Add lint/no-op-assignment

Author: NoahTheDuke

CHANGELOG.md

@@ -11,6 +11,7 @@ This changelog is loose. Versions are not semantic, they are incremental. Splint
 - `lint/no-catch`: Require `(try)` calls to have at least 1 `catch` (or `finally`) clause. Supports two styles: `:accept-finally` and `:only-catch`. `:accept-finally` will count a `finally` clause and not raise a warning, while `:only-catch` requires all `try` calls to have a `catch` clause.
 - `lint/catch-throwable`: Prefer specific Exceptions and Errors over `(catch Throwable t ...)`.
 - `lint/identical-branches`: Checks for identical branches of `if` and `cond` forms: `(if (pred) foo foo)`, `(cond (pred1) foo (pred2) foo)`. In `cond` branches, only checks consecutive branches as order of checks might be important otherwise.
+- `lint/no-op-assignment`: Avoid writing `(let [foo foo] ...)` or similar. No need to assign a variable to itself.
 
 ### Added
 

docs/rules/lint.md

@@ -12,6 +12,7 @@
 - [lint/dot-obj-method](#lintdot-obj-method)
 - [lint/duplicate-case-test](#lintduplicate-case-test)
 - [lint/duplicate-field-name](#lintduplicate-field-name)
+- [lint/existing-constant](#lintexisting-constant)
 - [lint/fn-wrapper](#lintfn-wrapper)
 - [lint/identical-branches](#lintidentical-branches)
 - [lint/if-else-nil](#lintif-else-nil)
@@ -30,6 +31,7 @@
 - [lint/misplaced-type-hint](#lintmisplaced-type-hint)
 - [lint/missing-body-in-when](#lintmissing-body-in-when)
 - [lint/no-catch](#lintno-catch)
+- [lint/no-op-assignment](#lintno-op-assignment)
 - [lint/not-empty?](#lintnot-empty)
 - [lint/prefer-method-values](#lintprefer-method-values)
 - [lint/prefer-require-over-use](#lintprefer-require-over-use)
@@ -288,6 +290,30 @@ with the same name, but it's good to catch these things early too.
 
 ---
 
+## lint/existing-constant
+
+| Enabled by default | Safe | Autocorrect | Version Added | Version Updated |
+| ------------------ | ---- | ----------- | ------------- | --------------- |
+| true               | true | false       | <<next>>      | <<next>>        |
+
+**NOTE:** Requires Clojure version 1.11.0.
+
+Java has `PI` and `E` constants built-in, and `clojure.math` exposes them directly. Better to use them instead of poorly approximating them with vars.
+
+### Examples
+
+```clojure
+; avoid
+(def pi 3.14)
+(def e 2.718)
+
+; prefer
+clojure.math/PI
+clojure.math/E
+```
+
+---
+
 ## lint/fn-wrapper
 
 | Enabled by default | Safe  | Autocorrect | Version Added | Version Updated |
@@ -757,6 +783,24 @@ With the default style `:accept-finally`, both `catch` and `finally` clauses are
 
 ---
 
+## lint/no-op-assignment
+
+| Enabled by default | Safe | Autocorrect | Version Added | Version Updated |
+| ------------------ | ---- | ----------- | ------------- | --------------- |
+| true               | true | false       | <<next>>      | <<next>>        |
+
+If the bind is a symbol and the expr is the same symbol, just use the expr directly. (Otherwise, indicates a potential bug.)
+
+### Examples
+
+```clojure
+; avoid
+(let [foo foo]
+  ...)
+```
+
+---
+
 ## lint/not-empty?
 
 | Enabled by default | Safe | Autocorrect | Version Added | Version Updated |

resources/config/default.edn

@@ -201,6 +201,12 @@
   :chosen-style :accept-finally
   :supported-styles [:accept-finally :only-catch]}
 
+ lint/no-op-assignment
+ {:description "Don't bind a symbol to the same symbol."
+  :enabled true
+  :added "<<next>>"
+  :updated "<<next>>"}
+
  lint/not-empty?
  {:description "Looks for `(not (empty?))` which matters for nil-punning."
   :enabled true

src/noahtheduke/splint.clj

@@ -46,6 +46,7 @@
    noahtheduke.splint.rules.lint.misplaced-type-hint
    noahtheduke.splint.rules.lint.missing-body-in-when
    noahtheduke.splint.rules.lint.no-catch
+   noahtheduke.splint.rules.lint.no-op-assignment
    noahtheduke.splint.rules.lint.not-empty
    noahtheduke.splint.rules.lint.prefer-method-values
    noahtheduke.splint.rules.lint.prefer-require-over-use

src/noahtheduke/splint/rules/lint/no_op_assignment.clj

@@ -0,0 +1,30 @@
+; This Source Code Form is subject to the terms of the Mozilla Public
+; License, v. 2.0. If a copy of the MPL was not distributed with this
+; file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+(ns ^:no-doc noahtheduke.splint.rules.lint.no-op-assignment
+  (:require
+   [noahtheduke.splint.diagnostic :refer [->diagnostic]]
+   [noahtheduke.splint.rules :refer [defrule]]))
+
+(set! *warn-on-reflection* true)
+
+(defrule lint/no-op-assignment
+  "If the bind is a symbol and the expr is the same symbol, just use the expr directly. (Otherwise, indicates a potential bug.)
+
+  @examples
+
+  ; avoid
+  (let [foo foo]
+    ...)
+  "
+  {:pattern '(let [?+bindings] ?*_)
+   :on-match (fn [ctx rule form {:syms [?bindings]}]
+               (when (even? (count ?bindings))
+                 (for [[bind expr] (partition 2 ?bindings)
+                       :when (and (symbol? bind)
+                               (= bind expr)
+                               (not (:splint/reader-cond (meta expr))))
+                       :let [new-form (with-meta (list bind expr)
+                                        (meta bind))]]
+                   (->diagnostic ctx rule new-form {:message "Avoid no-op assignment."}))))})

test/noahtheduke/splint/clj_kondo_test.clj

@@ -37,6 +37,7 @@
     lint/misplaced-type-hint 10
     lint/missing-body-in-when 2
     lint/no-catch 1
+    lint/no-op-assignment 2
     lint/prefer-require-over-use 4
     lint/redundant-str-call 18
     lint/thread-macro-one-arg 85
@@ -99,10 +100,11 @@
         diagnostics (delay (->> @results
                                 :diagnostics
                                 (group-by :rule-name)))]
+    ; (user/pprint (get @diagnostics 'lint/no-op-assignment))
     (it "has the right diagnostics"
       (expect
         (match?
          (m/equals clj-kondo-diagnostics)
          (update-vals* @diagnostics count))))
     (it "sums correctly"
-      (expect (= 1363 (count (:diagnostics @results)))))))
+      (expect (= 1365 (count (:diagnostics @results)))))))

test/noahtheduke/splint/netrunner_test.clj

@@ -94,6 +94,7 @@
         diagnostics (delay (->> @results
                                 :diagnostics
                                 (group-by :rule-name)))]
+    ; (user/pprint (get @diagnostics 'lint/no-op-assignment))
     (it "has the right diagnostics"
       (expect
         (match?

test/noahtheduke/splint/rules/lint/no_op_assignment_test.clj

@@ -0,0 +1,39 @@
+; This Source Code Form is subject to the terms of the Mozilla Public
+; License, v. 2.0. If a copy of the MPL was not distributed with this
+; file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+(ns noahtheduke.splint.rules.lint.no-op-assignment-test
+  (:require
+   [lazytest.core :refer [defdescribe it]]
+   [noahtheduke.splint.test-helpers :refer [expect-match single-rule-config]]))
+
+(set! *warn-on-reflection* true)
+
+(def rule-name 'lint/no-op-assignment)
+
+(defdescribe no-op-assignment-test
+  (it "handles the trivial case"
+    (expect-match
+      [{:rule-name rule-name
+        :form '(foo foo)
+        :message "Avoid no-op assignment."
+        :alt nil}]
+      "(let [foo foo] bar)"
+      (single-rule-config rule-name)))
+  (it "checks multiple cases at once"
+    (expect-match
+      [{:rule-name rule-name
+        :form '(bar bar)
+        :message "Avoid no-op assignment."
+        :alt nil}
+       {:rule-name rule-name
+        :form '(foo foo)
+        :message "Avoid no-op assignment."
+        :alt nil}]
+      "(let [foo 1 foo foo bar foo bar bar] bar)"
+      (single-rule-config rule-name)))
+  (it "doesn't raise when in a reader conditional"
+    (expect-match
+      nil
+      "(let [remote #?(:clj remote :cljs (foo bar))])"
+      (single-rule-config rule-name))))