Coverage regression for 3.10b4+ (nested if's?)

[skirpichev]

To Reproduce

For the pr diofant/diofant#1128 try:

$ pip install git+https://github.com/skirpichev/diofant.git@test-3.10
$ cd diofant
$ pip install pytest-cov
$ pytest -q -n0 --cov diofant --cov-report term-missing \
-m 'not slow and not xfail and not regression' diofant/tests/ntheory/test_ntheory.py | \
grep ntheory | grep residue_ntheory.py 
diofant/ntheory/residue_ntheory.py                   565      0    319      2    99%   283->exit, 288->exit

Expected behavior
Mentioned jumps are covered under CPython 3.9.

Additional context

Probably, related coverage failures are in the diofant/functions submodule (should be 100% covered). For instance:

$ pytest -q -n0 --cov diofant --cov-report term-missing \
-m 'not slow and not xfail and not regression' diofant/tests/functions | \
grep functions | grep diofant/functions/exponential.py
diofant/functions/elementary/exponential.py          320     10    194      7    96%   99-102, 334->exit, 342->exit, 376-377, 391-393, 401, 504->exit

Jumps 334->exit, 342->exit and 504->exit should be covered.

PS: I'll try to reduce examples.

[nedbat]

Thanks, I've reduced the function down and reported it to CPython as https://bugs.python.org/issue44626.

[nedbat]

I don't know if it's possible to indicate the other failures you are seeing. Some will likely be duplicates of this one, but there might be new scenarios also.

[skirpichev]

I don't know if it's possible to indicate the other failures you are seeing.

It's easy to reproduce the failure in the exponential.py (see the description). Other failures I've seen in the functions module looks like this one. I suspect the main issue of this report might be same, but I'm not sure.

BTW, to reproduce regressions in the exponential.py you can run just

$ pytest -q -n0 --cov diofant --cov-report term-missing -m 'not slow and not xfail and not regression' \
diofant/tests/functions/test_exponential.py

This should cover all mentioned jumps.

Some will likely be duplicates of this one, but there might be new scenarios also.

Yes, I'll try to examine them as well.

Some strange things happen, that looks like a coveragepy or codecov problems. For instance, I see increase or decrease of the lines hit number (there is no diff wrt the master branch). E.g. here.

[skirpichev]

UPD: For the second example I got 100% coverage of this "if" block by adding "else: pass" clause after the line 335.

I think, I've found a simplest example:

$ cat test.py 
def f(x):
    x -= 1
    if x:
        if x > 1 and x < 4:
            return False
    else:
        return True


def test_f():
    for x in range(5):
        f(x)
$ pytest --cov test --cov-report term-missing --cov-branch test.py 
============================= test session starts =============================
platform linux -- Python 3.9.2, pytest-6.2.4, py-1.10.0, pluggy-0.13.1
rootdir: /home/sk/bug
plugins: hypothesis-6.14.1, cov-2.12.1, doctestplus-0.9.0, forked-1.3.0, xdist-2.3.0, timeout-1.4.2
collected 1 item                                                                                                                                             

test.py .                                                                 [100%]

----------- coverage: platform linux, python 3.9.2-final-0 -----------
Name      Stmts   Miss Branch BrPart  Cover   Missing
-----------------------------------------------------
test.py       9      0      6      0   100%
-----------------------------------------------------
TOTAL         9      0      6      0   100%


============================= 1 passed in 0.16s ===============================

$ pytest --cov test --cov-report term-missing --cov-branch test.py 
========================== test session starts ===========================
platform linux -- Python 3.10.0b4+, pytest-6.2.4, py-1.10.0, pluggy-0.13.1
rootdir: /home/sk/bug
plugins: cov-2.12.1, forked-1.3.0, xdist-2.3.0, timeout-1.4.2, hypothesis-6.14.2
collected 1 item                                                                                                                                             

test.py .                                                                       [100%]

----------- coverage: platform linux, python 3.10.0-beta-4 -----------
Name      Stmts   Miss Branch BrPart  Cover   Missing
-----------------------------------------------------
test.py       9      0      6      1    93%   4->exit
-----------------------------------------------------
TOTAL         9      0      6      1    93%

========================= 1 passed in 0.58s =====================

Again, "else: pass" after line 5 does "fix" this regression.

[skirpichev]

Both problems seems to be resolved.