Fix clj-kondo#2199: add :syntax check for var names starting or endin…

…g with dot (clj-kondo#2201)

CHANGELOG.md

@@ -20,6 +20,7 @@ For a list of breaking changes, check [here](#breaking-changes).
 ## Unreleased
 
 - [#1804](https://github.com/clj-kondo/clj-kondo/issues/1804): new linter `:self-requiring-namespace`
+- [#2199](https://github.com/clj-kondo/clj-kondo/issues/2199): add `:syntax` check for var names starting or ending with dot (reserved by Clojure)
 - [#2179](https://github.com/clj-kondo/clj-kondo/issues/2179): consider alias-as-object usage in CLJS for :unused-alias linter
 - [#2183](https://github.com/clj-kondo/clj-kondo/issues/2183): respect `:level` in `:discouraged-var` config
 - [#2184](https://github.com/clj-kondo/clj-kondo/issues/2184): Add missing documentation for :single-logical-operand linter

src/clj_kondo/impl/analyzer.clj

@@ -547,7 +547,9 @@
         [name-node & children] (next (:children expr))
         name-node-meta-nodes (:meta name-node)
         name-node (when name-node (meta/lift-meta-content2 ctx name-node))
-        fn-name (:value name-node)
+        _ (utils/handle-ignore ctx name-node)
+        fn-name (some-> (:value name-node)
+                        (with-meta (meta name-node)))
         call (name (symbol-call expr))
         var-leading-meta (meta name-node)
         _ (when (identical? :clj (:lang ctx))

src/clj_kondo/impl/namespace.clj

@@ -149,6 +149,15 @@
        (analysis/reg-var! ctx filename expr-row expr-col
                           ns-sym var-sym
                           metadata))
+     (when (and (or (str/starts-with? var-sym ".")
+                    (str/ends-with? var-sym "."))
+                (and (not= '.. var-sym)
+                     (not (one-of ns-sym [cljs.core clojure.core]))))
+       (findings/reg-finding! ctx (node->line
+                                   filename (let [thing (if (meta var-sym) var-sym expr)]
+                                              thing)
+                                   :syntax
+                                   (str "Symbols starting or ending with dot (.) are reserved by Clojure: " var-sym) )))
      (when-not (:skip-reg-var ctx)
        (swap! namespaces update-in path
               (fn [ns]

test/clj_kondo/main_test.clj

@@ -1416,6 +1416,18 @@ foo/foo ;; this does use the private var
    '({:file "<stdin>", :row 1, :col 11, :level :error, :message "Unparsable libspec: [foo oh-no :as]"})
    (lint! "(require '[foo oh-no :as])" {:linters {:syntax {:level :error}}})))
 
+(deftest varname-syntax-test
+  ;; TODO: linter is triggered twice, why?
+  ;; TODO: clj-kondo/ignore doesn't work yet
+  (assert-submaps2
+   [{:file "<stdin>", :row 2, :col 7, :level :error, :message "Symbols starting or ending with dot (.) are reserved by Clojure: .foo"}
+    {:file "<stdin>", :row 3, :col 7, :level :error, :message "Symbols starting or ending with dot (.) are reserved by Clojure: bar."}]
+   (lint! "
+(defn .foo [])
+(defn bar. [])
+(defn #_:clj-kondo/ignore .dude. [])
+#_:clj-kondo/ignore (defn .dude2 [])" {:linters {:syntax {:level :error}}})))
+
 (deftest call-as-use-test
   (is (empty?
        (lint!