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split_jobs misses a /tmp dependency reached through a shell variable

The gap

split_jobs cuts a recipe into independently-scheduled jobs, then merges a producer with its consumer by union-find over shared literal /tmp paths (tmp_re). A consumer that names its artifact through a shell variable exposes no such token:

for t in tkinter_facade:test_nilpy_tkinter26 ... ; do \
  src=$${t%%:*}; bin=$${t##*:}; \
  timeout 120 xvfb-run -a $(TESTTMP)/$$bin > ...

make -n yields /tmp/$bin, so the job's token set was ['/tmp/test_nilpy_tkcb26'] — its own output only — while it RAN three binaries. No merge, no ordering, and the job failed with test_nilpy_tkinter26: not found whenever it did not happen to follow its producers in the shared per-run scratch.

Why this is a class, not an instance

The splitter's own comments already record two members, both solved with synthetic tokens: a .so located by soname, and a bare-/tmp LD_LIBRARY_PATH consumer. The comment's own phrase — "invisible to a filename scan" — describes this third member exactly. Each was found by a red job rather than at authoring time.

Suggested fix (T's call)

A lint over the job table rather than more token synthesis: flag any job whose text reaches /tmp through a variable — $(TESTTMP)/$$<var>, /tmp/$… in make -n output — and report it as an unmergeable dependency at authoring time. Token synthesis has now been extended twice per discovered instance; a lint catches the next spelling without predicting it, which is the property the previous two fixes lacked.

Cheap corroborating signal: a job that runs a binary it does not compile is suspicious on its own, independent of how the path is spelled.

Not to be confused with

bug-t-makefile-inner-timeouts-are-invisible-to-testmgrs-contention-logic (T, p55). That gap is real and separate — a timeout inside a make recipe genuinely cannot participate in testmgr's contention logic. It was the leading hypothesis for regression-test-nilpy-callbacks and measurement falsified it there (0.14 s against a 120 s ceiling); it should keep standing on its own evidence (crtl_exp2), with that job removed from its supporting set.

OPERATIONAL HEADS-UP FOR THE WATCHER — a selector id goes silent, by design

Relayed by the coordinator, because it changes a key twatch holds history under and the failure mode is misreading a silence.

As of 9f11b405d, the three tk jobs are merged into ONE ordered job whose first source is examples/tk/tkinter_facade.npy. Consequence:

test-nilpy#src:examples/tk/callbacks.npy   →  no longer selects anything

That id is this repo's regression-test-nilpy-callbacks key and the one the open- regression list has been carrying. Its disappearance is the fix landing, not a job vanishing or a suite silently losing coverage. Coverage is unchanged — the same three programs are compiled and run; they are now one job instead of three unordered ones, and the merged job compiles all three binaries it runs.

Verified statically by the coordinator rather than by running the tier: the loop's item list now spells each binary by full path, tkinter_facade first, so union-find has the literal tokens it needs and the merged job's first source is the facade.

Two things follow for T:

  1. When reconciling open regressions against a new sweep, treat test-nilpy#src:examples/tk/callbacks.npy as closed by rename, not as an untested job. If the reconciliation is automatic, this is the case that needs a human-visible note rather than a silent drop.
  2. Any historical red/green series held under the old id belongs to the same coverage and should be carried onto the merged job's id if that is cheap. If it is not cheap, say so rather than losing it quietly — the history is what makes the next bisect cheap.

A note on the lint suggestion above

The coordinator endorses it. Both earlier instances of this class (a .so found by soname, a bare-/tmp LD_LIBRARY_PATH consumer) were closed by adding one synthetic token per discovered spelling, and this is the third spelling. A per-spelling token predicts the next one; a lint over the job table does not have to. The two checks worth having are the ones this bug would have tripped on: flag any job that reaches /tmp through a variable, and flag any job that RUNS a binary it does not COMPILE.

That is the normalise-don't-special-case call, and it also explains why the fix here landed in the Makefile rather than in testmgr: the tool cannot resolve shell variables in general, so the recipe stating its own paths is the normalising fix rather than a second mechanism. The lint is what makes the recipe's obligation checkable.

Resolved 2026-08-19 by Track T (plexus-T) — the lint is shipped and enforced

tools/testmgr_tmp_var_devtest.py, picked up automatically by the new make tools-devtest target (limited + full tiers), so it runs rather than waiting to be remembered.

It flags /tmp/$ in executable recipe text — the spelling tmp_re cannot match at all, since $ is outside its character class, so the token is not merely wrong but absent. That is the property both mechanisms rest on: union-find merging (a producer with its consumer) and privatization (concurrent runs not sharing a file). This is why the lint is the right shape and a fourth synthetic token would not be: it does not have to predict the next spelling.

Comment lines are excluded, and that was not cosmetic. The first draft flagged the very recipe that FIXED the callbacks case, because its explanatory comment quotes the old /tmp/$bin spelling. A guard that trips on prose gets muted, and a muted guard is not a guard — the rule tstate_reader_devtest states, hit here within a minute of writing the check.

It found a live instance on its first run

[[bug-n-tk-got-files-are-invisible-to-testmgr-privatization]] — in the same recipe whose earlier fix was believed complete. 9f11b405d spelled the BINARIES by full path, which fixed the merge and closed the callbacks red. The output capture files are still $(TESTTMP)/$$src.got, so the three .got files are never privatized and two concurrent runs share them. The merge half is fixed; the privatization half was never in scope and nobody noticed, which is precisely this ticket's thesis about per-spelling fixes.

Filed for the owning lane rather than fixed here (T owns the tool, never the recipe), and carried in the devtest's KNOWN list so the guard stays green without the allowlist telling a lie — it prints the open instance on every run, and prints a "remove it from KNOWN and close its ticket" line the moment the recipe stops matching.

The second suggested check is split out, not silently dropped

"A job that RUNS a binary it does not COMPILE" is prototyped and deliberately not shipped: it yields 5-7 candidates depending on how recipe lines are segmented, and segmenting made it WORSE, which is the tell that the rule is not yet well-defined. Candidates and the reason are recorded in [[chore-t-lint-a-job-that-runs-a-binary-it-does-not-compile]] (p30) so the next attempt starts from data. The parent ticket calls it a "cheap corroborating signal"; the enforced half is the one that covers the spelling that has bitten twice.

On the operational heads-up above

test-nilpy#src:examples/tk/callbacks.npy going silent is confirmed here as the fix landing: the merged job's first source is examples/tk/tkinter_facade.npy, which is the selector the job now carries, and the same three programs are still compiled and run.

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