Build: Update ESLint to v9, migrate to flat config, lint dist files

Dist files linting is limited to checking if they're proper ES5.

Closes gh-2336

1 files changed, 162 insertions, 0 deletions

diff --git a/eslint.config.mjs b/eslint.config.mjs
new file mode 100644
index 000000000..4fb03f6b3
--- /dev/null
+++ b/eslint.config.mjs
@@ -0,0 +1,162 @@
+import jqueryConfig from "eslint-config-jquery";
+import globals from "globals";
+
+export default [
+	{
+		ignores: [
+			"dist/**/*",
+			"!dist/jquery-ui.js",
+			"!dist/jquery-ui.min.js",
+			"external/**/*",
+			"tests/lib/vendor/**/*",
+			"ui/vendor/**/*"
+		]
+	},
+
+	{
+		ignores: [ "dist/**/*" ],
+		rules: {
+			...jqueryConfig.rules,
+			"no-unused-vars": [
+				"error",
+				{
+					argsIgnorePattern: "^_",
+					caughtErrorsIgnorePattern: "^_"
+				}
+			]
+		}
+	},
+
+	{
+		files: [ "Gruntfile.js" ],
+		languageOptions: {
+			ecmaVersion: "latest",
+			sourceType: "commonjs",
+			globals: {
+				...globals.node
+			}
+		},
+		rules: {
+			strict: [ "error", "global" ]
+		}
+	},
+
+	{
+		files: [ "eslint.config.mjs" ],
+		languageOptions: {
+			ecmaVersion: "latest",
+			sourceType: "module",
+			globals: {
+				...globals.node
+			}
+		},
+		rules: {
+			strict: [ "error", "global" ]
+		}
+	},
+
+	// Source, demos
+	{
+		files: [ "ui/**/*.js", "demos/**/*.js" ],
+		languageOptions: {
+			ecmaVersion: 5,
+			sourceType: "script",
+			globals: {
+				...globals.browser,
+				...globals.jquery,
+				define: false,
+				Globalize: false
+			}
+		},
+		rules: {
+			strict: [ "error", "function" ],
+
+			// The following rule is relaxed due to too many violations:
+			"no-unused-vars": [
+				"error",
+				{
+					args: "after-used",
+					argsIgnorePattern: "^_",
+					caughtErrorsIgnorePattern: "^_"
+				}
+			],
+
+			// Too many violations:
+			camelcase: "off",
+			"no-nested-ternary": "off"
+		}
+	},
+	{
+		files: [ "ui/i18n/**/*.js" ],
+		rules: {
+
+			// We want to keep all the strings in separate single lines
+			"max-len": "off"
+		}
+	},
+
+	// Dist files
+	// For dist files, we don't include any jQuery rules on purpose.
+	// We just want to make sure the files are correct ES5.
+	{
+		files: [ "dist/jquery-ui.js", "dist/jquery-ui.min.js" ],
+		languageOptions: {
+			ecmaVersion: 5,
+			sourceType: "script"
+		},
+		linterOptions: {
+			reportUnusedDisableDirectives: "off"
+		}
+	},
+
+	// Build
+	{
+		files: [ "build/**/*.js" ],
+		languageOptions: {
+			ecmaVersion: "latest",
+			sourceType: "commonjs",
+			globals: {
+				...globals.node
+			}
+		},
+		rules: {
+			"no-implicit-globals": "error",
+			strict: [ "error", "global" ]
+		}
+	},
+
+	// Demos
+	{
+		files: [ "demos/**/*.js" ],
+		languageOptions: {
+			globals: {
+				require: true
+			}
+		}
+	},
+
+	// Tests
+	{
+		files: [ "tests/**/*.js" ],
+		languageOptions: {
+			ecmaVersion: 5,
+			sourceType: "script",
+			globals: {
+				...globals.browser,
+				...globals.jquery,
+				define: false,
+				Globalize: false,
+				QUnit: false,
+				require: true,
+				requirejs: true
+			}
+		},
+		"rules": {
+
+			// Too many violations:
+			"max-len": "off",
+			"no-unused-vars": "off",
+			strict: "off" // ideally, `[ "error", "function" ]`
+		}
+	}
+];