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ci(nix): retain Xvfb diagnostics for capture probes #707

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ci(nix): retain Xvfb diagnostics for capture probes
My-Denia Sep 18, 2026
1acfd99
ci(nix): keep the run_cli mapping printable on the errexit path
My-Denia Sep 18, 2026
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59 changes: 58 additions & 1 deletion .github/workflows/nix-build.yml
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Original file line number Diff line number Diff line change
Expand Up @@ -322,9 +322,37 @@ jobs:
# makes the rates comparable across runs; reading them unlabelled is the
# mistake this counter exists to prevent.
RUN_CLI_N=0
# Each invocation gets a fresh Xvfb, allocated by `xvfb-run -a` to a
# display number this script never learns, and when an enumeration
# call hangs (#462) the open question is which allocation it hung
# on. Neither the number nor the server's own output is observable
# today: xvfb-run's default error file is /dev/null. So record both,
# keyed by the invocation counter above. `-e` is xvfb-run's own
# error-file channel -- it appends the Xvfb server's output there
# from the moment the server spawns, which is why an empty file is
# still a valid result. The display is recorded from inside the
# environment xvfb-run actually exported to the command: a shim
# writes $DISPLAY and execs the CLI, leaving its argv, environment
# and post-exec process tree as they were. Both files are written
# before the CLI can hang, so a timeout kill cannot lose them.
XVFB_DIAG=/tmp/xvfb-diag
mkdir -p "$XVFB_DIAG"
run_cli() {
RUN_CLI_N=$((RUN_CLI_N + 1))
timeout --signal=TERM --kill-after=10s "${CLI_TIMEOUT:-120}" xvfb-run -a -s "$XVFB_SCREEN" ./result/bin/openscreen "$@"
local rc=0
# `|| rc=$?`, not a bare call: errexit is live inside the function
# at the one unguarded call site below, and a bare failing timeout
# kills the step before the mapping line gets to print -- the two
# files survive either way, but the line is the part the step log
# keeps. Same shape the guarded callers already use for RC.
timeout --signal=TERM --kill-after=10s "${CLI_TIMEOUT:-120}" \
xvfb-run -a -s "$XVFB_SCREEN" -e "$XVFB_DIAG/run-cli-$RUN_CLI_N.xvfb.log" \
sh -c 'printf "%s\n" "$DISPLAY" >"$1"; shift; exec "$@"' \
xvfb-diag "$XVFB_DIAG/run-cli-$RUN_CLI_N.display" ./result/bin/openscreen "$@" || rc=$?
# The status that reaches the caller must stay the command's own,
# or the HUNG/OK/FAILED accounting above would read the echo's.
echo "run_cli #$RUN_CLI_N: DISPLAY=$(cat "$XVFB_DIAG/run-cli-$RUN_CLI_N.display" 2>/dev/null || echo unknown), Xvfb output in $XVFB_DIAG/run-cli-$RUN_CLI_N.xvfb.log"
return "$rc"
}

SANDBOX=""
Expand Down Expand Up @@ -544,6 +572,20 @@ jobs:
fi
fi

# The allocations the invocations above actually got, in one place:
# most callers redirect run_cli's stdout into per-attempt files, so
# the per-invocation echo above lands there rather than here. An
# invocation number plus these two files is the whole mapping #462
# asks for, and the artifact step after this one keeps the files
# once the runner is gone.
echo "--- Xvfb allocations (run_cli -> display -> server output) ---"
for d in "$XVFB_DIAG"/*.display; do
[ -e "$d" ] || break
n=${d##*/run-cli-}; n=${n%.display}
printf 'run_cli #%s: DISPLAY=%s, server output: run-cli-%s.xvfb.log (%s bytes)\n' \
"$n" "$(cat "$d")" "$n" "$(wc -c <"$XVFB_DIAG/run-cli-$n.xvfb.log" 2>/dev/null || echo 0)"
done

# One verdict, after both questions have been asked. Enumeration being
# flaky must not hide whether export works, which is the whole point of
# having packaged the compositor addon.
Expand All @@ -565,3 +607,18 @@ jobs:
if [ "$EXPORT_OK" -ne 1 ] || [ "$OK" -eq 0 ]; then
exit 1
fi

# The Xvfb allocation files the smoke step records per run_cli
# invocation, and nothing else: #462's open question is below the
# Electron API, so this evidence has to outlive the runner. always(),
# because the run that hangs is exactly the one where the smoke step
# has already failed. Warn rather than error when absent: a job whose
# build died before the smoke step has no allocations to keep.
- name: Upload Xvfb diagnostics
if: always()
uses: actions/upload-artifact@v7
with:
name: xvfb-diagnostics
path: /tmp/xvfb-diag/
if-no-files-found: warn
retention-days: 14
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