feat: singularize variable name in autofix for prefer-array-find rule

rules/no-for-loop.js

@@ -1,9 +1,10 @@
 'use strict';
-const {singular} = require('pluralize');
 const {isClosingParenToken} = require('eslint-utils');
 const getDocumentationUrl = require('./utils/get-documentation-url');
 const isLiteralValue = require('./utils/is-literal-value');
 const avoidCapture = require('./utils/avoid-capture');
+const getChildScopesRecursive = require('./utils/get-child-scopes-recursive');
+const singular = require('./utils/singular');
 
 const MESSAGE_ID = 'no-for-loop';
 const messages = {
@@ -268,18 +269,6 @@ const getReferencesInChildScopes = (scope, name) => {
 	];
 };
 
-const getChildScopesRecursive = scope => [
-	scope,
-	...scope.childScopes.flatMap(scope => getChildScopesRecursive(scope))
-];
-
-const getSingularName = originalName => {
-	const singularName = singular(originalName);
-	if (singularName !== originalName) {
-		return singularName;
-	}
-};
-
 const create = context => {
 	const sourceCode = context.getSourceCode();
 	const {scopeManager, text: sourceCodeText} = sourceCode;
@@ -361,7 +350,7 @@ const create = context => {
 
 					const index = indexIdentifierName;
 					const element = elementIdentifierName ||
-						avoidCapture(getSingularName(arrayIdentifierName) || defaultElementName, getChildScopesRecursive(bodyScope), context.parserOptions.ecmaVersion);
+						avoidCapture(singular(arrayIdentifierName) || defaultElementName, getChildScopesRecursive(bodyScope), context.parserOptions.ecmaVersion);
 					const array = arrayIdentifierName;
 
 					let declarationElement = element;

rules/prefer-array-find.js

@@ -3,6 +3,10 @@ const {isParenthesized, findVariable} = require('eslint-utils');
 const getDocumentationUrl = require('./utils/get-documentation-url');
 const methodSelector = require('./utils/method-selector');
 const getVariableIdentifiers = require('./utils/get-variable-identifiers');
+const renameVariable = require('./utils/rename-variable');
+const avoidCapture = require('./utils/avoid-capture');
+const getChildScopesRecursive = require('./utils/get-child-scopes-recursive');
+const singular = require('./utils/singular');
 
 const ERROR_ZERO_INDEX = 'error-zero-index';
 const ERROR_SHIFT = 'error-shift';
@@ -288,6 +292,14 @@ const create = context => {
 				problem.fix = function * (fixer) {
 					yield fixer.replaceText(node.init.callee.property, 'find');
 
+					const singularName = singular(node.id.name);
+					if (singularName) {
+						// Rename variable to be singularized now that it refers to a single item in the array instead of the entire array.
+						const singularizedName = avoidCapture(singularName, getChildScopesRecursive(context.getScope()), context.parserOptions.ecmaVersion);
+						const scope = context.getScope();
+						yield * renameVariable(findVariable(scope, node.id), singularizedName, fixer);
+					}
+
 					for (const node of zeroIndexNodes) {
 						yield fixer.removeRange([node.object.range[1], node.range[1]]);
 					}

rules/utils/get-child-scopes-recursive.js

@@ -0,0 +1,14 @@
+'use strict';
+
+/**
+Gather a list of all Scopes starting recursively from the input Scope.
+
+@param {Scope} scope - The Scope to start checking from.
+@returns {Scope[]} - The resulting Scopes.
+*/
+const getChildScopesRecursive = scope => [
+	scope,
+	...scope.childScopes.flatMap(scope => getChildScopesRecursive(scope))
+];
+
+module.exports = getChildScopesRecursive;

rules/utils/singular.js

@@ -0,0 +1,18 @@
+'use strict';
+
+const {singular: pluralizeSingular} = require('pluralize');
+
+/**
+Singularizes a word/name, i.e. `items` to `item`.
+
+@param {string} original - The word/name to singularize.
+@returns {string|undefined} - The singularized result, or `undefined` if attempting singularization resulted in no change.
+*/
+const singular = original => {
+	const singularized = pluralizeSingular(original);
+	if (singularized !== original) {
+		return singularized;
+	}
+};
+
+module.exports = singular;

test/prefer-array-find.mjs

@@ -145,6 +145,7 @@ ruleTester.run('prefer-array-find', rule, {
 		'function a([foo] = array.filter(bar)) {}',
 		// Not `ArrayPattern`
 		'const foo = array.filter(bar)',
+		'const items = array.filter(bar)', // Plural variable name.
 		'const {0: foo} = array.filter(bar)',
 		// `elements`
 		'const [] = array.filter(bar)',
@@ -175,6 +176,12 @@ ruleTester.run('prefer-array-find', rule, {
 			output: 'const foo = array.find(bar)',
 			errors: [{messageId: ERROR_DESTRUCTURING_DECLARATION}]
 		},
+		{
+			// Plural variable name.
+			code: 'const [items] = array.filter(bar)',
+			output: 'const items = array.find(bar)',
+			errors: [{messageId: ERROR_DESTRUCTURING_DECLARATION}]
+		},
 		{
 			code: 'const [foo] = array.filter(bar, thisArgument)',
 			output: 'const foo = array.find(bar, thisArgument)',
@@ -376,6 +383,7 @@ ruleTester.run('prefer-array-find', rule, {
 		'function a([foo] = array.filter(bar)) {}',
 		// Not `ArrayPattern`
 		'foo = array.filter(bar)',
+		'items = array.filter(bar)', // Plural variable name.
 		'({foo} = array.filter(bar))',
 		// `elements`
 		'[] = array.filter(bar)',
@@ -626,7 +634,11 @@ ruleTester.run('prefer-array-find', rule, {
 		// More or less argument(s)
 		'const foo = array.filter(); const first = foo[0]',
 		'const foo = array.filter(bar, thisArgument, extraArgument); const first = foo[0]',
-		'const foo = array.filter(...bar); const first = foo[0]'
+		'const foo = array.filter(...bar); const first = foo[0]',
+
+		// Singularization
+		'const item = array.find(bar), first = item;', // Already singular variable name.
+		'let items = array.filter(bar); console.log(items[0]); items = [1,2,3]; console.log(items[0]);' // Reassigning array variable.
 	],
 	invalid: [
 		{
@@ -669,6 +681,37 @@ ruleTester.run('prefer-array-find', rule, {
 			output: 'const foo = array.find(bar); ({propOfFirst = unicorn} = foo);',
 			errors: [{messageId: ERROR_DECLARATION}]
 		},
+
+		// Singularization
+		{
+			// Multiple usages and child scope.
+			code: outdent`
+				const items = array.filter(bar);
+				const first = items[0];
+				console.log(items[0]);
+				function foo() { return items[0]; }
+			`,
+			output: outdent`
+				const item = array.find(bar);
+				const first = item;
+				console.log(item);
+				function foo() { return item; }
+			`,
+			errors: [{messageId: ERROR_DECLARATION}]
+		},
+		{
+			// Variable name collision.
+			code: 'const item = {}; const items = array.filter(bar); console.log(items[0]);',
+			output: 'const item = {}; const item_ = array.find(bar); console.log(item_);',
+			errors: [{messageId: ERROR_DECLARATION}]
+		},
+		{
+			// Variable defined with `let`.
+			code: 'let items = array.filter(bar); console.log(items[0]);',
+			output: 'let item = array.find(bar); console.log(item);',
+			errors: [{messageId: ERROR_DECLARATION}]
+		},
+
 		// Not fixable
 		{
 			code: 'const foo = array.filter(bar); const [first = bar] = foo;',