std.process: Do not kill process group 2 in unittest

[helmutg]

When passing a Pid object to tryWait(), its processId will be changed to Pid.terminated, which happens to be -2. Passing this value to kill() will kill the process group 2 on Posix systems. If you run the build and test suite using this process group, the test case will kill the entire build.

Bug-Debian: https://bugs.debian.org/1089007

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[CyberShadow]

Thanks, but wouldn't it make more sense to have kill throw ProcessException if it's passed a Pid with pid == terminated? That seems to be the intention of the test.

[helmutg]

Thanks, but wouldn't it make more sense to have kill throw ProcessException if it's passed a Pid with pid == terminated? That seems to be the intention of the test.

That is a very reasonable question. Thank you for the review. Is the kill function supposed to be able to kill process groups? Do process groups exist on Windows? Does existing code assume that kill kills process groups? Whether changing kill is better depends on the answers to these questions.

What I am proposing here is a minimum viable solution that makes gcc build rather than fail its build. If changing kill, we change behavior and may break other code that assumes the ability to kill process groups. That seems like a risky affair and it feels unlikely that such a patch would be backported into older gcc releases.

[CyberShadow]

Is the kill function supposed to be able to kill process groups?

No, I think it is designed to only kill child processes, created using other std.process functions.

Does existing code assume that kill kills process groups?

Seems highly unlikely. The unittest in question seems to assume that kill will throw a ProcessException if pid == terminated, but it passing previously seemed to be accidental and contingent on a process group with the number 2 not existing.

What I am proposing here is a minimum viable solution that makes gcc build rather than fail its build. If changing kill, we change behavior and may break other code that assumes the ability to kill process groups. That seems like a risky affair and it feels unlikely that such a patch would be backported into older gcc releases.

True. We can go forward with this change as well, though I would add a TODO to note that the condition may not be what was originally intended to be tested.

Let's see what other Phobos maintainers say as well. @schveiguy ?

not applicable.

[CyberShadow]

#10601