-//! 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>
//!
//! -----
//!
//! 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) panic_context: &'a dyn Fn() -> String,
+ 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
}
/// 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."
// 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()
- }
-
- #[track_caller]
- pub(super) fn bug(&self, info: &str) -> ! {
- panic!("bug: {}\n{}", info, (self.panic_context)());
- }
}
#[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 {
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![] }
}
/// 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 {
- fill_subpats(sub_set, unreachable_pats, cx);
- }
- }
- SubPatSet::Alt { subpats, pat, alt_count, .. } => {
- let expanded = pat.expand_or_pat(cx);
- for i in 0..*alt_count {
- let sub_set = subpats.get(&i).unwrap_or(&SubPatSet::Empty);
- if sub_set.is_empty() {
- // Found a unreachable subpattern.
- unreachable_pats.push(expanded[i]);
- } else {
- fill_subpats(sub_set, unreachable_pats, cx);
- }
- }
- }
+ 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);
}
}
-
- 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 }
- }
- 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
}
}
/// 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(),
}
}
(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
/// `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()
}
///
/// 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);
/// `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
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,
}
/// 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
///
/// 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: Vec<_> = arms
+ 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.
projects / rust.git / blobdiff