(super) fn replace_with_pattern_arguments( + &self, + pat: PatId, + cx: &MatchCheckCtx<'_>, + ) -> Self { + match &cx.pattern_arena.borrow()[pat] { + Pat::Ref { pat: subpattern, .. } => { + assert_eq!(self.len(), 1); + Fields::from_single_pattern(*subpattern) + } + Pat::Tuple { args: subpatterns, ellipsis } => { + // FIXME(iDawer) handle ellipsis. + // XXX(iDawer): in rustc, this is handled by HIR->TypedHIR lowering + // rustc_mir_build::thir::pattern::PatCtxt::lower_tuple_subpats(..) + self.replace_with_fieldpats(subpatterns.iter().copied()) + } + + Pat::Wild => self.clone(), + pat => todo!("Fields::replace_with_pattern_arguments({:?})", pat), + // Pat::Missing => {} + // Pat::Or(_) => {} + // Pat::Record { path, args, ellipsis } => {} + // Pat::Range { start, end } => {} + // Pat::Slice { prefix, slice, suffix } => {} + // Pat::Path(_) => {} + // Pat::Lit(_) => {} + // Pat::Bind { mode, name, subpat } => {} + // Pat::TupleStruct { path, args, ellipsis } => {} + // Pat::Box { inner } => {} + // Pat::ConstBlock(_) => {} + } + } +} + +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() +} + +#[test] +fn it_works() {} diff --git a/crates/hir_ty/src/diagnostics/pattern/usefulness.rs b/crates/hir_ty/src/diagnostics/pattern/usefulness.rs new file mode 100644 index 000000000..f5f6bf494 --- /dev/null +++ b/crates/hir_ty/src/diagnostics/pattern/usefulness.rs @@ -0,0 +1,736 @@ +// Based on rust-lang/rust 1.52.0-nightly (25c15cdbe 2021-04-22) +// rust/compiler/rustc_mir_build/src/thir/pattern/usefulness.rs + +use std::{cell::RefCell, iter::FromIterator, ops::Index, sync::Arc}; + +use base_db::CrateId; +use hir_def::{ + body::Body, + expr::{ExprId, Pat, PatId}, +}; +use la_arena::Arena; +use once_cell::unsync::OnceCell; +use rustc_hash::FxHashMap; +use smallvec::{smallvec, SmallVec}; + +use crate::{db::HirDatabase, InferenceResult, Ty}; + +use super::deconstruct_pat::{Constructor, Fields, SplitWildcard}; + +use self::{ + helper::{Captures, PatIdExt}, + Usefulness::*, + WitnessPreference::*, +}; + +pub(crate) struct MatchCheckCtx<'a> { + pub(crate) krate: CrateId, + pub(crate) match_expr: ExprId, + pub(crate) body: Arc, + pub(crate) infer: &'a InferenceResult, + pub(crate) db: &'a dyn HirDatabase, + /// Patterns from self.body.pats plus generated by the check. + pub(crate) pattern_arena: &'a RefCell, +} + +impl<'a> MatchCheckCtx<'a> { + pub(super) fn is_uninhabited(&self, ty: &Ty) -> bool { + // FIXME(iDawer) implement exhaustive_patterns feature. More info in: + // Tracking issue for RFC 1872: exhaustive_patterns feature https://github.com/rust-lang/rust/issues/51085 + false + } + + pub(super) fn alloc_pat(&self, pat: Pat, ty: &Ty) -> PatId { + self.pattern_arena.borrow_mut().alloc(pat, ty) + } + + /// Get type of a pattern. Handles expanded patterns. + pub(super) fn type_of(&self, pat: PatId) -> Ty { + let type_of_expanded_pat = self.pattern_arena.borrow().type_of_epat.get(&pat).cloned(); + type_of_expanded_pat.unwrap_or_else(|| self.infer[pat].clone()) + } +} + +#[derive(Clone)] +pub(super) struct PatCtxt<'a> { + pub(super) cx: &'a MatchCheckCtx<'a>, + /// Type of the current column under investigation. + pub(super) ty: Ty, + /// Whether the current pattern is the whole pattern as found in a match arm, or if it's a + /// subpattern. + pub(super) is_top_level: bool, +} + +impl PatIdExt for PatId { + fn is_wildcard(self, cx: &MatchCheckCtx<'_>) -> bool { + matches!(cx.pattern_arena.borrow()[self], Pat::Bind { subpat: None, .. } | Pat::Wild) + } + + fn is_or_pat(self, cx: &MatchCheckCtx<'_>) -> bool { + matches!(cx.pattern_arena.borrow()[self], Pat::Or(..)) + } + + /// Recursively expand this pattern into its subpatterns. Only useful for or-patterns. + fn expand_or_pat(self, cx: &MatchCheckCtx<'_>) -> Vec { + fn expand(pat: PatId, vec: &mut Vec, pat_arena: &PatternArena) { + if let Pat::Or(pats) = &pat_arena[pat] { + for &pat in pats { + expand(pat, vec, pat_arena); + } + } else { + vec.push(pat) + } + } + + let pat_arena = cx.pattern_arena.borrow(); + let mut pats = Vec::new(); + expand(self, &mut pats, &pat_arena); + pats + } +} + +/// A row of a matrix. Rows of len 1 are very common, which is why `SmallVec[_; 2]` +/// works well. +#[derive(Clone)] +pub(super) struct PatStack { + pats: SmallVec<[PatId; 2]>, + /// Cache for the constructor of the head + head_ctor: OnceCell, +} + +impl PatStack { + fn from_pattern(pat: PatId) -> Self { + Self::from_vec(smallvec![pat]) + } + + fn from_vec(vec: SmallVec<[PatId; 2]>) -> Self { + PatStack { pats: vec, head_ctor: OnceCell::new() } + } + + fn is_empty(&self) -> bool { + self.pats.is_empty() + } + + fn len(&self) -> usize { + self.pats.len() + } + + fn head(&self) -> PatId { + self.pats[0] + } + + #[inline] + fn head_ctor(&self, cx: &MatchCheckCtx<'_>) -> &Constructor { + self.head_ctor.get_or_init(|| Constructor::from_pat(cx, self.head())) + } + + fn iter(&self) -> impl Iterator + '_ { + self.pats.iter().copied() + } + + // Recursively expand the first pattern into its subpatterns. Only useful if the pattern is an + // or-pattern. Panics if `self` is empty. + fn expand_or_pat(&self, cx: &MatchCheckCtx<'_>) -> impl Iterator + '_ { + self.head().expand_or_pat(cx).into_iter().map(move |pat| { + let mut new_patstack = PatStack::from_pattern(pat); + new_patstack.pats.extend_from_slice(&self.pats[1..]); + new_patstack + }) + } + + /// This computes `S(self.head_ctor(), self)`. See top of the file for explanations. + /// + /// Structure patterns with a partial wild pattern (Foo { a: 42, .. }) have their missing + /// fields filled with wild patterns. + /// + /// This is roughly the inverse of `Constructor::apply`. + fn pop_head_constructor( + &self, + ctor_wild_subpatterns: &Fields, + cx: &MatchCheckCtx<'_>, + ) -> PatStack { + // We pop the head pattern and push the new fields extracted from the arguments of + // `self.head()`. + let mut new_fields = + ctor_wild_subpatterns.replace_with_pattern_arguments(self.head(), cx).into_patterns(); + new_fields.extend_from_slice(&self.pats[1..]); + PatStack::from_vec(new_fields) + } +} + +impl Default for PatStack { + fn default() -> Self { + Self::from_vec(smallvec![]) + } +} + +impl PartialEq for PatStack { + fn eq(&self, other: &Self) -> bool { + self.pats == other.pats + } +} + +impl FromIterator for PatStack { + fn from_iter(iter: T) -> Self + where + T: IntoIterator, + { + Self::from_vec(iter.into_iter().collect()) + } +} + +#[derive(Clone)] +pub(super) struct Matrix { + patterns: Vec, +} + +impl Matrix { + fn empty() -> Self { + Matrix { patterns: vec![] } + } + + /// Number of columns of this matrix. `None` is the matrix is empty. + pub(super) fn column_count(&self) -> Option { + self.patterns.get(0).map(|r| r.len()) + } + + /// Pushes a new row to the matrix. If the row starts with an or-pattern, this recursively + /// expands it. + fn push(&mut self, row: PatStack, cx: &MatchCheckCtx<'_>) { + if !row.is_empty() && row.head().is_or_pat(cx) { + for row in row.expand_or_pat(cx) { + self.patterns.push(row); + } + } else { + self.patterns.push(row); + } + } + + /// Iterate over the first component of each row + fn heads(&self) -> impl Iterator + '_ { + self.patterns.iter().map(|r| r.head()) + } + + /// Iterate over the first constructor of each row. + fn head_ctors<'a>( + &'a self, + cx: &'a MatchCheckCtx<'_>, + ) -> impl Iterator + Clone { + self.patterns.iter().map(move |r| r.head_ctor(cx)) + } + + /// This computes `S(constructor, self)`. See top of the file for explanations. + fn specialize_constructor( + &self, + pcx: &PatCtxt<'_>, + ctor: &Constructor, + ctor_wild_subpatterns: &Fields, + ) -> Matrix { + let rows = self + .patterns + .iter() + .filter(|r| ctor.is_covered_by(pcx, r.head_ctor(pcx.cx))) + .map(|r| r.pop_head_constructor(ctor_wild_subpatterns, pcx.cx)); + Matrix::from_iter(rows, pcx.cx) + } + + fn from_iter(rows: impl IntoIterator, cx: &MatchCheckCtx<'_>) -> Matrix { + let mut matrix = Matrix::empty(); + for x in rows { + // Using `push` ensures we correctly expand or-patterns. + matrix.push(x, cx); + } + matrix + } +} + +#[derive(Debug, Clone)] +enum SubPatSet { + /// The empty set. This means the pattern is unreachable. + Empty, + /// The set containing the full pattern. + Full, + /// If the pattern is a pattern with a constructor or a pattern-stack, we store a set for each + /// of its subpatterns. Missing entries in the map are implicitly full, because that's the + /// common case. + Seq { subpats: FxHashMap }, + /// If the pattern is an or-pattern, we store a set for each of its alternatives. Missing + /// entries in the map are implicitly empty. Note: we always flatten nested or-patterns. + Alt { + subpats: FxHashMap, + /// Counts the total number of alternatives in the pattern + alt_count: usize, + /// We keep the pattern around to retrieve spans. + pat: PatId, + }, +} + +impl SubPatSet { + fn full() -> Self { + SubPatSet::Full + } + + fn empty() -> Self { + SubPatSet::Empty + } + + fn is_empty(&self) -> bool { + match self { + SubPatSet::Empty => true, + SubPatSet::Full => false, + // If any subpattern in a sequence is unreachable, the whole pattern is unreachable. + SubPatSet::Seq { subpats } => subpats.values().any(|set| set.is_empty()), + // An or-pattern is reachable if any of its alternatives is. + SubPatSet::Alt { subpats, .. } => subpats.values().all(|set| set.is_empty()), + } + } + + fn is_full(&self) -> bool { + match self { + SubPatSet::Empty => false, + SubPatSet::Full => true, + // The whole pattern is reachable only when all its alternatives are. + SubPatSet::Seq { subpats } => subpats.values().all(|sub_set| sub_set.is_full()), + // The whole or-pattern is reachable only when all its alternatives are. + SubPatSet::Alt { subpats, alt_count, .. } => { + subpats.len() == *alt_count && subpats.values().all(|set| set.is_full()) + } + } + } + + /// Union `self` with `other`, mutating `self`. + fn union(&mut self, other: Self) { + use SubPatSet::*; + // Union with full stays full; union with empty changes nothing. + if self.is_full() || other.is_empty() { + return; + } else if self.is_empty() { + *self = other; + return; + } else if other.is_full() { + *self = Full; + return; + } + + match (&mut *self, other) { + (Seq { .. }, Seq { .. }) => { + todo!() + } + (Alt { .. }, Alt { .. }) => { + todo!() + } + _ => panic!("bug"), + } + } + + /// Returns a list of the spans of the unreachable subpatterns. If `self` is empty (i.e. the + /// whole pattern is unreachable) we return `None`. + fn list_unreachable_spans(&self) -> Option> { + if self.is_empty() { + return None; + } + if self.is_full() { + // No subpatterns are unreachable. + return Some(Vec::new()); + } + todo!() + } + + /// When `self` refers to a patstack that was obtained from specialization, after running + /// `unspecialize` it will refer to the original patstack before specialization. + fn unspecialize(self, arity: usize) -> Self { + use SubPatSet::*; + match self { + Full => Full, + Empty => Empty, + Seq { subpats } => { + todo!() + } + Alt { .. } => panic!("bug"), + } + } + + /// When `self` refers to a patstack that was obtained from splitting an or-pattern, after + /// running `unspecialize` it will refer to the original patstack before splitting. + /// + /// For example: + /// ``` + /// match Some(true) { + /// Some(true) => {} + /// None | Some(true | false) => {} + /// } + /// ``` + /// Here `None` would return the full set and `Some(true | false)` would return the set + /// containing `false`. After `unsplit_or_pat`, we want the set to contain `None` and `false`. + /// This is what this function does. + fn unsplit_or_pat(mut self, alt_id: usize, alt_count: usize, pat: PatId) -> Self { + todo!() + } +} + +/// This carries the results of computing usefulness, as described at the top of the file. When +/// checking usefulness of a match branch, we use the `NoWitnesses` variant, which also keeps track +/// of potential unreachable sub-patterns (in the presence of or-patterns). When checking +/// exhaustiveness of a whole match, we use the `WithWitnesses` variant, which carries a list of +/// witnesses of non-exhaustiveness when there are any. +/// Which variant to use is dictated by `WitnessPreference`. +#[derive(Clone, Debug)] +enum Usefulness { + /// Carries a set of subpatterns that have been found to be reachable. If empty, this indicates + /// the whole pattern is unreachable. If not, this indicates that the pattern is reachable but + /// that some sub-patterns may be unreachable (due to or-patterns). In the absence of + /// or-patterns this will always be either `Empty` (the whole pattern is unreachable) or `Full` + /// (the whole pattern is reachable). + NoWitnesses(SubPatSet), + /// Carries a list of witnesses of non-exhaustiveness. If empty, indicates that the whole + /// pattern is unreachable. + WithWitnesses(Vec), +} + +impl Usefulness { + fn new_useful(preference: WitnessPreference) -> Self { + match preference { + ConstructWitness => WithWitnesses(vec![Witness(vec![])]), + LeaveOutWitness => NoWitnesses(SubPatSet::full()), + } + } + fn new_not_useful(preference: WitnessPreference) -> Self { + match preference { + ConstructWitness => WithWitnesses(vec![]), + LeaveOutWitness => NoWitnesses(SubPatSet::empty()), + } + } + + /// Combine usefulnesses from two branches. This is an associative operation. + fn extend(&mut self, other: Self) { + match (&mut *self, other) { + (WithWitnesses(_), WithWitnesses(o)) if o.is_empty() => {} + (WithWitnesses(s), WithWitnesses(o)) if s.is_empty() => *self = WithWitnesses(o), + (WithWitnesses(s), WithWitnesses(o)) => s.extend(o), + (NoWitnesses(s), NoWitnesses(o)) => s.union(o), + _ => unreachable!(), + } + } + + /// When trying several branches and each returns a `Usefulness`, we need to combine the + /// results together. + fn merge(pref: WitnessPreference, usefulnesses: impl Iterator) -> Self { + let mut ret = Self::new_not_useful(pref); + for u in usefulnesses { + ret.extend(u); + if let NoWitnesses(subpats) = &ret { + if subpats.is_full() { + // Once we reach the full set, more unions won't change the result. + return ret; + } + } + } + ret + } + + /// After calculating the usefulness for a branch of an or-pattern, call this to make this + /// usefulness mergeable with those from the other branches. + fn unsplit_or_pat(self, alt_id: usize, alt_count: usize, pat: PatId) -> Self { + match self { + NoWitnesses(subpats) => NoWitnesses(subpats.unsplit_or_pat(alt_id, alt_count, pat)), + WithWitnesses(_) => panic!("bug"), + } + } + + /// After calculating usefulness after a specialization, call this to recontruct a usefulness + /// that makes sense for the matrix pre-specialization. This new usefulness can then be merged + /// with the results of specializing with the other constructors. + fn apply_constructor( + self, + pcx: &PatCtxt<'_>, + matrix: &Matrix, + ctor: &Constructor, + ctor_wild_subpatterns: &Fields, + ) -> Self { + match self { + WithWitnesses(witnesses) if witnesses.is_empty() => WithWitnesses(witnesses), + WithWitnesses(w) => { + let new_witnesses = if matches!(ctor, Constructor::Missing) { + let mut split_wildcard = SplitWildcard::new(pcx); + split_wildcard.split(pcx, matrix.head_ctors(pcx.cx)); + } else { + todo!("Usefulness::apply_constructor({:?})", ctor) + }; + todo!("Usefulness::apply_constructor({:?})", ctor) + } + NoWitnesses(subpats) => NoWitnesses(subpats.unspecialize(ctor_wild_subpatterns.len())), + } + } +} + +#[derive(Copy, Clone, Debug)] +enum WitnessPreference { + ConstructWitness, + LeaveOutWitness, +} + +#[derive(Clone, Debug)] +pub(crate) struct Witness(Vec); + +impl Witness { + /// Asserts that the witness contains a single pattern, and returns it. + fn single_pattern(self) -> Pat { + assert_eq!(self.0.len(), 1); + self.0.into_iter().next().unwrap() + } + + /// Constructs a partial witness for a pattern given a list of + /// patterns expanded by the specialization step. + /// + /// When a pattern P is discovered to be useful, this function is used bottom-up + /// to reconstruct a complete witness, e.g., a pattern P' that covers a subset + /// of values, V, where each value in that set is not covered by any previously + /// used patterns and is covered by the pattern P'. Examples: + /// + /// left_ty: tuple of 3 elements + /// pats: [10, 20, _] => (10, 20, _) + /// + /// left_ty: struct X { a: (bool, &'static str), b: usize} + /// pats: [(false, "foo"), 42] => X { a: (false, "foo"), b: 42 } + fn apply_constructor( + mut self, + pcx: &PatCtxt<'_>, + ctor: &Constructor, + ctor_wild_subpatterns: &Fields, + ) -> Self { + let pat = { + let len = self.0.len(); + let arity = ctor_wild_subpatterns.len(); + let pats = self.0.drain((len - arity)..).rev(); + ctor_wild_subpatterns.replace_fields(pcx.cx, pats).apply(pcx, ctor) + }; + + self.0.push(pat); + + self + } +} + +/// Algorithm from . +/// The algorithm from the paper has been modified to correctly handle empty +/// types. The changes are: +/// (0) We don't exit early if the pattern matrix has zero rows. We just +/// continue to recurse over columns. +/// (1) all_constructors will only return constructors that are statically +/// possible. E.g., it will only return `Ok` for `Result`. +/// +/// This finds whether a (row) vector `v` of patterns is 'useful' in relation +/// to a set of such vectors `m` - this is defined as there being a set of +/// inputs that will match `v` but not any of the sets in `m`. +/// +/// All the patterns at each column of the `matrix ++ v` matrix must have the same type. +/// +/// This is used both for reachability checking (if a pattern isn't useful in +/// relation to preceding patterns, it is not reachable) and exhaustiveness +/// checking (if a wildcard pattern is useful in relation to a matrix, the +/// matrix isn't exhaustive). +/// +/// `is_under_guard` is used to inform if the pattern has a guard. If it +/// has one it must not be inserted into the matrix. This shouldn't be +/// relied on for soundness. +fn is_useful( + cx: &MatchCheckCtx<'_>, + matrix: &Matrix, + v: &PatStack, + witness_preference: WitnessPreference, + is_under_guard: bool, + is_top_level: bool, +) -> Usefulness { + let Matrix { patterns: rows, .. } = matrix; + + // The base case. We are pattern-matching on () and the return value is + // based on whether our matrix has a row or not. + // NOTE: This could potentially be optimized by checking rows.is_empty() + // first and then, if v is non-empty, the return value is based on whether + // the type of the tuple we're checking is inhabited or not. + if v.is_empty() { + let ret = if rows.is_empty() { + Usefulness::new_useful(witness_preference) + } else { + Usefulness::new_not_useful(witness_preference) + }; + return ret; + } + + assert!(rows.iter().all(|r| r.len() == v.len())); + + // FIXME(Nadrieril): Hack to work around type normalization issues (see rust-lang/rust#72476). + // TODO(iDawer): ty.as_reference() + let ty = matrix.heads().next().map_or(cx.type_of(v.head()), |r| cx.type_of(r)); + let pcx = PatCtxt { cx, ty, is_top_level }; + + // If the first pattern is an or-pattern, expand it. + let ret = if v.head().is_or_pat(cx) { + //expanding or-pattern + let v_head = v.head(); + let vs: Vec<_> = v.expand_or_pat(cx).collect(); + let alt_count = vs.len(); + // We try each or-pattern branch in turn. + let mut matrix = matrix.clone(); + let usefulnesses = vs.into_iter().enumerate().map(|(i, v)| { + let usefulness = is_useful(cx, &matrix, &v, witness_preference, is_under_guard, false); + // If pattern has a guard don't add it to the matrix. + if !is_under_guard { + // We push the already-seen patterns into the matrix in order to detect redundant + // branches like `Some(_) | Some(0)`. + matrix.push(v, cx); + } + usefulness.unsplit_or_pat(i, alt_count, v_head) + }); + Usefulness::merge(witness_preference, usefulnesses) + } else { + let v_ctor = v.head_ctor(cx); + // if let Constructor::IntRange(ctor_range) = v_ctor { + // // Lint on likely incorrect range patterns (#63987) + // ctor_range.lint_overlapping_range_endpoints( + // pcx, + // matrix.head_ctors_and_spans(cx), + // matrix.column_count().unwrap_or(0), + // hir_id, + // ) + // } + + // We split the head constructor of `v`. + let split_ctors = v_ctor.split(&pcx, matrix.head_ctors(cx)); + // For each constructor, we compute whether there's a value that starts with it that would + // witness the usefulness of `v`. + let start_matrix = matrix; + let usefulnesses = split_ctors.into_iter().map(|ctor| { + // debug!("specialize({:?})", ctor); + // We cache the result of `Fields::wildcards` because it is used a lot. + let ctor_wild_subpatterns = Fields::wildcards(&pcx, &ctor); + let spec_matrix = + start_matrix.specialize_constructor(&pcx, &ctor, &ctor_wild_subpatterns); + let v = v.pop_head_constructor(&ctor_wild_subpatterns, cx); + let usefulness = + is_useful(cx, &spec_matrix, &v, witness_preference, is_under_guard, false); + usefulness.apply_constructor(&pcx, start_matrix, &ctor, &ctor_wild_subpatterns) + }); + Usefulness::merge(witness_preference, usefulnesses) + }; + + ret +} + +/// The arm of a match expression. +#[derive(Clone, Copy)] +pub(crate) struct MatchArm { + pub(crate) pat: PatId, + pub(crate) has_guard: bool, +} + +/// Indicates whether or not a given arm is reachable. +#[derive(Clone, Debug)] +pub(crate) enum Reachability { + /// The arm is reachable. This additionally carries a set of or-pattern branches that have been + /// found to be unreachable despite the overall arm being reachable. Used only in the presence + /// of or-patterns, otherwise it stays empty. + Reachable(Vec<()>), + /// The arm is unreachable. + Unreachable, +} +/// The output of checking a match for exhaustiveness and arm reachability. +pub(crate) struct UsefulnessReport { + /// For each arm of the input, whether that arm is reachable after the arms above it. + pub(crate) arm_usefulness: Vec<(MatchArm, Reachability)>, + /// If the match is exhaustive, this is empty. If not, this contains witnesses for the lack of + /// exhaustiveness. + pub(crate) non_exhaustiveness_witnesses: Vec, +} + +pub(crate) fn compute_match_usefulness( + cx: &MatchCheckCtx<'_>, + arms: &[MatchArm], +) -> UsefulnessReport { + let mut matrix = Matrix::empty(); + let arm_usefulness: Vec<_> = arms + .iter() + .copied() + .map(|arm| { + let v = PatStack::from_pattern(arm.pat); + let usefulness = is_useful(cx, &matrix, &v, LeaveOutWitness, arm.has_guard, true); + if !arm.has_guard { + matrix.push(v, cx); + } + let reachability = match usefulness { + NoWitnesses(subpats) if subpats.is_empty() => Reachability::Unreachable, + NoWitnesses(subpats) => { + Reachability::Reachable(subpats.list_unreachable_spans().unwrap()) + } + WithWitnesses(..) => panic!("bug"), + }; + (arm, reachability) + }) + .collect(); + + let wild_pattern = cx.pattern_arena.borrow_mut().alloc(Pat::Wild, &cx.infer[cx.match_expr]); + let v = PatStack::from_pattern(wild_pattern); + let usefulness = is_useful(cx, &matrix, &v, LeaveOutWitness, false, true); + let non_exhaustiveness_witnesses = match usefulness { + // TODO: ConstructWitness + // WithWitnesses(pats) => pats.into_iter().map(Witness::single_pattern).collect(), + // NoWitnesses(_) => panic!("bug"), + NoWitnesses(subpats) if subpats.is_empty() => Vec::new(), + NoWitnesses(subpats) => vec![Pat::Wild], + WithWitnesses(..) => panic!("bug"), + }; + UsefulnessReport { arm_usefulness, non_exhaustiveness_witnesses } +} + +pub(crate) struct PatternArena { + arena: Arena, + /// Types of expanded patterns. + type_of_epat: FxHashMap, +} + +impl PatternArena { + pub(crate) fn clone_from(pats: &Arena) -> RefCell { + PatternArena { arena: pats.clone(), type_of_epat: Default::default() }.into() + } + + fn alloc(&mut self, pat: Pat, ty: &Ty) -> PatId { + let id = self.arena.alloc(pat); + self.type_of_epat.insert(id, ty.clone()); + id + } +} + +impl Index for PatternArena { + type Output = Pat; + + fn index(&self, pat: PatId) -> &Pat { + &self.arena[pat] + } +} + +mod helper { + use hir_def::expr::{Pat, PatId}; + + use super::MatchCheckCtx; + + pub(super) trait PatIdExt: Sized { + fn is_wildcard(self, cx: &MatchCheckCtx<'_>) -> bool; + fn is_or_pat(self, cx: &MatchCheckCtx<'_>) -> bool; + fn expand_or_pat(self, cx: &MatchCheckCtx<'_>) -> Vec; + } + + // Copy-pasted from rust/compiler/rustc_data_structures/src/captures.rs + /// "Signaling" trait used in impl trait to tag lifetimes that you may + /// need to capture but don't really need for other reasons. + /// Basically a workaround; see [this comment] for details. + /// + /// [this comment]: https://github.com/rust-lang/rust/issues/34511#issuecomment-373423999 + // FIXME(eddyb) false positive, the lifetime parameter is "phantom" but needed. + #[allow(unused_lifetimes)] + pub trait Captures<'a> {} + + impl<'a, T: ?Sized> Captures<'a> for T {} +} + +#[test] +fn it_works() {} -- cgit v1.2.3