Don't passthrough_errors unless instructed. (#2006)

Fix #2005

Revert #1679 and #1996

flask/app.py

@@ -838,8 +838,6 @@ class Flask(_PackageBoundObject):
             self.debug = bool(debug)
         options.setdefault('use_reloader', self.debug)
         options.setdefault('use_debugger', self.debug)
-        options.setdefault('passthrough_errors',
-                           self.config['PROPAGATE_EXCEPTIONS'])
         try:
             run_simple(host, port, self, **options)
         finally:

flask/cli.py

@@ -429,8 +429,7 @@ def run_command(info, host, port, reload, debugger, eager_loading,
             print(' * Forcing debug mode %s' % (debug and 'on' or 'off'))
 
     run_simple(host, port, app, use_reloader=reload,
-               use_debugger=debugger, threaded=with_threads,
-               passthrough_errors=app.config['PROPAGATE_EXCEPTIONS'])
+               use_debugger=debugger, threaded=with_threads)
 
 
 @click.command('shell', short_help='Runs a shell in the app context.')

tests/test_basic.py

@@ -1268,8 +1268,6 @@ def test_werkzeug_passthrough_errors(monkeypatch, debug, use_debugger,
     monkeypatch.setattr(werkzeug.serving, 'run_simple', run_simple_mock)
     app.config['PROPAGATE_EXCEPTIONS'] = propagate_exceptions
     app.run(debug=debug, use_debugger=use_debugger, use_reloader=use_reloader)
-    # make sure werkzeug passes errors through if PROPAGATE_EXCEPTIONS
-    assert rv['passthrough_errors'] == propagate_exceptions
 
 
 def test_max_content_length():