Merge pull request #30639 from davidungar/rdar-60840456-custom-attr-on-extension

Start lookup *outside* of D when D is, e.g. an ExtensionDecl

Author: David Ungar

lib/Sema/TypeCheckAttr.cpp

@@ -2643,7 +2643,7 @@ void AttributeChecker::visitFrozenAttr(FrozenAttr *attr) {
 }
 
 void AttributeChecker::visitCustomAttr(CustomAttr *attr) {
-  auto dc = D->getInnermostDeclContext();
+  auto dc = D->getDeclContext();
 
   // Figure out which nominal declaration this custom attribute refers to.
   auto nominal = evaluateOrDefault(

test/NameBinding/custom-attr-on-extension.swift

@@ -0,0 +1,9 @@
+// RUN: %target-swift-frontend -typecheck %s -verify
+
+// Trips an assertion if an ASTScope lookup is attempted into the innermost
+// DeclContext of the extension.
+
+struct Ty{}
+
+@foo extension Ty {} // expected-error {{unknown attribute 'foo'}}
+