[Clang] Fix crash in CIndex, when visiting a static_assert without message

[kiloalphaindia]

Summary

After implementation of "[Clang] Implement P2741R3 - user-generated static_assert messages" (47ccfd7a89e2a9a747a7114db18db1376324799c) the c indexer crashes when handling a static_assert w/o any message.
This is caused by using dyn_cast to get the literal string, which isn't working on nullptr.

[cor3ntin]

clang/tools/libclang/CIndex.cpp

1297

It's probably better to cast to Expr and visit it unconditionally. But it could always be null, so dyn_cast_if_present is probably correct.
dyn_cast_if_present<Expr> should be what we want then

[kiloalphaindia]

Yes, that's a good idea. Now kdevelop also highlights the message-expression properly.

[kiloalphaindia]

Sorry... forgot formatting... removed commented code... changed "Hallo Welt!" to english

[cor3ntin]

There is a failed unit test, can you look into it?

[aaron.ballman]

clang/unittests/libclang/LibclangTest.cpp

1201

This is going to be testing whatever STL headers are installed on the developer's machine; instead of including the STL header, you should mock up the std::string_view class so we're always testing something consistently.

[kiloalphaindia]

Yes, I think so, too. Will have a look this evening.

[kiloalphaindia]

The test is no more using any includes now. Hopefully this fixes it, otherwise I will have to add something that prints the diagnostic.

I don't have write permissions on the repository. Please commit it when OK.

[cor3ntin]

In D156053#4531015, @kiloalphaindia wrote:

The test is no more using any includes now. Hopefully this fixes it, otherwise I will have to add something that prints the diagnostic.

I don't have write permissions on the repository. Please commit it when OK.

Will do! (once the test pass) What name / email address should we use for commiting?

[kiloalphaindia]

Please use Kai Stierand <[e-mail]> as in 5d859a1cdee3c15dce692767ee3e9ad03a8c4c1b

clang/tools/libclang/CIndex.cpp

if (VisitNestedNameSpecifierLoc(QualifierLoc))
       return true;
 
   return false;
 }
 
 bool CursorVisitor::VisitStaticAssertDecl(StaticAssertDecl *D) {
   if (Visit(MakeCXCursor(D->getAssertExpr(), StmtParent, TU, RegionOfInterest)))
     return true;
-  if (auto *Message = dyn_cast<StringLiteral>(D->getMessage()))
+  if (auto *Message = dyn_cast_if_present<StringLiteral>(D->getMessage()))
     if (Visit(MakeCXCursor(Message, StmtParent, TU, RegionOfInterest)))
       return true;
   return false;
 }
 
 bool CursorVisitor::VisitFriendDecl(FriendDecl *D) {
   if (NamedDecl *FriendD = D->getFriendDecl()) {
     if (Visit(MakeCXCursor(FriendD, TU, RegionOfInterest)))

clang/unittests/libclang/LibclangTest.cpp

if (cursor.kind == CXCursor_UnaryOperator) {
                 CXUnaryOperator_PostInc);
       return CXChildVisit_Break;
     }
 
     return CXChildVisit_Recurse;
   });
 }
 
+TEST_F(LibclangParseTest, VisitStaticAssertDecl_noMessage) {
+  const char testSource[] = R"cpp(static_assert(true))cpp";
+  std::string fileName = "main.cpp";
+  WriteFile(fileName, testSource);
+  const char *Args[] = {"-xc++"};
+  ClangTU = clang_parseTranslationUnit(Index, fileName.c_str(), Args, 1,
+                                       nullptr, 0, TUFlags);
+
+  std::optional<CXCursor> typeRefCsr;
+  Traverse([&](CXCursor cursor, CXCursor parent) -> CXChildVisitResult {
+    if (cursor.kind == CXCursor_StaticAssert) {
+      typeRefCsr.emplace(cursor);
+    }
+    return CXChildVisit_Recurse;
+  });
+  ASSERT_TRUE(typeRefCsr.has_value());
+  EXPECT_EQ(fromCXString(clang_getCursorSpelling(*typeRefCsr)), "");
+}
+
 class LibclangRewriteTest : public LibclangParseTest {
 public:
   CXRewriter Rew = nullptr;
   std::string Filename;
   CXFile File = nullptr;
 
   void SetUp() override {
     LibclangParseTest::SetUp();
     Filename = "file.cpp";
     WriteFile(Filename, "int main() { return 0; }");
     ClangTU = clang_parseTranslationUnit(Index, Filename.c_str(), nullptr, 0,
                                          nullptr, 0, TUFlags);
     Rew = clang_CXRewriter_create(ClangTU);
     File = clang_getFile(ClangTU, Filename.c_str());
   }
   void TearDown() override {