feat: say why a scenario's processes died - #652
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ykhrustalev wants to merge 3 commits into
Open
ykhrustalev wants to merge 3 commits into
ykhrustalev wants to merge 3 commits into
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On a timeout, terminate_child() sent one SIGTERM and then blocked in wait() with no bound. A cargo process that ignores the signal, or that has been stopped and so never receives it, hung the whole run at that point. Wait only for a short grace period, then SIGKILL the process group. This needs a second signal, so the errno handling moves into a signal_group() helper rather than being duplicated.
Tests can leave processes running after they exit: a helper a test spawned and forgot, or a test binary that was never reaped. Until now cargo-mutants only signalled the child's process group on a timeout, so on a normal exit those processes survived and kept allocating while later mutants were tested, in a window where no cargo phase is running at all. Sweep the group in the process layer, so every phase gets it: once the direct child exits with any status, SIGTERM the group, wait a bounded grace period, then SIGKILL whatever is left. What was reaped goes into the scenario log, and the pids into the debug log, enumerated from /proc on Linux. Windows has no process groups and the job object equivalent is out of scope, so the sweep is a no-op there.
A mutant caught because its tests were killed is indistinguishable, in the counts, from one caught by a failing assertion -- which is exactly what you want to know when diagnosing a run. Carry the process group sweep's findings on each phase result, and render them, with the name of any signal that killed the phase, in parentheses on the outcome line, in the scenario log, and in outcomes.json. Classification is deliberately untouched: this only makes the reason visible.
This was referenced Sep 16, 2026
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Problem
A mutant caught because the kernel killed its tests looks, in the counts, exactly like one caught by a failing assertion — which is the thing you want to know when diagnosing a run.
Solution
sweepfield inoutcomes.json.Testing
Stacked on #648 → #650; only the last commit is new here. Split out of #647 as requested.