prefer-spread: Forbid use of Array#toSpliced() to copy array (#2034)

sindresorhus · Feb 1, 2023 · 4ada50e · 4ada50e
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diff --git a/docs/rules/prefer-spread.md b/docs/rules/prefer-spread.md
@@ -1,4 +1,4 @@
-# Prefer the spread operator over `Array.from(…)`, `Array#concat(…)`, `Array#slice()` and `String#split('')`
+# Prefer the spread operator over `Array.from(…)`, `Array#concat(…)`, `Array#{slice,toSpliced}()` and `String#split('')`
 
 💼 This rule is enabled in the ✅ `recommended` [config](https://github.com/sindresorhus/eslint-plugin-unicorn#preset-configs).
 
@@ -25,6 +25,10 @@ Enforces the use of [the spread operator (`...`)](https://developer.mozilla.org/
 
 	Variables named `arrayBuffer`, `blob`, `buffer`, `file`, and `this` are ignored.
 
+- `Array#toSpliced()`
+
+	Shallow copy an `Array`.
+
 - `String#split('')`
 
 	Split a string into an array of characters.
@@ -47,6 +51,14 @@ const array = array1.concat(array2);
 const copy = array.slice();
 ```
 
+```js
+const copy = array.slice(0);
+```
+
+```js
+const copy = array.toSpliced();
+```
+
 ```js
 const characters = string.split('');
 ```

diff --git a/readme.md b/readme.md
@@ -145,7 +145,7 @@ If you don't use the preset, ensure you use the same `env` and `parserOptions` c
 | [prefer-regexp-test](docs/rules/prefer-regexp-test.md)                                           | Prefer `RegExp#test()` over `String#match()` and `RegExp#exec()`.                                                                                                                                                 | ✅  | 🔧 | 💡 |
 | [prefer-set-has](docs/rules/prefer-set-has.md)                                                   | Prefer `Set#has()` over `Array#includes()` when checking for existence or non-existence.                                                                                                                          | ✅  | 🔧 | 💡 |
 | [prefer-set-size](docs/rules/prefer-set-size.md)                                                 | Prefer using `Set#size` instead of `Array#length`.                                                                                                                                                                | ✅  | 🔧 |    |
-| [prefer-spread](docs/rules/prefer-spread.md)                                                     | Prefer the spread operator over `Array.from(…)`, `Array#concat(…)`, `Array#slice()` and `String#split('')`.                                                                                                       | ✅  | 🔧 | 💡 |
+| [prefer-spread](docs/rules/prefer-spread.md)                                                     | Prefer the spread operator over `Array.from(…)`, `Array#concat(…)`, `Array#{slice,toSpliced}()` and `String#split('')`.                                                                                           | ✅  | 🔧 | 💡 |
 | [prefer-string-replace-all](docs/rules/prefer-string-replace-all.md)                             | Prefer `String#replaceAll()` over regex searches with the global flag.                                                                                                                                            |    | 🔧 |    |
 | [prefer-string-slice](docs/rules/prefer-string-slice.md)                                         | Prefer `String#slice()` over `String#substr()` and `String#substring()`.                                                                                                                                          | ✅  | 🔧 |    |
 | [prefer-string-starts-ends-with](docs/rules/prefer-string-starts-ends-with.md)                   | Prefer `String#startsWith()` & `String#endsWith()` over `RegExp#test()`.                                                                                                                                          | ✅  | 🔧 | 💡 |

diff --git a/rules/prefer-spread.js b/rules/prefer-spread.js
@@ -16,6 +16,7 @@ const isMethodNamed = require('./utils/is-method-named.js');
 const ERROR_ARRAY_FROM = 'array-from';
 const ERROR_ARRAY_CONCAT = 'array-concat';
 const ERROR_ARRAY_SLICE = 'array-slice';
+const ERROR_ARRAY_TO_SPLICED = 'array-to-spliced';
 const ERROR_STRING_SPLIT = 'string-split';
 const SUGGESTION_CONCAT_ARGUMENT_IS_SPREADABLE = 'argument-is-spreadable';
 const SUGGESTION_CONCAT_ARGUMENT_IS_NOT_SPREADABLE = 'argument-is-not-spreadable';
@@ -26,6 +27,7 @@ const messages = {
 	[ERROR_ARRAY_FROM]: 'Prefer the spread operator over `Array.from(…)`.',
 	[ERROR_ARRAY_CONCAT]: 'Prefer the spread operator over `Array#concat(…)`.',
 	[ERROR_ARRAY_SLICE]: 'Prefer the spread operator over `Array#slice()`.',
+	[ERROR_ARRAY_TO_SPLICED]: 'Prefer the spread operator over `Array#toSpliced()`.',
 	[ERROR_STRING_SPLIT]: 'Prefer the spread operator over `String#split(\'\')`.',
 	[SUGGESTION_CONCAT_ARGUMENT_IS_SPREADABLE]: 'First argument is an `array`.',
 	[SUGGESTION_CONCAT_ARGUMENT_IS_NOT_SPREADABLE]: 'First argument is not an `array`.',
@@ -56,6 +58,14 @@ const arraySliceCallSelector = [
 	'[callee.object.type!="ArrayExpression"]',
 ].join('');
 
+const arrayToSplicedCallSelector = [
+	methodCallSelector({
+		method: 'toSpliced',
+		argumentsLength: 0,
+	}),
+	'[callee.object.type!="ArrayExpression"]',
+].join('');
+
 const ignoredSliceCallee = [
 	'arrayBuffer',
 	'blob',
@@ -444,6 +454,13 @@ const create = context => {
 				fix: methodCallToSpread(node, sourceCode),
 			};
 		},
+		[arrayToSplicedCallSelector](node) {
+			return {
+				node: node.callee.property,
+				messageId: ERROR_ARRAY_TO_SPLICED,
+				fix: methodCallToSpread(node, sourceCode),
+			};
+		},
 		[stringSplitCallSelector](node) {
 			const [separator] = node.arguments;
 			if (!isLiteral(separator, '')) {
@@ -495,7 +512,7 @@ module.exports = {
 	meta: {
 		type: 'suggestion',
 		docs: {
-			description: 'Prefer the spread operator over `Array.from(…)`, `Array#concat(…)`, `Array#slice()` and `String#split(\'\')`.',
+			description: 'Prefer the spread operator over `Array.from(…)`, `Array#concat(…)`, `Array#{slice,toSpliced}()` and `String#split(\'\')`.',
 		},
 		fixable: 'code',
 		hasSuggestions: true,

diff --git a/test/prefer-spread.mjs b/test/prefer-spread.mjs
@@ -347,6 +347,45 @@ test.snapshot({
 	],
 });
 
+// `Array#toSpliced`
+test.snapshot({
+	valid: [
+		'new Array.toSpliced()',
+		'toSpliced()',
+		'array[toSpliced]()',
+		'array.toSpliced',
+		'array.toSpliced(0)',
+		'array.toSpliced(...[])',
+		'array.toSpliced(...[0])',
+		'array.toSpliced(0 + 0)',
+		'array.toSpliced("")',
+		'array.toSpliced(null)',
+		'const ZERO = 0;array.toSpliced(0, ZERO)',
+		'array.toSpliced(0, array.length)',
+		'array.toSpliced(0, 0)',
+		'array.notToSpliced()',
+		// Why would someone write these
+		'[...foo].toSpliced()',
+		'[foo].toSpliced()',
+		'array.toSpliced(100, 0)',
+		'array.toSpliced(-1, 0)',
+	],
+	invalid: [
+		'array.toSpliced()',
+		'array.toSpliced().toSpliced()',
+		'const copy = array.toSpliced()',
+		'(( (( (( array )).toSpliced ))() ))',
+		// Semicolon
+		outdent`
+			bar()
+			foo.toSpliced()
+		`,
+		// `{String,TypedArray}#toSpliced` are wrongly detected
+		'"".toSpliced()',
+		'new Uint8Array([10, 20, 30, 40, 50]).toSpliced()',
+	],
+});
+
 // `String#slice('')`
 test.snapshot({
 	valid: [

diff --git a/test/snapshots/prefer-spread.mjs.md b/test/snapshots/prefer-spread.mjs.md
@@ -2268,6 +2268,128 @@ Generated by [AVA](https://avajs.dev).
         |       ^^^^^ Prefer the spread operator over \`Array#slice()\`.␊
     `
 
+## Invalid #1
+      1 | array.toSpliced()
+
+> Output
+
+    `␊
+      1 | [...array]␊
+    `
+
+> Error 1/1
+
+    `␊
+    > 1 | array.toSpliced()␊
+        |       ^^^^^^^^^ Prefer the spread operator over \`Array#toSpliced()\`.␊
+    `
+
+## Invalid #2
+      1 | array.toSpliced().toSpliced()
+
+> Output
+
+    `␊
+      1 | [...array].toSpliced()␊
+    `
+
+> Error 1/2
+
+    `␊
+    > 1 | array.toSpliced().toSpliced()␊
+        |       ^^^^^^^^^ Prefer the spread operator over \`Array#toSpliced()\`.␊
+    `
+
+> Error 2/2
+
+    `␊
+    > 1 | array.toSpliced().toSpliced()␊
+        |                   ^^^^^^^^^ Prefer the spread operator over \`Array#toSpliced()\`.␊
+    `
+
+## Invalid #3
+      1 | const copy = array.toSpliced()
+
+> Output
+
+    `␊
+      1 | const copy = [...array]␊
+    `
+
+> Error 1/1
+
+    `␊
+    > 1 | const copy = array.toSpliced()␊
+        |                    ^^^^^^^^^ Prefer the spread operator over \`Array#toSpliced()\`.␊
+    `
+
+## Invalid #4
+      1 | (( (( (( array )).toSpliced ))() ))
+
+> Output
+
+    `␊
+      1 | (( [...(( (( array )) ))] ))␊
+    `
+
+> Error 1/1
+
+    `␊
+    > 1 | (( (( (( array )).toSpliced ))() ))␊
+        |                   ^^^^^^^^^ Prefer the spread operator over \`Array#toSpliced()\`.␊
+    `
+
+## Invalid #5
+      1 | bar()
+      2 | foo.toSpliced()
+
+> Output
+
+    `␊
+      1 | bar()␊
+      2 | ;[...foo]␊
+    `
+
+> Error 1/1
+
+    `␊
+      1 | bar()␊
+    > 2 | foo.toSpliced()␊
+        |     ^^^^^^^^^ Prefer the spread operator over \`Array#toSpliced()\`.␊
+    `
+
+## Invalid #6
+      1 | "".toSpliced()
+
+> Output
+
+    `␊
+      1 | [...""]␊
+    `
+
+> Error 1/1
+
+    `␊
+    > 1 | "".toSpliced()␊
+        |    ^^^^^^^^^ Prefer the spread operator over \`Array#toSpliced()\`.␊
+    `
+
+## Invalid #7
+      1 | new Uint8Array([10, 20, 30, 40, 50]).toSpliced()
+
+> Output
+
+    `␊
+      1 | [...new Uint8Array([10, 20, 30, 40, 50])]␊
+    `
+
+> Error 1/1
+
+    `␊
+    > 1 | new Uint8Array([10, 20, 30, 40, 50]).toSpliced()␊
+        |                                      ^^^^^^^^^ Prefer the spread operator over \`Array#toSpliced()\`.␊
+    `
+
 ## Invalid #1
       1 | "string".split("")
 

diff --git a/test/snapshots/prefer-spread.mjs.snap b/test/snapshots/prefer-spread.mjs.snap