werkzeug 0.15.0: mystery "generated" module when invoking coverage

[asottile]

This seems to be a minimal reproduction:

(note I made a virtualenv one level up to avoid that being in the coverage output)

.coveragerc

[run]
source = .

t.py

import flask

app = flask.Flask(__name__)

@app.route('/foo/<a>')
def hello(a):
    return 'world'


# pretend this is a test
with app.test_request_context():
    with app.test_client() as client:
        client.get(flask.url_for('hello', a='1'))

runtime

$ bash -xc 'coverage erase && coverage run t.py && coverage report && coverage xml'
+ coverage erase
+ coverage run t.py
+ coverage report
generated   NoSource: No source for code: '/tmp/t/generated'.
Aborting report output, consider using -i.
Name    Stmts   Miss  Cover
---------------------------
t.py        7      0   100%
+ coverage xml
No source for code: '/tmp/t/generated'.
Aborting report output, consider using -i.

triage (?)

This appears to come from here:

werkzeug/src/werkzeug/routing.py

Line 1111 in 86f7bdf

"generated",

or, at least, that's the only instance of 'generated' or "generated" in my site-packages -- so I may be guessing a bit here.

This is causing CI failures in https://github.com/asottile/git-code-debt

workaround

A workaround appears to be setting this:

[run]
# ...
omit =
    *generated

in .coveragerc

though ideally I wouldn't have to exclude this 🤔

[davidism]

When Rule generates its build code, CodeType.filename is set to "generated". It should probably be set to __file__.

werkzeug/src/werkzeug/routing.py

Lines 1102 to 1115 in 86f7bdf

	code_args = [
	argcount,
	len(self.var),
	peak_stack + len(self.var),
	flags,
	ops,
	tuple(self.consts),
	(),
	tuple(self.var),
	"generated",
	"<builder:%r>" % self.rule.rule,
	1,
	b"",
	]

[asottile]

I think None would also work (?)

[davidism]

@asottile I'll give that a try. Was about to write this whole thing, so I'll post anyway. :-)

---

For clarity, the code above is better as a dict:

code_args = {
    "argcount": argcount,
    "nlocals": len(self.var),
    "stacksize": peak_stack + len(self.var),
    "flags": flags,
    "codestring": ops,
    "constants": tuple(self.consts),
    "names": (),
    "varnames": tuple(self.var),
    "filename": __file__,
    "name": "_build_unknown" if append_unknown else "_build",
    "firstlineno": 1,
    "lnotab": b"",
}
if not PY2:
    code_args["kwonlyargcount"] = 0
co = types.CodeType(**code_args)

I'm not really sure what the correct answer is. It's weird that this isn't causing the same error in Werkzeug's own coverage. How will coverage react if I tell it that the generated function is part of that module, what line do I say it starts on, what does it do when the lnotab table is empty, etc.?

[davidism]

CodeType doesn't work with keyword arguments. :-(

[asottile]

inspecting the coverage data I see two arcs, one from (-1, 1) and the other from (1, -1), nonsense it seems

I think werkzeug itself avoids this due to:

werkzeug/setup.cfg

Lines 18 to 22 in 86f7bdf

	[coverage:run]
	branch = True
	source =
	werkzeug
	tests

Which avoids the "generated" file at .

[davidism]

Tests still pass with None, could you try patching that locally and see if it fixes your project's coverage?

[asottile]

woops, my suggestion was wrong, and I'm concerned about the test suite now 😨

+ coverage run t.py
Traceback (most recent call last):
  File "t.py", line 3, in <module>
    app = flask.Flask(__name__)
  File "/tmp/venv/lib/python3.6/site-packages/flask/app.py", line 562, in __init__
    view_func=self.send_static_file
  File "/tmp/venv/lib/python3.6/site-packages/flask/app.py", line 66, in wrapper_func
    return f(self, *args, **kwargs)
  File "/tmp/venv/lib/python3.6/site-packages/flask/app.py", line 1216, in add_url_rule
    self.url_map.add(rule)
  File "/tmp/venv/lib/python3.6/site-packages/werkzeug/routing.py", line 1563, in add
    rule.bind(self)
  File "/tmp/venv/lib/python3.6/site-packages/werkzeug/routing.py", line 710, in bind
    self.compile()
  File "/tmp/venv/lib/python3.6/site-packages/werkzeug/routing.py", line 766, in compile
    self._build = self._compile_builder(False)
  File "/tmp/venv/lib/python3.6/site-packages/werkzeug/routing.py", line 1129, in _compile_builder
    return self.BuilderCompiler(self).compile(append_unknown)
  File "/tmp/venv/lib/python3.6/site-packages/werkzeug/routing.py", line 1120, in compile
    co = types.CodeType(*code_args)
TypeError: code() argument 10 must be str, not None

Setting it to "" instead seems to work

[davidism]

🤦‍♂️ I didn't actually set it to None.

[asottile]

It looks like exec uses "<string>" for that value:

>>> s = 'print("hi")\ndef f(): pass\nprint(repr(f.__code__.co_filename))'
>>> exec(s)
hi
'<string>'

[davidism]

Yeah, I was looking at compile too. Does coverage skip those?

[asottile]

yep!

(this is in coverage/control.py in the released version I'm using, but here's the moved source):

https://github.com/nedbat/coveragepy/blob/28d223b4265242e08dac4bb016270dbc1b4482cb/coverage/inorout.py#L240-L245

[davidism]

Yeah, just found that, it skips empty or < prefix. Debating whether I should use something specific like "<werkzeug routing>" or just the empty string.

[asottile]

I'd go with "<werkzeug routing>"