Anchor the macro-resolution request on the declaration to which the macro is attached

The macro-resolution request for an attached macro was expressed in
terms of the custom attribute and the declaration context enclosing the
attribute. While the declaration context is the correct one for
resolving the types and arguments of the custom attribute, the
declaration provides a better anchor for cases where the same
attribute applies to multiple declarations, e.g., with
member-attribute macros, leading to false cyclic references.

Author: DougGregor

include/swift/AST/TypeCheckRequests.h

@@ -3258,7 +3258,7 @@ void simple_display(llvm::raw_ostream &out,
 class ResolveMacroRequest
     : public SimpleRequest<ResolveMacroRequest,
                            ConcreteDeclRef(UnresolvedMacroReference,
-                                           DeclContext *),
+                                           const Decl *),
                            RequestFlags::Cached> {
 public:
   using SimpleRequest::SimpleRequest;
@@ -3268,7 +3268,7 @@ class ResolveMacroRequest
 
   ConcreteDeclRef
   evaluate(Evaluator &evaluator, UnresolvedMacroReference macroRef,
-           DeclContext *dc) const;
+           const Decl *decl) const;
 
 public:
   bool isCached() const { return true; }

include/swift/AST/TypeCheckerTypeIDZone.def

@@ -349,7 +349,7 @@ SWIFT_REQUEST(TypeChecker, ResolveImplicitMemberRequest,
               evaluator::SideEffect(NominalTypeDecl *, ImplicitMemberAction),
               Uncached, NoLocationInfo)
 SWIFT_REQUEST(TypeChecker, ResolveMacroRequest,
-              ConcreteDeclRef(UnresolvedMacroReference, DeclContext *),
+              ConcreteDeclRef(UnresolvedMacroReference, const Decl *),
               Cached, NoLocationInfo)
 SWIFT_REQUEST(TypeChecker, ResolveTypeEraserTypeRequest,
               Type(ProtocolDecl *, TypeEraserAttr *),

lib/AST/Decl.cpp

@@ -445,7 +445,7 @@ void Decl::forEachAttachedMacro(MacroRole role,
 MacroDecl *Decl::getResolvedMacro(CustomAttr *customAttr) const {
   auto declRef = evaluateOrDefault(
       getASTContext().evaluator,
-      ResolveMacroRequest{customAttr, getDeclContext()},
+      ResolveMacroRequest{customAttr, this},
       ConcreteDeclRef());
 
   return dyn_cast_or_null<MacroDecl>(declRef.getDecl());

lib/Sema/TypeCheckDeclPrimary.cpp

@@ -3796,7 +3796,7 @@ ExpandMacroExpansionDeclRequest::evaluate(Evaluator &evaluator,
 
   // Resolve macro candidates.
   auto macro = evaluateOrDefault(
-      ctx.evaluator, ResolveMacroRequest{MED, dc},
+      ctx.evaluator, ResolveMacroRequest{MED, MED},
       ConcreteDeclRef());
   if (!macro)
     return None;

lib/Sema/TypeCheckMacros.cpp

@@ -1478,7 +1478,9 @@ swift::expandConformances(CustomAttr *attr, MacroDecl *macro,
 ConcreteDeclRef
 ResolveMacroRequest::evaluate(Evaluator &evaluator,
                               UnresolvedMacroReference macroRef,
-                              DeclContext *dc) const {
+                              const Decl *decl) const {
+  auto dc = decl->getDeclContext();
+
   // Macro expressions and declarations have their own stored macro
   // reference. Use it if it's there.
   if (auto *expr = macroRef.getExpr()) {