CRAP (Change Risk Anti-Pattern) metric for Clojure projects.

Combines cyclomatic complexity with test coverage to identify functions that are both complex and under-tested — the riskiest code to change.

Add to your project's deps.edn:

:cov  {:extra-deps {cloverage/cloverage {:mvn/version "1.2.4"}}
       :main-opts ["-m" "speclj.cloverage" "--" "-p" "src" "-s" "spec"]}
:crap {:extra-deps {io.github.unclebob/crap4clj
                     {:git/url "https://github.com/unclebob/crap4clj"
                      :git/sha "<current-sha>"}}
       :main-opts ["-m" "crap4clj.core"]}

Run:

clj -M:crap    # deletes old coverage, runs Cloverage, analyzes

crap4clj automatically deletes stale coverage reports, runs clj -M:cov --lcov (falling back to clj -M:cov if needed), and then analyzes the results. Your project must have a :cov alias configured with Cloverage.

The example above uses speclj.cloverage as the runner. For clojure.test projects, use cloverage.coverage instead:

:cov  {:extra-deps {cloverage/cloverage {:mvn/version "1.2.4"}}
       :main-opts ["-m" "cloverage.coverage" "-p" "src" "-s" "test"]}

CRAP Report
===========
Function                       Namespace                            CC   Cov%     CRAP
-------------------------------------------------------------------------------------
complex-fn                     my.namespace                         12   45.0%    130.2
simple-fn                      my.namespace                          1  100.0%      1.0

Pass module name fragments as arguments to filter:

clj -M:crap combat movement    # only files matching "combat" or "movement"

crap4clj uses coverage in this order:

1. per-source-file HTML (target/coverage/...<source>.html)
2. target/coverage/lcov.info (file-accurate line coverage)
3. namespace HTML fallback (.../<namespace>.clj.html or .cljc.html)

For split-file namespace patterns (multiple files loaded into one namespace via in-ns + load), LCOV is the reliable option for per-function scoring because it preserves physical source file paths.

If only namespace fallback HTML is available, crap4clj uses defn name matching and does not reuse mismatched line ranges. Unmatched functions are reported as N/A (indeterminate) and a warning is printed to stderr.

Namespace fallback lookup checks:

1. per-file path (for example target/coverage/foo/bar.clj.html)
2. namespace .clj path (for example target/coverage/foo/bar.clj.html)
3. namespace .cljc path (for example target/coverage/foo/bar.cljc.html)

To enable LCOV in your :cov alias, include Cloverage's --lcov output option so target/coverage/lcov.info is generated.

CRAP(fn) = CC² × (1 - coverage)³ + CC

• CC = cyclomatic complexity (decision points + 1)
• coverage = fraction of forms covered by tests (from Cloverage)

Decision points that increase cyclomatic complexity:

• if, if-not, if-let, if-some
• when, when-not, when-let, when-some, when-first
• and, or
• loop, catch
• Each clause in cond, condp, case, cond->, cond->>
• Each step in some->, some->>

crap4clj includes a SKILL.md for use as a Claude Code skill. Add it to your project's .claude/settings.json:

{
  "skills": [
    "https://github.com/unclebob/crap4clj/blob/master/SKILL.md"
  ]
}

Then ask Claude Code for a "CRAP report" and it will know how to set up and run the tool.

clj -M:spec    # run tests
clj -M:crap    # run on own source

Copyright (c) Robert C. Martin. All rights reserved.