save-analysis: Process bounds in impl trait only in argument position

Author: Xanewok

src/librustc_save_analysis/dump_visitor.rs

@@ -385,7 +385,12 @@ impl<'l, 'tcx> DumpVisitor<'l, 'tcx> {
             }
 
             if let ast::FunctionRetTy::Ty(ref ret_ty) = decl.output {
-                v.visit_ty(&ret_ty);
+                if let ast::TyKind::ImplTrait(..) = ret_ty.node {
+                    // FIXME: Opaque type desugaring prevents us from easily
+                    // processing trait bounds. See `visit_ty` for more details.
+                } else {
+                    v.visit_ty(&ret_ty);
+                }
             }
 
             v.visit_block(&body);
@@ -1439,6 +1444,18 @@ impl<'l, 'tcx> Visitor<'l> for DumpVisitor<'l, 'tcx> {
                 self.visit_ty(element);
                 self.nest_tables(length.id, |v| v.visit_expr(&length.value));
             }
+            ast::TyKind::ImplTrait(id, ref bounds) => {
+                // FIXME: As of writing, the opaque type lowering introduces
+                // another DefPath scope/segment (used to declare the resulting
+                // opaque type item).
+                // However, the synthetic scope does *not* have associated
+                // typeck tables, which means we can't nest it and we fire an
+                // assertion when resolving the qualified type paths in trait
+                // bounds...
+                // This will panic if called on return type `impl Trait`, which
+                // we guard against in `process_fn`.
+                self.nest_tables(id, |v| v.process_bounds(bounds));
+            }
             _ => visit::walk_ty(self, t),
         }
     }

src/test/ui/save-analysis/issue-63663.rs

@@ -1,15 +1,20 @@
 // check-pass
 // compile-flags: -Zsave-analysis
 
-// Check that this doesn't ICE when processing associated const in formal
-// argument and return type of functions defined inside function/method scope.
-
 pub trait Trait {
     type Assoc;
 }
 
 pub struct A;
 
+trait Generic<T> {}
+impl<T> Generic<T> for () {}
+
+// Don't ICE when resolving type paths in return type `impl Trait`
+fn assoc_in_opaque_type_bounds<U: Trait>() -> impl Generic<U::Assoc> {}
+
+// Check that this doesn't ICE when processing associated const in formal
+// argument and return type of functions defined inside function/method scope.
 pub fn func() {
     fn _inner1<U: Trait>(_: U::Assoc) {}
     fn _inner2<U: Trait>() -> U::Assoc { unimplemented!() }