feat: add avoid-reverse rule (fixes #12)

Author: freaktechnik

README.md

@@ -15,6 +15,8 @@ Rules for Array functions and methods.
      - [Examples](#examples-1)
    - [`prefer-array-from`](#prefer-array-from)
      - [Examples](#examples-2)
+   - [`avoid-reverse`](#avoid-reverse)
+     - [Examples](#examples-3)
  - [`array-func/recommended` Configuration](#array-funcrecommended-configuration)
    - [Using the Configuration](#using-the-configuration)
  - [License](#license)
@@ -151,6 +153,42 @@ const arrayCopy = Array.from(array);
 const characterArray = Array.from("string");
 ```
 
+### `avoid-reverse`
+Avoid reversing the array and running a method on it if there is an equivalent
+of the method operating on the array from the other end.
+
+There are two operations with such equivalents: `indexOf` with `lastIndexOf` and
+`reduce` with `reduceRight`.
+
+This rule is auto fixable.
+
+#### Examples
+Code that triggers this rule:
+```js
+const lastIndex = array.reverse().indexOf(1);
+
+const firstIndex = array.reverse().lastIndexOf(1);
+
+const sum = array.reverse().reduce((p, c) => p + c, 0);
+
+const reverseSum = array.reverse().reduceRight((p, c) => p + c, 0);
+```
+
+Code that doesn't trigger this rule:
+```js
+const lastIndex = array.lastIndexOf(1);
+
+const firstIndex = array.indexOf(1);
+
+const sum = array.reduce((p, c) => p + c, 0);
+
+const reverseSum = array.reduceRight((p, c) => p + c, 0);
+
+const reverseArray = array.reverse();
+
+const reverseMap = array.reverse().map((r) => r + 1);
+```
+
 ## `array-func/recommended` Configuration
 The recommended configuration will set your parser ECMA Version to 2015, since that's when the Array functions and methods were added.
 
@@ -159,6 +197,7 @@ Rule | Error level | Fixable
 `from-map` | Error | Yes
 `no-unnecessary-this-arg` | Error | Sometimes
 `prefer-array-from` | Error | Yes
+`avoid-reverse` | Error | Yes
 
 ### Using the Configuration
 To enable this configuration use the `extends` property in your `.eslintrc.json` config file (may look different for other config file styles):

index.js

@@ -8,7 +8,8 @@ module.exports = {
     rules: {
         "from-map": require("./rules/from-map"),
         "no-unnecessary-this-arg": require("./rules/no-unnecessary-this-arg"),
-        "prefer-array-from": require("./rules/prefer-array-from")
+        "prefer-array-from": require("./rules/prefer-array-from"),
+        "avoid-reverse": require("./rules/avoid-reverse")
     },
     configs: {
         recommended: {
@@ -19,7 +20,8 @@ module.exports = {
             rules: {
                 "array-func/from-map": "error",
                 "array-func/no-unnecessary-this-arg": "error",
-                "array-func/prefer-array-from": "error"
+                "array-func/prefer-array-from": "error",
+                "array-func/avoid-reverse": "error"
             }
         }
     }

rules/avoid-reverse.js

@@ -0,0 +1,59 @@
+/**
+ * @author Martin Giger
+ * @license MIT
+ */
+"use strict";
+
+const {
+    isMethod,
+    getParent
+} = require("../lib/helpers/call-expression");
+
+const REPLACEMENTS = {
+    indexOf: "lastIndexOf",
+    reduce: "reduceRight",
+    lastIndexOf: "indexOf",
+    reduceRight: "reduce"
+};
+
+module.exports = {
+    meta: {
+        docs: {
+            description: "Prefer methods operating from the right over reversing the array",
+            recommended: true
+        },
+        schema: [],
+        fixable: "code"
+    },
+    create(context) {
+        return {
+            "CallExpression:exit"(node) {
+                if(Object.keys(REPLACEMENTS).every((m) => !isMethod(node, m))) {
+                    return;
+                }
+
+                const parent = getParent(node);
+                if(!isMethod(parent, 'reverse')) {
+                    return;
+                }
+
+                const reversed = REPLACEMENTS[node.callee.property.name];
+
+                context.report({
+                    node: node.callee.property,
+                    loc: {
+                        start: parent.callee.property.loc.start,
+                        end: node.callee.property.loc.end
+                    },
+                    message: `Prefer using ${reversed} over reversing the array and ${node.callee.property.name}`,
+                    fix(fixer) {
+                        return fixer.replaceTextRange([
+                            parent.callee.property.start,
+                            node.callee.property.end
+                        ], reversed);
+                    }
+                });
+            }
+        };
+    }
+};

test/rules/avoid-reverse.js

@@ -0,0 +1,58 @@
+import test from 'ava';
+import AvaRuleTester from 'eslint-ava-rule-tester';
+import rule from '../../rules/avoid-reverse';
+
+const ruleTester = new AvaRuleTester(test, {
+    parserOptions: {
+        ecmaVersion: 2015
+    }
+});
+
+ruleTester.run('from-map', rule, {
+    valid: [
+        'array.lastIndexOf(1)',
+        'array.indexOf(1)',
+        'array.reduce((p, c) => p + c, 0)',
+        'array.reduceRight((p, c) => p + c, 0)',
+        'array.reverse()',
+        'array.reverse().map((r) => r + 1)'
+    ],
+    invalid: [
+        {
+            code: 'array.reverse().indexOf(1)',
+            errors: [ {
+                message: 'Prefer using lastIndexOf over reversing the array and indexOf',
+                column: 7,
+                line: 1
+            } ],
+            output: 'array.lastIndexOf(1)'
+        },
+        {
+            code: 'array.reverse().lastIndexOf(1)',
+            errors: [ {
+                message: 'Prefer using indexOf over reversing the array and lastIndexOf',
+                column: 7,
+                line: 1
+            } ],
+            output: 'array.indexOf(1)'
+        },
+        {
+            code: 'array.reverse().reduce((p, c) => p + c, 0)',
+            errors: [ {
+                message: 'Prefer using reduceRight over reversing the array and reduce',
+                column: 7,
+                line: 1
+            } ],
+            output: 'array.reduceRight((p, c) => p + c, 0)'
+        },
+        {
+            code: 'array.reverse().reduceRight((p, c) => p + c, 0)',
+            errors: [ {
+                message: 'Prefer using reduce over reversing the array and reduceRight',
+                column: 7,
+                line: 1
+            } ],
+            output: 'array.reduce((p, c) => p + c, 0)'
+        }
+    ]
+});