Fix clj-kondo#1954: new :uninitialized-var linter

CHANGELOG.md

@@ -19,6 +19,7 @@ For a list of breaking changes, check [here](#breaking-changes).
 
 - [#1976](https://github.com/clj-kondo/clj-kondo/issues/1976): warn about using multiple bindings after varargs (`&`) symbol in fn syntax
 - Add arity checks for code `def`
+- [#1954](https://github.com/clj-kondo/clj-kondo/issues/1954): new `:uninitialized-var` linter. See [docs]().
 - [#1971](https://github.com/clj-kondo/clj-kondo/issues/1971): false positive `:redundant-fn-wrapper` with syntax-quoted body
 - [#1984](https://github.com/clj-kondo/clj-kondo/issues/1984): lint java constructor calls as unresolved-symbol when using dot notation.
 - [#1970](https://github.com/clj-kondo/clj-kondo/issues/1970): `:dynamic-var-not-earmuffed` should be opt-in

doc/linters.md

@@ -1215,6 +1215,18 @@ You can add or override type annotations. See
 
 *Example message:* `j is not bound in this destructuring form`.
 
+### Uninitialized var
+
+*Keyword:* `:uninitialized-var`
+
+*Description:* warn on var without initial value
+
+*Default level:* `:off` (will become `:warning` in the future)
+
+*Example trigger:* `(def x)`
+
+*Example message:* `Uninitialized var`
+
 ### Unused binding
 
 *Keyword:* `:unused-binding`.

src/clj_kondo/impl/analyzer.clj

@@ -1101,6 +1101,8 @@
         core-def? (one-of (first (:callstack ctx)) [[clojure.core def] [cljs.core def]])
         _ (when (and core-def? children)
             (findings/reg-finding! ctx (utils/node->line (:filename ctx) expr :invalid-arity "Too many arguments to def")))
+        _ (when-not child
+            (findings/reg-finding! ctx (utils/node->line (:filename ctx) expr :uninitialized-var "Uninitialized var")))
         [extra-meta extra-meta-node children] (if (and defmulti?
                                                        child
                                                        (identical? :map (utils/tag child)))

src/clj_kondo/impl/config.clj

@@ -141,7 +141,9 @@
               :dynamic-var-not-earmuffed {:level :off}
               :earmuffed-var-not-dynamic {:level :warning}
               :duplicate-field {:level :error}
-              :aliased-namespace-var-usage {:level :warning}}
+              :aliased-namespace-var-usage {:level :warning}
+              :uninitialized-var {;; will be :warning in a future release
+                                  :level :off}}
     ;; :hooks {:macroexpand ... :analyze-call ...}
     :lint-as {cats.core/->= clojure.core/->
               cats.core/->>= clojure.core/->>

test/clj_kondo/uninitialized_var_test.clj

@@ -0,0 +1,13 @@
+(ns clj-kondo.uninitialized-var-test
+  (:require
+   [clj-kondo.test-utils :as tu :refer [lint! assert-submaps2]]
+   [clojure.test :as t :refer [deftest is testing]]))
+
+(deftest uninitialized-var-test
+  (assert-submaps2
+   [{:row 1,
+     :col 1,
+     :level :warning,
+     :message "Uninitialized var"}]
+   (lint! "(def x)" {:linters {:uninitialized-var {:level :warning}}})))
+