CRAP gate

CRAP = CC² × (1 − coverage)³ + CC per function, where CC is cyclomatic complexity. Complex code without tests scores high. The gate stops new debt and makes touched hotspots shrink. The scorer is Crapper (make crap), and the rules live in scripts/crap/policy.ts with thresholds in scripts/crap/thresholds.ts.

Where reports come from

• make crap-check (or bun scripts/crap/check.ts --base <ref>): the files changed since the merge-base with origin/main, in the working tree. Exit 0 pass, 1 violations, 2 tool error.
• The agent hook: after a git commit or git push bash call, Xum appends the report to the tool result (warn mode). In block mode the hook stops the command before it runs. scripts/crap/agent-gate.sh holds the mode. A bash call that exits non-zero gets no report, even when a git commit in it succeeded before a later command failed. Run make crap-check then.
• CI: the Quality / CRAP job summary and its annotations. It is informational.

Without coverage, scores are CC. With --coverage <lcov>, scores are CRAP.

Reading a finding

VIOLATION floor-cc     src/x.ts:10-25 route: CC 30 -> 31 (head CRAP 31 above 30: must not grow)

• The growth line is CRAP 30 with coverage, CC 10 without. An existing function may grow while its head stays at or below the line. Above it, CC and CRAP must not grow. A reduction always passes, at any size, so a hotspot can shrink one step at a time.
• The new-function limit is CRAP 15 with coverage and CC 8 without.
• crap-tax is always a warning: a comment or one-line fix in a hotspot passes, with a nudge to shrink it.
• When the changed files' total CC drops, new-function findings are warnings (net-extraction relief): splitting a hotspot is allowed even if one piece is still above the limit.
• Moving a step out of a function raises the total CC by 1. Such a move is also a warning (move relief) when the kept functions lost at least as much CC as the new functions hold decision points (CC − 1 each), and the new function is at most CC 20. A rename gets no relief.
• With coverage, both reliefs need the new function at CRAP 30 or less. An untested piece above that stays a violation: test it or shrink it.
• The function name and line range are in the report. Identity is path::namespace::name, so renaming a function makes it new.

The two repairs

1. Shrink the function. Extract pure logic into a named function with its own tests. In React, move state and effects into a named hook, or a part of the tree into a child component, each with its own tests.
2. Test it. Coverage lowers CRAP, so this repairs only reports with coverage (--coverage <lcov>, the CI job's new-function findings). The hook and a plain make crap-check score CC alone: tests cannot clear their floor-cc or new-function findings, so shrink the function instead (or keep it at CC 10 or less). A test must assert behavior that would fail if the code broke.

Anti-gaming rules

Never do these to lower a score:

• Replace ?. or ?? with !, as casts, or other unchecked assumptions. Crapper counts ?. and ?? as decisions, but removing a real check hides a bug instead of removing complexity.
• Add tests without meaningful assertions (coverage probes, snapshot-only or expect(true) tests).
• Split code into one-caller helpers that only pass state through. The CC moves, the complexity stays, and the reader pays twice.
• Move or rename a function only to reset its history.

Crap-Debt

When a violation cannot be fixed in this change (a hotfix, a generated file), add a Crap-Debt: <reason> trailer to the commit, or the crap-debt label to the PR in CI. Every violation becomes a warning, and the report lists each use. Name the follow-up in the reason.