Incorrect coverage with branching and continue

[nedbat]

Originally reported by Eli Skeggs (Bitbucket: skeggse, GitHub: skeggse)

---

Here's a simple python script:

#!python

up = iter('ta')

while True:
  char = next(up)
  if char == 't': continue
  break

The html coverage resulting from both coverage run --branch example.py or coverage run --branch --timid example.py, reports that the continue statement was never executed. If the continue statement is bumped down a line, it works as expected.

coverage --version reports version 4.1 with C extension

---

• Bitbucket: https://bitbucket.org/ned/coveragepy/issue/496

[nedbat]

Can you show what you mean by "bumped down a line"?

[nedbat]

Original comment by Eli Skeggs (Bitbucket: skeggse, GitHub: skeggse)

---

Sure:

#!python

up = iter('ta')

while True:
  char = next(up)
  if char == 't':
    continue
  break

[nedbat]

I tried reproducing your problem, but I see 100% coverage:

$ cat bug496.py
up = iter('ta')

while True:
  char = next(up)
  if char == 't': continue
  break
$ coverage run --branch bug496.py
$ coverage report -m
Name        Stmts   Miss Branch BrPart  Cover   Missing
-------------------------------------------------------
bug496.py       5      0      4      0   100%

[nedbat]

Original comment by Eli Skeggs (Bitbucket: skeggse, GitHub: skeggse)

---

So it's an environment issue, I guess? What would impact this?

I'm running Python 3.5.1, on Arch Linux 4.5.3-1-ARCH

#!bash

$ cat example.py 
up = iter('ta')

while True:
  char = next(up)
  if char == 't': continue
  break
$ coverage run --branch example.py 
$ coverage report -m
Name         Stmts   Miss Branch BrPart  Cover   Missing
--------------------------------------------------------
example.py       5      0      2      1    86%   5->3

[nedbat]

Original comment by Eli Skeggs (Bitbucket: skeggse, GitHub: skeggse)

---

I'm able to reproduce on a hosted Ubuntu VM running Python 3.4.3 (it also has 2.7 installed, and if I install Coverage.py with pip2, I can't reproduce the issue). I sent you some instructions on getting quick access to said VM.

[nedbat]

OK, I've reproduced it: Python 3.4 shows the missing branch, Python 2.7 does not.

[nedbat]

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

---

The fix should be coordinated with #502 because it is in the same vicinity.

[nedbat]

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

---

This probably happens because process_continue_exits fails to take into account that the first line of the while is the first line of the body when the condition is a constant in python-3.

[nedbat]

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

---

For the record the proposed fix is at https://bitbucket.org/ned/coveragepy/pull-requests/104/arcs-from-continue-must-go-to_top-instead/diff

[nedbat]

Fix #496, while-true loop with a continue.

→ <<cset bd2f12dd55da (bb)>>

[nedbat]

Fixed in bd2f12dd55da (bb), which will be in version 4.3.

[nedbat]

BTW, the problem isn't about the "continue" being on the same line as the if. It's about a constant while condition (while True), and a continue statement.

[nedbat]

This fix was released as part of Coverage.py 4.3.