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| -rw-r--r-- | src/librustc_mir/hair/pattern/mod.rs | 24 |
1 files changed, 24 insertions, 0 deletions
diff --git a/src/librustc_mir/hair/pattern/mod.rs b/src/librustc_mir/hair/pattern/mod.rs index a15452043b3..aea5016ab34 100644 --- a/src/librustc_mir/hair/pattern/mod.rs +++ b/src/librustc_mir/hair/pattern/mod.rs @@ -1145,6 +1145,30 @@ impl<'a, 'tcx> PatternContext<'a, 'tcx> { } } +/// This method traverses the structure of `ty`, trying to find an +/// instance of an ADT (i.e. struct or enum) that was declared without +/// the `#[structural_match]` attribute. +/// +/// The "structure of a type" includes all components that would be +/// considered when doing a pattern match on a constant of that +/// type. +/// +/// * This means this method descends into fields of structs/enums, +/// and also descends into the inner type `T` of `&T` and `&mut T` +/// +/// * The traversal doesn't dereference unsafe pointers (`*const T`, +/// `*mut T`), and it does not visit the type arguments of an +/// instantiated generic like `PhantomData<T>`. +/// +/// The reason we do this search is Rust currently require all ADT's +/// reachable from a constant's type to be annotated with +/// `#[structural_match]`, an attribute which essentially says that +/// the implementation of `PartialEq::eq` behaves *equivalently* to a +/// comparison against the unfolded structure. +/// +/// For more background on why Rust has this requirement, and issues +/// that arose when the requirement was not enforced completely, see +/// Rust RFC 1445, rust-lang/rust#61188, and rust-lang/rust#62307. fn search_for_adt_without_structural_match<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> Option<&'tcx AdtDef> |