chore: migrate to ESLint 9 with flat config

eslint.config.js

@@ -0,0 +1,59 @@
+const AutomatticPlugin = require( '@automattic/eslint-plugin-wpvip' );
+const ReactPlugin = require( 'eslint-plugin-react' );
+const ReactHooksPlugin = require( 'eslint-plugin-react-hooks' );
+const JsxA11yPlugin = require( 'eslint-plugin-jsx-a11y' );
+
+module.exports = [
+	{
+		ignores: [
+			'node_modules/**/*',
+			'**/dist/**/*',
+			'vendor/**/*',
+			'**/*.build.js',
+		],
+	},
+	// Use individual configs instead of "recommended" to avoid react-hooks flat config bug
+	// in @automattic/eslint-plugin-wpvip@1.0.0 (uses legacy plugins array format)
+	...AutomatticPlugin.configs.javascript,
+	...AutomatticPlugin.configs.testing,
+	// Manually configure React with correct flat config exports
+	ReactPlugin.configs.flat.recommended,
+	ReactHooksPlugin.configs.flat.recommended,
+	JsxA11yPlugin.flatConfigs.recommended,
+	{
+		settings: {
+			react: {
+				version: 'detect',
+			},
+		},
+		rules: {
+			// Project-specific rule overrides (matching previous .eslintrc.js)
+			'no-prototype-builtins': 'off',
+			'no-eval': 'off',
+			complexity: 'off',
+			camelcase: 'off',
+			'no-undef': 'off',
+			'valid-jsdoc': 'off',
+			'react/prop-types': 'off',
+			'react/react-in-jsx-scope': 'off',
+			'react-hooks/rules-of-hooks': 'off',
+			'no-redeclare': 'off',
+			'no-shadow': 'off',
+			'no-nested-ternary': 'off',
+			'no-var': 'off',
+			'no-unused-vars': 'off',
+			'no-useless-escape': 'off',
+			'prefer-const': 'off',
+			'no-global-assign': 'off',
+			'no-constant-binary-expression': 'off',
+			'valid-typeof': 'off',
+			eqeqeq: 'off',
+			radix: 'off',
+			'no-eq-null': 'off',
+			'array-callback-return': 'off',
+			'no-unused-expressions': 'off',
+			'no-alert': 'off',
+			'no-lonely-if': 'off',
+		},
+	},
+];

modules/calendar/lib/react/calendar-date-change-buttons/index.js

@@ -35,9 +35,7 @@ const moveByWeeks = ( addOrSubtract, beginningOfWeek, pageUrl, filterValues, wee
 		queryArgFilters.start_date = beginningOfWeek;
 	}
 
-	queryArgFilters.start_date = moment( queryArgFilters.start_date, 'YYYY-MM-DD' )
-		[ addOrSubtract ]( weeksNumber, 'weeks' )
-		.format( 'YYYY-MM-DD' );
+	queryArgFilters.start_date = moment( queryArgFilters.start_date, 'YYYY-MM-DD' )[ addOrSubtract ]( weeksNumber, 'weeks' ).format( 'YYYY-MM-DD' );
 
 	return addQueryArgs( pageUrl, queryArgFilters );
 };

modules/calendar/lib/react/calendar.react.js

@@ -17,9 +17,9 @@ import './style.react.scss';
 function flatDeep( arr, d = 1 ) {
 	return d > 0
 		? arr.reduce(
-				( acc, val ) => acc.concat( Array.isArray( val ) ? flatDeep( val, d - 1 ) : val ),
-				[]
-		  )
+			( acc, val ) => acc.concat( Array.isArray( val ) ? flatDeep( val, d - 1 ) : val ),
+			[]
+		)
 		: arr.slice();
 }
 

modules/calendar/lib/react/combobox/index.js

@@ -28,8 +28,8 @@ import './style.react.scss';
 function getItems( filter, items ) {
 	return filter
 		? matchSorter( items, filter, {
-				keys: [ 'name' ],
-		  } )
+			keys: [ 'name' ],
+		} )
 		: items;
 }