ClangClient: Receive done() signal only once

Before this change the done() signal was emitted 3 times
in a row. The reason was that first one was coming
synchonously from handleGotoDefinitionResult(), while
2 others were scheluded with queued connections.
So, the handler for done() signal was called 3 times.
The first invocation calls deleteLater() and clears
the pointer, while the object is still alive.
Before the request to delete later gets dispatched,
the 2 remaining done() emissions are dispatched,
so the handler is still called 2 times.

One possible solution would be to disconnect from
done() signal inside a handler. However, the done()
signal shouldn't be called many times, so this fix
ensures the done() is emitted only once.

This fixes the following prinouts:
"QCoreApplication::postEvent: Unexpected null receiver"
issued twice on every follow symbol interaction.

Amends 650bc260c6

Change-Id: I9b440a80386aca3462eda323e51a76696e53fa6b
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/clangcodemodel/clangdswitchdecldef.cpp

@@ -68,6 +68,7 @@ public:
     const LinkHandler callback;
     optional<ClangdAstNode> ast;
     optional<DocumentSymbolsResult> docSymbols;
+    bool done = false;
 };
 
 ClangdSwitchDeclDef::ClangdSwitchDeclDef(ClangdClient *client, TextDocument *doc,
@@ -75,14 +76,14 @@ ClangdSwitchDeclDef::ClangdSwitchDeclDef(ClangdClient *client, TextDocument *doc
     : QObject(client), d(new Private(this, client, doc, cursor, editorWidget, callback))
 {
     // Abort if the user does something else with the document in the meantime.
-    connect(doc, &TextDocument::contentsChanged, this, &ClangdSwitchDeclDef::done,
+    connect(doc, &TextDocument::contentsChanged, this, &ClangdSwitchDeclDef::emitDone,
             Qt::QueuedConnection);
     if (editorWidget) {
         connect(editorWidget, &CppEditorWidget::cursorPositionChanged,
-                this, &ClangdSwitchDeclDef::done, Qt::QueuedConnection);
+                this, &ClangdSwitchDeclDef::emitDone, Qt::QueuedConnection);
     }
     connect(qApp, &QApplication::focusChanged,
-            this, &ClangdSwitchDeclDef::done, Qt::QueuedConnection);
+            this, &ClangdSwitchDeclDef::emitDone, Qt::QueuedConnection);
 
     connect(client->documentSymbolCache(), &DocumentSymbolCache::gotSymbols, this,
             [this](const DocumentUri &uri, const DocumentSymbolsResult &symbols) {
@@ -101,11 +102,11 @@ ClangdSwitchDeclDef::ClangdSwitchDeclDef(ClangdClient *client, TextDocument *doc
         if (!self)
             return;
          if (!d->document) {
-             emit done();
+             emitDone();
              return;
          }
         if (!ast.isValid()) {
-            emit done();
+            emitDone();
             return;
         }
         d->ast = ast;
@@ -122,6 +123,15 @@ ClangdSwitchDeclDef::~ClangdSwitchDeclDef()
     delete d;
 }
 
+void ClangdSwitchDeclDef::emitDone()
+{
+    if (d->done)
+        return;
+
+    d->done = true;
+    emit done();
+}
+
 optional<ClangdAstNode> ClangdSwitchDeclDef::Private::getFunctionNode() const
 {
     QTC_ASSERT(ast, return {});
@@ -160,7 +170,7 @@ QTextCursor ClangdSwitchDeclDef::Private::cursorForFunctionName(const ClangdAstN
 void ClangdSwitchDeclDef::Private::handleDeclDefSwitchReplies()
 {
     if (!document) {
-        emit q->done();
+        q->emitDone();
         return;
     }
 
@@ -171,7 +181,7 @@ void ClangdSwitchDeclDef::Private::handleDeclDefSwitchReplies()
         ast->print(0);
     const Utils::optional<ClangdAstNode> functionNode = getFunctionNode();
     if (!functionNode) {
-        emit q->done();
+        q->emitDone();
         return;
     }
 
@@ -182,7 +192,7 @@ void ClangdSwitchDeclDef::Private::handleDeclDefSwitchReplies()
         client->followSymbol(document.data(), funcNameCursor, editorWidget, callback,
                              true, false);
     }
-    emit q->done();
+    q->emitDone();
 }
 
 } // namespace ClangCodeModel::Internal