prefer-array-find and prefer-at: Fix crash on LHS zero index access

rules/prefer-array-find.js

@@ -1,6 +1,10 @@
 'use strict';
 const {isParenthesized, findVariable} = require('eslint-utils');
-const {not, methodCallSelector} = require('./selectors/index.js');
+const {
+	not,
+	methodCallSelector,
+	notLeftHandSideSelector
+} = require('./selectors/index.js');
 const getVariableIdentifiers = require('./utils/get-variable-identifiers.js');
 const renameVariable = require('./utils/rename-variable.js');
 const avoidCapture = require('./utils/avoid-capture.js');
@@ -51,6 +55,7 @@ const zeroIndexSelector = [
 	'[computed!=false]',
 	'[property.type="Literal"]',
 	'[property.raw="0"]',
+	notLeftHandSideSelector(),
 	methodCallSelector({
 		...filterMethodSelectorOptions,
 		path: 'object'

rules/prefer-at.js

@@ -9,6 +9,7 @@ const {
 const {isNodeMatchesNameOrPath} = require('./utils/is-node-matches.js');
 const needsSemicolon = require('./utils/needs-semicolon.js');
 const shouldAddParenthesesToMemberExpressionObject = require('./utils/should-add-parentheses-to-member-expression-object.js');
+const isLeftSideHand = require('./utils/is-left-hand-side.js');
 const {
 	getNegativeIndexLengthNode,
 	removeLengthNode
@@ -85,6 +86,10 @@ function checkSliceCall(node) {
 
 	let firstElementGetMethod = '';
 	if (isZeroIndexAccess(node)) {
+		if (isLeftSideHand(node.parent)) {
+			return;
+		}
+
 		firstElementGetMethod = 'zero-index';
 	} else if (isArrayShiftCall(node)) {
 		firstElementGetMethod = 'shift';

rules/selectors/not-left-hand-side.js

@@ -4,6 +4,7 @@ const not = require('./negation.js');
 function notLeftHandSideSelector(path) {
 	const prefix = path ? `${path}.` : '';
 
+	// Keep logic sync with `../utils/is-left-hand-side.js`
 	return not([
 		`[${prefix}type="AssignmentExpression"] > .left`,
 		`[${prefix}type="UpdateExpression"] > .argument`,

rules/utils/is-left-hand-side.js

@@ -0,0 +1,13 @@
+'use strict';
+
+// Keep logic sync with `../selector/not-left-hand-side.js`
+const isLeftHandSide = node =>
+	(node.parent.type === 'AssignmentExpression' && node.parent.left === node) ||
+	(node.parent.type === 'UpdateExpression' && node.parent.argument === node) ||
+	(
+		node.parent.type === 'UnaryExpression' &&
+		node.parent.operator === 'delete' &&
+		node.parent.argument === node
+	);
+
+module.exports = isLeftHandSide;

test/prefer-array-find.mjs

@@ -39,7 +39,12 @@ test({
 		// More or less argument(s)
 		'array.filter()[0]',
 		'array.filter(foo, thisArgument, extraArgument)[0]',
-		'array.filter(...foo)[0]'
+		'array.filter(...foo)[0]',
+		// LHS
+		'array.filter(foo)[0] += 1',
+		'++ array.filter(foo)[0]',
+		'array.filter(foo)[0]--',
+		'delete array.filter(foo)[0]'
 	],
 	invalid: [
 		{

test/prefer-at.mjs

@@ -77,7 +77,12 @@ test.snapshot({
 		'array.slice(-1).shift?.()',
 		'array.slice(-1)?.shift()',
 		'array.slice(-1).shift(...[])',
-		'new array.slice(-1).shift()'
+		'new array.slice(-1).shift()',
+		// LHS
+		'array.slice(-1)[0] += 1',
+		'++ array.slice(-1)[0]',
+		'array.slice(-1)[0] --',
+		'delete array.slice(-1)[0]'
 	],
 	invalid: [
 		'array.slice(-1)[0]',