Merge pull request #64807 from DougGregor/innermost-macro-context-5.9

Author: DougGregor

lib/AST/Decl.cpp

@@ -574,6 +574,8 @@ DeclContext *Decl::getInnermostDeclContext() const {
     return const_cast<ExtensionDecl*>(ext);
   if (auto topLevel = dyn_cast<TopLevelCodeDecl>(this))
     return const_cast<TopLevelCodeDecl*>(topLevel);
+  if (auto macro = dyn_cast<MacroDecl>(this))
+    return const_cast<MacroDecl*>(macro);
 
   return getDeclContext();
 }

test/Macros/macros_diagnostics.swift

@@ -169,3 +169,13 @@ func test() {
   let _: [MacroOrType.Nested] = []
   _ = [MacroOrType.Nested]()
 }
+
+// Make sure we have the right declaration context for type-checking the result
+// types of macros. At one point, we would reject the following macro.
+protocol MyProto {
+}
+struct MyStruct<T: MyProto> {
+}
+
+@freestanding(expression) macro myMacro<T : MyProto>(_ value: MyStruct<T>) -> MyStruct<T> = #externalMacro(module: "A", type: "B")
+// expected-warning@-1{{external macro implementation type}}