prefer-array-find: Singularize variable name in autofix (#1243)

Co-authored-by: fisker Cheung <lionkay@gmail.com>

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 +3,11 @@ 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 extendFixRange = require('./utils/extend-fix-range');
 
 const ERROR_ZERO_INDEX = 'error-zero-index';
 const ERROR_SHIFT = 'error-shift';
@@ -94,10 +99,10 @@ const destructuringAssignmentSelector = [
 // Need add `()` to the `AssignmentExpression`
 // - `ObjectExpression`: `[{foo}] = array.filter(bar)` fix to `{foo} = array.find(bar)`
 // - `ObjectPattern`: `[{foo = baz}] = array.filter(bar)`
-const assignmentNeedParenthesize = (node, source) => {
+const assignmentNeedParenthesize = (node, sourceCode) => {
 	const isAssign = node.type === 'AssignmentExpression';
 
-	if (!isAssign || isParenthesized(node, source)) {
+	if (!isAssign || isParenthesized(node, sourceCode)) {
 		return false;
 	}
 
@@ -143,36 +148,36 @@ const getDestructuringLeftAndRight = node => {
 	return {};
 };
 
-function * fixDestructuring(node, source, fixer) {
+function * fixDestructuring(node, sourceCode, fixer) {
 	const {left} = getDestructuringLeftAndRight(node);
 	const [element] = left.elements;
 
-	const leftText = source.getText(element.type === 'AssignmentPattern' ? element.left : element);
+	const leftText = sourceCode.getText(element.type === 'AssignmentPattern' ? element.left : element);
 	yield fixer.replaceText(left, leftText);
 
 	// `AssignmentExpression` always starts with `[` or `(`, so we don't need check ASI
-	if (assignmentNeedParenthesize(node, source)) {
+	if (assignmentNeedParenthesize(node, sourceCode)) {
 		yield fixer.insertTextBefore(node, '(');
 		yield fixer.insertTextAfter(node, ')');
 	}
 }
 
 const hasDefaultValue = node => getDestructuringLeftAndRight(node).left.elements[0].type === 'AssignmentPattern';
 
-const fixDestructuringDefaultValue = (node, source, fixer, operator) => {
+const fixDestructuringDefaultValue = (node, sourceCode, fixer, operator) => {
 	const {left, right} = getDestructuringLeftAndRight(node);
 	const [element] = left.elements;
 	const defaultValue = element.right;
-	let defaultValueText = source.getText(defaultValue);
+	let defaultValueText = sourceCode.getText(defaultValue);
 
-	if (isParenthesized(defaultValue, source) || hasLowerPrecedence(defaultValue, operator)) {
+	if (isParenthesized(defaultValue, sourceCode) || hasLowerPrecedence(defaultValue, operator)) {
 		defaultValueText = `(${defaultValueText})`;
 	}
 
 	return fixer.insertTextAfter(right, ` ${operator} ${defaultValueText}`);
 };
 
-const fixDestructuringAndReplaceFilter = (source, node) => {
+const fixDestructuringAndReplaceFilter = (sourceCode, node) => {
 	const {property} = getDestructuringLeftAndRight(node).right.callee;
 
 	let suggest;
@@ -186,14 +191,14 @@ const fixDestructuringAndReplaceFilter = (source, node) => {
 			messageId,
 			* fix(fixer) {
 				yield fixer.replaceText(property, 'find');
-				yield fixDestructuringDefaultValue(node, source, fixer, operator);
-				yield * fixDestructuring(node, source, fixer);
+				yield fixDestructuringDefaultValue(node, sourceCode, fixer, operator);
+				yield * fixDestructuring(node, sourceCode, fixer);
 			}
 		}));
 	} else {
 		fix = function * (fixer) {
 			yield fixer.replaceText(property, 'find');
-			yield * fixDestructuring(node, source, fixer);
+			yield * fixDestructuring(node, sourceCode, fixer);
 		};
 	}
 
@@ -221,7 +226,7 @@ const isDestructuringFirstElement = node => {
 };
 
 const create = context => {
-	const source = context.getSourceCode();
+	const sourceCode = context.getSourceCode();
 
 	return {
 		[zeroIndexSelector](node) {
@@ -248,18 +253,19 @@ const create = context => {
 			context.report({
 				node: node.init.callee.property,
 				messageId: ERROR_DESTRUCTURING_DECLARATION,
-				...fixDestructuringAndReplaceFilter(source, node)
+				...fixDestructuringAndReplaceFilter(sourceCode, node)
 			});
 		},
 		[destructuringAssignmentSelector](node) {
 			context.report({
 				node: node.right.callee.property,
 				messageId: ERROR_DESTRUCTURING_ASSIGNMENT,
-				...fixDestructuringAndReplaceFilter(source, node)
+				...fixDestructuringAndReplaceFilter(sourceCode, node)
 			});
 		},
 		[filterVariableSelector](node) {
-			const variable = findVariable(context.getScope(), node.id);
+			const scope = context.getScope();
+			const variable = findVariable(scope, node.id);
 			const identifiers = getVariableIdentifiers(variable).filter(identifier => identifier !== node.id);
 
 			if (identifiers.length === 0) {
@@ -288,12 +294,22 @@ 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(scope), context.parserOptions.ecmaVersion);
+						yield * renameVariable(variable, singularizedName, fixer);
+
+						// Prevent possible variable conflicts
+						yield * extendFixRange(fixer, sourceCode.ast.range);
+					}
+
 					for (const node of zeroIndexNodes) {
 						yield fixer.removeRange([node.object.range[1], node.range[1]]);
 					}
 
 					for (const node of destructuringNodes) {
-						yield * fixDestructuring(node, source, fixer);
+						yield * fixDestructuring(node, sourceCode, fixer);
 					}
 				};
 			}

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 +681,126 @@ 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}]
+		},
+		{
+			code: outdent`
+				const item = 1;
+				function f() {
+					const items = array.filter(bar);
+					console.log(items[0]);
+				}
+			`,
+			output: outdent`
+				const item = 1;
+				function f() {
+					const item_ = array.find(bar);
+					console.log(item_);
+				}
+			`,
+			errors: [{messageId: ERROR_DECLARATION}]
+		},
+		{
+			code: outdent`
+				const items = array.filter(bar);
+				function f() {
+					const item = 1;
+					const item_ = 2;
+					console.log(items[0]);
+				}
+			`,
+			output: outdent`
+				const item__ = array.find(bar);
+				function f() {
+					const item = 1;
+					const item_ = 2;
+					console.log(item__);
+				}
+			`,
+			errors: [{messageId: ERROR_DECLARATION}]
+		},
+		{
+			code: outdent`
+				const items = array.filter(bar);
+				function f() {
+					console.log(items[0], item);
+				}
+			`,
+			output: outdent`
+				const item_ = array.find(bar);
+				function f() {
+					console.log(item_, item);
+				}
+			`,
+			errors: [{messageId: ERROR_DECLARATION}]
+		},
+		{
+			code: outdent`
+				const items = array.filter(bar);
+				console.log(items[0]);
+				function f(item) {
+					return item;
+				}
+			`,
+			output: outdent`
+				const item_ = array.find(bar);
+				console.log(item_);
+				function f(item) {
+					return item;
+				}
+			`,
+			errors: [{messageId: ERROR_DECLARATION}]
+		},
+		{
+			code: outdent`
+				function f() {
+					const items = array.filter(bar);
+					console.log(items[0]);
+				}
+				function f2(item) {
+					return item;
+				}
+			`,
+			output: outdent`
+				function f() {
+					const item = array.find(bar);
+					console.log(item);
+				}
+				function f2(item) {
+					return item;
+				}
+			`,
+			errors: [{messageId: ERROR_DECLARATION}]
+		},
+
 		// Not fixable
 		{
 			code: 'const foo = array.filter(bar); const [first = bar] = foo;',