Add Array.from() support to prefer-set-size rule

rules/prefer-set-size.js

@@ -1,6 +1,6 @@
 import {findVariable} from '@eslint-community/eslint-utils';
 import {fixSpaceAroundKeyword} from './fix/index.js';
-import {isNewExpression, isMemberExpression} from './ast/index.js';
+import {isNewExpression, isMemberExpression, isMethodCall} from './ast/index.js';
 
 const MESSAGE_ID = 'prefer-set-size';
 const messages = {
@@ -36,24 +36,49 @@ function isSet(node, scope) {
 		&& isNewSet(definition.node.init);
 }
 
-// `[...set].length` -> `set.size`
-function fix(context, lengthAccessNodes) {
+function getSetNode(memberExpressionObject) {
+	// `[...set].length`
+	if (
+		memberExpressionObject.type === 'ArrayExpression'
+		&& memberExpressionObject.elements.length === 1
+		&& memberExpressionObject.elements[0]?.type === 'SpreadElement'
+	) {
+		return memberExpressionObject.elements[0].argument;
+	}
+
+	// `Array.from(set).length`
+	if (
+		isMethodCall(memberExpressionObject, {
+			object: 'Array',
+			method: 'from',
+			argumentsLength: 1,
+			optionalCall: false,
+			optionalMember: false,
+		})
+	) {
+		return memberExpressionObject.arguments[0];
+	}
+}
+
+function createFix(context, lengthAccessNode, set) {
 	const {sourceCode} = context;
 	const {
-		object: arrayExpression,
+		object: array,
 		property,
-	} = lengthAccessNodes;
-	const set = arrayExpression.elements[0].argument;
+	} = lengthAccessNode;
 
-	if (sourceCode.getCommentsInside(arrayExpression).length > sourceCode.getCommentsInside(set).length) {
+	if (sourceCode.getCommentsInside(array).length > sourceCode.getCommentsInside(set).length) {
 		return;
 	}
 
 	/** @param {import('eslint').Rule.RuleFixer} fixer */
 	return function * (fixer) {
 		yield fixer.replaceText(property, 'size');
-		yield fixer.replaceText(arrayExpression, sourceCode.getText(set));
-		yield fixSpaceAroundKeyword(fixer, lengthAccessNodes, context);
+		yield fixer.replaceText(array, sourceCode.getText(set));
+
+		if (array.type === 'ArrayExpression') {
+			yield fixSpaceAroundKeyword(fixer, lengthAccessNode, context);
+		}
 	};
 }
 
@@ -67,22 +92,19 @@ const create = context => {
 				property: 'length',
 				optional: false,
 			})
-			|| node.object.type !== 'ArrayExpression'
-			|| node.object.elements.length !== 1
-			|| node.object.elements[0]?.type !== 'SpreadElement'
 		) {
 			return;
 		}
 
-		const maybeSet = node.object.elements[0].argument;
-		if (!isSet(maybeSet, sourceCode.getScope(maybeSet))) {
+		const set = getSetNode(node.object);
+		if (!set || !isSet(set, sourceCode.getScope(set))) {
 			return;
 		}
 
 		return {
 			node: node.property,
 			messageId: MESSAGE_ID,
-			fix: fix(context, node),
+			fix: createFix(context, node, set),
 		};
 	});
 };

test/prefer-set-size.js

@@ -22,6 +22,23 @@ test.snapshot({
 		'[...foo].length',
 		'var foo = new Set(); var foo = new Set(); [...foo].length',
 		'[,].length',
+		// `Array.from` — valid cases
+		'Array.from(foo).length',
+		'Array.from(new NotSet(array)).length',
+		'Array.from(Set(array)).length',
+		'Array.from(new Set(array)).notLength',
+		'Array.from(new Set(array))?.length',
+		'Array.from(new Set(array))[length]',
+		'Array.from(new Set(array))["length"]',
+		'Array.from(new Set(array), mapFn).length',
+		'Array?.from(new Set(array)).length',
+		'Array.from?.(new Set(array)).length',
+		'const foo = new NotSet([]);Array.from(foo).length;',
+		'let foo = new Set([]);Array.from(foo).length;',
+		'const {foo} = new Set([]);Array.from(foo).length;',
+		'const [foo] = new Set([]);Array.from(foo).length;',
+		'var foo = new Set(); var foo = new Set(); Array.from(foo).length',
+		'NotArray.from(new Set(array)).length',
 	],
 	invalid: [
 		'[...new Set(array)].length',
@@ -43,5 +60,20 @@ test.snapshot({
 		`,
 		'[/* comment */...new Set(array)].length',
 		'[...new /* comment */ Set(array)].length',
+		// `Array.from` — invalid cases
+		'Array.from(new Set(array)).length',
+		outdent`
+			const foo = new Set([]);
+			console.log(Array.from(foo).length);
+		`,
+		'Array.from((( new Set(array) ))).length',
+		'(( Array.from(new Set(array)) )).length',
+		'Array.from(/* comment */ new Set(array)).length',
+		'Array.from(new /* comment */ Set(array)).length',
+		outdent`
+			function isUnique(array) {
+				return Array.from(new Set(array)).length === array.length
+			}
+		`,
 	],
 });

test/snapshots/prefer-set-size.js.md

@@ -183,3 +183,142 @@ Generated by [AVA](https://avajs.dev).
     Output:␊
       1 | new /* comment */ Set(array).size␊
     `
+
+## invalid(10): Array.from(new Set(array)).length
+
+> Input
+
+    `␊
+      1 | Array.from(new Set(array)).length␊
+    `
+
+> Error 1/1
+
+    `␊
+    Message:␊
+    > 1 | Array.from(new Set(array)).length␊
+        |                            ^^^^^^ Prefer using \`Set#size\` instead of \`Array#length\`.␊
+    ␊
+    Output:␊
+      1 | new Set(array).size␊
+    `
+
+## invalid(11): const foo = new Set([]); console.log(Array.from(foo).length);
+
+> Input
+
+    `␊
+      1 | const foo = new Set([]);␊
+      2 | console.log(Array.from(foo).length);␊
+    `
+
+> Error 1/1
+
+    `␊
+    Message:␊
+      1 | const foo = new Set([]);␊
+    > 2 | console.log(Array.from(foo).length);␊
+        |                             ^^^^^^ Prefer using \`Set#size\` instead of \`Array#length\`.␊
+    ␊
+    Output:␊
+      1 | const foo = new Set([]);␊
+      2 | console.log(foo.size);␊
+    `
+
+## invalid(12): Array.from((( new Set(array) ))).length
+
+> Input
+
+    `␊
+      1 | Array.from((( new Set(array) ))).length␊
+    `
+
+> Error 1/1
+
+    `␊
+    Message:␊
+    > 1 | Array.from((( new Set(array) ))).length␊
+        |                                  ^^^^^^ Prefer using \`Set#size\` instead of \`Array#length\`.␊
+    ␊
+    Output:␊
+      1 | new Set(array).size␊
+    `
+
+## invalid(13): (( Array.from(new Set(array)) )).length
+
+> Input
+
+    `␊
+      1 | (( Array.from(new Set(array)) )).length␊
+    `
+
+> Error 1/1
+
+    `␊
+    Message:␊
+    > 1 | (( Array.from(new Set(array)) )).length␊
+        |                                  ^^^^^^ Prefer using \`Set#size\` instead of \`Array#length\`.␊
+    ␊
+    Output:␊
+      1 | (( new Set(array) )).size␊
+    `
+
+## invalid(14): Array.from(/* comment */ new Set(array)).length
+
+> Input
+
+    `␊
+      1 | Array.from(/* comment */ new Set(array)).length␊
+    `
+
+> Error 1/1
+
+    `␊
+    Message:␊
+    > 1 | Array.from(/* comment */ new Set(array)).length␊
+        |                                          ^^^^^^ Prefer using \`Set#size\` instead of \`Array#length\`.␊
+    `
+
+## invalid(15): Array.from(new /* comment */ Set(array)).length
+
+> Input
+
+    `␊
+      1 | Array.from(new /* comment */ Set(array)).length␊
+    `
+
+> Error 1/1
+
+    `␊
+    Message:␊
+    > 1 | Array.from(new /* comment */ Set(array)).length␊
+        |                                          ^^^^^^ Prefer using \`Set#size\` instead of \`Array#length\`.␊
+    ␊
+    Output:␊
+      1 | new /* comment */ Set(array).size␊
+    `
+
+## invalid(16): function isUnique(array) { return Array.from(new Set(array)).length === array.length }
+
+> Input
+
+    `␊
+      1 | function isUnique(array) {␊
+      2 | 	return Array.from(new Set(array)).length === array.length␊
+      3 | }␊
+    `
+
+> Error 1/1
+
+    `␊
+    Message:␊
+      1 | function isUnique(array) {␊
+    > 2 | 	return Array.from(new Set(array)).length === array.length␊
+        | 	                                  ^^^^^^ Prefer using \`Set#size\` instead of \`Array#length\`.␊
+      3 | }␊
+    ␊
+    Output:␊
+      1 | function isUnique(array) {␊
+      2 | 	return new Set(array).size === array.length␊
+      3 | }␊
+    `