`RequestContext.match_request` is moved from `__init__` to `push`. This
causes matching to happen later, when the app context is available.
This enables URL converters that use things such as the database.
After pallets/werkzeug#1577, mismatched configured and real server
names will show a warning in addition to raising 404. This caused
tests that did this deliberately to fail.
This patch removes the pytest fixture we were using to fail on
warnings, instead using the standard `-Werror` option. This speeds
up the tests by ~3x.
Before, returning a `bool` from a route caused the error
```
[2019-05-31 10:08:42,216] ERROR in app: Exception on / [GET]
Traceback (most recent call last):
File "/Users/johnzeringue/Documents/ts-open/flask/flask/app.py", line 2070, in make_response
rv = self.response_class.force_type(rv, request.environ)
File "/Users/johnzeringue/Documents/ts-open/flask/env/lib/python3.7/site-packages/werkzeug/wrappers/base_response.py", line 269, in force_type
response = BaseResponse(*_run_wsgi_app(response, environ))
File "/Users/johnzeringue/Documents/ts-open/flask/env/lib/python3.7/site-packages/werkzeug/wrappers/base_response.py", line 26, in _run_wsgi_app
return _run_wsgi_app(*args)
File "/Users/johnzeringue/Documents/ts-open/flask/env/lib/python3.7/site-packages/werkzeug/test.py", line 1119, in run_wsgi_app
app_rv = app(environ, start_response)
TypeError: 'bool' object is not callable
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/Users/johnzeringue/Documents/ts-open/flask/flask/app.py", line 2393, in wsgi_app
response = self.full_dispatch_request()
File "/Users/johnzeringue/Documents/ts-open/flask/flask/app.py", line 1906, in full_dispatch_request
return self.finalize_request(rv)
File "/Users/johnzeringue/Documents/ts-open/flask/flask/app.py", line 1921, in finalize_request
response = self.make_response(rv)
File "/Users/johnzeringue/Documents/ts-open/flask/flask/app.py", line 2078, in make_response
reraise(TypeError, new_error, sys.exc_info()[2])
File "/Users/johnzeringue/Documents/ts-open/flask/flask/_compat.py", line 39, in reraise
raise value.with_traceback(tb)
File "/Users/johnzeringue/Documents/ts-open/flask/flask/app.py", line 2070, in make_response
rv = self.response_class.force_type(rv, request.environ)
File "/Users/johnzeringue/Documents/ts-open/flask/env/lib/python3.7/site-packages/werkzeug/wrappers/base_response.py", line 269, in force_type
response = BaseResponse(*_run_wsgi_app(response, environ))
File "/Users/johnzeringue/Documents/ts-open/flask/env/lib/python3.7/site-packages/werkzeug/wrappers/base_response.py", line 26, in _run_wsgi_app
return _run_wsgi_app(*args)
File "/Users/johnzeringue/Documents/ts-open/flask/env/lib/python3.7/site-packages/werkzeug/test.py", line 1119, in run_wsgi_app
app_rv = app(environ, start_response)
TypeError: 'bool' object is not callable
The view function did not return a valid response. The return type must be a string, tuple, Response instance, or WSGI callable, but it was a bool.
```
Now, it returns the more readable
```
[2019-05-31 10:36:19,500] ERROR in app: Exception on / [GET]
Traceback (most recent call last):
File "/Users/johnzeringue/Documents/ts-open/flask/flask/app.py", line 2400, in wsgi_app
response = self.full_dispatch_request()
File "/Users/johnzeringue/Documents/ts-open/flask/flask/app.py", line 1907, in full_dispatch_request
return self.finalize_request(rv)
File "/Users/johnzeringue/Documents/ts-open/flask/flask/app.py", line 1922, in finalize_request
response = self.make_response(rv)
File "/Users/johnzeringue/Documents/ts-open/flask/flask/app.py", line 2085, in make_response
" {rv.__class__.__name__}.".format(rv=rv))
TypeError: The view function did not return a valid response. The return type must be a string, dict, tuple, Response instance, or WSGI callable, but it was a bool.
```
Fixes#3214
