Only declarations that are members of a type or extension can have member attributes

The last step in breaking the cycle through visible declaration lookup,
e.g., with invalid code. Prior to this, we would get a false cyclic
reference through the parameters of a function when they try to find
property wrappers on the parameters.

Author: DougGregor

lib/Sema/TypeCheckMacros.cpp

@@ -474,7 +474,7 @@ ArrayRef<unsigned> ExpandMemberAttributeMacros::evaluate(Evaluator &evaluator,
     return { };
 
   auto *parentDecl = decl->getDeclContext()->getAsDecl();
-  if (!parentDecl)
+  if (!parentDecl || !isa<IterableDeclContext>(parentDecl))
     return { };
 
   if (isa<PatternBindingDecl>(decl))

test/Macros/macro_expand_peers.swift

@@ -145,9 +145,8 @@ struct S2 {
   }
 
   #if TEST_DIAGNOSTICS
-  // FIXME: Causes reference cycles
-  // should have error {{cannot find 'nonexistent' in scope}}
-  // @addCompletionHandlerArbitrarily(nonexistent)
+  // expected-error@+1 {{cannot find 'nonexistent' in scope}}
+  @addCompletionHandlerArbitrarily(nonexistent)
   func h(a: Int, for b: String, _ value: Double) async -> String {
     return b
   }