Change Flask.__init__ to accept two new keyword arguments, host_matching and static_host. (#1560)

This enables host_matching to be set properly by the time the constructor adds
the static route, and enables the static route to be properly associated with
the required host.

Previously, you could only enable host_matching once your app was already
instantiated (e.g. app.url_map.host_matching = True), but at that point
the constructor would have already added the static route without host matching
and an associated host, leaving the static route in a broken state.

Fixes #1559.

tests/test_basic.py

@@ -1188,6 +1188,25 @@ def test_static_url_path():
         assert flask.url_for('static', filename='index.html') == '/foo/index.html'
 
 
+def test_static_route_with_host_matching():
+    app = flask.Flask(__name__, host_matching=True, static_host='example.com')
+    c = app.test_client()
+    rv = c.get('http://example.com/static/index.html')
+    assert rv.status_code == 200
+    rv.close()
+    with app.test_request_context():
+       rv = flask.url_for('static', filename='index.html', _external=True)
+       assert rv == 'http://example.com/static/index.html'
+    # Providing static_host without host_matching=True should error.
+    with pytest.raises(Exception):
+        flask.Flask(__name__, static_host='example.com')
+    # Providing host_matching=True with static_folder but without static_host should error.
+    with pytest.raises(Exception):
+        flask.Flask(__name__, host_matching=True)
+    # Providing host_matching=True without static_host but with static_folder=None should not error.
+    flask.Flask(__name__, host_matching=True, static_folder=None)
+
+
 def test_none_response():
     app = flask.Flask(__name__)
     app.testing = True