[analyzer] Fix crash when building CFG with variable of incomplete type

[mboehme]

Summary

I've included a unit test with a function template containing a variable
of incomplete type. Clang compiles this without errors (the standard
does not require a diagnostic in this case). Without the fix, this case
triggers the crash.

[klimek]

lg

lib/Analysis/CFG.cpp

LocalScope* CFGBuilder::addLocalScopeForVarDecl(VarDecl *VD,
   while (const ConstantArrayType *AT = Context->getAsConstantArrayType(QT)) {
     if (AT->getSize() == 0)
       return Scope;
     QT = AT->getElementType();
   }
 
   // Check if type is a C++ class with non-trivial destructor.
   if (const CXXRecordDecl *CD = QT->getAsCXXRecordDecl())
-    if (!CD->hasTrivialDestructor()) {
+    if (CD->hasDefinition() && !CD->hasTrivialDestructor()) {
       // Add the variable to scope
       Scope = createOrReuseLocalScope(Scope);
       Scope->addVar(VD);
       ScopePos = Scope->begin();
     }
   return Scope;
 }
 

unittests/Analysis/CFGTest.cpp

public:
   BuildResult TheBuildResult = ToolRan;
 
   void run(const ast_matchers::MatchFinder::MatchResult &Result) override {
     const auto *Func = Result.Nodes.getNodeAs<FunctionDecl>("func");
     Stmt *Body = Func->getBody();
     if (!Body)
       return;
     TheBuildResult = SawFunctionBody;
-    if (CFG::buildCFG(nullptr, Body, Result.Context, CFG::BuildOptions()))
+    CFG::BuildOptions Options;
+    Options.AddImplicitDtors = true;
+    if (CFG::buildCFG(nullptr, Body, Result.Context, Options))
         TheBuildResult = BuiltCFG;
   }
 };
 
 BuildResult BuildCFG(const char *Code) {
   CFGCallback Callback;
 
   ast_matchers::MatchFinder Finder;

 TEST(CFG, DeleteExpressionOnDependentType) {
   const char *Code = "template<class T>\n"
                      "void f(T t) {\n"
                      "  delete t;\n"
                      "}\n";
   EXPECT_EQ(BuiltCFG, BuildCFG(Code));
 }
 
+// Constructing a CFG on a function template with a variable of incomplete type
+// should not crash.
+TEST(CFG, VariableOfIncompleteType) {
+  const char *Code = "template<class T> void f() {\n"
+                     "  class Undefined;\n"
+                     "  Undefined u;\n"
+                     "}\n";
+  EXPECT_EQ(BuiltCFG, BuildCFG(Code));
+}
+
 } // namespace
 } // namespace analysis
 } // namespace clang