Fix crash in Sema when wrongly assuming VarDecl init is not value dependent.

[teemperor]

Summary

The attached test case crashes Sema as we call IsVariableAConstantExpression which has as a precondition
that we don't call it on a VarDecl with a value dependent init expression.

[v.g.vassilev]

Could you double-check if we can add this to an existing test? Would test/SemaCXX/pr25181-crash-on-invalid.cpp fit and potentially rename it.

test/SemaCXX/cxx11-odr-use-crash-on-invalid.cpp

8

Looks like this line has spacing problems.

[v.g.vassilev]

@teemperor, should we land this?

[v.g.vassilev]

According to godbolt this example does not crash anymore.

lib/Sema/SemaExpr.cpp

   // Per C++11 [basic.def.odr], a variable is odr-used "unless it satisfies
   // the requirements for appearing in a constant expression (5.19) and, if
   // it is an object, the lvalue-to-rvalue conversion (4.1)
   // is immediately applied."  We check the first part here, and
   // Sema::UpdateMarkingForLValueToRValue deals with the second part.
   // Note that we use the C++11 definition everywhere because nothing in
   // C++03 depends on whether we get the C++03 version correct. The second
   // part does not apply to references, since they are not objects.
-  if (OdrUseContext && E &&
+  bool InitIsValueDependent =
+      Var->hasInit() && Var->getInit()->isValueDependent();
+  if (OdrUseContext && E && !InitIsValueDependent &&
       IsVariableAConstantExpression(Var, SemaRef.Context)) {
     // A reference initialized by a constant expression can never be
     // odr-used, so simply ignore it.
     if (!Var->getType()->isReferenceType())
       SemaRef.MaybeODRUseExprs.insert(E);
   } else if (OdrUseContext) {
     MarkVarDeclODRUsed(Var, Loc, SemaRef,
                        /*MaxFunctionScopeIndex ptr*/ nullptr);

test/SemaCXX/cxx11-odr-use-crash-on-invalid.cpp

+// RUN: %clang_cc1  -fsyntax-only -verify -std=c++11 %s
+// Don't crash due to the 'c :' as the return type of d.
+
+template <typename a>
+int b() {}
+template <typename c>
+c : d() { // expected-error {{unexpected ':'}} \
+                                // expected-error {{nested name specifier 'c::' for declaration does not refer}}
+  c &e = b<c>;
+  auto i = e;
+}