diff options
Diffstat (limited to 'compiler/rustc_pattern_analysis/src')
| -rw-r--r-- | compiler/rustc_pattern_analysis/src/lib.rs | 3 | ||||
| -rw-r--r-- | compiler/rustc_pattern_analysis/src/lints.rs | 2 | ||||
| -rw-r--r-- | compiler/rustc_pattern_analysis/src/pat.rs | 78 | ||||
| -rw-r--r-- | compiler/rustc_pattern_analysis/src/rustc.rs | 2 | ||||
| -rw-r--r-- | compiler/rustc_pattern_analysis/src/usefulness.rs | 91 |
5 files changed, 91 insertions, 85 deletions
diff --git a/compiler/rustc_pattern_analysis/src/lib.rs b/compiler/rustc_pattern_analysis/src/lib.rs index 1a151e72488..164dc36b679 100644 --- a/compiler/rustc_pattern_analysis/src/lib.rs +++ b/compiler/rustc_pattern_analysis/src/lib.rs @@ -1,5 +1,8 @@ //! Analysis of patterns, notably match exhaustiveness checking. +#![allow(rustc::untranslatable_diagnostic)] +#![allow(rustc::diagnostic_outside_of_impl)] + pub mod constructor; #[cfg(feature = "rustc")] pub mod errors; diff --git a/compiler/rustc_pattern_analysis/src/lints.rs b/compiler/rustc_pattern_analysis/src/lints.rs index 3f1497540d2..30e775733de 100644 --- a/compiler/rustc_pattern_analysis/src/lints.rs +++ b/compiler/rustc_pattern_analysis/src/lints.rs @@ -10,7 +10,7 @@ use crate::MatchArm; /// Traverse the patterns to collect any variants of a non_exhaustive enum that fail to be mentioned /// in a given column. #[instrument(level = "debug", skip(cx), ret)] -fn collect_nonexhaustive_missing_variants<'a, 'p, 'tcx>( +fn collect_nonexhaustive_missing_variants<'p, 'tcx>( cx: &RustcMatchCheckCtxt<'p, 'tcx>, column: &PatternColumn<'p, RustcMatchCheckCtxt<'p, 'tcx>>, ) -> Result<Vec<WitnessPat<'p, 'tcx>>, ErrorGuaranteed> { diff --git a/compiler/rustc_pattern_analysis/src/pat.rs b/compiler/rustc_pattern_analysis/src/pat.rs index 9bde23c7bf1..d9b2b31643d 100644 --- a/compiler/rustc_pattern_analysis/src/pat.rs +++ b/compiler/rustc_pattern_analysis/src/pat.rs @@ -1,6 +1,5 @@ //! As explained in [`crate::usefulness`], values and patterns are made from constructors applied to //! fields. This file defines types that represent patterns in this way. -use std::cell::Cell; use std::fmt; use smallvec::{smallvec, SmallVec}; @@ -10,12 +9,20 @@ use crate::TypeCx; use self::Constructor::*; +/// A globally unique id to distinguish patterns. +#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)] +pub(crate) struct PatId(u32); +impl PatId { + fn new() -> Self { + use std::sync::atomic::{AtomicU32, Ordering}; + static PAT_ID: AtomicU32 = AtomicU32::new(0); + PatId(PAT_ID.fetch_add(1, Ordering::SeqCst)) + } +} + /// Values and patterns can be represented as a constructor applied to some fields. This represents -/// a pattern in this form. -/// This also uses interior mutability to keep track of whether the pattern has been found reachable -/// during analysis. For this reason they cannot be cloned. -/// A `DeconstructedPat` will almost always come from user input; the only exception are some -/// `Wildcard`s introduced during specialization. +/// a pattern in this form. A `DeconstructedPat` will almost always come from user input; the only +/// exception are some `Wildcard`s introduced during pattern lowering. /// /// Note that the number of fields may not match the fields declared in the original struct/variant. /// This happens if a private or `non_exhaustive` field is uninhabited, because the code mustn't @@ -28,19 +35,13 @@ pub struct DeconstructedPat<Cx: TypeCx> { /// Extra data to store in a pattern. `None` if the pattern is a wildcard that does not /// correspond to a user-supplied pattern. data: Option<Cx::PatData>, - /// Whether removing this arm would change the behavior of the match expression. - useful: Cell<bool>, + /// Globally-unique id used to track usefulness at the level of subpatterns. + pub(crate) uid: PatId, } impl<Cx: TypeCx> DeconstructedPat<Cx> { pub fn wildcard(ty: Cx::Ty) -> Self { - DeconstructedPat { - ctor: Wildcard, - fields: Vec::new(), - ty, - data: None, - useful: Cell::new(false), - } + DeconstructedPat { ctor: Wildcard, fields: Vec::new(), ty, data: None, uid: PatId::new() } } pub fn new( @@ -49,7 +50,7 @@ impl<Cx: TypeCx> DeconstructedPat<Cx> { ty: Cx::Ty, data: Cx::PatData, ) -> Self { - DeconstructedPat { ctor, fields, ty, data: Some(data), useful: Cell::new(false) } + DeconstructedPat { ctor, fields, ty, data: Some(data), uid: PatId::new() } } pub(crate) fn is_or_pat(&self) -> bool { @@ -107,39 +108,16 @@ impl<Cx: TypeCx> DeconstructedPat<Cx> { } } - /// We keep track for each pattern if it was ever useful during the analysis. This is used with - /// `redundant_subpatterns` to report redundant subpatterns arising from or patterns. - pub(crate) fn set_useful(&self) { - self.useful.set(true) - } - pub(crate) fn is_useful(&self) -> bool { - if self.useful.get() { - true - } else if self.is_or_pat() && self.iter_fields().any(|f| f.is_useful()) { - // We always expand or patterns in the matrix, so we will never see the actual - // or-pattern (the one with constructor `Or`) in the column. As such, it will not be - // marked as useful itself, only its children will. We recover this information here. - self.set_useful(); - true - } else { - false + /// Walk top-down and call `it` in each place where a pattern occurs + /// starting with the root pattern `walk` is called on. If `it` returns + /// false then we will descend no further but siblings will be processed. + pub fn walk<'a>(&'a self, it: &mut impl FnMut(&'a Self) -> bool) { + if !it(self) { + return; } - } - /// Report the subpatterns that were not useful, if any. - pub(crate) fn redundant_subpatterns(&self) -> Vec<&Self> { - let mut subpats = Vec::new(); - self.collect_redundant_subpatterns(&mut subpats); - subpats - } - fn collect_redundant_subpatterns<'a>(&'a self, subpats: &mut Vec<&'a Self>) { - // We don't look at subpatterns if we already reported the whole pattern as redundant. - if !self.is_useful() { - subpats.push(self); - } else { - for p in self.iter_fields() { - p.collect_redundant_subpatterns(subpats); - } + for p in self.iter_fields() { + p.walk(it) } } } @@ -284,12 +262,6 @@ impl<'p, Cx: TypeCx> PatOrWild<'p, Cx> { PatOrWild::Pat(pat) => pat.specialize(other_ctor, ctor_arity), } } - - pub(crate) fn set_useful(&self) { - if let PatOrWild::Pat(pat) = self { - pat.set_useful() - } - } } impl<'p, Cx: TypeCx> fmt::Debug for PatOrWild<'p, Cx> { diff --git a/compiler/rustc_pattern_analysis/src/rustc.rs b/compiler/rustc_pattern_analysis/src/rustc.rs index a8fe0cb6a1d..5b62731e202 100644 --- a/compiler/rustc_pattern_analysis/src/rustc.rs +++ b/compiler/rustc_pattern_analysis/src/rustc.rs @@ -173,7 +173,7 @@ impl<'p, 'tcx: 'p> RustcMatchCheckCtxt<'p, 'tcx> { variant.fields.iter().enumerate().filter_map(move |(i, field)| { let ty = field.ty(cx.tcx, args); - // `field.ty()` doesn't normalize after substituting. + // `field.ty()` doesn't normalize after instantiating. let ty = cx.tcx.normalize_erasing_regions(cx.param_env, ty); let is_visible = adt.is_enum() || field.vis.is_accessible_from(cx.module, cx.tcx); let is_uninhabited = (cx.tcx.features().exhaustive_patterns diff --git a/compiler/rustc_pattern_analysis/src/usefulness.rs b/compiler/rustc_pattern_analysis/src/usefulness.rs index 90fcb63dc1d..a24da448766 100644 --- a/compiler/rustc_pattern_analysis/src/usefulness.rs +++ b/compiler/rustc_pattern_analysis/src/usefulness.rs @@ -466,13 +466,9 @@ //! first pattern of a row in the matrix is an or-pattern, we expand it by duplicating the rest of //! the row as necessary. This is handled automatically in [`Matrix`]. //! -//! This makes usefulness tracking subtle, because we also want to compute whether an alternative -//! of an or-pattern is redundant, e.g. in `Some(_) | Some(0)`. We track usefulness of each -//! subpattern by interior mutability in [`DeconstructedPat`] with `set_useful`/`is_useful`. -//! -//! It's unfortunate that we have to use interior mutability, but believe me (Nadrieril), I have -//! tried [other](https://github.com/rust-lang/rust/pull/80104) -//! [solutions](https://github.com/rust-lang/rust/pull/80632) and nothing is remotely as simple. +//! This makes usefulness tracking subtle, because we also want to compute whether an alternative of +//! an or-pattern is redundant, e.g. in `Some(_) | Some(0)`. We therefore track usefulness of each +//! subpattern of the match. //! //! //! @@ -713,12 +709,13 @@ //! I (Nadrieril) prefer to put new tests in `ui/pattern/usefulness` unless there's a specific //! reason not to, for example if they crucially depend on a particular feature like `or_patterns`. +use rustc_hash::FxHashSet; use rustc_index::bit_set::BitSet; use smallvec::{smallvec, SmallVec}; use std::fmt; use crate::constructor::{Constructor, ConstructorSet, IntRange}; -use crate::pat::{DeconstructedPat, PatOrWild, WitnessPat}; +use crate::pat::{DeconstructedPat, PatId, PatOrWild, WitnessPat}; use crate::{Captures, MatchArm, TypeCx}; use self::ValidityConstraint::*; @@ -731,16 +728,12 @@ pub fn ensure_sufficient_stack<R>(f: impl FnOnce() -> R) -> R { } /// Context that provides information for usefulness checking. -pub struct UsefulnessCtxt<'a, Cx: TypeCx> { +struct UsefulnessCtxt<'a, Cx: TypeCx> { /// The context for type information. - pub tycx: &'a Cx, -} - -impl<'a, Cx: TypeCx> Copy for UsefulnessCtxt<'a, Cx> {} -impl<'a, Cx: TypeCx> Clone for UsefulnessCtxt<'a, Cx> { - fn clone(&self) -> Self { - Self { tycx: self.tycx } - } + tycx: &'a Cx, + /// Collect the patterns found useful during usefulness checking. This is used to lint + /// unreachable (sub)patterns. + useful_subpatterns: FxHashSet<PatId>, } /// Context that provides information local to a place under investigation. @@ -1435,7 +1428,7 @@ impl<Cx: TypeCx> WitnessMatrix<Cx> { /// We can however get false negatives because exhaustiveness does not explore all cases. See the /// section on relevancy at the top of the file. fn collect_overlapping_range_endpoints<'p, Cx: TypeCx>( - mcx: UsefulnessCtxt<'_, Cx>, + mcx: &mut UsefulnessCtxt<'_, Cx>, overlap_range: IntRange, matrix: &Matrix<'p, Cx>, specialized_matrix: &Matrix<'p, Cx>, @@ -1495,8 +1488,8 @@ fn collect_overlapping_range_endpoints<'p, Cx: TypeCx>( /// The core of the algorithm. /// /// This recursively computes witnesses of the non-exhaustiveness of `matrix` (if any). Also tracks -/// usefulness of each row in the matrix (in `row.useful`). We track usefulness of each -/// subpattern using interior mutability in `DeconstructedPat`. +/// usefulness of each row in the matrix (in `row.useful`). We track usefulness of each subpattern +/// in `mcx.useful_subpatterns`. /// /// The input `Matrix` and the output `WitnessMatrix` together match the type exhaustively. /// @@ -1508,7 +1501,7 @@ fn collect_overlapping_range_endpoints<'p, Cx: TypeCx>( /// This is all explained at the top of the file. #[instrument(level = "debug", skip(mcx), ret)] fn compute_exhaustiveness_and_usefulness<'a, 'p, Cx: TypeCx>( - mcx: UsefulnessCtxt<'a, Cx>, + mcx: &mut UsefulnessCtxt<'a, Cx>, matrix: &mut Matrix<'p, Cx>, ) -> Result<WitnessMatrix<Cx>, Cx::Error> { debug_assert!(matrix.rows().all(|r| r.len() == matrix.column_count())); @@ -1594,7 +1587,9 @@ fn compute_exhaustiveness_and_usefulness<'a, 'p, Cx: TypeCx>( // Record usefulness in the patterns. for row in matrix.rows() { if row.useful { - row.head().set_useful(); + if let PatOrWild::Pat(pat) = row.head() { + mcx.useful_subpatterns.insert(pat.uid); + } } } @@ -1613,6 +1608,47 @@ pub enum Usefulness<'p, Cx: TypeCx> { Redundant, } +/// Report whether this pattern was found useful, and its subpatterns that were not useful if any. +fn collect_pattern_usefulness<'p, Cx: TypeCx>( + useful_subpatterns: &FxHashSet<PatId>, + pat: &'p DeconstructedPat<Cx>, +) -> Usefulness<'p, Cx> { + fn pat_is_useful<'p, Cx: TypeCx>( + useful_subpatterns: &FxHashSet<PatId>, + pat: &'p DeconstructedPat<Cx>, + ) -> bool { + if useful_subpatterns.contains(&pat.uid) { + true + } else if pat.is_or_pat() && pat.iter_fields().any(|f| pat_is_useful(useful_subpatterns, f)) + { + // We always expand or patterns in the matrix, so we will never see the actual + // or-pattern (the one with constructor `Or`) in the column. As such, it will not be + // marked as useful itself, only its children will. We recover this information here. + true + } else { + false + } + } + + let mut redundant_subpats = Vec::new(); + pat.walk(&mut |p| { + if pat_is_useful(useful_subpatterns, p) { + // The pattern is useful, so we recurse to find redundant subpatterns. + true + } else { + // The pattern is redundant. + redundant_subpats.push(p); + false // stop recursing + } + }); + + if pat_is_useful(useful_subpatterns, pat) { + Usefulness::Useful(redundant_subpats) + } else { + Usefulness::Redundant + } +} + /// The output of checking a match for exhaustiveness and arm usefulness. pub struct UsefulnessReport<'p, Cx: TypeCx> { /// For each arm of the input, whether that arm is useful after the arms above it. @@ -1630,9 +1666,9 @@ pub fn compute_match_usefulness<'p, Cx: TypeCx>( scrut_ty: Cx::Ty, scrut_validity: ValidityConstraint, ) -> Result<UsefulnessReport<'p, Cx>, Cx::Error> { - let cx = UsefulnessCtxt { tycx }; + let mut cx = UsefulnessCtxt { tycx, useful_subpatterns: FxHashSet::default() }; let mut matrix = Matrix::new(arms, scrut_ty, scrut_validity); - let non_exhaustiveness_witnesses = compute_exhaustiveness_and_usefulness(cx, &mut matrix)?; + let non_exhaustiveness_witnesses = compute_exhaustiveness_and_usefulness(&mut cx, &mut matrix)?; let non_exhaustiveness_witnesses: Vec<_> = non_exhaustiveness_witnesses.single_column(); let arm_usefulness: Vec<_> = arms @@ -1640,12 +1676,7 @@ pub fn compute_match_usefulness<'p, Cx: TypeCx>( .copied() .map(|arm| { debug!(?arm); - // We warn when a pattern is not useful. - let usefulness = if arm.pat.is_useful() { - Usefulness::Useful(arm.pat.redundant_subpatterns()) - } else { - Usefulness::Redundant - }; + let usefulness = collect_pattern_usefulness(&cx.useful_subpatterns, arm.pat); (arm, usefulness) }) .collect(); |