GUI: add explicit close hook to FGDialog

Allow triggering close of dialogs explicitly, rather than relying on
ref-count drop to delete them. Compat dialogs have a Nasal peer and
we can't rely on GC to cause a timely close of the dialog.

src/GUI/FGPUICompatDialog.cxx

@@ -47,6 +47,8 @@ public:
     }
 
 private:
+    // the Nasal peer does not hold an owning reference to the
+    // main dialog object (dialogs are owned by the NewGUI subsystem)
     SGWeakPtr<FGPUICompatDialog> _dialog;
 };
 
@@ -107,9 +109,14 @@ FGPUICompatDialog::FGPUICompatDialog(SGPropertyNode* props) : FGDialog(props),
 }
 
 FGPUICompatDialog::~FGPUICompatDialog()
+{
+    // nothing to do, all work was done in close()
+}
+
+void FGPUICompatDialog::close()
 {
     if (_peer) {
-        _peer->callMethod<void>("doClose");
+        _peer->callMethod<void>("onClose");
     }
     
     _props->setIntValue("lastx", getX());
@@ -124,6 +131,8 @@ FGPUICompatDialog::~FGPUICompatDialog()
         }
         nas->deleteModule(_module.c_str());
     }
+
+    _peer.clear();
 }
 
 bool FGPUICompatDialog::init()

src/GUI/FGPUICompatDialog.hxx

@@ -112,6 +112,8 @@ public:
     double width() const;
     double height() const;
 
+    void close() override;
+
 private:
     friend naRef f_makeDialogPeer(const nasal::CallContext& ctx);
     friend naRef f_dialogRootObject(FGPUICompatDialog& dialog, naContext c);

src/GUI/FGPUIDialog.cxx

@@ -1464,6 +1464,11 @@ void FGPUIDialog::applySize(puObject* object)
     object->setSize(w, h);
 }
 
+void FGPUIDialog::close()
+{
+    // no-op for PUI version
+}
+
 ////////////////////////////////////////////////////////////////////////
 // Implementation of FGDialog::PropertyObject.
 ////////////////////////////////////////////////////////////////////////

src/GUI/FGPUIDialog.hxx

@@ -102,6 +102,8 @@ public:
      */
     virtual void update();
 
+    void close() override;
+
     /**
      * Recompute the dialog's layout
      */

src/GUI/dialog.hxx

@@ -63,6 +63,14 @@ public:
 
     virtual const char *getName() { return ""; }
     virtual void bringToFront() {}
+
+    /**
+     * @brief Close the dialog. This should actually close the GUI
+     * assets associated, if you want an 'are you sure?' interaction, it
+     * needs to be handled in advance of this interaction.
+     */
+    virtual void close() = 0;
+
 protected:
     /**
      * Construct a new GUI widget configured by a property tree.

src/GUI/new_gui.cxx

@@ -331,12 +331,19 @@ NewGUI::closeActiveDialog ()
     if (_active_dialog == 0)
         return false;
 
+    // TODO support a request-close callback here, optionally
+    // many places in code assume this code-path does an
+    // immediate close, but for some UI paths it would be nice to
+    // allow some dialogs the chance to inervene
+
     // Kill any entries in _active_dialogs...  Is there an STL
     // algorithm to do (delete map entries by value, not key)?  I hate
     // the STL :) -Andy
     auto iter = _active_dialogs.begin();
     for(/**/; iter != _active_dialogs.end(); iter++) {
         if(iter->second == _active_dialog) {
+            _active_dialog->close();
+
             _active_dialogs.erase(iter);
             // iter is no longer valid
             break;