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fix(csharp-ci): install dotnet-coverage per job, not into the shared global tools dir - #41
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…global tools dir Every runner slot on a shared self-hosted host runs as one Unix user and shared ~/.dotnet/tools. A job whose pin differed uninstalled the global dotnet-coverage while another slot's dotnet-coverage merge was running, crashing it with a Microsoft.CodeCoverage.Instrumentation FileNotFoundException (exit 134). Install into $RUNNER_TEMP with --tool-path and prepend it to GITHUB_PATH instead.
monsieurleberre
marked this pull request as ready for review
September 28, 2026 23:42
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Problem
The
Install dotnet-coveragestep incsharp-ci.yamlinstalled the tool globally withdotnet tool install -g. On a self-hosted host that runs several runner slots as the same Unix user, every slot shares one~/.dotnet/tools. Consumers pin different versions throughMicrosoft.Testing.Extensions.CodeCoverage, and since #31 each job uninstalls and reinstalls the global tool whenever its pin differs from the version already there.This was measured on 2026-09-28 on two slots of one host:
22:12:21.8994Z: a job pinned to 18.11.0 loggeddotnet-coverage 18.11.2 installed, want 18.11.0 — reinstallingand uninstalled 18.11.2.22:12:21.9037Z: another repo'sdotnet-coverage mergestep on a different slot, pinned to 18.11.2, crashed with aMicrosoft.CodeCoverage.InstrumentationFileNotFoundException(exit 134).Consumers currently pin at least four different versions (18.9.0 to 18.11.2), so these overlaps are routine.
Fix
scripts/install-dotnet-coverage.shnow installs the pinned version with--tool-path "$RUNNER_TEMP/dotnet-coverage-<version>"and prepends that directory toGITHUB_PATH.RUNNER_TEMPis private to the runner slot and wiped between jobs, which is the same precedent #33 set for go-ci. Because the global tool is never touched, no job can pull a binary out from under another job.GITHUB_PATHentries go ahead of the runner'sPATH, so a stale globaldotnet-coverageleft in~/.dotnet/toolsis shadowed rather than used. The script fails loud ifRUNNER_TEMPorGITHUB_PATHis unset.This needs no change on the runner host.
Verification
test/install-dotnet-coverage_test.shwas rewritten for the new contract. It checks the job-private tool path, theGITHUB_PATHline, a separate path per pin, an install failure leavingGITHUB_PATHuntouched, and a usage error and missingRUNNER_TEMPmaking no dotnet call.dotnet-coverage --versionresolved to it through the emitted path, and adotnet-coverage merge -f coberturaexited 0. A second run in the same job is idempotent.Rollout
All callers use
csharp-ci.yaml@v2, so the fix reaches them only after a maintainer tags a release (v2.4.2) and movesv2. Nothing has been tagged.