:used-underscore-binding reports false positives with clojure.core.match/match

[camsaul]

version

clj-kondo v2023.07.13

macro usage

Yes, clojure.core.match/match

platform

Native version installed via Homebrew on Linux

editor

N/A

problem

If you enable the :used-underscored-binding linter, a form like

(clojure.core.match/match [:name x y]
  [:name _ _]
  "Ok")

triggers a

Used binding is marked as unused: _

warning. This is a a false positive, since _ has a special meaning in clojure.core.match/match. It's not used in the macroexpansion either:

(let [ocr-149912 :name x x y y]
  (try
    (cond (= ocr-149912 :name) "Ok" :else (throw clojure.core.match/backtrack))
    (catch Exception e__46989__auto__
      (if (identical? e__46989__auto__ clojure.core.match/backtrack)
        (throw (java.lang.IllegalArgumentException. (str "No matching clause: " ocr-149912 " " x " " y)))
        (throw e__46989__auto__)))))

repro

(ns repro
  (:require [clojure.core.match :as match]))

(let [x 1 y 2]
  (match/match [:name x y]
    [:name _ _]
    "Ok"))

config

{:linters {:used-underscored-binding {:level :warning}}}

expected behavior

Since this is a part of Clojure core, it would be nice if it worked out of the box. If that's not possible, it would be nice if the :used-underscore-binding linter was configurable and could be disabled inside of specific forms clojure.core.match forms without needing a :clj-kondo/ignore every time you use it

[borkdude]

Thanks, makes sense

[borkdude]

$ clj -M:clj-kondo/dev --lint - --config '{:linters {:used-underscored-binding {:level :warning}}}' <<< "(require '[clojure.core.match]) (declare x y) (clojure.core.match/match [:name x y]
  [:name _ _]
  \"Ok\")"
<stdin>:2:10: warning: Used binding is marked as unused: _