clangbackend: Work around wrong cursor info from libclang

Alias type declarations of in-place struct definitions are not reliably
getting their cursor exposed, so the surrounding context is reported
instead, which causes the wrong lexical parent to be deduced. To the
user, this manifests itself as a wrong hierarchy being displayed in the
outline.
We try to detect this condition and correct it manually.

Task-number: QTCREATORBUG-24875
Change-Id: Ib4e177efa9148697eddde986a91fdd5d7b272d76
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/tools/clangbackend/source/token.cpp

@@ -90,8 +90,37 @@ std::vector<Cursor> Tokens::annotate() const
 
     std::vector<CXCursor> cxCursors;
     cxCursors.resize(m_tokens.size());
-    clang_annotateTokens(m_cxTranslationUnit, m_tokens.front().cx(),
+
-                         static_cast<unsigned>(m_tokens.size()), cxCursors.data());
+    clang_annotateTokens(m_cxTranslationUnit, m_tokens.front().cx(), m_tokens.size(), cxCursors.data());
+
+    // The alias declaration "using S = struct {}" results in libclang reporting the type
+    // of the surrounding scope (e.g. a namespace or class) for the cursor corresponding to
+    // the token "S" (QTCREATORBUG-24875). We need to correct this manually.
+    // TODO: Investigate whether we can fix this in libclang itself.
+    for (int i = 1; i < int(m_tokens.size()) - 2; ++i) {
+        const Token &tok = m_tokens.at(i);
+        const Token &prevTok = m_tokens.at(i - 1);
+        const Token &nextTok = m_tokens.at(i + 1);
+        if (tok.kind() == CXToken_Identifier
+                && prevTok.kind() == CXToken_Keyword
+                && prevTok.spelling() == "using"
+                && nextTok.spelling() == "="
+                && cxCursors.at(i).kind != CXCursor_TypeAliasDecl) {
+            // If the surrounding scope is a namespace, the correct type is reported for the token
+            // after the identifier, i.e. the "=" symbol. Otherwise, it's not reported at all,
+            // and we have to use the cursor after that, which should be the aliased type.
+            // Note that we cannot use the next cursors in the cxCursors array, because
+            // clang_annotateTokens() reports the surrounding scope for all of these.
+            CXCursor nextCursor = clang_getCursor(m_cxTranslationUnit, clang_getTokenLocation(
+                                                      m_cxTranslationUnit, *nextTok.cx()));
+            if (nextCursor.kind != CXCursor_TypeAliasDecl) {
+                nextCursor = clang_getCursor(m_cxTranslationUnit, clang_getTokenLocation(
+                                                 m_cxTranslationUnit, *m_tokens.at(i + 2).cx()));
+            }
+            cxCursors[i] = nextCursor;
+        }
+    }
+
     cursors.reserve(cxCursors.size());
     for (const CXCursor &cxCursor : cxCursors)
         cursors.emplace_back(cxCursor);