Prevent crash when we can't write to editor cache or config path

This can happen if users somehow got wrong user permissions assigned to
their Godot cache, config or data paths (e.g. `~/.config/godot`).

The error messages should give them a hint as to what the issue may be.

Fixes #33199.

There may be other situations that still lead to a crash, we need to
review all uses of `FileAccess::open` with `FileAccess::WRITE` mode to
ensure that proper pointer validation is done.

1 files changed, 13 insertions, 8 deletions

diff --git a/editor/editor_resource_preview.cpp b/editor/editor_resource_preview.cpp
index 65a1704770..55f9347045 100644
--- a/editor/editor_resource_preview.cpp
+++ b/editor/editor_resource_preview.cpp
@@ -201,9 +201,8 @@ void EditorResourcePreview::_generate_preview(Ref<ImageTexture> &r_texture, Ref<
 			if (has_small_texture) {
 				ResourceSaver::save(cache_base + "_small.png", r_small_texture);
 			}
-			Error err;
-			FileAccess *f = FileAccess::open(cache_base + ".txt", FileAccess::WRITE, &err);
-			ERR_FAIL_COND_MSG(err != OK, "Cannot create file '" + cache_base + ".txt'.");
+			FileAccess *f = FileAccess::open(cache_base + ".txt", FileAccess::WRITE);
+			ERR_FAIL_COND_MSG(!f, "Cannot create file '" + cache_base + ".txt'. Check user write permissions.");
 			f->store_line(itos(thumbnail_size));
 			f->store_line(itos(has_small_texture));
 			f->store_line(itos(FileAccess::get_modified_time(p_item.path)));
@@ -295,11 +294,17 @@ void EditorResourcePreview::_thread() {
 								//update modified time
 
 								f = FileAccess::open(file, FileAccess::WRITE);
-								f->store_line(itos(thumbnail_size));
-								f->store_line(itos(has_small_texture));
-								f->store_line(itos(modtime));
-								f->store_line(md5);
-								memdelete(f);
+								if (!f) {
+									// Not returning as this would leave the thread hanging and would require
+									// some proper cleanup/disabling of resource preview generation.
+									ERR_PRINTS("Cannot create file '" + file + "'. Check user write permissions.");
+								} else {
+									f->store_line(itos(thumbnail_size));
+									f->store_line(itos(has_small_texture));
+									f->store_line(itos(modtime));
+									f->store_line(md5);
+									memdelete(f);
+								}
 							}
 						} else {
 							memdelete(f);