reconfigure the app from run command and method

extract templates_auto_reload to property
continues #1910
closes #1907

CHANGES

@@ -79,6 +79,8 @@ Major release, unreleased
 - Removed error handler caching because it caused unexpected results for some
   exception inheritance hierarchies. Register handlers explicitly for each
   exception if you don't want to traverse the MRO. (`#2362`_)
+- Template auto reloading will honor the ``run`` command's ``debug`` flag even
+  if ``app.jinja_env`` was already accessed. (`#2373`_)
 
 .. _#1489: https://github.com/pallets/flask/pull/1489
 .. _#1621: https://github.com/pallets/flask/pull/1621
@@ -102,6 +104,7 @@ Major release, unreleased
 .. _#2354: https://github.com/pallets/flask/pull/2354
 .. _#2358: https://github.com/pallets/flask/pull/2358
 .. _#2362: https://github.com/pallets/flask/pull/2362
+.. _#2373: https://github.com/pallets/flask/pull/2373
 
 Version 0.12.2
 --------------

flask/app.py

@@ -703,6 +703,28 @@ class Flask(_PackageBoundObject):
         """
         return open(os.path.join(self.instance_path, resource), mode)
 
+    def _get_templates_auto_reload(self):
+        """Reload templates when they are changed. Used by
+        :meth:`create_jinja_environment`.
+
+        This attribute can be configured with :data:`TEMPLATES_AUTO_RELOAD`. If
+        not set, it will be enabled in debug mode.
+
+        .. versionadded:: 1.0
+            This property was added but the underlying config and behavior
+            already existed.
+        """
+        rv = self.config['TEMPLATES_AUTO_RELOAD']
+        return rv if rv is not None else self.debug
+
+    def _set_templates_auto_reload(self, value):
+        self.config['TEMPLATES_AUTO_RELOAD'] = value
+
+    templates_auto_reload = property(
+        _get_templates_auto_reload, _set_templates_auto_reload
+    )
+    del _get_templates_auto_reload, _set_templates_auto_reload
+
     def create_jinja_environment(self):
         """Creates the Jinja2 environment based on :attr:`jinja_options`
         and :meth:`select_jinja_autoescape`.  Since 0.7 this also adds
@@ -715,13 +737,13 @@ class Flask(_PackageBoundObject):
            ``TEMPLATES_AUTO_RELOAD`` configuration option.
         """
         options = dict(self.jinja_options)
+
         if 'autoescape' not in options:
             options['autoescape'] = self.select_jinja_autoescape
+
         if 'auto_reload' not in options:
-            if self.config['TEMPLATES_AUTO_RELOAD'] is not None:
-                options['auto_reload'] = self.config['TEMPLATES_AUTO_RELOAD']
-            else:
-                options['auto_reload'] = self.debug
+            options['auto_reload'] = self.templates_auto_reload
+
         rv = self.jinja_environment(self, **options)
         rv.globals.update(
             url_for=url_for,
@@ -806,6 +828,22 @@ class Flask(_PackageBoundObject):
             rv.update(processor())
         return rv
 
+    def _reconfigure_for_run_debug(self, debug):
+        """The ``run`` commands will set the application's debug flag. Some
+        application configuration may already be calculated based on the
+        previous debug value. This method will recalculate affected values.
+
+        Called by the :func:`flask.cli.run` command or :meth:`Flask.run`
+        method if the debug flag is set explicitly in the call.
+
+        :param debug: the new value of the debug flag
+
+        .. versionadded:: 1.0
+            Reconfigures ``app.jinja_env.auto_reload``.
+        """
+        self.debug = debug
+        self.jinja_env.auto_reload = self.templates_auto_reload
+
     def run(self, host=None, port=None, debug=None, **options):
         """Runs the application on a local development server.
 
@@ -859,21 +897,24 @@ class Flask(_PackageBoundObject):
             explain_ignored_app_run()
             return
 
-        from werkzeug.serving import run_simple
+        if debug is not None:
+            self._reconfigure_for_run_debug(bool(debug))
+
         _host = '127.0.0.1'
         _port = 5000
         server_name = self.config.get("SERVER_NAME")
         sn_host, sn_port = None, None
+
         if server_name:
             sn_host, _, sn_port = server_name.partition(':')
+
         host = host or sn_host or _host
         port = int(port or sn_port or _port)
-        if debug is not None:
-            self.debug = bool(debug)
         options.setdefault('use_reloader', self.debug)
         options.setdefault('use_debugger', self.debug)
-        if debug:
-            self.jinja_env.auto_reload = True
+
+        from werkzeug.serving import run_simple
+
         try:
             run_simple(host, port, self, **options)
         finally:

flask/cli.py

@@ -319,8 +319,10 @@ class ScriptInfo(object):
         be returned.
         """
         __traceback_hide__ = True
+
         if self._loaded_app is not None:
             return self._loaded_app
+
         if self.create_app is not None:
             rv = call_factory(self.create_app, self)
         else:
@@ -330,10 +332,14 @@ class ScriptInfo(object):
                     'the FLASK_APP environment variable.\n\nFor more '
                     'information see '
                     'http://flask.pocoo.org/docs/latest/quickstart/')
+
             rv = locate_app(self, self.app_import_path)
+
         debug = get_debug_flag()
+
         if debug is not None:
-            rv.debug = debug
+            rv._reconfigure_for_run_debug(debug)
+
         self._loaded_app = rv
         return rv