Document Folder::setVirtualFilesEnabled(bool)

The procedure is tested in `Vfs::wipeDehydratedVirtualFiles()`.

src/gui/folder.cpp

@@ -769,10 +769,16 @@ void Folder::setVirtualFilesEnabled(bool enabled)
     }
 
     if (newMode != _definition.virtualFilesMode) {
+        // This is tested in TestSyncVirtualFiles::testWipeVirtualSuffixFiles, so for changes here, have them reflected in that test.
+
         // TODO: Must wait for current sync to finish!
         OC_ENFORCE(!isSyncRunning());
+
+        // Wipe the dehydrated files from the DB, they will get downloaded on the next sync. We need to do this, otherwise the files
+        // are in the DB but not on disk, so the client assumes they are deleted, and removes them from the remote.
         _vfs->wipeDehydratedVirtualFiles();
 
+        // Tear down the VFS
         _vfs->stop();
         _vfs->unregisterFolder();
 
@@ -782,6 +788,7 @@ void Folder::setVirtualFilesEnabled(bool enabled)
         _vfsIsReady = false;
         _vfs.reset(VfsPluginManager::instance().createVfsFromPlugin(newMode).release());
 
+        // Restart VFS.
         _definition.virtualFilesMode = newMode;
         startVfs();
         saveToSettings();

test/testsyncvirtualfiles.cpp

@@ -862,6 +862,8 @@ private slots:
 
     void testWipeVirtualSuffixFiles()
     {
+        // This tests the procedure done in Folder::setVirtualFilesEnabled. For changes here, make sure they are reflected in that method.
+
         FakeFolder fakeFolder{ FileInfo{} };
         setupVfs(fakeFolder);