[Sema] Fix a pair of crashes when generating exception specifiers with an error'ed field for a template class' default ctor.

[erichkeane]

Summary

The two examples in the test would both cause a compiler assert when attempting to calculate
the exception specifier for the default constructor for the template classes. The problem was
that dependents of this function expect that Field->getInClassInitializer (including canThrow) is
not nullptr. However, if the template's initializer has an error, exactly that situation happens.

This patch simply sets the field to be invalid.

[erichkeane]

Ping? I Added the three of you because you were all on the git-blame list, but if you have better ideas on someone to review this, it would be appreciated.

-Erich

[rnk]

Looks like the correct fix, thanks!

cfe/trunk/lib/Sema/SemaDeclCXX.cpp

if (!Pattern) {
       for (auto L : Lookup)
         if (isa<FieldDecl>(L)) {
           Pattern = cast<FieldDecl>(L);
           break;
         }
       assert(Pattern && "We must have set the Pattern!");
     }
 
-    if (InstantiateInClassInitializer(Loc, Field, Pattern,
+    if (!Pattern->hasInClassInitializer() ||
+        InstantiateInClassInitializer(Loc, Field, Pattern,
                                       getTemplateInstantiationArgs(Field))) {
       // Don't diagnose this again.
       Field->setInvalidDecl();
       return ExprError();
     }
     return CXXDefaultInitExpr::Create(Context, Loc, Field);
   }
 

cfe/trunk/test/SemaCXX/init-expr-crash.cpp

+// RUN: %clang_cc1 %s -fsyntax-only -verify -std=c++11
+
+// Test reproduces a pair of crashes that were caused by code attempting
+// to materialize a default constructor's exception specifier.
+
+template <class T> struct A {
+  static T tab[];
+
+  const int M = UNDEFINED; // expected-error {{use of undeclared identifier}}
+
+  int main()
+  {
+    A<char> a;
+
+    return 0;
+  }
+};
+
+template <class T> struct B {
+  static T tab[];
+
+  // expected-error@+1 {{invalid application of 'sizeof' to an incomplete type}}
+  const int N = sizeof(B<char>::tab) / sizeof(char);
+
+  int main()
+  {
+    B<char> b;
+
+    return 0;
+  }
+};