Auto merge of #88135 - crlf0710:trait_upcasting_part_3, r=nikomatsakis

Trait upcasting coercion (part 3)

By using separate candidates for each possible choice, this fixes type-checking issues in previous commits.

r? `@nikomatsakis`

1 files changed, 2 insertions, 13 deletions

diff --git a/compiler/rustc_codegen_ssa/src/base.rs b/compiler/rustc_codegen_ssa/src/base.rs
index 064a51c8f60..a5143a755fe 100644
--- a/compiler/rustc_codegen_ssa/src/base.rs
+++ b/compiler/rustc_codegen_ssa/src/base.rs
@@ -150,19 +150,8 @@ pub fn unsized_info<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
 
             // trait upcasting coercion
 
-            // if both of the two `principal`s are `None`, this function would have returned early above.
-            // and if one of the two `principal`s is `None`, typechecking would have rejected this case.
-            let principal_a = data_a
-                .principal()
-                .expect("unsized_info: missing principal trait for trait upcasting coercion");
-            let principal_b = data_b
-                .principal()
-                .expect("unsized_info: missing principal trait for trait upcasting coercion");
-
-            let vptr_entry_idx = cx.tcx().vtable_trait_upcasting_coercion_new_vptr_slot((
-                principal_a.with_self_ty(cx.tcx(), source),
-                principal_b.with_self_ty(cx.tcx(), source),
-            ));
+            let vptr_entry_idx =
+                cx.tcx().vtable_trait_upcasting_coercion_new_vptr_slot((source, target));
 
             if let Some(entry_idx) = vptr_entry_idx {
                 let ptr_ty = cx.type_i8p();