[AST][RecoveryExpr] Popagate the error-bit from a VarDecl's initializer to DeclRefExpr.

The error-bit was missing, if a DeclRefExpr (which refers to a VarDecl
with a contains-errors initializer).

It could cause different violations in clang -- the DeclRefExpr is value-dependent,
but not contains-errors, `ABC<DeclRefExpr>` could produce a non-error
and non-dependent type in non-template context, which will lead to
crashes in constexpr evaluation.

Reviewed By: sammccall

Differential Revision: https://reviews.llvm.org/D86048

2 files changed, 13 insertions, 3 deletions

diff --git a/clang/lib/AST/ComputeDependence.cpp b/clang/lib/AST/ComputeDependence.cpp
index 320025e..f8dfeed 100644
--- a/clang/lib/AST/ComputeDependence.cpp
+++ b/clang/lib/AST/ComputeDependence.cpp
@@ -466,10 +466,12 @@ ExprDependence clang::computeDependence(DeclRefExpr *E, const ASTContext &Ctx) {
              : Var->getType()->isIntegralOrEnumerationType()) &&
         (Var->getType().isConstQualified() ||
          Var->getType()->isReferenceType())) {
-      if (const Expr *Init = Var->getAnyInitializer())
-        if (Init->isValueDependent()) {
+      if (const Expr *Init = Var->getAnyInitializer()) {
+        if (Init->isValueDependent())
           Deps |= ExprDependence::ValueInstantiation;
-        }
+        if (Init->containsErrors())
+          Deps |= ExprDependence::Error;
+      }
     }
 
     // (VD) - FIXME: Missing from the standard:
diff --git a/clang/test/Sema/invalid-member.cpp b/clang/test/Sema/invalid-member.cpp
index 9559ead..57ee187 100644
--- a/clang/test/Sema/invalid-member.cpp
+++ b/clang/test/Sema/invalid-member.cpp
@@ -19,3 +19,11 @@ class Z {
 };
 // Should be able to evaluate sizeof without crashing.
 static_assert(sizeof(Z) == 1, "No valid members");
+
+constexpr int N = undef; // expected-error {{use of undeclared identifier}}
+template<int a>
+class ABC {};
+class T {
+  ABC<N> abc;
+};
+static_assert(sizeof(T) == 1, "No valid members");