incorrect branch reporting with __debug__

[nedbat]

Originally reported by John Theodore Goetz (Bitbucket: theodoregoetz, GitHub: theodoregoetz)

---

Coverage report indicates a missing branch with __debug__ within an if/else block. Note if a pass is added after the if __debug__ then coverage is correctly shown as 100%.

#!python

for value in [True, False]:
    if value:
        if __debug__:
            x = 1
        #pass  # required for coverage to show 100%
    else:
        x = 2

Running coverage in both __debug__ and with python -O (appending the results):

#!bash

python -mcoverage erase
python -mcoverage run --branch prog.py
python -O -mcoverage run --branch --append prog.py
python -mcoverage report -m

Results in the following:

#!bash

Name       Stmts   Miss Branch BrPart  Cover   Missing
------------------------------------------------------
prog2.py       4      0      4      1    88%   2->1

---

• Bitbucket: https://bitbucket.org/ned/coveragepy/issue/522

[nedbat]

Original comment by Loic Dachary (Bitbucket: dachary, GitHub: dachary)

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Reproduced the issue as instructed at 24aff3d7bfd5 (bb) with python-2.7.12 and python-3.5

[nedbat]

Original comment by Loic Dachary (Bitbucket: dachary, GitHub: dachary)

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As of 813a3f0 (bb) the coverage shows 100%, the bug has been fixed and this issue can be closed

[nedbat]

Original comment by Loic Dachary (Bitbucket: dachary, GitHub: dachary)

---

@nedbat is there anything I can do before this issue can be closed ?

[nedbat]

Using the latest code, I still see the behavior originally reported. Leaving open.

[nedbat]

A simpler case will show the problem:

$ cat bug522.py
one = 1
for value in [True, False]:
    if value:
        if one:
            x = 1
    else:
        x = 2

for value in [True, False]:
    if value:
        if 1:
            x = 1
    else:
        x = 2
$ python -m coverage run --branch bug522.py
$ python -m coverage report -m
Name        Stmts   Miss Branch BrPart  Cover   Missing
-------------------------------------------------------
bug522.py      10      0     10      2    90%   4->2, 10->9

The "if 1:" statement doesn't appear in the compiled bytecode, so it's being removed from consideration, which makes the branch be attributed to 10->9 rather than 11->9.

[nedbat]

We treat constant expressions specially in while loops, but not in if's.

[nedbat]

Fixed in 7d90fa43b338 (bb).

[nedbat]

This was shipped in 4.3.2.