Fix #1842: Add exclude to :used-underscored-binding (#1843)

Co-authored-by: staifa <frantisek.stainer@flexiana.com>
Co-authored-by: Michiel Borkent <michielborkent@gmail.com>

CHANGELOG.md

@@ -4,6 +4,7 @@ For a list of breaking changes, check [here](#breaking-changes).
 
 ## Unreleased
 
+- [#1842](https://github.com/clj-kondo/clj-kondo/issues/1842): Add exclude to `:used-underscored-binding` ([@staifa](https://github.com/staifa))
 - [#1840](https://github.com/clj-kondo/clj-kondo/issues/1840): Fix warning in `.cljs` and `.cljc` for `:aliased-namespace-symbol` in interop calls. ([@NoahTheDuke](https://github.com/NoahTheDuke))
 
 ## 2022.10.14

doc/linters.md

@@ -1181,6 +1181,22 @@ These warnings can be enabled by setting the level to `:warning` or
 {:linters {:used-underscored-binding {:level :warning}}}
 ```
 
+To suppress the above warning:
+
+``` clojure
+{:linters {:used-underscored-binding {:level :warning
+                                      :exclude [_x]}}}
+```
+
+A regex is also supported:
+
+``` clojure
+{:linters {:used-underscored-binding {:level :warning
+                                      :exclude ["^_x.*$"]}}}
+```
+
+This will exclude all bindings starting with `_x`.
+
 ### Unknown :require option
 
 *Keyword:* `:unknown-require-option`

src/clj_kondo/impl/config.clj

@@ -419,6 +419,19 @@
       (let [excluded (delayed-cfg config)]
         (contains? excluded sym-ns)))))
 
+(def used-underscored-binding-excluded?
+  (let [delayed-cfg (fn [config]
+                      (let [excluded (get-in config [:linters :used-underscored-binding :exclude])
+                            syms (set (filter symbol? excluded))
+                            regexes (map re-pattern (filter string? excluded))]
+                        {:syms syms :regexes regexes}))
+        delayed-cfg (memoize delayed-cfg)]
+    (fn [config binding-sym]
+      (let [{:keys [:syms :regexes]} (delayed-cfg config)]
+        (or (contains? syms binding-sym)
+            (let [binding-str (str binding-sym)]
+              (boolean (some #(re-find % binding-str) regexes))))))))
+
 (defn ns-group* [config ns-name filename]
   (or (some (fn [{:keys [pattern
                          filename-pattern

src/clj_kondo/impl/linters.clj

@@ -577,7 +577,9 @@
                                (remove :clj-kondo/mark-used)
                                (remove :clj-kondo.impl/generated)
                                (filter #(str/starts-with? (str (:name %)) "_")))
-                              (:used-bindings ns))]
+                              (:used-bindings ns))
+                :when (not (config/used-underscored-binding-excluded? (:config ctx)
+                                                                      (:name binding)))]
           (findings/reg-finding!
            ctx
            {:type :used-underscored-binding

test/clj_kondo/bindings_test.clj

@@ -354,6 +354,15 @@
       :message "Used binding is marked as unused: _"})
    (lint! "(let [_ 1] _)"
           '{:linters {:used-underscored-binding {:level :warning}}}))
+  (assert-submaps
+   '({:file "<stdin>",
+      :row 1,
+      :col 7,
+      :level :warning,
+      :message "Used binding is marked as unused: _x"})
+   (lint! "(let [_x 0 {:keys [a _bar] :as _c} v]  [a _bar _x _c])"
+          '{:linters {:used-underscored-binding {:level :warning
+                                                 :exclude [_c "^_b.*$"]}}}))
   (is (empty?  (lint! "(let [_x 0 {:keys [a b] :as _c} v]  [a b _x _c])"
                       '{:linters {:used-underscored-binding {:level :off}}})))
   (is (empty? (lint! "(doto (Object.) (.method))"