Merge pull request #2297 from HndrkMkt/#2265-auto-detect-create-app-function

Auto-detect create_app() in find_best_app() #2265

CHANGES

@@ -40,6 +40,8 @@ Major release, unreleased
 - Allow IP address as exact session cookie domain. (`#2282`_)
 - ``SESSION_COOKIE_DOMAIN`` is set if it is detected through ``SERVER_NAME``.
   (`#2282`_)
+- Auto-detect zero-argument app factory called ``create_app`` or ``make_app``
+  from ``FLASK_APP``. (`#2297`_)
 
 .. _#1489: https://github.com/pallets/flask/pull/1489
 .. _#1898: https://github.com/pallets/flask/pull/1898
@@ -50,6 +52,7 @@ Major release, unreleased
 .. _#2256: https://github.com/pallets/flask/pull/2256
 .. _#2259: https://github.com/pallets/flask/pull/2259
 .. _#2282: https://github.com/pallets/flask/pull/2282
+.. _#2297: https://github.com/pallets/flask/pull/2297
 
 Version 0.12.2
 --------------

flask/cli.py

@@ -35,21 +35,48 @@ def find_best_app(module):
     from . import Flask
 
     # Search for the most common names first.
-    for attr_name in 'app', 'application':
+    for attr_name in ('app', 'application'):
         app = getattr(module, attr_name, None)
-        if app is not None and isinstance(app, Flask):
+        if isinstance(app, Flask):
             return app
 
     # Otherwise find the only object that is a Flask instance.
-    matches = [v for k, v in iteritems(module.__dict__)
-               if isinstance(v, Flask)]
+    matches = [
+        v for k, v in iteritems(module.__dict__) if isinstance(v, Flask)
+    ]
 
     if len(matches) == 1:
         return matches[0]
-    raise NoAppException('Failed to find application in module "%s".  Are '
-                         'you sure it contains a Flask application?  Maybe '
-                         'you wrapped it in a WSGI middleware or you are '
-                         'using a factory function.' % module.__name__)
+    elif len(matches) > 1:
+        raise NoAppException(
+            'Auto-detected multiple Flask applications in module "{module}".'
+            ' Use "FLASK_APP={module}:name" to specify the correct'
+            ' one.'.format(module=module.__name__)
+        )
+
+    # Search for app factory callables.
+    for attr_name in ('create_app', 'make_app'):
+        app_factory = getattr(module, attr_name, None)
+
+        if callable(app_factory):
+            try:
+                app = app_factory()
+
+                if isinstance(app, Flask):
+                    return app
+            except TypeError:
+                raise NoAppException(
+                    'Auto-detected "{callable}()" in module "{module}", but '
+                    'could not call it without specifying arguments.'.format(
+                        callable=attr_name, module=module.__name__
+                    )
+                )
+
+    raise NoAppException(
+        'Failed to find application in module "{module}". Are you sure '
+        'it contains a Flask application? Maybe you wrapped it in a WSGI '
+        'middleware.'.format(module=module.__name__)
+    )
 
 
 def prepare_exec_for_file(filename):

tests/test_cli.py

@@ -51,6 +51,34 @@ def test_find_best_app(test_apps):
         myapp = Flask('appname')
     assert find_best_app(Module) == Module.myapp
 
+    class Module:
+        @staticmethod
+        def create_app():
+            return Flask('appname')
+    assert isinstance(find_best_app(Module), Flask)
+    assert find_best_app(Module).name == 'appname'
+
+    class Module:
+        @staticmethod
+        def make_app():
+            return Flask('appname')
+    assert isinstance(find_best_app(Module), Flask)
+    assert find_best_app(Module).name == 'appname'
+
+    class Module:
+        myapp = Flask('appname1')
+        @staticmethod
+        def create_app():
+            return Flask('appname2')
+    assert find_best_app(Module) == Module.myapp
+
+    class Module:
+        myapp = Flask('appname1')
+        @staticmethod
+        def create_app(foo):
+            return Flask('appname2')
+    assert find_best_app(Module) == Module.myapp
+
     class Module:
         pass
     pytest.raises(NoAppException, find_best_app, Module)
@@ -60,6 +88,12 @@ def test_find_best_app(test_apps):
         myapp2 = Flask('appname2')
     pytest.raises(NoAppException, find_best_app, Module)
 
+    class Module:
+        @staticmethod
+        def create_app(foo):
+            return Flask('appname2')
+    pytest.raises(NoAppException, find_best_app, Module)
+
 
 def test_prepare_exec_for_file(test_apps):
     """Expect the correct path to be set and the correct module name to be returned.