diff options
| -rw-r--r-- | compiler/rustc_mir_build/src/thir/pattern/deconstruct_pat.rs | 8 | ||||
| -rw-r--r-- | compiler/rustc_mir_build/src/thir/pattern/usefulness.rs | 16 |
2 files changed, 20 insertions, 4 deletions
diff --git a/compiler/rustc_mir_build/src/thir/pattern/deconstruct_pat.rs b/compiler/rustc_mir_build/src/thir/pattern/deconstruct_pat.rs index 9af13781312..6a77146138b 100644 --- a/compiler/rustc_mir_build/src/thir/pattern/deconstruct_pat.rs +++ b/compiler/rustc_mir_build/src/thir/pattern/deconstruct_pat.rs @@ -844,8 +844,8 @@ impl<'tcx> Constructor<'tcx> { } /// Faster version of `is_covered_by` when applied to many constructors. `used_ctors` is - /// assumed to be built from `matrix.head_ctors()` with wildcards filtered out, and `self` is - /// assumed to have been split from a wildcard. + /// assumed to be built from `matrix.head_ctors()` with wildcards and opaques filtered out, + /// and `self` is assumed to have been split from a wildcard. fn is_covered_by_any<'p>( &self, pcx: &PatCtxt<'_, 'p, 'tcx>, @@ -894,7 +894,7 @@ impl<'tcx> Constructor<'tcx> { /// in `to_ctors`: in some cases we only return `Missing`. #[derive(Debug)] pub(super) struct SplitWildcard<'tcx> { - /// Constructors seen in the matrix. + /// Constructors (other than wildcards and opaques) seen in the matrix. matrix_ctors: Vec<Constructor<'tcx>>, /// All the constructors for this type all_ctors: SmallVec<[Constructor<'tcx>; 1]>, @@ -1037,7 +1037,7 @@ impl<'tcx> SplitWildcard<'tcx> { // Since `all_ctors` never contains wildcards, this won't recurse further. self.all_ctors = self.all_ctors.iter().flat_map(|ctor| ctor.split(pcx, ctors.clone())).collect(); - self.matrix_ctors = ctors.filter(|c| !c.is_wildcard()).cloned().collect(); + self.matrix_ctors = ctors.filter(|c| !matches!(c, Wildcard | Opaque)).cloned().collect(); } /// Whether there are any value constructors for this type that are not present in the matrix. diff --git a/compiler/rustc_mir_build/src/thir/pattern/usefulness.rs b/compiler/rustc_mir_build/src/thir/pattern/usefulness.rs index f229b10c447..e5b63506906 100644 --- a/compiler/rustc_mir_build/src/thir/pattern/usefulness.rs +++ b/compiler/rustc_mir_build/src/thir/pattern/usefulness.rs @@ -288,6 +288,22 @@ //! //! 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. +//! +//! # Constants in patterns +//! +//! There are two kinds of constants in patterns: +//! +//! * literals (`1`, `true`, `"foo"`) +//! * named or inline consts (`FOO`, `const { 5 + 6 }`) +//! +//! The latter are converted into other patterns with literals at the leaves. For example +//! `const_to_pat(const { [1, 2, 3] })` becomes an `Array(vec![Const(1), Const(2), Const(3)])` +//! pattern. This gets problematic when comparing the constant via `==` would behave differently +//! from matching on the constant converted to a pattern. Situations like that can occur, when +//! the user implements `PartialEq` manually, and thus could make `==` behave arbitrarily different. +//! In order to honor the `==` implementation, constants of types that implement `PartialEq` manually +//! stay as a full constant and become an `Opaque` pattern. These `Opaque` patterns do not participate +//! in exhaustiveness, specialization or overlap checking. use self::ArmType::*; use self::Usefulness::*; |