[clang][Interp] Handle invalid CXXCtorInitializer expressions

Their type might be a null type, in which case we need to abort here.

Author: tbaederr

clang/lib/AST/Interp/ByteCodeStmtGen.cpp

@@ -144,6 +144,10 @@ bool ByteCodeStmtGen<Emitter>::visitFunc(const FunctionDecl *F) {
 
   auto emitFieldInitializer = [&](const Record::Field *F, unsigned FieldOffset,
                                   const Expr *InitExpr) -> bool {
+    // We don't know what to do with these, so just return false.
+    if (InitExpr->getType().isNull())
+      return false;
+
     if (std::optional<PrimType> T = this->classify(InitExpr)) {
       if (!this->visit(InitExpr))
         return false;

clang/test/AST/Interp/records.cpp

@@ -1228,3 +1228,14 @@ namespace InheritedConstructor {
     constexpr S s(1);
   }
 }
+
+namespace InvalidCtorInitializer {
+  struct X {
+    int Y;
+    constexpr X() // expected-note {{declared here}}
+        : Y(fo_o_()) {} // both-error {{use of undeclared identifier 'fo_o_'}}
+  };
+  // no crash on evaluating the constexpr ctor.
+  constexpr int Z = X().Y; // both-error {{constexpr variable 'Z' must be initialized by a constant expression}} \
+                           // expected-note {{undefined constructor 'X'}}
+}