[CodeComplete] Offer completion suggestions for default argument values inside the macro declaration

We were not type checking the default argument initializer because `MacroDecl` is not an `AbstractFucntionDecl`. Add `MacroDecl` to the list of nodes we know how to get parameters from.

rdar://108163564

Author: ahoppen

lib/Sema/TypeCheckStmt.cpp

@@ -2366,13 +2366,15 @@ bool TypeCheckASTNodeAtLocRequest::evaluate(
         }
       }
     } else if (auto *defaultArg = dyn_cast<DefaultArgumentInitializer>(DC)) {
+      ParamDecl *Param = nullptr;
       if (auto *AFD = dyn_cast<AbstractFunctionDecl>(defaultArg->getParent())) {
-        auto *Param = AFD->getParameters()->get(defaultArg->getIndex());
-        (void)Param->getTypeCheckedDefaultExpr();
-        return false;
+        Param = AFD->getParameters()->get(defaultArg->getIndex());
+      } else if (auto *MD = dyn_cast<MacroDecl>(defaultArg->getParent())) {
+        Param = MD->getParameterList()->get(defaultArg->getIndex());
+      } else if (auto *SD = dyn_cast<SubscriptDecl>(defaultArg->getParent())) {
+        Param = SD->getIndices()->get(defaultArg->getIndex());
       }
-      if (auto *SD = dyn_cast<SubscriptDecl>(defaultArg->getParent())) {
-        auto *Param = SD->getIndices()->get(defaultArg->getIndex());
+      if (Param) {
         (void)Param->getTypeCheckedDefaultExpr();
         return false;
       }

test/IDE/complete_macro_declaration.swift

@@ -0,0 +1,7 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-ide-test -batch-code-completion -source-filename %s -filecheck %raw-FileCheck -completion-output-dir %t
+
+let globalVar = 1
+macro expect(file: Int = #^DEFAULT_ARG^#) = #externalMacro(module: "MyModule", type: "MyMacro")
+
+// DEFAULT_ARG: Decl[GlobalVar]/CurrModule/TypeRelation[Convertible]: globalVar[#Int#]; name=globalVar