Unnamed repository; edit this file 'description' to name the repository.
Diffstat (limited to 'crates/hir_ty/src/diagnostics/match_check/usefulness.rs')
| -rw-r--r-- | crates/hir_ty/src/diagnostics/match_check/usefulness.rs | 754 |
1 files changed, 192 insertions, 562 deletions
diff --git a/crates/hir_ty/src/diagnostics/match_check/usefulness.rs b/crates/hir_ty/src/diagnostics/match_check/usefulness.rs index 43545708e5..e8a13955d2 100644 --- a/crates/hir_ty/src/diagnostics/match_check/usefulness.rs +++ b/crates/hir_ty/src/diagnostics/match_check/usefulness.rs @@ -1,5 +1,5 @@ -//! Based on rust-lang/rust 1.52.0-nightly (25c15cdbe 2021-04-22) -//! <https://github.com/rust-lang/rust/blob/25c15cdbe/compiler/rustc_mir_build/src/thir/pattern/usefulness.rs> +//! Based on rust-lang/rust (last sync f31622a50 2021-11-12) +//! <https://github.com/rust-lang/rust/blob/f31622a50/compiler/rustc_mir_build/src/thir/pattern/usefulness.rs> //! //! ----- //! @@ -271,33 +271,27 @@ //! The details are not necessary to understand this file, so we explain them in //! [`super::deconstruct_pat`]. Splitting is done by the [`Constructor::split`] function. -use std::{cell::RefCell, iter::FromIterator}; +use std::iter::once; -use hir_def::{expr::ExprId, HasModule, ModuleId}; -use la_arena::Arena; -use once_cell::unsync::OnceCell; -use rustc_hash::FxHashMap; +use hir_def::{AdtId, DefWithBodyId, HasModule, ModuleId}; use smallvec::{smallvec, SmallVec}; +use typed_arena::Arena; -use crate::{db::HirDatabase, InferenceResult, Interner, Ty}; +use crate::{db::HirDatabase, Ty, TyExt}; -use super::{ - deconstruct_pat::{Constructor, Fields, SplitWildcard}, - Pat, PatId, PatKind, PatternFoldable, PatternFolder, -}; +use super::deconstruct_pat::{Constructor, DeconstructedPat, Fields, SplitWildcard}; -use self::{helper::PatIdExt, Usefulness::*, WitnessPreference::*}; +use self::{helper::Captures, ArmType::*, Usefulness::*}; -pub(crate) struct MatchCheckCtx<'a> { +pub(crate) struct MatchCheckCtx<'a, 'p> { pub(crate) module: ModuleId, - pub(crate) match_expr: ExprId, - pub(crate) infer: &'a InferenceResult, + pub(crate) body: DefWithBodyId, pub(crate) db: &'a dyn HirDatabase, /// Lowered patterns from arms plus generated by the check. - pub(crate) pattern_arena: &'a RefCell<PatternArena>, + pub(crate) pattern_arena: &'p Arena<DeconstructedPat<'p>>, } -impl<'a> MatchCheckCtx<'a> { +impl<'a, 'p> MatchCheckCtx<'a, 'p> { 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 @@ -305,12 +299,16 @@ impl<'a> MatchCheckCtx<'a> { } /// Returns whether the given type is an enum from another crate declared `#[non_exhaustive]`. - pub(super) fn is_foreign_non_exhaustive_enum(&self, enum_id: hir_def::EnumId) -> bool { - let has_non_exhaustive_attr = - self.db.attrs(enum_id.into()).by_key("non_exhaustive").exists(); - let is_local = - hir_def::AdtId::from(enum_id).module(self.db.upcast()).krate() == self.module.krate(); - has_non_exhaustive_attr && !is_local + pub(super) fn is_foreign_non_exhaustive_enum(&self, ty: &Ty) -> bool { + match ty.as_adt() { + Some((adt @ AdtId::EnumId(_), _)) => { + let has_non_exhaustive_attr = + self.db.attrs(adt.into()).by_key("non_exhaustive").exists(); + let is_local = adt.module(self.db.upcast()).krate() == self.module.krate(); + has_non_exhaustive_attr && !is_local + } + _ => false, + } } // Rust feature described as "Allows exhaustive pattern matching on types that contain uninhabited types." @@ -318,92 +316,34 @@ impl<'a> MatchCheckCtx<'a> { // FIXME see MatchCheckCtx::is_uninhabited false } - - pub(super) fn alloc_pat(&self, pat: Pat) -> PatId { - self.pattern_arena.borrow_mut().alloc(pat) - } - - /// Get type of a pattern. Handles expanded patterns. - pub(super) fn type_of(&self, pat: PatId) -> Ty { - self.pattern_arena.borrow()[pat].ty.clone() - } } #[derive(Copy, Clone)] -pub(super) struct PatCtxt<'a> { - pub(super) cx: &'a MatchCheckCtx<'a>, +pub(super) struct PatCtxt<'a, 'p> { + pub(super) cx: &'a MatchCheckCtx<'a, 'p>, /// Type of the current column under investigation. pub(super) ty: &'a 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, -} - -pub(crate) fn expand_pattern(pat: Pat) -> Pat { - LiteralExpander.fold_pattern(&pat) -} - -struct LiteralExpander; - -impl PatternFolder for LiteralExpander { - fn fold_pattern(&mut self, pat: &Pat) -> Pat { - match (pat.ty.kind(Interner), pat.kind.as_ref()) { - (_, PatKind::Binding { subpattern: Some(s), .. }) => s.fold_with(self), - _ => pat.super_fold_with(self), - } - } -} - -impl Pat { - fn _is_wildcard(&self) -> bool { - matches!(*self.kind, PatKind::Binding { subpattern: None, .. } | PatKind::Wild) - } -} - -impl PatIdExt for PatId { - fn is_or_pat(self, cx: &MatchCheckCtx<'_>) -> bool { - matches!(*cx.pattern_arena.borrow()[self].kind, PatKind::Or { .. }) - } - - /// Recursively expand this pattern into its subpatterns. Only useful for or-patterns. - fn expand_or_pat(self, cx: &MatchCheckCtx<'_>) -> Vec<Self> { - fn expand(pat: PatId, vec: &mut Vec<PatId>, pat_arena: &mut PatternArena) { - if let PatKind::Or { pats } = pat_arena[pat].kind.as_ref() { - // FIXME(iDawer): Factor out pattern deep cloning. See discussion: - // https://github.com/rust-analyzer/rust-analyzer/pull/8717#discussion_r633086640 - let pats = pats.clone(); - for pat in pats { - let pat = pat_arena.alloc(pat.clone()); - expand(pat, vec, pat_arena); - } - } else { - vec.push(pat) - } - } - - let mut pat_arena = cx.pattern_arena.borrow_mut(); - let mut pats = Vec::new(); - expand(self, &mut pats, &mut pat_arena); - pats - } + /// Wether the current pattern is from a `non_exhaustive` enum. + pub(super) is_non_exhaustive: bool, } /// 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<Constructor>, +pub(super) struct PatStack<'p> { + pats: SmallVec<[&'p DeconstructedPat<'p>; 2]>, } -impl PatStack { - fn from_pattern(pat: PatId) -> Self { +impl<'p> PatStack<'p> { + fn from_pattern(pat: &'p DeconstructedPat<'p>) -> Self { Self::from_vec(smallvec![pat]) } - fn from_vec(vec: SmallVec<[PatId; 2]>) -> Self { - PatStack { pats: vec, head_ctor: OnceCell::new() } + fn from_vec(vec: SmallVec<[&'p DeconstructedPat<'p>; 2]>) -> Self { + PatStack { pats: vec } } fn is_empty(&self) -> bool { @@ -414,73 +354,42 @@ impl PatStack { self.pats.len() } - fn head(&self) -> PatId { + fn head(&self) -> &'p DeconstructedPat<'p> { self.pats[0] } - #[inline] - fn head_ctor(&self, cx: &MatchCheckCtx<'_>) -> &Constructor { - self.head_ctor.get_or_init(|| Constructor::from_pat(cx, self.head())) - } - // 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<Item = PatStack> + '_ { - self.head().expand_or_pat(cx).into_iter().map(move |pat| { + fn expand_or_pat(&self) -> impl Iterator<Item = PatStack<'p>> + Captures<'_> { + self.head().iter_fields().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. + /// 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 { + fn pop_head_constructor(&self, cx: &MatchCheckCtx<'_, 'p>, ctor: &Constructor) -> PatStack<'p> { // 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(); + let mut new_fields: SmallVec<[_; 2]> = self.head().specialize(cx, ctor); 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<PatId> for PatStack { - fn from_iter<T>(iter: T) -> Self - where - T: IntoIterator<Item = PatId>, - { - Self::from_vec(iter.into_iter().collect()) - } -} - /// A 2D matrix. #[derive(Clone)] -pub(super) struct Matrix { - patterns: Vec<PatStack>, +pub(super) struct Matrix<'p> { + patterns: Vec<PatStack<'p>>, } -impl Matrix { +impl<'p> Matrix<'p> { fn empty() -> Self { Matrix { patterns: vec![] } } @@ -492,295 +401,29 @@ impl Matrix { /// 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); - } + fn push(&mut self, row: PatStack<'p>) { + if !row.is_empty() && row.head().is_or_pat() { + self.patterns.extend(row.expand_or_pat()); } else { self.patterns.push(row); } } /// Iterate over the first component of each row - fn heads(&self) -> impl Iterator<Item = PatId> + '_ { + fn heads(&self) -> impl Iterator<Item = &'p DeconstructedPat<'p>> + Clone + Captures<'_> { 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<Item = &'a Constructor> + 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<Item = PatStack>, cx: &MatchCheckCtx<'_>) -> Matrix { + fn specialize_constructor(&self, pcx: PatCtxt<'_, 'p>, ctor: &Constructor) -> Matrix<'p> { let mut matrix = Matrix::empty(); - for x in rows { - // Using `push` ensures we correctly expand or-patterns. - matrix.push(x, cx); - } - matrix - } -} - -/// Given a pattern or a pattern-stack, this struct captures a set of its subpatterns. We use that -/// to track reachable sub-patterns arising from 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). When there are or-patterns, some subpatterns may be reachable while others -/// aren't. In this case the whole pattern still counts as reachable, but we will lint the -/// unreachable subpatterns. -/// -/// This supports a limited set of operations, so not all possible sets of subpatterns can be -/// represented. That's ok, we only want the ones that make sense for our usage. -/// -/// What we're doing is illustrated by this: -/// ``` -/// match (true, 0) { -/// (true, 0) => {} -/// (_, 1) => {} -/// (true | false, 0 | 1) => {} -/// } -/// ``` -/// When we try the alternatives of the `true | false` or-pattern, the last `0` is reachable in the -/// `false` alternative but not the `true`. So overall it is reachable. By contrast, the last `1` -/// is not reachable in either alternative, so we want to signal this to the user. -/// Therefore we take the union of sets of reachable patterns coming from different alternatives in -/// order to figure out which subpatterns are overall reachable. -/// -/// Invariant: we try to construct the smallest representation we can. In particular if -/// `self.is_empty()` we ensure that `self` is `Empty`, and same with `Full`. This is not important -/// for correctness currently. -#[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<usize, SubPatSet> }, - /// 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<usize, SubPatSet>, - /// 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 { subpats: s_set }, Seq { subpats: mut o_set }) => { - s_set.retain(|i, s_sub_set| { - // Missing entries count as full. - let o_sub_set = o_set.remove(i).unwrap_or(Full); - s_sub_set.union(o_sub_set); - // We drop full entries. - !s_sub_set.is_full() - }); - // Everything left in `o_set` is missing from `s_set`, i.e. counts as full. Since - // unioning with full returns full, we can drop those entries. - } - (Alt { subpats: s_set, .. }, Alt { subpats: mut o_set, .. }) => { - s_set.retain(|i, s_sub_set| { - // Missing entries count as empty. - let o_sub_set = o_set.remove(i).unwrap_or(Empty); - s_sub_set.union(o_sub_set); - // We drop empty entries. - !s_sub_set.is_empty() - }); - // Everything left in `o_set` is missing from `s_set`, i.e. counts as empty. Since - // unioning with empty changes nothing, we can take those entries as is. - s_set.extend(o_set); - } - _ => panic!("bug"), - } - - if self.is_full() { - *self = Full; - } - } - - /// Returns a list of the unreachable subpatterns. If `self` is empty (i.e. the - /// whole pattern is unreachable) we return `None`. - fn list_unreachable_subpatterns(&self, cx: &MatchCheckCtx<'_>) -> Option<Vec<PatId>> { - /// Panics if `set.is_empty()`. - fn fill_subpats( - set: &SubPatSet, - unreachable_pats: &mut Vec<PatId>, - cx: &MatchCheckCtx<'_>, - ) { - match set { - SubPatSet::Empty => panic!("bug"), - SubPatSet::Full => {} - SubPatSet::Seq { subpats } => { - for sub_set in subpats.values() { - fill_subpats(sub_set, unreachable_pats, cx); - } - } - SubPatSet::Alt { subpats, pat, alt_count, .. } => { - let expanded = pat.expand_or_pat(cx); - for (i, &expanded) in expanded.iter().enumerate().take(*alt_count) { - let sub_set = subpats.get(&i).unwrap_or(&SubPatSet::Empty); - if sub_set.is_empty() { - // Found an unreachable subpattern. - unreachable_pats.push(expanded); - } else { - fill_subpats(sub_set, unreachable_pats, cx); - } - } - } - } - } - - if self.is_empty() { - return None; - } - if self.is_full() { - // No subpatterns are unreachable. - return Some(Vec::new()); - } - let mut unreachable_pats = Vec::new(); - fill_subpats(self, &mut unreachable_pats, cx); - Some(unreachable_pats) - } - - /// 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 } => { - // We gather the first `arity` subpatterns together and shift the remaining ones. - let mut new_subpats = FxHashMap::default(); - let mut new_subpats_first_col = FxHashMap::default(); - for (i, sub_set) in subpats { - if i < arity { - // The first `arity` indices are now part of the pattern in the first - // column. - new_subpats_first_col.insert(i, sub_set); - } else { - // Indices after `arity` are simply shifted - new_subpats.insert(i - arity + 1, sub_set); - } - } - // If `new_subpats_first_col` has no entries it counts as full, so we can omit it. - if !new_subpats_first_col.is_empty() { - new_subpats.insert(0, Seq { subpats: new_subpats_first_col }); - } - Seq { subpats: new_subpats } + for row in &self.patterns { + if ctor.is_covered_by(pcx, row.head().ctor()) { + let new_row = row.pop_head_constructor(pcx.cx, ctor); + matrix.push(new_row); } - Alt { .. } => panic!("bug"), // `self` is a patstack - } - } - - /// 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 { - use SubPatSet::*; - if self.is_empty() { - return Empty; } - - // Subpatterns coming from inside the or-pattern alternative itself, e.g. in `None | Some(0 - // | 1)`. - let set_first_col = match &mut self { - Full => Full, - Seq { subpats } => subpats.remove(&0).unwrap_or(Full), - Empty => unreachable!(), - Alt { .. } => panic!("bug"), // `self` is a patstack - }; - let mut subpats_first_col = FxHashMap::default(); - subpats_first_col.insert(alt_id, set_first_col); - let set_first_col = Alt { subpats: subpats_first_col, pat, alt_count }; - - let mut subpats = match self { - Full => FxHashMap::default(), - Seq { subpats } => subpats, - Empty => unreachable!(), - Alt { .. } => panic!("bug"), // `self` is a patstack - }; - subpats.insert(0, set_first_col); - Seq { subpats } + matrix } } @@ -789,31 +432,34 @@ impl SubPatSet { /// 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), +/// Which variant to use is dictated by `ArmType`. +enum Usefulness<'p> { + /// If we don't care about witnesses, simply remember if the pattern was useful. + NoWitnesses { useful: bool }, /// Carries a list of witnesses of non-exhaustiveness. If empty, indicates that the whole /// pattern is unreachable. - WithWitnesses(Vec<Witness>), + WithWitnesses(Vec<Witness<'p>>), } -impl Usefulness { - fn new_useful(preference: WitnessPreference) -> Self { +impl<'p> Usefulness<'p> { + fn new_useful(preference: ArmType) -> Self { match preference { - ConstructWitness => WithWitnesses(vec![Witness(vec![])]), - LeaveOutWitness => NoWitnesses(SubPatSet::full()), + // A single (empty) witness of reachability. + FakeExtraWildcard => WithWitnesses(vec![Witness(vec![])]), + RealArm => NoWitnesses { useful: true }, } } - fn new_not_useful(preference: WitnessPreference) -> Self { + fn new_not_useful(preference: ArmType) -> Self { match preference { - ConstructWitness => WithWitnesses(vec![]), - LeaveOutWitness => NoWitnesses(SubPatSet::empty()), + FakeExtraWildcard => WithWitnesses(vec![]), + RealArm => NoWitnesses { useful: false }, + } + } + + fn is_useful(&self) -> bool { + match self { + Usefulness::NoWitnesses { useful } => *useful, + Usefulness::WithWitnesses(witnesses) => !witnesses.is_empty(), } } @@ -823,89 +469,96 @@ impl Usefulness { (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<Item = Self>) -> 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; - } + (NoWitnesses { useful: s_useful }, NoWitnesses { useful: o_useful }) => { + *s_useful = *s_useful || o_useful } - } - 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"), + _ => unreachable!(), } } - /// After calculating usefulness after a specialization, call this to recontruct a usefulness + /// After calculating usefulness after a specialization, call this to reconstruct 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, + pcx: PatCtxt<'_, 'p>, + matrix: &Matrix<'p>, ctor: &Constructor, - ctor_wild_subpatterns: &Fields, ) -> Self { match self { - WithWitnesses(witnesses) if witnesses.is_empty() => WithWitnesses(witnesses), + NoWitnesses { .. } => self, + WithWitnesses(ref witnesses) if witnesses.is_empty() => self, WithWitnesses(witnesses) => { - let new_witnesses = if matches!(ctor, Constructor::Missing) { - let mut split_wildcard = SplitWildcard::new(pcx); - split_wildcard.split(pcx, matrix.head_ctors(pcx.cx)); - // Construct for each missing constructor a "wild" version of this - // constructor, that matches everything that can be built with - // it. For example, if `ctor` is a `Constructor::Variant` for - // `Option::Some`, we get the pattern `Some(_)`. - let new_patterns: Vec<_> = split_wildcard - .iter_missing(pcx) - .map(|missing_ctor| { - Fields::wildcards(pcx, missing_ctor).apply(pcx, missing_ctor) - }) - .collect(); + let new_witnesses = if let Constructor::Missing { .. } = ctor { + // We got the special `Missing` constructor, so each of the missing constructors + // gives a new pattern that is not caught by the match. We list those patterns. + let new_patterns = if pcx.is_non_exhaustive { + // Here we don't want the user to try to list all variants, we want them to add + // a wildcard, so we only suggest that. + vec![DeconstructedPat::wildcard(pcx.ty.clone())] + } else { + let mut split_wildcard = SplitWildcard::new(pcx); + split_wildcard.split(pcx, matrix.heads().map(DeconstructedPat::ctor)); + + // This lets us know if we skipped any variants because they are marked + // `doc(hidden)` or they are unstable feature gate (only stdlib types). + let mut hide_variant_show_wild = false; + // Construct for each missing constructor a "wild" version of this + // constructor, that matches everything that can be built with + // it. For example, if `ctor` is a `Constructor::Variant` for + // `Option::Some`, we get the pattern `Some(_)`. + let mut new: Vec<DeconstructedPat<'_>> = split_wildcard + .iter_missing(pcx) + .filter_map(|missing_ctor| { + // Check if this variant is marked `doc(hidden)` + if missing_ctor.is_doc_hidden_variant(pcx) + || missing_ctor.is_unstable_variant(pcx) + { + hide_variant_show_wild = true; + return None; + } + Some(DeconstructedPat::wild_from_ctor(pcx, missing_ctor.clone())) + }) + .collect(); + + if hide_variant_show_wild { + new.push(DeconstructedPat::wildcard(pcx.ty.clone())) + } + + new + }; + witnesses .into_iter() .flat_map(|witness| { new_patterns.iter().map(move |pat| { - let mut witness = witness.clone(); - witness.0.push(pat.clone()); - witness + Witness( + witness + .0 + .iter() + .chain(once(pat)) + .map(DeconstructedPat::clone_and_forget_reachability) + .collect(), + ) }) }) .collect() } else { witnesses .into_iter() - .map(|witness| witness.apply_constructor(pcx, ctor, ctor_wild_subpatterns)) + .map(|witness| witness.apply_constructor(pcx, ctor)) .collect() }; WithWitnesses(new_witnesses) } - NoWitnesses(subpats) => NoWitnesses(subpats.unspecialize(ctor_wild_subpatterns.len())), } } } #[derive(Copy, Clone, Debug)] -enum WitnessPreference { - ConstructWitness, - LeaveOutWitness, +enum ArmType { + FakeExtraWildcard, + RealArm, } /// A witness of non-exhaustiveness for error reporting, represented @@ -941,12 +594,11 @@ enum WitnessPreference { /// `Witness(vec![Pair(Some(_), true)])` /// /// The final `Pair(Some(_), true)` is then the resulting witness. -#[derive(Clone, Debug)] -pub(crate) struct Witness(Vec<Pat>); +pub(crate) struct Witness<'p>(Vec<DeconstructedPat<'p>>); -impl Witness { +impl<'p> Witness<'p> { /// Asserts that the witness contains a single pattern, and returns it. - fn single_pattern(self) -> Pat { + fn single_pattern(self) -> DeconstructedPat<'p> { assert_eq!(self.0.len(), 1); self.0.into_iter().next().unwrap() } @@ -964,17 +616,13 @@ impl Witness { /// /// 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 { + fn apply_constructor(mut self, pcx: PatCtxt<'_, 'p>, ctor: &Constructor) -> Self { let pat = { let len = self.0.len(); - let arity = ctor_wild_subpatterns.len(); + let arity = ctor.arity(pcx); let pats = self.0.drain((len - arity)..).rev(); - ctor_wild_subpatterns.replace_fields(pcx.cx, pats).apply(pcx, ctor) + let fields = Fields::from_iter(pcx.cx, pats); + DeconstructedPat::new(ctor.clone(), fields, pcx.ty.clone()) }; self.0.push(pat); @@ -1005,14 +653,14 @@ impl Witness { /// `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, +fn is_useful<'p>( + cx: &MatchCheckCtx<'_, 'p>, + matrix: &Matrix<'p>, + v: &PatStack<'p>, + witness_preference: ArmType, is_under_guard: bool, is_top_level: bool, -) -> Usefulness { +) -> Usefulness<'p> { let Matrix { patterns: rows, .. } = matrix; // The base case. We are pattern-matching on () and the return value is @@ -1029,69 +677,62 @@ fn is_useful( return ret; } - assert!(rows.iter().all(|r| r.len() == v.len())); + debug_assert!(rows.iter().all(|r| r.len() == v.len())); - // FIXME(Nadrieril): Hack to work around type normalization issues (see rust-lang/rust#72476). - let ty = matrix.heads().next().map_or(cx.type_of(v.head()), |r| cx.type_of(r)); - let pcx = PatCtxt { cx, ty: &ty, is_top_level }; + let ty = v.head().ty(); + let is_non_exhaustive = cx.is_foreign_non_exhaustive_enum(ty); + let pcx = PatCtxt { cx, ty, is_top_level, is_non_exhaustive }; // 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(); + let mut ret = Usefulness::new_not_useful(witness_preference); + if v.head().is_or_pat() { // We try each or-pattern branch in turn. let mut matrix = matrix.clone(); - let usefulnesses = vs.into_iter().enumerate().map(|(i, v)| { + for v in v.expand_or_pat() { let usefulness = is_useful(cx, &matrix, &v, witness_preference, is_under_guard, false); + ret.extend(usefulness); // 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); + matrix.push(v); } - 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, - // ) - // } + let v_ctor = v.head().ctor(); + + // FIXME: implement `overlapping_range_endpoints` lint // We split the head constructor of `v`. - let split_ctors = v_ctor.split(pcx, matrix.head_ctors(cx)); + let split_ctors = v_ctor.split(pcx, matrix.heads().map(DeconstructedPat::ctor)); // 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); + for ctor in split_ctors { // 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 spec_matrix = start_matrix.specialize_constructor(pcx, &ctor); + let v = v.pop_head_constructor(cx, &ctor); 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) + let usefulness = usefulness.apply_constructor(pcx, start_matrix, &ctor); + + // FIXME: implement `non_exhaustive_omitted_patterns` lint + + ret.extend(usefulness); + } }; + if ret.is_useful() { + v.head().set_reachable(); + } + ret } /// The arm of a match expression. #[derive(Clone, Copy)] -pub(crate) struct MatchArm { - pub(crate) pat: PatId, +pub(crate) struct MatchArm<'p> { + pub(crate) pat: &'p DeconstructedPat<'p>, pub(crate) has_guard: bool, } @@ -1101,18 +742,19 @@ 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<PatId>), + // FIXME: store ureachable subpattern IDs + Reachable, /// The arm is unreachable. Unreachable, } /// The output of checking a match for exhaustiveness and arm reachability. -pub(crate) struct UsefulnessReport { +pub(crate) struct UsefulnessReport<'p> { /// For each arm of the input, whether that arm is reachable after the arms above it. - pub(crate) _arm_usefulness: Vec<(MatchArm, Reachability)>, + pub(crate) _arm_usefulness: Vec<(MatchArm<'p>, 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<Pat>, + pub(crate) non_exhaustiveness_witnesses: Vec<DeconstructedPat<'p>>, } /// The entrypoint for the usefulness algorithm. Computes whether a match is exhaustive and which @@ -1120,53 +762,41 @@ pub(crate) struct UsefulnessReport { /// /// Note: the input patterns must have been lowered through /// `check_match::MatchVisitor::lower_pattern`. -pub(crate) fn compute_match_usefulness( - cx: &MatchCheckCtx<'_>, - arms: &[MatchArm], -) -> UsefulnessReport { +pub(crate) fn compute_match_usefulness<'p>( + cx: &MatchCheckCtx<'_, 'p>, + arms: &[MatchArm<'p>], + scrut_ty: &Ty, +) -> UsefulnessReport<'p> { let mut matrix = Matrix::empty(); let arm_usefulness = arms .iter() .copied() .map(|arm| { let v = PatStack::from_pattern(arm.pat); - let usefulness = is_useful(cx, &matrix, &v, LeaveOutWitness, arm.has_guard, true); + is_useful(cx, &matrix, &v, RealArm, arm.has_guard, true); if !arm.has_guard { - matrix.push(v, cx); + matrix.push(v); } - let reachability = match usefulness { - NoWitnesses(subpats) if subpats.is_empty() => Reachability::Unreachable, - NoWitnesses(subpats) => { - Reachability::Reachable(subpats.list_unreachable_subpatterns(cx).unwrap()) - } - WithWitnesses(..) => panic!("bug"), + let reachability = if arm.pat.is_reachable() { + Reachability::Reachable + } else { + Reachability::Unreachable }; (arm, reachability) }) .collect(); - let wild_pattern = - cx.pattern_arena.borrow_mut().alloc(Pat::wildcard_from_ty(cx.infer[cx.match_expr].clone())); + let wild_pattern = cx.pattern_arena.alloc(DeconstructedPat::wildcard(scrut_ty.clone())); let v = PatStack::from_pattern(wild_pattern); - let usefulness = is_useful(cx, &matrix, &v, ConstructWitness, false, true); + let usefulness = is_useful(cx, &matrix, &v, FakeExtraWildcard, false, true); let non_exhaustiveness_witnesses = match usefulness { WithWitnesses(pats) => pats.into_iter().map(Witness::single_pattern).collect(), - NoWitnesses(_) => panic!("bug"), + NoWitnesses { .. } => panic!("bug"), }; UsefulnessReport { _arm_usefulness: arm_usefulness, non_exhaustiveness_witnesses } } -pub(crate) type PatternArena = Arena<Pat>; - -mod helper { - 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<Self>; - } - +pub(crate) mod helper { // 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. |