Prevent recursive importing (hack)

Prevents recursion when importing files due to the ill nature of EditorProgress.
The progress dialog will have to be entirely rewritten after 4.0 is out due to it being a constant source of bugs.
In the meantime, this fixes the problem.

Fixes #53871. Supersedes #73159.

editor/editor_file_system.cpp

@@ -1237,10 +1237,23 @@ void EditorFileSystem::_notification(int p_what) {
 
 		case NOTIFICATION_PROCESS: {
 			if (use_threads) {
+				/** This hack exists because of the EditorProgress nature
+				 *  of processing events recursively. This needs to be rewritten
+				 *  at some point entirely, but in the meantime the following
+				 *  hack prevents deadlock on import.
+				 */
+
+				static bool prevent_recursive_process_hack = false;
+				if (prevent_recursive_process_hack) {
+					break;
+				}
+
+				prevent_recursive_process_hack = true;
+
+				bool done_importing = false;
+
 				if (scanning_changes) {
 					if (scanning_changes_done) {
-						scanning_changes = false;
-
 						set_process(false);
 
 						thread_sources.wait_to_finish();
@@ -1251,6 +1264,8 @@ void EditorFileSystem::_notification(int p_what) {
 						}
 						emit_signal(SNAME("sources_changed"), sources_changed.size() > 0);
 						first_scan = false;
+						scanning_changes = false; // Changed to false here to prevent recursive triggering of scan thread.
+						done_importing = true;
 					}
 				} else if (!scanning && thread.is_started()) {
 					set_process(false);
@@ -1268,10 +1283,12 @@ void EditorFileSystem::_notification(int p_what) {
 					first_scan = false;
 				}
 
-				if (!is_processing() && scan_changes_pending) {
+				if (done_importing && scan_changes_pending) {
 					scan_changes_pending = false;
 					scan_changes();
 				}
+
+				prevent_recursive_process_hack = false;
 			}
 		} break;
 	}
@@ -2180,6 +2197,7 @@ void EditorFileSystem::_reimport_thread(uint32_t p_index, ImportThreadData *p_im
 }
 
 void EditorFileSystem::reimport_files(const Vector<String> &p_files) {
+	ERR_FAIL_COND_MSG(importing, "Attempted to call reimport_files() recursively, this is not allowed.");
 	importing = true;
 
 	Vector<String> reloads;