PyAPI: improve warnings when addons from extensions repos fail to load

scripts/modules/addon_utils.py

@@ -373,8 +373,32 @@ def enable(module_name, *, default_set=False, persistent=False, handle_error=Non
             # If the add-on doesn't exist, don't print full trace-back because the back-trace is in this case
             # is verbose without any useful details. A missing path is better communicated in a short message.
             # Account for `ImportError` & `ModuleNotFoundError`.
-            if isinstance(ex, ImportError) and ex.name == module_name:
-                print("Add-on not loaded:", repr(module_name), "cause:", str(ex))
+            if isinstance(ex, ImportError):
+                if ex.name == module_name:
+                    print("Add-on not loaded: \"%s\", cause: %s" % (module_name, str(ex)))
+
+                # Issue with an add-on from an extension repository, report a useful message.
+                elif module_name.startswith(ex.name + ".") and module_name.startswith(_ext_base_pkg_idname + "."):
+                    repo_id = module_name[len(_ext_base_pkg_idname) + 1:].rpartition(".")[0]
+                    repo = next(
+                        (repo for repo in _preferences.filepaths.extension_repos if repo.module == repo_id),
+                        None,
+                    )
+                    if repo is None:
+                        print(
+                            "Add-on not loaded: \"%s\", cause: extension repository \"%s\" doesn't exist" %
+                            (module_name, repo_id)
+                        )
+                    elif not repo.enabled:
+                        print(
+                            "Add-on not loaded: \"%s\", cause: extension repository \"%s\" is disabled" %
+                            (module_name, repo_id)
+                        )
+                    else:
+                        # The repository exists and is enabled, it should have imported.
+                        print("Add-on not loaded: \"%s\", cause: %s" % (module_name, str(ex)))
+                else:
+                    handle_error(ex)
             else:
                 handle_error(ex)