clangbackend: Work around libclang cursor bug

... involving accessing the member of a nested anonymous union from
within the surrounding class. libclang reports a CXCursor_CXXThisExpr
for this location instead of a CXCursor_MemberRefExpr. However, the
latter is still locatable in the AST, so we can correct this.

Fixes: QTCREATORBUG-25342
Change-Id: I1eba13d5153205a52b3689d8ad52493a56b76c07
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

src/tools/clangbackend/source/clangfollowsymbol.cpp

@@ -95,6 +95,16 @@ FollowSymbolResult FollowSymbol::followSymbol(CXTranslationUnit tu,
         return SourceRangeContainer();
 
     Cursor cursor{cursors[tokenIndex]};
+    if (cursor.kind() == CXCursor_CXXThisExpr && tokenSpelling != "this") { // QTCREATORBUG-25342
+        cursor.semanticParent().visit([&cursor](CXCursor current, CXCursor parent) {
+            if (current == cursor && parent.kind == CXCursor_MemberRefExpr
+                    && cursor.sourceLocation() == Cursor(parent).sourceLocation()) {
+                cursor = parent;
+                return CXChildVisit_Break;
+            }
+            return CXChildVisit_Recurse;
+        });
+    }
 
     if (cursor.kind() == CXCursor_InclusionDirective) {
         CXFile file = clang_getIncludedFile(cursors[tokenIndex].cx());

tests/unit/unittest/clangfollowsymbol-test.cpp

@@ -209,6 +209,13 @@ TEST_F(FollowSymbol, CursorOnMemberReference)
     ASSERT_THAT(memberDeclaration, MatchesHeaderSourceRange(38, 18, 6));
 }
 
+TEST_F(FollowSymbol, CursorOnMemberReferenceAnonymousUnion)
+{
+    const auto memberDeclaration = followSymbol(91, 20);
+
+    ASSERT_THAT(memberDeclaration, MatchesSourceRange(86, 13, 1));
+}
+
 TEST_F(FollowSymbol, CursorOnMemberDeclaration)
 {
     const auto sameMemberDeclaration = followHeaderSymbol(38, 18);

tests/unit/unittest/data/followsymbol_main.cpp

@@ -80,3 +80,16 @@ int Bar::operator&() {
 Bar& Bar::operator[](int) {
     return *this;
 }
+
+struct S {
+    union  {
+        int i = 12;
+        void *something;
+    };
+    int func(bool b) {
+        if (b)
+            return i;
+        int i = 42;
+        return i;
+    }
+};