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A deliberate exit status never reaches the process: rbgo -e 'exit 3' exits 0 #676
Description
rbgo -e 'exit 3' exits 0, where MRI exits 3. Every spelling of a
deliberate non-zero exit is lost, so rbgo cannot signal failure to a shell,
a Makefile or a CI step.
Measured against MRI 4.0.5 (ruby 4.0.5 (2026-05-20) +PRISM [arm64-darwin25])
on the branch of #675:
| program | MRI status | rbgo status |
|---|---|---|
exit 3 |
3 | 0 |
exit false |
1 | 0 |
exit!(4) |
4 | 0 |
abort "boom" |
1 | 0 |
raise "x" |
1 | 1 (correct) |
exit 0 |
0 | 0 (correct) |
Process.exit(5) |
5 | 1, NoMethodError (see below) |
Process.exit!(6) |
6 | 1, NoMethodError (see below) |
The VM half is already correct — only the front-end's last step is missing
This is not a SystemExit implementation gap. Everything inside the VM behaves
as MRI does:
$ rbgo -e 'begin; exit 3; rescue SystemExit => e; puts "status=#{e.status} success=#{e.success?}"; end'
status=3 success=false # identical to MRI
$ rbgo -e 'at_exit { puts "atexit ran" }; exit 3'
atexit ran # identical to MRI; only the status differs
$ rbgo -e 'begin; exit 3; ensure; puts "ensure ran"; end'
ensure ran # identical to MRI; only the status differs
SystemExit is raised, carries the right status and success?, is rescuable,
and at_exit and ensure both run. The defect is at exactly one boundary: the
CLI never translates a terminal SystemExit into the process's exit code. MRI
does this in main() → ruby_run_node → ruby_cleanup, which calls
error_handle and returns ex from the SystemExit's status
(eval.c/ruby.c, tag v3_4_0).
abort follows from the same cause: rb_f_abort raises SystemExit with
status 1 (process.c).
Second, separate defect: Process.exit is private
MRI declares exit, exit! and abort as module functions on Process
(Init_process: rb_define_module_function(rb_mProcess, "exit", ...)), so
Process.exit(5) is public. rbgo only has the private Kernel copies, so the
qualified spelling raises NoMethodError. Worth fixing together, but it is a
different cause from the status loss.
What this does NOT affect
The ruby/spec ratchet is unaffected: scripts/conformance/rubyspec/run.sh
scores each file by parsing the RBGO_RESULT pass=… fail=… line the shim
prints, not by reading the child's exit status. I checked this before filing,
because a harness that read the status would have been scoring every file as a
success. Every conformance total measured so far stands.
Found while verifying which stream Kernel#abort's message reaches, in #667.
Activity
tannevaled commentedon Sep 26, 2026
Correction to this issue's central claim, which was mine and was wrong.
I wrote: "This is not a
SystemExitimplementation gap. Everything inside the VMbehaves as MRI does … The defect is at exactly one boundary: the CLI never
translates a terminal
SystemExitinto the process's exit code."That localisation is false.
internal/vm/vm.go:1131deliberately discards it,and says so:
So no front-end change alone could have fixed it. The status was never handed out
of the VM to be translated.
Why I got it wrong, since the reasoning error is the reusable part. I probed
what Ruby code can observe:
rescue SystemExitsees the right status,at_exitruns,
ensureruns. All three are true. I inferred "everything inside is correct,therefore only the last step outside is missing" — and that does not follow. Those
probes establish that the exception is raised and unwinds correctly; they say
nothing about whether its value survives the VM's own boundary. Observability
from inside the language is not evidence about where a value is dropped on the way
out.
The comment above is also worth reading as its own lesson: the discard was a
correct decision for the problem it was written for (a CLI ending in
exitshouldnot print a backtrace) and became wrong when the exit status started to matter.
The premise moved; the code did not.
Fixed in #693, which had to touch
vm.gofor exactly this reason and flagged it asoutside its granted file set.
Two further corrections from that work, both to figures in this issue's neighbour
#691:
quoted from three runs;
Process.exitbeing private was right, and the fix makes all nine spellingsbyte-identical to MRI 4.0.5 across 20 runs each.
signal+exit: a self-directed signal becomes a Ruby exception, and a d…