made ImportError verbose in cli.py

CHANGES.rst

@@ -10,6 +10,8 @@ Unreleased
     removed in Flask 2.1, while remaining compatible with both in
     2.0.x. Use ``response.request.environ`` instead. :pr:`4341`
 -   Fix type annotation for ``errorhandler`` decorator. :issue:`4295`
+-   Revert a change to the CLI that caused it to hide ``ImportError``
+    tracebacks when importing the application. :issue:`4307`
 
 
 Version 2.0.2

src/flask/cli.py

@@ -258,15 +258,16 @@ def locate_app(script_info, module_name, app_name, raise_if_not_found=True):
 
     try:
         __import__(module_name)
-    except ImportError as e:
+    except ImportError:
         # Reraise the ImportError if it occurred within the imported module.
         # Determine this by checking whether the trace has a depth > 1.
         if sys.exc_info()[2].tb_next:
             raise NoAppException(
-                f"While importing {module_name!r}, an ImportError was raised."
-            ) from e
+                f"While importing {module_name!r}, an ImportError was"
+                f" raised:\n\n{traceback.format_exc()}"
+            ) from None
         elif raise_if_not_found:
-            raise NoAppException(f"Could not import {module_name!r}.") from e
+            raise NoAppException(f"Could not import {module_name!r}.") from None
         else:
             return