bca07265a4
The metamorphic tests compile the program twice per step — once under `nim ic`, once as the `nim c` reference — which is 100+ compilations for the category, each fanning out a compiler process per module per stage. On a machine short of RAM that swaps, and the symptoms read exactly like a deadlock: processes at 0% CPU, no output, a different test "stuck" every run, and the same compilation finishing in seconds standalone. It is not a deadlock. A `nim ic` parent at 0% CPU is waiting on its children, and the test name does keep changing if you watch long enough. Writing this down because it has now been misdiagnosed as a testament/`nim ic` interaction more than once, by me, before I measured `vm_stat` and `vm.swapusage`. Also records the fan-out caps (`--parallelBuild:N`, `-d:icJobs:N`, `-d:icNoParallel`), that serial mode is what makes per-process diagnostic output readable rather than interleaved, that `testament r` cannot run a multi-step metamorphic file, and that `*_temp.nim` are gitignored scratch rather than tests. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01XEF7FJvUkGKvG9LSGuEaNR
Running tests/ic
./bin/testament --nim:<your compiler> cat ic
The metamorphic tests are expensive, and look hung when they are not
16 of the tests carry #? metamorphic. Each has 3–4 #!STEP directives, and
every step compiles the program twice — once under nim ic, once with
nim c as the reference oracle. That is 100+ full compilations for the
category. Under --ic:on each compilation additionally fans out one backend
process per module per stage, and each of those is a compiler holding its own
module graph (~800MB peak).
A nim ic parent sitting at 0% CPU is normal. It is waiting on its
children. It is not a deadlock, and neither is a metamorphic test that occupies
the runner for many minutes. Before concluding anything is stuck, check that the
test NAME changes over a few minutes — that is the difference between slow and
hung, and it is easy to get wrong.
On a memory-constrained machine the fan-out will swap. The symptoms are exactly
the ones that read as a deadlock: several processes at 0% CPU, no output, a
different test "stuck" on every run, and the same compilation finishing in
seconds when run on its own. Check vm_stat (page-ins per second) and
sysctl vm.swapusage before looking for a bug. This was diagnosed as a
testament/nim ic interaction more than once before anyone measured.
Cap the fan-out to fit the machine — precedence documented at deps.nim's
let parallel:
--parallelBuild:N # standard flag, given meaning under IC
-d:icJobs:N # same cap, legacy define
-d:icNoParallel # serial, and non-interleaved child output
Serial output matters for a second reason: the parallel backend processes share
one stderr, so any per-process diagnostic printing (NIM_IC_BNODE_GRIND,
-d:icCanRaiseLog) interleaves and produces torn lines. Either use
-d:icNoParallel or parse defensively and count what you dropped.
Running a single test
testament r tests/ic/<file>.nim works for the ordinary tests. It does NOT work
for the metamorphic ones — the multi-step files carry several discard """
spec blocks and the single-test path rejects them with "duplicate specStart".
Those only run through cat ic.
Files matching tests/ic/*_temp.nim are ignored by git (see .gitignore) and
are scratch, not tests: several import helper modules that do not exist and fail
for that reason alone.