Clj-kondo: a linter for Clojure code that sparks joy @ ClojuTRE 2019

Clj-kondo is a linter for Clojure code that sparks joy. It analyzes your code without evaluating it and detects arity errors, redundant expressions, unused requires, missing test assertions and more. It provides fast editor feedback because it runs instantly as a native binary, not depending on a REPL in a JVM. In this talk we will see what it can do, how it is implemented and how it compares to other Clojure linters.

Transcript

1. Michiel Borkent
   
   @borkdude
   
   

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2. Word origins
   

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3. Clojure linters
   Linter Focus CLJS? Macroexpand? Execution
   Eastwood General No core + user JVM
   Kibit Idioms No No JVM
   Joker General Yes core Go native
   Cljfmt Formatting Yes n/a JVM
   How to ns How to ns Yes n/a Clojure JVM
   Clj-kondo General Yes core GraalVM native / JVM
   

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4. Clj-kondo origin story
   • I've been a happy joker user since 2017
   
   • Wanted to add a feature:
   
   (defn foo [x] (def x 1))
   • Joker is written in Go, can it be done in Clojure?
   • Tried with Clojure on GraalVM (native = fast startup like joker)
   
   • Success with rewrite-clj which is based on tools.reader
   
   • Writing more linting features was too much fun!
   

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5. Invalid code is still data
   

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8. Arity errors
   

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11. REPL state
    

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12. REPL state
    $ clj-kondo --lint src
    | grep "unresolved symbol c"
    src/dre/analytics/authors.clj:585:41:
    info: unresolved symbol c
    

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13. Unused let and fn bindings
    

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14. Unresolved symbols
    

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15. Redundant let + do
    

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16. Missing test assertion
    

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17. Style: don't refer :all
    

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18. Ns form cleanup
    

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19. Ns form cleanup
    

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20. Type checking
    

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21. Editor support
    

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22. .clj-kondo
    • .clj-kondo/config.edn
    
    • Shared configuration, intended for version control
    
    • .clj-kondo/.cache
    
    • Automatically updated when changing code in editor
    
    • Contains arity and other info about linted code
    
    • Allows linter to reason about multiple namespaces
    
    • Populate with lib info: clj-kondo --lint $(clj -Spath)
    

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23. Config
    from
    manifold.deferred
    Clj-kondo doesn't know how to lint this macro
    

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24. Config
    

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25. Analysis export
    

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26. Who uses clj-kondo?
    Github #438
    Add your company to the list:
    

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27. Thank you
    https://github.com/borkdude/clj-kondo
    

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