Use a query rather than recomputing the tail repeatedly

1 files changed, 7 insertions, 0 deletions

diff --git a/compiler/rustc_middle/src/query/mod.rs b/compiler/rustc_middle/src/query/mod.rs
index a1df27ac788..40d0028db86 100644
--- a/compiler/rustc_middle/src/query/mod.rs
+++ b/compiler/rustc_middle/src/query/mod.rs
@@ -1026,6 +1026,13 @@ rustc_queries! {
         separate_provide_extern
     }
 
+    /// Given an `impl_def_id`, return true if the self type is guaranteed to be unsized due
+    /// to either being one of the built-in unsized types (str/slice/dyn) or to be a struct
+    /// whose tail is one of those types.
+    query impl_self_is_guaranteed_unsized(impl_def_id: DefId) -> bool {
+        desc { |tcx| "computing whether `{}` has a guaranteed unsized self type", tcx.def_path_str(impl_def_id) }
+    }
+
     /// Maps a `DefId` of a type to a list of its inherent impls.
     /// Contains implementations of methods that are inherent to a type.
     /// Methods in these implementations don't need to be exported.