CRAP scores for Clojure, Java, Go, TypeScript, Rust, and Python. One run detects the language of each source file, applies that language's complexity and coverage rules, and writes the snapshot uml-viewer already reads.

The formula is the one from crap4clj, crap4java, and crap4go:

CRAP = CC² × (1 − coverage)³ + CC

CC is cyclomatic complexity. coverage is the fraction of the function exercised by tests. A score of 1–5 is low risk, 5–30 is worth a look, and 30+ is complex and under-tested.

./crapper

The first run creates .venv and installs the tool. From a project root it walks the tree, skips test, spec, vendor, node_modules, and target, and writes two results:

• a table on stdout, worst score first
• .metrics/crap.edn, replaced on every successful analysis

./crapper --no-coverage                  # complexity only; coverage is N/A
./crapper --use-existing-coverage        # read reports already on disk
./crapper src/demo/core.clj src/ui       # these files and trees
./crapper --changed                      # git additions and edits
./crapper combat                         # path fragment, same idea as crap4clj
./crapper --threshold 30                 # exit 2 when the worst score is higher

.metrics/crap.edn has the same shape crap4clj writes:

{:entries [{:name "place"
            :namespace "demo.Board"
            :complexity 3
            :coverage 75.0
            :crap 3.1}]}

uml-viewer groups entries by :namespace and joins each operation on :name. nil coverage is what --no-coverage writes: complexity only, and CRAP is nil too. A function the coverage report does not mention scores 0%.

Rename or move is a new entry. There is no identity matching across runs.

Clojure follows crap4clj: if / when and their variants, and, or, loop, catch, and each clause of cond, condp, case, cond->, cond->>, some->, and some->>. Coverage prefers Cloverage's per-line form counts and falls back to LCOV.

Java follows crap4java: if, loops, catch, ?:, each switch label, and && / ||. Constructors and methods inside anonymous classes are omitted. Coverage is JaCoCo's INSTRUCTION counter.

Go follows crap4go: if, for, range, each switch and select clause, and && / ||. Coverage is go test -coverprofile.

TypeScript, TSX, and JavaScript (.js, .jsx, .mjs, .cjs) use the same structural decisions as Java, including && inside JSX, plus ?? and ?.. Top-level functions, class methods, and top-level arrow functions are entries. An inline Express callback — .get, .post, .put, .patch, .delete, .head, .options, .all, .use, and .route(path).get(...) — is its own entry, named GET /users. A second callback on that same route is GET /users#2. Its decisions are not also charged to the enclosing function. Other nested callbacks stay inside the enclosing function. Coverage is LCOV. When the report has branch records (BRDA) inside a function, the score uses those branches; a function with no branches uses line hits. A coverage script is used as-is. A Vitest project runs vitest --coverage (installing @vitest/coverage-v8 into node_modules when it is missing, without editing package.json). Other test scripts are wrapped in c8.

Rust counts if, loops, each match arm, ?, and && / ||. mod tests is skipped. Coverage is LCOV from cargo llvm-cov or cargo tarpaulin, run in the nearest directory that contains Cargo.toml. When neither tool is installed, the run installs cargo-llvm-cov.

Python counts if, elif, for, while, except, each match case, a comprehension filter, a conditional expression, and each and / or. Nested functions stay inside the enclosing function. Coverage is LCOV from coverage.py, running pytest when the project uses it and unittest otherwise. coverage and pytest are installed into the project's interpreter when they are missing.

By default a run deletes the previous report for each language it is about to measure and regenerates it:

A missing tool or a failed test run scores that language at 0% and still writes the snapshot. Pass --coverage-command to replace those defaults with one command of your own. --no-coverage is the run that leaves coverage and CRAP as N/A.

python3 -m venv .venv
.venv/bin/pip install -e '.[dev]'
.venv/bin/pytest