UI: Warning When Dragging Non-Blend File Onto Executable

Dragging a non-Blend file onto the Blender executable currently
silently fails with Blender just aborting. With this PR any files used
as file argument will load Blender and show a warning if the file does
not exist or is not a blend file. Blend files that cannot be read are
treated as they are now.

Pull Request: https://projects.blender.org/blender/blender/pulls/139128

source/blender/windowmanager/intern/wm_event_system.cc

@@ -814,6 +814,8 @@ void wm_event_do_notifiers(bContext *C)
   wm_test_autorun_warning(C);
   /* Deprecation warning. */
   wm_test_gpu_backend_fallback(C);
+  /* Foreign File warning. */
+  wm_test_foreign_file_warning(C);
 
   GPU_render_end();
 }

source/blender/windowmanager/intern/wm_files.cc

@@ -4287,6 +4287,35 @@ void wm_test_autorun_warning(bContext *C)
   }
 }
 
+void wm_test_foreign_file_warning(bContext *C)
+{
+  if (!G_MAIN->is_read_invalid) {
+    return;
+  }
+
+  G_MAIN->is_read_invalid = false;
+
+  wmWindowManager *wm = CTX_wm_manager(C);
+  wmWindow *win = (wm->winactive) ? wm->winactive : static_cast<wmWindow *>(wm->windows.first);
+
+  if (win) {
+    /* We want this warning on the Main window, not a child window even if active. See #118765. */
+    if (win->parent) {
+      win = win->parent;
+    }
+
+    wmWindow *prevwin = CTX_wm_window(C);
+    CTX_wm_window_set(C, win);
+    UI_alert(C,
+             RPT_("Unable to Load File"),
+             RPT_("The file specified is not a valid Blend document."),
+             ALERT_ICON_ERROR,
+             false);
+
+    CTX_wm_window_set(C, prevwin);
+  }
+}
+
 /** \} */
 
 /* -------------------------------------------------------------------- */

source/blender/windowmanager/wm_window.hh

@@ -143,3 +143,4 @@ wmOperatorStatus wm_window_new_main_exec(bContext *C, wmOperator *op);
 
 void wm_test_autorun_revert_action_set(wmOperatorType *ot, PointerRNA *ptr);
 void wm_test_autorun_warning(bContext *C);
+void wm_test_foreign_file_warning(bContext *C);

source/creator/creator_args.cc

@@ -2674,16 +2674,17 @@ static bool handle_load_file(bContext *C, const char *filepath_arg, const bool l
     if (load_empty_file == false) {
       error_msg = error_msg_generic;
     }
-    else if (BLI_exists(filepath)) {
+    else if (BLI_exists(filepath) && BKE_blendfile_extension_check(filepath)) {
       /* When a file is found but can't be loaded, handling it as a new file
        * could cause it to be unintentionally overwritten (data loss).
        * Further this is almost certainly not that a user would expect or want.
        * If they do, they can delete the file beforehand. */
       error_msg = error_msg_generic;
     }
-    else if (!BKE_blendfile_extension_check(filepath)) {
-      /* Unrelated arguments should not be treated as new blend files. */
-      error_msg = "argument has no '.blend' file extension, not using as new file";
+    else {
+      /* Non-blend or non-existing. Continue loading and give warning. */
+      G_MAIN->is_read_invalid = true;
+      return true;
     }
 
     if (error_msg) {