[ASTImporter] Add test for C++ casts and fix broken const_cast importing.

[teemperor]

Summary

The ASTImporter does currently not handle const_casts. This patch adds the
missing const_cast importer code and the test case that discovered this.

[a_sidorin]

Thank you!

tools/clang-import-test/clang-import-test.cpp

197

Is this option set to check dynamic_cast?

[teemperor]

• Added comment why we enable RTTI.

lib/AST/ASTImporter.cpp

Expr *ASTNodeImporter::VisitCXXNamedCastExpr(CXXNamedCastExpr *E) {
   } else if (isa<CXXDynamicCastExpr>(E)) {
     return CXXDynamicCastExpr::Create(
         Importer.getToContext(), ToType, VK, CK, ToOp, &BasePath,
         ToWritten, ToOperatorLoc, ToRParenLoc, ToAngleBrackets);
   } else if (isa<CXXReinterpretCastExpr>(E)) {
     return CXXReinterpretCastExpr::Create(
         Importer.getToContext(), ToType, VK, CK, ToOp, &BasePath,
         ToWritten, ToOperatorLoc, ToRParenLoc, ToAngleBrackets);
+  } else if (isa<CXXConstCastExpr>(E)) {
+    return CXXConstCastExpr::Create(Importer.getToContext(), ToType, VK, ToOp,
+                                    ToWritten, ToOperatorLoc, ToRParenLoc,
+                                    ToAngleBrackets);
   } else {
     return nullptr;
   }
 }
 
 Expr *ASTNodeImporter::VisitSubstNonTypeTemplateParmExpr(
     SubstNonTypeTemplateParmExpr *E) {
   QualType T = Importer.Import(E->getType());

test/Import/cxx-casts/Inputs/F.cpp

+struct A {
+  virtual ~A() {}
+};
+struct B : public A {};
+
+void f() {
+  const A *b = new B();
+  const B *c1 = dynamic_cast<const B *>(b);
+  const B *c2 = static_cast<const B *>(b);
+  const B *c3 = reinterpret_cast<const B *>(b);
+  A *c4 = const_cast<A *>(b);
+}

test/Import/cxx-casts/test.cpp

+// RUN: clang-import-test -dump-ast -import %S/Inputs/F.cpp -expression %s | FileCheck %s
+
+// CHECK: CXXDynamicCastExpr
+// CHECK-SAME: dynamic_cast
+// CHECK-SAME: <Dynamic>
+
+// CHECK: CXXStaticCastExpr
+// CHECK-SAME: static_cast
+// CHECK-SAME: <BaseToDerived (A)>
+
+// CHECK: CXXReinterpretCastExpr
+// CHECK-SAME: reinterpret_cast
+// CHECK-SAME: <BitCast>
+
+// CHECK: CXXConstCastExpr
+// CHECK-SAME: const_cast
+// CHECK-SAME: <NoOp>
+
+void expr() {
+  f();
+}

tools/clang-import-test/clang-import-test.cpp

std::unique_ptr<CompilerInstance> BuildCompilerInstance() {
   Inv->getLangOpts()->Bool = true;
   Inv->getLangOpts()->WChar = true;
   Inv->getLangOpts()->Blocks = true;
   Inv->getLangOpts()->DebuggerSupport = true;
   Inv->getLangOpts()->SpellChecking = false;
   Inv->getLangOpts()->ThreadsafeStatics = false;
   Inv->getLangOpts()->AccessControl = false;
   Inv->getLangOpts()->DollarIdents = true;
+  // Needed for testing dynamic_cast.
+  Inv->getLangOpts()->RTTI = true;
   Inv->getCodeGenOpts().setDebugInfo(codegenoptions::FullDebugInfo);
   Inv->getTargetOpts().Triple = llvm::sys::getDefaultTargetTriple();
 
   Ins->setInvocation(std::move(Inv));
 
   TargetInfo *TI = TargetInfo::CreateTargetInfo(
       Ins->getDiagnostics(), Ins->getInvocation().TargetOpts);
   Ins->setTarget(TI);