diff options
Diffstat (limited to 'compiler')
| -rw-r--r-- | compiler/rustc_mir_build/src/thir/pattern/_match.rs | 120 | ||||
| -rw-r--r-- | compiler/rustc_mir_build/src/thir/pattern/check_match.rs | 7 |
2 files changed, 93 insertions, 34 deletions
diff --git a/compiler/rustc_mir_build/src/thir/pattern/_match.rs b/compiler/rustc_mir_build/src/thir/pattern/_match.rs index bc85d45d867..5e7e81eba62 100644 --- a/compiler/rustc_mir_build/src/thir/pattern/_match.rs +++ b/compiler/rustc_mir_build/src/thir/pattern/_match.rs @@ -1,5 +1,11 @@ -//! Note: most of the tests relevant to this file can be found (at the time of writing) in -//! src/tests/ui/pattern/usefulness. +//! Note: tests specific to this file can be found in: +//! - ui/pattern/usefulness +//! - ui/or-patterns +//! - ui/consts/const_in_pattern +//! - ui/rfc-2008-non-exhaustive +//! - probably many others +//! I (Nadrieril) prefer to put new tests in `ui/pattern/usefulness` unless there's a specific +//! reason not to, for example if they depend on a particular feature like or_patterns. //! //! This file includes the logic for exhaustiveness and usefulness checking for //! pattern-matching. Specifically, given a list of patterns for a type, we can @@ -1361,8 +1367,9 @@ impl<'p, 'tcx> Fields<'p, 'tcx> { #[derive(Clone, Debug)] crate enum Usefulness<'tcx> { - /// Carries a list of unreachable subpatterns. Used only in the presence of or-patterns. - Useful(Vec<Span>), + /// Carries, for each column in the matrix, a set of sub-branches that have been found to be + /// unreachable. Used only in the presence of or-patterns, otherwise it stays empty. + Useful(Vec<FxHashSet<Span>>), /// Carries a list of witnesses of non-exhaustiveness. UsefulWithWitness(Vec<Witness<'tcx>>), NotUseful, @@ -1410,6 +1417,23 @@ impl<'tcx> Usefulness<'tcx> { }; UsefulWithWitness(new_witnesses) } + Useful(mut unreachables) => { + if !unreachables.is_empty() { + // When we apply a constructor, there are `arity` columns of the matrix that + // corresponded to its arguments. All the unreachables found in these columns + // will, after `apply`, come from the first column. So we take the union of all + // the corresponding sets and put them in the first column. + // Note that `arity` may be 0, in which case we just push a new empty set. + let len = unreachables.len(); + let arity = ctor_wild_subpatterns.len(); + let mut unioned = FxHashSet::default(); + for set in unreachables.drain((len - arity)..) { + unioned.extend(set) + } + unreachables.push(unioned); + } + Useful(unreachables) + } x => x, } } @@ -2091,13 +2115,14 @@ crate fn is_useful<'p, 'tcx>( // If the first pattern is an or-pattern, expand it. if let Some(vs) = v.expand_or_pat() { - // We need to push the already-seen patterns into the matrix in order to detect redundant - // branches like `Some(_) | Some(0)`. We also keep track of the unreachable subpatterns. - let mut matrix = matrix.clone(); - // `Vec` of all the unreachable branches of the current or-pattern. - let mut unreachable_branches = Vec::new(); - // Subpatterns that are unreachable from all branches. E.g. in the following case, the last - // `true` is unreachable only from one branch, so it is overall reachable. + // We expand the or pattern, trying each of its branches in turn and keeping careful track + // of possible unreachable sub-branches. + // + // If two branches have detected some unreachable sub-branches, we need to be careful. If + // they were detected in columns that are not the current one, we want to keep only the + // sub-branches that were unreachable in _all_ branches. Eg. in the following, the last + // `true` is unreachable in the second branch of the first or-pattern, but not otherwise. + // Therefore we don't want to lint that it is unreachable. // // ``` // match (true, true) { @@ -2105,41 +2130,72 @@ crate fn is_useful<'p, 'tcx>( // (false | true, false | true) => {} // } // ``` - let mut unreachable_subpats = FxHashSet::default(); - // Whether any branch at all is useful. + // If however the sub-branches come from the current column, they come from the inside of + // the current or-pattern, and we want to keep them all. Eg. in the following, we _do_ want + // to lint that the last `false` is unreachable. + // ``` + // match None { + // Some(false) => {} + // None | Some(true | false) => {} + // } + // ``` + + let mut matrix = matrix.clone(); + // We keep track of sub-branches separately depending on whether they come from this column + // or from others. + let mut unreachables_this_column: FxHashSet<Span> = FxHashSet::default(); + let mut unreachables_other_columns: Vec<FxHashSet<Span>> = Vec::default(); + // Whether at least one branch is reachable. let mut any_is_useful = false; for v in vs { let res = is_useful(cx, &matrix, &v, witness_preference, hir_id, is_under_guard, false); match res { - Useful(pats) => { - if !any_is_useful { - any_is_useful = true; - // Initialize with the first set of unreachable subpatterns encountered. - unreachable_subpats = pats.into_iter().collect(); - } else { - // Keep the patterns unreachable from both this and previous branches. - unreachable_subpats = - pats.into_iter().filter(|p| unreachable_subpats.contains(p)).collect(); + Useful(unreachables) => { + if let Some((this_column, other_columns)) = unreachables.split_last() { + // We keep the union of unreachables found in the first column. + unreachables_this_column.extend(this_column); + // We keep the intersection of unreachables found in other columns. + if unreachables_other_columns.is_empty() { + unreachables_other_columns = other_columns.to_vec(); + } else { + unreachables_other_columns = unreachables_other_columns + .into_iter() + .zip(other_columns) + .map(|(x, y)| x.intersection(&y).copied().collect()) + .collect(); + } } + any_is_useful = true; } - NotUseful => unreachable_branches.push(v.head().span), - UsefulWithWitness(_) => { - bug!("Encountered or-pat in `v` during exhaustiveness checking") + NotUseful => { + unreachables_this_column.insert(v.head().span); } + UsefulWithWitness(_) => bug!( + "encountered or-pat in the expansion of `_` during exhaustiveness checking" + ), } - // If pattern has a guard don't add it to the matrix + + // 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); } } - if any_is_useful { - // Collect all the unreachable patterns. - unreachable_branches.extend(unreachable_subpats); - return Useful(unreachable_branches); + + return if any_is_useful { + let mut unreachables = if unreachables_other_columns.is_empty() { + let n_columns = v.len(); + (0..n_columns - 1).map(|_| FxHashSet::default()).collect() + } else { + unreachables_other_columns + }; + unreachables.push(unreachables_this_column); + Useful(unreachables) } else { - return NotUseful; - } + NotUseful + }; } // FIXME(Nadrieril): Hack to work around type normalization issues (see #72476). diff --git a/compiler/rustc_mir_build/src/thir/pattern/check_match.rs b/compiler/rustc_mir_build/src/thir/pattern/check_match.rs index 30b700a1d4f..205ad850c0c 100644 --- a/compiler/rustc_mir_build/src/thir/pattern/check_match.rs +++ b/compiler/rustc_mir_build/src/thir/pattern/check_match.rs @@ -389,8 +389,11 @@ fn check_arms<'p, 'tcx>( hir::MatchSource::AwaitDesugar | hir::MatchSource::TryDesugar => {} } } - Useful(unreachable_subpatterns) => { - for span in unreachable_subpatterns { + Useful(unreachables) => { + let mut unreachables: Vec<_> = unreachables.into_iter().flatten().collect(); + // Emit lints in the order in which they occur in the file. + unreachables.sort_unstable(); + for span in unreachables { unreachable_pattern(cx.tcx, span, id, None); } } |