CppTools/Clang: Announce only removed project parts

...and not all projects parts of a project if it is closed.

Re-produce with:
  open a project A with subdirs (e.g. qtcreator.pro)
  open a subdir project from project A (e.g. cppeditor.pro)
  close project A
  --> The project part representing the subdir is announced as removed
      although it is still open.

The clang code model was the only affected user - affected translation
units were not parsed/updated anymore
("ERROR: ProjectPartDoesNotExistMessage").

Change-Id: Ia79341ce201e3b4aefff9f597920dbc6f7d67634
Reviewed-by: David Schulz <david.schulz@theqtcompany.com>

src/plugins/cpptools/cppmodelmanager.cpp

@@ -996,34 +996,34 @@ void CppModelManager::delayedGC()
         d->m_delayedGcTimer.start(500);
 }
 
-static QStringList idsOfAllProjectParts(const ProjectInfo &projectInfo)
+static QStringList removedProjectParts(const QStringList &before, const QStringList &after)
 {
-    QStringList projectPaths;
-    foreach (const ProjectPart::Ptr &part, projectInfo.projectParts())
-        projectPaths << part->id();
-    return projectPaths;
+    QSet<QString> b = before.toSet();
+    b.subtract(after.toSet());
+
+    return b.toList();
 }
 
 void CppModelManager::onAboutToRemoveProject(ProjectExplorer::Project *project)
 {
-    QStringList projectPartIds;
+    QStringList idsOfRemovedProjectParts;
 
     d->m_projectToIndexerCanceled.remove(project);
 
     {
         QMutexLocker locker(&d->m_projectMutex);
         d->m_dirty = true;
-
-        // Save paths
-        const ProjectInfo projectInfo = d->m_projectToProjectsInfo.value(project, ProjectInfo());
-        projectPartIds = idsOfAllProjectParts(projectInfo);
+        const QStringList projectPartsIdsBefore = d->m_projectPartIdToProjectProjectPart.keys();
 
         d->m_projectToProjectsInfo.remove(project);
         recalculateProjectPartMappings();
+
+        const QStringList projectPartsIdsAfter = d->m_projectPartIdToProjectProjectPart.keys();
+        idsOfRemovedProjectParts = removedProjectParts(projectPartsIdsBefore, projectPartsIdsAfter);
     }
 
-    if (!projectPartIds.isEmpty())
-        emit projectPartsRemoved(projectPartIds);
+    if (!idsOfRemovedProjectParts.isEmpty())
+        emit projectPartsRemoved(idsOfRemovedProjectParts);
 
     delayedGC();
 }