[Sema] Avoid member attribute cycle in ResolveMacroRequest

If we have a custom attribute on a type that does a qualified lookup
into the same type, we need to be able to expand member attribute
macros for that type. As such, the check to see if we already have
a nominal for the attribute would hit a cycle. Limit this check such
that it only applies to local vars, which is the only case where it
actually matters.

rdar://163961797

Author: hamishknight

lib/Sema/TypeCheckMacros.cpp

@@ -2242,8 +2242,12 @@ ResolveMacroRequest::evaluate(Evaluator &evaluator,
   // So bail out to prevent diagnostics from the contraint system.
   if (auto *attr = macroRef.getAttr()) {
     // If we already resolved this CustomAttr to a nominal, this isn't for a
-    // macro.
-    if (attr->getNominalDecl())
+    // macro. This can only currently be the case for property wrappers, so
+    // limit the check here to avoid request cycles for member attribute macros
+    // in cases where the attribute refers to a nested type in the type it's
+    // attached to, since the qualified lookup there needs to expand member
+    // attributes.
+    if (attr->shouldPreferPropertyWrapperOverMacro() && attr->getNominalDecl())
       return ConcreteDeclRef();
 
     auto foundMacros = namelookup::lookupMacros(dc, macroRef.getModuleName(),

test/NameLookup/rdar163961797.swift

@@ -0,0 +1,10 @@
+// RUN: %target-typecheck-verify-swift
+
+// Make sure we don't end up with a request cycle here, since looking up 'S.Actor'
+// requires expanding member attribute macros for 'S'.
+@S.Actor
+struct S {
+  @globalActor actor Actor: GlobalActor {
+    public static let shared = S.Actor()
+  }
+}