[clang] Fix a null pointer dereference.

Summary:
Sometimes expression inside switch statement can be invalid, for
example type might be incomplete. In those cases code were causing a null
pointer dereference. This patch fixes that.

Reviewers: sammccall, ioeric, hokein

Reviewed By: sammccall

Subscribers: arphaman, cfe-commits

Differential Revision: https://reviews.llvm.org/D53561

llvm-svn: 345029

clang/lib/Sema/SemaCodeComplete.cpp

@@ -4419,6 +4419,9 @@ void Sema::CodeCompleteCase(Scope *S) {
     return;
 
   SwitchStmt *Switch = getCurFunction()->SwitchStack.back().getPointer();
+  // Condition expression might be invalid, do not continue in this case.
+  if (!Switch->getCond())
+    return;
   QualType type = Switch->getCond()->IgnoreImplicit()->getType();
   if (!type->isEnumeralType()) {
     CodeCompleteExpressionData Data(type);

clang/test/Index/complete-switch.c

@@ -0,0 +1,10 @@
+void f() {
+  auto foo = bar;
+  switch(foo) {
+    case x:
+      break;
+  }
+}
+
+// RUN: not %clang_cc1 -fsyntax-only -code-completion-at=%s:4:10 %s | FileCheck %s -allow-empty
+// CHECK-NOT: COMPLETION: foo