Fix bug where coverage data is not saved on SIGTERM

[LewisGaul]

Fixes #1599

Failing test prior to the fix:

$python -m pytest tests/test_concurrency.py -k Sigterm
bringing up nodes...
...                                                                                                                            [100%] [100%]F [100%]
============================================================== FAILURES ==============================================================
___________________________________________ SigtermTest.test_sigterm_threading_saves_data ____________________________________________
[gw2] linux -- Python 3.8.10 /mnt/c/Users/legaul/repos/coveragepy/venv/bin/python

self = <tests.test_concurrency.SigtermTest object at 0x7f7ffc8f75e0>

    def test_sigterm_threading_saves_data(self) -> None:
        # A terminated process should save its coverage data.
        self.make_file("handler.py", """\
            import os, signal

            print("START", flush=True)
            print("SIGTERM", flush=True)
            os.kill(os.getpid(), signal.SIGTERM)
            print("NOT HERE", flush=True)
            """)
        self.make_file(".coveragerc", """\
            [run]
            # The default concurrency option.
            concurrency = thread
            sigterm = true
            """)
        out = self.run_command("coverage run handler.py")
        assert out == "START\nSIGTERM\nTerminated\n"
        out = self.run_command("coverage report -m")
        expected = "handler.py 5 1 80% 6"
>       assert self.squeezed_lines(out)[2] == expected
E       IndexError: list index out of range

/mnt/c/Users/legaul/repos/coveragepy/tests/test_concurrency.py:774: IndexError
-------------------------------------------------------- Captured stdout call --------------------------------------------------------
START
SIGTERM
Terminated

No data to report.

-------------------------------------------------------- Captured stdout call --------------------------------------------------------
START
SIGTERM
Terminated

No data to report.

-------------------------------------------------------- Captured stdout call --------------------------------------------------------
START
SIGTERM
Terminated

No data to report.

====================================================== short test summary info =======================================================
FAILED tests/test_concurrency.py::SigtermTest::test_sigterm_threading_saves_data - IndexError: list index out of range
1 failed, 3 passed in 3.17s

[nedbat]

I'm curious why _auto_save isn't true, but I've only just taken a quick look at this pull request.

[LewisGaul]

Yeah I wondered that at first - it's being set by the auto_data arg to the Coverage class, which defaults to False and is passed as True by multiproc.ProcessWithCoverage, i.e. only in the multiprocessing case.

[LewisGaul]

That said, I'm more than happy with solving this another way - more than anything this proposed change serves as an illustration for what's going wrong!

[nedbat]

I'm trying to think this through. On the one hand it seems odd: if _auto_save is false, then we won't save the data if the process ends normally, but we will if it's terminated? But on the other, sigterm=true is documented as "to capture data at unusual process ends," which this definitely is.

Maybe the answer is that _auto_save is only needed for the subprocess case. For main processes, something else will be handling the data saving at normal process termination, and this is fine to put here.

I like that you have a test demonstrating the issue. event == "sigterm" will only happen if sigterm=true is in the settings, so clearly the user wanted sigterm handling.

Let's merge it!

[nedbat]

This is now released as part of coverage 7.2.3.