CppTools: Fix dead lock on project unloading

...with the clang code model.

In updateProjectInfo() we lock the project mutex and emit a signal.
However, the correspondig slot in the clang code model will call back
into a function that needs to lock the mutex, too:

    CppTools::CppModelManager::workingCopy // dead locks here
    CppTools::BaseEditorDocumentParser::InMemoryInfo::InMemoryInfo
    ClangCodeModel::Internal::ClangEditorDocumentProcessor::run
    ClangCodeModel::Internal::ModelManagerSupportClang::unregisterTranslationUnitsWithProjectParts
    ClangCodeModel::Internal::ModelManagerSupportClang::onProjectPartsRemoved
     ...
    CppTools::CppModelManager::projectPartsRemoved
    CppTools::CppModelManager::updateProjectInfo // emits here

Fixed by emitting the signal after releasing the mutex.

Change-Id: Id3f3cd22b0604f343ada56ea13c26f0dc1a75bd6
Reviewed-by: Marco Bubke <marco.bubke@theqtcompany.com>

src/plugins/cpptools/cppmodelmanager.cpp

@@ -831,6 +831,7 @@ QFuture<void> CppModelManager::updateProjectInfo(const ProjectInfo &newProjectIn
         return QFuture<void>();
 
     QSet<QString> filesToReindex;
+    QStringList removedProjectParts;
     bool filesRemoved = false;
 
     { // Only hold the mutex for a limited scope, so the dumping afterwards does not deadlock.
@@ -876,8 +877,7 @@ QFuture<void> CppModelManager::updateProjectInfo(const ProjectInfo &newProjectIn
                 }
             }
 
-            // Announce removed project parts
-            emit projectPartsRemoved(comparer.removedProjectParts());
+            removedProjectParts = comparer.removedProjectParts();
 
         // A new project was opened/created, do a full indexing
         } else {
@@ -899,6 +899,10 @@ QFuture<void> CppModelManager::updateProjectInfo(const ProjectInfo &newProjectIn
     if (filesRemoved)
         GC();
 
+    // Announce removed project parts
+    if (!removedProjectParts.isEmpty())
+        emit projectPartsRemoved(removedProjectParts);
+
     // Announce added project parts
     emit projectPartsUpdated(newProjectInfo.project().data());