Fix infinite recursion for invalid declaration

[DmitryPolukhin]

Summary

Fix for a case found by fuzzing PR23057 (comment #25 https://llvm.org/bugs/show_bug.cgi?id=23057#c25).

[kcc]

LGTM, and thanks!

lib/AST/Decl.cpp

if (!Var->isStaticLocal())
       return LinkageInfo::none();
   }
 
   ASTContext &Context = D->getASTContext();
   if (!Context.getLangOpts().CPlusPlus)
     return LinkageInfo::none();
 
   const Decl *OuterD = getOutermostFuncOrBlockContext(D);
-  if (!OuterD)
+  if (!OuterD || OuterD->isInvalidDecl())
     return LinkageInfo::none();
 
   LinkageInfo LV;
   if (const auto *BD = dyn_cast<BlockDecl>(OuterD)) {
     if (!BD->getBlockManglingNumber())
       return LinkageInfo::none();
 
     LV = getLVForClosure(BD->getDeclContext()->getRedeclContext(),

test/SemaCXX/linkage-invalid-decl.cpp

+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+// This invalid declaration used to call infinite recursion in linkage
+// calculation for enum as a function argument.
+inline foo(A)(enum E;
+// expected-error@-1 {{unknown type name 'foo'}}
+// expected-error@-2 {{ISO C++ forbids forward references to 'enum' types}}
+// expected-error@-3 {{expected ')'}}
+// expected-note@-4 {{to match this '('}}