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Diffstat (limited to 'compiler/rustc_pattern_analysis/src/lints.rs')
| -rw-r--r-- | compiler/rustc_pattern_analysis/src/lints.rs | 296 |
1 files changed, 296 insertions, 0 deletions
diff --git a/compiler/rustc_pattern_analysis/src/lints.rs b/compiler/rustc_pattern_analysis/src/lints.rs new file mode 100644 index 000000000..072ef4836 --- /dev/null +++ b/compiler/rustc_pattern_analysis/src/lints.rs @@ -0,0 +1,296 @@ +use smallvec::SmallVec; + +use rustc_data_structures::captures::Captures; +use rustc_middle::ty::{self, Ty}; +use rustc_session::lint; +use rustc_session::lint::builtin::NON_EXHAUSTIVE_OMITTED_PATTERNS; +use rustc_span::Span; + +use crate::constructor::{IntRange, MaybeInfiniteInt}; +use crate::errors::{ + NonExhaustiveOmittedPattern, NonExhaustiveOmittedPatternLintOnArm, Overlap, + OverlappingRangeEndpoints, Uncovered, +}; +use crate::rustc::{ + Constructor, DeconstructedPat, MatchArm, MatchCtxt, PlaceCtxt, RustcMatchCheckCtxt, + SplitConstructorSet, WitnessPat, +}; +use crate::TypeCx; + +/// A column of patterns in the matrix, where a column is the intuitive notion of "subpatterns that +/// inspect the same subvalue/place". +/// This is used to traverse patterns column-by-column for lints. Despite similarities with the +/// algorithm in [`crate::usefulness`], this does a different traversal. Notably this is linear in +/// the depth of patterns, whereas `compute_exhaustiveness_and_usefulness` is worst-case exponential +/// (exhaustiveness is NP-complete). The core difference is that we treat sub-columns separately. +/// +/// This must not contain an or-pattern. `specialize` takes care to expand them. +/// +/// This is not used in the main algorithm; only in lints. +#[derive(Debug)] +pub(crate) struct PatternColumn<'a, 'p, 'tcx> { + patterns: Vec<&'a DeconstructedPat<'p, 'tcx>>, +} + +impl<'a, 'p, 'tcx> PatternColumn<'a, 'p, 'tcx> { + pub(crate) fn new(arms: &[MatchArm<'p, 'tcx>]) -> Self { + let mut patterns = Vec::with_capacity(arms.len()); + for arm in arms { + if arm.pat.is_or_pat() { + patterns.extend(arm.pat.flatten_or_pat()) + } else { + patterns.push(arm.pat) + } + } + Self { patterns } + } + + fn is_empty(&self) -> bool { + self.patterns.is_empty() + } + fn head_ty(&self) -> Option<Ty<'tcx>> { + if self.patterns.len() == 0 { + return None; + } + // If the type is opaque and it is revealed anywhere in the column, we take the revealed + // version. Otherwise we could encounter constructors for the revealed type and crash. + let first_ty = self.patterns[0].ty(); + if RustcMatchCheckCtxt::is_opaque_ty(first_ty) { + for pat in &self.patterns { + let ty = pat.ty(); + if !RustcMatchCheckCtxt::is_opaque_ty(ty) { + return Some(ty); + } + } + } + Some(first_ty) + } + + /// Do constructor splitting on the constructors of the column. + fn analyze_ctors(&self, pcx: &PlaceCtxt<'_, 'p, 'tcx>) -> SplitConstructorSet<'p, 'tcx> { + let column_ctors = self.patterns.iter().map(|p| p.ctor()); + pcx.ctors_for_ty().split(pcx, column_ctors) + } + + fn iter<'b>(&'b self) -> impl Iterator<Item = &'a DeconstructedPat<'p, 'tcx>> + Captures<'b> { + self.patterns.iter().copied() + } + + /// Does specialization: given a constructor, this takes the patterns from the column that match + /// the constructor, and outputs their fields. + /// This returns one column per field of the constructor. They usually all have the same length + /// (the number of patterns in `self` that matched `ctor`), except that we expand or-patterns + /// which may change the lengths. + fn specialize( + &self, + pcx: &PlaceCtxt<'a, 'p, 'tcx>, + ctor: &Constructor<'p, 'tcx>, + ) -> Vec<PatternColumn<'a, 'p, 'tcx>> { + let arity = ctor.arity(pcx); + if arity == 0 { + return Vec::new(); + } + + // We specialize the column by `ctor`. This gives us `arity`-many columns of patterns. These + // columns may have different lengths in the presence of or-patterns (this is why we can't + // reuse `Matrix`). + let mut specialized_columns: Vec<_> = + (0..arity).map(|_| Self { patterns: Vec::new() }).collect(); + let relevant_patterns = + self.patterns.iter().filter(|pat| ctor.is_covered_by(pcx, pat.ctor())); + for pat in relevant_patterns { + let specialized = pat.specialize(pcx, ctor); + for (subpat, column) in specialized.iter().zip(&mut specialized_columns) { + if subpat.is_or_pat() { + column.patterns.extend(subpat.flatten_or_pat()) + } else { + column.patterns.push(subpat) + } + } + } + + assert!( + !specialized_columns[0].is_empty(), + "ctor {ctor:?} was listed as present but isn't; + there is an inconsistency between `Constructor::is_covered_by` and `ConstructorSet::split`" + ); + specialized_columns + } +} + +/// 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>( + cx: MatchCtxt<'a, 'p, 'tcx>, + column: &PatternColumn<'a, 'p, 'tcx>, +) -> Vec<WitnessPat<'p, 'tcx>> { + let Some(ty) = column.head_ty() else { + return Vec::new(); + }; + let pcx = &PlaceCtxt::new_dummy(cx, ty); + + let set = column.analyze_ctors(pcx); + if set.present.is_empty() { + // We can't consistently handle the case where no constructors are present (since this would + // require digging deep through any type in case there's a non_exhaustive enum somewhere), + // so for consistency we refuse to handle the top-level case, where we could handle it. + return vec![]; + } + + let mut witnesses = Vec::new(); + if cx.tycx.is_foreign_non_exhaustive_enum(ty) { + witnesses.extend( + set.missing + .into_iter() + // This will list missing visible variants. + .filter(|c| !matches!(c, Constructor::Hidden | Constructor::NonExhaustive)) + .map(|missing_ctor| WitnessPat::wild_from_ctor(pcx, missing_ctor)), + ) + } + + // Recurse into the fields. + for ctor in set.present { + let specialized_columns = column.specialize(pcx, &ctor); + let wild_pat = WitnessPat::wild_from_ctor(pcx, ctor); + for (i, col_i) in specialized_columns.iter().enumerate() { + // Compute witnesses for each column. + let wits_for_col_i = collect_nonexhaustive_missing_variants(cx, col_i); + // For each witness, we build a new pattern in the shape of `ctor(_, _, wit, _, _)`, + // adding enough wildcards to match `arity`. + for wit in wits_for_col_i { + let mut pat = wild_pat.clone(); + pat.fields[i] = wit; + witnesses.push(pat); + } + } + } + witnesses +} + +pub(crate) fn lint_nonexhaustive_missing_variants<'a, 'p, 'tcx>( + cx: MatchCtxt<'a, 'p, 'tcx>, + arms: &[MatchArm<'p, 'tcx>], + pat_column: &PatternColumn<'a, 'p, 'tcx>, + scrut_ty: Ty<'tcx>, +) { + let rcx: &RustcMatchCheckCtxt<'_, '_> = cx.tycx; + if !matches!( + rcx.tcx.lint_level_at_node(NON_EXHAUSTIVE_OMITTED_PATTERNS, rcx.match_lint_level).0, + rustc_session::lint::Level::Allow + ) { + let witnesses = collect_nonexhaustive_missing_variants(cx, pat_column); + if !witnesses.is_empty() { + // Report that a match of a `non_exhaustive` enum marked with `non_exhaustive_omitted_patterns` + // is not exhaustive enough. + // + // NB: The partner lint for structs lives in `compiler/rustc_hir_analysis/src/check/pat.rs`. + rcx.tcx.emit_spanned_lint( + NON_EXHAUSTIVE_OMITTED_PATTERNS, + rcx.match_lint_level, + rcx.scrut_span, + NonExhaustiveOmittedPattern { + scrut_ty, + uncovered: Uncovered::new(rcx.scrut_span, rcx, witnesses), + }, + ); + } + } else { + // We used to allow putting the `#[allow(non_exhaustive_omitted_patterns)]` on a match + // arm. This no longer makes sense so we warn users, to avoid silently breaking their + // usage of the lint. + for arm in arms { + let (lint_level, lint_level_source) = + rcx.tcx.lint_level_at_node(NON_EXHAUSTIVE_OMITTED_PATTERNS, arm.arm_data); + if !matches!(lint_level, rustc_session::lint::Level::Allow) { + let decorator = NonExhaustiveOmittedPatternLintOnArm { + lint_span: lint_level_source.span(), + suggest_lint_on_match: rcx.whole_match_span.map(|span| span.shrink_to_lo()), + lint_level: lint_level.as_str(), + lint_name: "non_exhaustive_omitted_patterns", + }; + + use rustc_errors::DecorateLint; + let mut err = rcx.tcx.sess.struct_span_warn(*arm.pat.data(), ""); + err.set_primary_message(decorator.msg()); + decorator.decorate_lint(&mut err); + err.emit(); + } + } + } +} + +/// Traverse the patterns to warn the user about ranges that overlap on their endpoints. +#[instrument(level = "debug", skip(cx))] +pub(crate) fn lint_overlapping_range_endpoints<'a, 'p, 'tcx>( + cx: MatchCtxt<'a, 'p, 'tcx>, + column: &PatternColumn<'a, 'p, 'tcx>, +) { + let Some(ty) = column.head_ty() else { + return; + }; + let pcx = &PlaceCtxt::new_dummy(cx, ty); + let rcx: &RustcMatchCheckCtxt<'_, '_> = cx.tycx; + + let set = column.analyze_ctors(pcx); + + if matches!(ty.kind(), ty::Char | ty::Int(_) | ty::Uint(_)) { + let emit_lint = |overlap: &IntRange, this_span: Span, overlapped_spans: &[Span]| { + let overlap_as_pat = rcx.hoist_pat_range(overlap, ty); + let overlaps: Vec<_> = overlapped_spans + .iter() + .copied() + .map(|span| Overlap { range: overlap_as_pat.clone(), span }) + .collect(); + rcx.tcx.emit_spanned_lint( + lint::builtin::OVERLAPPING_RANGE_ENDPOINTS, + rcx.match_lint_level, + this_span, + OverlappingRangeEndpoints { overlap: overlaps, range: this_span }, + ); + }; + + // If two ranges overlapped, the split set will contain their intersection as a singleton. + let split_int_ranges = set.present.iter().filter_map(|c| c.as_int_range()); + for overlap_range in split_int_ranges.clone() { + if overlap_range.is_singleton() { + let overlap: MaybeInfiniteInt = overlap_range.lo; + // Ranges that look like `lo..=overlap`. + let mut prefixes: SmallVec<[_; 1]> = Default::default(); + // Ranges that look like `overlap..=hi`. + let mut suffixes: SmallVec<[_; 1]> = Default::default(); + // Iterate on patterns that contained `overlap`. + for pat in column.iter() { + let this_span = *pat.data(); + let Constructor::IntRange(this_range) = pat.ctor() else { continue }; + if this_range.is_singleton() { + // Don't lint when one of the ranges is a singleton. + continue; + } + if this_range.lo == overlap { + // `this_range` looks like `overlap..=this_range.hi`; it overlaps with any + // ranges that look like `lo..=overlap`. + if !prefixes.is_empty() { + emit_lint(overlap_range, this_span, &prefixes); + } + suffixes.push(this_span) + } else if this_range.hi == overlap.plus_one() { + // `this_range` looks like `this_range.lo..=overlap`; it overlaps with any + // ranges that look like `overlap..=hi`. + if !suffixes.is_empty() { + emit_lint(overlap_range, this_span, &suffixes); + } + prefixes.push(this_span) + } + } + } + } + } else { + // Recurse into the fields. + for ctor in set.present { + for col in column.specialize(pcx, &ctor) { + lint_overlapping_range_endpoints(cx, &col); + } + } + } +} |