Import app from wsgi.py or app.py if FLASK_APP is not defined

Fixes #2376

flask/cli.py

@@ -172,11 +172,12 @@ def prepare_exec_for_file(filename):
         if not os.path.isfile(os.path.join(dirpath, '__init__.py')):
             break
 
+    if sys.path[0] != dirpath:
         sys.path.insert(0, dirpath)
     return '.'.join(module[::-1])
 
 
-def locate_app(script_info, app_id):
+def locate_app(script_info, app_id, raise_if_not_found=True):
     """Attempts to locate the application."""
     __traceback_hide__ = True
     if ':' in app_id:
@@ -194,11 +195,13 @@ def locate_app(script_info, app_id):
             stack_trace = traceback.format_exc()
             raise NoAppException('There was an error trying to import'
                                  ' the app (%s):\n%s' % (module, stack_trace))
-        else:
+        elif raise_if_not_found:
             raise NoAppException('The file/path provided (%s) does not appear'
                                  ' to exist.  Please verify the path is '
                                  'correct.  If app is not on PYTHONPATH, '
                                  'ensure the extension is .py' % module)
+        else:
+            return
 
     mod = sys.modules[module]
     if app_obj is None:
@@ -326,15 +329,23 @@ class ScriptInfo(object):
         if self.create_app is not None:
             rv = call_factory(self.create_app, self)
         else:
-            if not self.app_import_path:
+            if self.app_import_path:
+                rv = locate_app(self, self.app_import_path)
+            else:
+                for module in ['wsgi.py', 'app.py']:
+                    import_path = prepare_exec_for_file(module)
+                    rv = locate_app(self, import_path,
+                                    raise_if_not_found=False)
+                    if rv:
+                        break
+            if not rv:
                 raise NoAppException(
                     'Could not locate Flask application. You did not provide '
-                    'the FLASK_APP environment variable.\n\nFor more '
-                    'information see '
+                    'the FLASK_APP environment variable, and a wsgi.py or '
+                    'app.py module was not found in the current directory.\n\n'
+                    'For 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:

tests/test_apps/helloworld/hello.py

@@ -0,0 +1,6 @@
+from flask import Flask
+app = Flask(__name__)
+
+@app.route("/")
+def hello():
+    return "Hello World!"

tests/test_apps/helloworld/wsgi.py

@@ -0,0 +1 @@
+from hello import app

tests/test_cli.py

@@ -181,6 +181,8 @@ def test_locate_app(test_apps):
         script_info, "cliapp.factory:create_app ()")
     pytest.raises(
         NoAppException, locate_app, script_info, "cliapp.importerrorapp")
+    assert locate_app(script_info, "notanpp.py",
+                      raise_if_not_found=False) is None
 
 
 def test_find_default_import_path(test_apps, monkeypatch, tmpdir):
@@ -214,7 +216,7 @@ def test_get_version(test_apps, capsys):
     assert py_ver in out
 
 
-def test_scriptinfo(test_apps):
+def test_scriptinfo(test_apps, monkeypatch):
     """Test of ScriptInfo."""
     obj = ScriptInfo(app_import_path="cliapp.app:testapp")
     assert obj.load_app().name == "testapp"
@@ -228,6 +230,24 @@ def test_scriptinfo(test_apps):
     assert app.name == "createapp"
     assert obj.load_app() == app
 
+    obj = ScriptInfo()
+    pytest.raises(
+        NoAppException, obj.load_app)
+
+    # import app from wsgi.py in current directory
+    monkeypatch.chdir(os.path.abspath(
+        os.path.join(os.path.dirname(__file__), 'test_apps', 'helloworld')))
+    obj = ScriptInfo()
+    app = obj.load_app()
+    assert app.name == 'hello'
+
+    # import app from app.py in current directory
+    monkeypatch.chdir(os.path.abspath(
+        os.path.join(os.path.dirname(__file__), 'test_apps', 'cliapp')))
+    obj = ScriptInfo()
+    app = obj.load_app()
+    assert app.name == 'testapp'
+
 
 def test_with_appcontext(runner):
     """Test of with_appcontext."""