[FEATURE] Add a "Revert Project" option to Project menu

Discards all unsaved changes to a project and reverts to the last
saved version of the project

src/app/qgisapp.cpp

@@ -1323,6 +1323,13 @@ QgisApp::QgisApp( QSplashScreen *splash, bool restorePlugins, bool skipVersionCh
   }
 #endif
 
+  auto toggleRevert = [ = ]
+  {
+    mActionRevertProject->setEnabled( QgsProject::instance()->isDirty() &&!QgsProject::instance()->fileName().isEmpty() );
+  };
+  connect( QgsProject::instance(), &QgsProject::isDirtyChanged, mActionRevertProject, toggleRevert );
+  connect( QgsProject::instance(), &QgsProject::fileNameChanged, mActionRevertProject, toggleRevert );
+
 } // QgisApp ctor
 
 QgisApp::QgisApp()
@@ -1880,6 +1887,7 @@ void QgisApp::createActions()
   connect( mActionNewProject, &QAction::triggered, this, [ = ] { fileNew(); } );
   connect( mActionNewBlankProject, &QAction::triggered, this, &QgisApp::fileNewBlank );
   connect( mActionOpenProject, &QAction::triggered, this, &QgisApp::fileOpen );
+  connect( mActionRevertProject, &QAction::triggered, this, &QgisApp::fileRevert );
   connect( mActionSaveProject, &QAction::triggered, this, &QgisApp::fileSave );
   connect( mActionCloseProject, &QAction::triggered, this, &QgisApp::fileClose );
   connect( mActionSaveProjectAs, &QAction::triggered, this, &QgisApp::fileSaveAs );
@@ -5478,6 +5486,17 @@ void QgisApp::fileOpen()
   }
 }
 
+void QgisApp::fileRevert()
+{
+  if ( QMessageBox::question( this, tr( "Revert Project" ),
+                              tr( "Are you sure you want to discard all unsaved changes the current project?" ),
+                              QMessageBox::Yes | QMessageBox::No, QMessageBox::No ) == QMessageBox::No )
+    return;
+
+  // re-open the current project
+  addProject( QgsProject::instance()->fileInfo().filePath() );
+}
+
 void QgisApp::enableProjectMacros()
 {
   mTrustedMacros = true;

src/app/qgisapp.h

@@ -1227,6 +1227,8 @@ class APP_EXPORT QgisApp : public QMainWindow, private Ui::MainWindow
     void saveMapAsPdf();
     //! Open a project
     void fileOpen();
+    //! Revert unsaved changes to a project
+    void fileRevert();
     //! Create a new project
     bool fileNew();
     //! Create a new blank project (no template)

src/ui/qgisapp.ui

@@ -46,6 +46,7 @@
     <addaction name="mActionOpenProject"/>
     <addaction name="mProjectFromTemplateMenu"/>
     <addaction name="mRecentProjectsMenu"/>
+    <addaction name="mActionRevertProject"/>
     <addaction name="mActionCloseProject"/>
     <addaction name="separator"/>
     <addaction name="mActionSaveProject"/>
@@ -2968,6 +2969,14 @@ Acts on currently active editable layer</string>
     <string>Close Project</string>
    </property>
   </action>
+  <action name="mActionRevertProject">
+   <property name="text">
+    <string>Revert Project…</string>
+   </property>
+   <property name="toolTip">
+    <string>Revert Project to Saved version</string>
+   </property>
+  </action>
  </widget>
  <resources>
   <include location="../../images/images.qrc"/>