crap4clj — CRAP Metric for Clojure

Computes the CRAP (Change Risk Anti-Pattern) score for every

defn

and

defn-

in a Clojure project. CRAP combines cyclomatic complexity with test coverage to identify functions that are both complex and under-tested.

Setup

Add both a

:cov

alias (Cloverage) and a

:crap

alias to the 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"]}

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"]}

Adjust the

-p

(source path) and

-s

(test path) flags in

:cov

to match your project layout.

Usage

# Analyze all source files under src/
clj -M:crap

# Filter to specific modules
clj -M:crap combat movement

crap4clj automatically deletes stale coverage reports, runs

clj -M:cov

, and then analyzes the results.

Output

A table sorted by CRAP score (worst first):

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

Interpreting Scores

CRAP Score	Meaning
1-5	Clean — low complexity, well tested
5-30	Moderate — consider refactoring or adding tests
30+	Crappy — high complexity with poor coverage

How It Works

1. Deletes old coverage reports and runs Cloverage (

   clj -M:cov

   )
2. Finds all

   .clj

   and

   .cljc

   files under

   src/

3. Extracts

   defn

   /

   defn-

   functions with line ranges
4. Computes cyclomatic complexity (if/when/cond/condp/case/cond->/cond->>/some->/some->>/and/or/loop/catch)
5. Reads Cloverage HTML for per-line form coverage
6. Applies CRAP formula:

   CC² × (1 - cov)³ + CC

7. Sorts by CRAP score descending and prints report