Utils: Add a way to (shutdown-)guard pre-created objects

Some classes use private c'tors and a friend function for creation.

Since friendship is not transitive this cannot (nicely) be extended
to the GuardedObject implementation.

In the quest to achieve a uniform 'void setupFoo()' signature to
the outside, keep the creation of the guarded object were it is,
but allow it to be taken over bey a GuardedObject.

This setup still requires the _d_'tor to be public, but less
"dangerous" then a public c'tor - assuming there is some danger
in having that at all.

Use it for the PythoSettings and LanguageClientManager setup.

Change-Id: Ica114a0bb901d33d79c847910a2383ac1bc9e49a
Reviewed-by: David Schulz <david.schulz@qt.io>

src/libs/utils/shutdownguard.h

@@ -18,15 +18,18 @@ template <class T>
 class GuardedObject
 {
 public:
-    GuardedObject()
-        : m_object(new T)
+    GuardedObject(T *obj)
+        : m_object(obj)
     {
         QObject::connect(shutdownGuard(), &QObject::destroyed, shutdownGuard(), [this] {
             delete m_object;
             m_object = nullptr;
         });
     }
-    ~GuardedObject() = default;
+
+    GuardedObject()
+        : GuardedObject(new T)
+    {}
 
     T *get() const { return m_object; }
 

src/plugins/languageclient/languageclientmanager.cpp

@@ -29,6 +29,7 @@
 
 #include <utils/algorithm.h>
 #include <utils/theme/theme.h>
+#include <utils/shutdownguard.h>
 #include <utils/utilsicons.h>
 
 #include <QTimer>
@@ -50,8 +51,7 @@ class LanguageClientManagerPrivate
     LanguageFunctionsFilter m_functionFilter;
 };
 
-LanguageClientManager::LanguageClientManager(QObject *parent)
-    : QObject(parent)
+LanguageClientManager::LanguageClientManager()
 {
     setObjectName("LanguageClientManager");
 
@@ -742,9 +742,9 @@ bool LanguageClientManager::isShutdownFinished()
            && managerInstance->m_scheduledForDeletion.isEmpty();
 }
 
-void setupLanguageClientManager(QObject *guard)
+void setupLanguageClientManager()
 {
-    (void) new LanguageClientManager(guard);
+    static Utils::GuardedObject theLanguageClientManager{new LanguageClientManager};
 }
 
 } // namespace LanguageClient

src/plugins/languageclient/languageclientmanager.h

@@ -33,6 +33,8 @@ class LANGUAGECLIENT_EXPORT LanguageClientManager : public QObject
     Q_DISABLE_COPY_MOVE(LanguageClientManager)
 
 public:
+    ~LanguageClientManager() override;
+
     static void clientStarted(Client *client);
     static void clientFinished(Client *client);
     static Client *startClient(const BaseSettings *setting, ProjectExplorer::Project *project = nullptr);
@@ -98,10 +100,9 @@ signals:
     void openCallHierarchy();
 
 private:
-    explicit LanguageClientManager(QObject *parent);
-    ~LanguageClientManager() override;
+    LanguageClientManager();
 
-    friend void setupLanguageClientManager(QObject *guard);
+    friend void setupLanguageClientManager();
 
     void updateProject(ProjectExplorer::Project *project);
     void projectAdded(ProjectExplorer::Project *project);
@@ -127,6 +128,6 @@ template<typename T> bool LanguageClientManager::hasClients()
     });
 }
 
-void setupLanguageClientManager(QObject *guard);
+void setupLanguageClientManager();
 
 } // namespace LanguageClient

src/plugins/languageclient/languageclientplugin.cpp

@@ -50,7 +50,7 @@ void LanguageClientPlugin::initialize()
     setupCallHierarchyFactory();
     setupTypeHierarchyFactory();
     setupLanguageClientProjectPanel();
-    setupLanguageClientManager(this);
+    setupLanguageClientManager();
     setupLanguageClientOutline();
 
 #ifdef WITH_TESTS

src/plugins/python/pythonplugin.cpp

@@ -90,7 +90,7 @@ class PythonPlugin final : public ExtensionSystem::IPlugin
         setupPythonDebugWorker();
         setupPythonOutputParser();
 
-        setupPythonSettings(this);
+        setupPythonSettings();
         setupPythonWizard();
 
         setupPipSupport(this);

src/plugins/python/pythonsettings.cpp

@@ -36,6 +36,7 @@
 #include <utils/qtcassert.h>
 #include <utils/treemodel.h>
 #include <utils/utilsicons.h>
+#include <utils/shutdownguard.h>
 
 #include <QCheckBox>
 #include <QComboBox>
@@ -1169,10 +1170,9 @@ Interpreter PythonSettings::interpreter(const QString &interpreterId)
                                 Utils::equal(&Interpreter::id, interpreterId));
 }
 
-void setupPythonSettings(QObject *guard)
+void setupPythonSettings()
 {
-    new PythonSettings; // Initializes settingsInstance
-    settingsInstance->setParent(guard);
+    static GuardedObject thePythonSettings{new PythonSettings};
 }
 
 Utils::ListModel<ProjectExplorer::Interpreter> *createInterpreterModel(QObject *parent)

src/plugins/python/pythonsettings.h

@@ -78,7 +78,8 @@ private:
     static void saveSettings();
 };
 
-void setupPythonSettings(QObject *guard);
+void setupPythonSettings();
+
 Utils::ListModel<ProjectExplorer::Interpreter> *createInterpreterModel(QObject *parent);
 
 } // Python::Internal