chore: migrate to ESLint v9 and Flat Config

Author: taeold

.eslintignore

@@ -0,0 +1,111 @@
+const { FlatCompat } = require("@eslint/eslintrc");
+const js = require("@eslint/js");
+const path = require("path");
+
+const compat = new FlatCompat({
+    baseDirectory: __dirname,
+    recommendedConfig: js.configs.recommended,
+    allConfig: js.configs.all
+});
+
+module.exports = [
+    {
+        ignores: [
+            "lib/",
+            "dev/",
+            "node_modules/",
+            "coverage/",
+            "docgen/",
+            "v1/",
+            "v2/",
+            "logger/",
+            "dist/",
+            "spec/fixtures/",
+            "scripts/**/*.js",
+            "protos/",
+            ".prettierrc.js",
+            "eslint.config.js",
+            "scripts/bin-test/sources/esm-ext/index.mjs",
+        ],
+    },
+    ...compat.extends(
+        "eslint:recommended",
+        "plugin:@typescript-eslint/recommended",
+        "plugin:@typescript-eslint/recommended-requiring-type-checking",
+        "plugin:jsdoc/recommended",
+        "google",
+        "prettier"
+    ),
+    {
+        languageOptions: {
+            parser: require("@typescript-eslint/parser"),
+            parserOptions: {
+                project: "tsconfig.json",
+                tsconfigRootDir: __dirname,
+            },
+            ecmaVersion: 2018,
+            sourceType: "module",
+        },
+        plugins: {
+            "prettier": require("eslint-plugin-prettier"),
+        },
+        rules: {
+            "jsdoc/newline-after-description": "off",
+            "jsdoc/require-jsdoc": ["warn", { publicOnly: true }],
+            "jsdoc/check-tag-names": ["warn", { definedTags: ["alpha", "remarks", "typeParam", "packageDocumentation", "hidden"] }],
+            "no-restricted-globals": ["error", "name", "length"],
+            "prefer-arrow-callback": "error",
+            "prettier/prettier": "off",
+            "require-atomic-updates": "off", // This rule is so noisy and isn't useful: https://github.com/eslint/eslint/issues/11899
+            "require-jsdoc": "off", // This rule is deprecated and superseded by jsdoc/require-jsdoc.
+            "valid-jsdoc": "off", // This is deprecated but included in recommended configs.
+            "no-prototype-builtins": "warn",
+            "no-useless-escape": "warn",
+            "prefer-promise-reject-errors": "warn",
+        },
+    },
+    {
+        files: ["**/*.ts"],
+        rules: {
+            "jsdoc/require-param-type": "off",
+            "jsdoc/require-returns-type": "off",
+            // Google style guide allows us to omit trivial parameters and returns
+            "jsdoc/require-param": "off",
+            "jsdoc/require-returns": "off",
+
+            "@typescript-eslint/no-invalid-this": "error",
+            "@typescript-eslint/no-unused-vars": ["error", { argsIgnorePattern: "^_", caughtErrorsIgnorePattern: "^_" }], // Unused vars should not exist.
+            "@typescript-eslint/no-misused-promises": "warn", // rule does not work with async handlers for express.
+            "no-invalid-this": "off", // Turned off in favor of @typescript-eslint/no-invalid-this.
+            "no-unused-vars": "off", // Off in favor of @typescript-eslint/no-unused-vars.
+            eqeqeq: ["error", "always", { null: "ignore" }],
+            camelcase: ["error", { properties: "never" }], // snake_case allowed in properties iif to satisfy an external contract / style
+
+            // Ideally, all these warning should be error - let's fix them in the future.
+            "@typescript-eslint/no-unsafe-argument": "warn",
+            "@typescript-eslint/no-unsafe-assignment": "warn",
+            "@typescript-eslint/no-unsafe-call": "warn",
+            "@typescript-eslint/no-unsafe-member-access": "warn",
+            "@typescript-eslint/no-unsafe-return": "warn",
+            "@typescript-eslint/restrict-template-expressions": "warn",
+            "@typescript-eslint/no-explicit-any": "warn",
+            "@typescript-eslint/no-redundant-type-constituents": "warn",
+            "@typescript-eslint/no-base-to-string": "warn",
+            "@typescript-eslint/no-duplicate-type-constituents": "warn",
+            "@typescript-eslint/no-require-imports": "warn",
+            "@typescript-eslint/no-empty-object-type": "warn",
+            "@typescript-eslint/prefer-promise-reject-errors": "warn",
+        },
+    },
+    {
+        files: ["**/*.spec.ts", "**/*.spec.js", "spec/helper.ts", "scripts/bin-test/**/*.ts", "integration_test/**/*.ts"],
+        languageOptions: {
+            globals: {
+                mocha: true,
+            },
+        },
+        rules: {
+            "@typescript-eslint/no-unused-expressions": "off",
+        }
+    },
+];

.eslintrc.js

@@ -13,8 +13,8 @@ export const pubsubTests: any = functions
     let testId: string;
     try {
       testId = m.json.testId;
-    } catch (e) {
-      /* Ignored. Covered in another test case that `event.data.json` works. */
+    } catch (_e) {
+      // Ignored. Covered in another test case that `event.data.json` works.
     }
 
     return new TestSuite<PubsubMessage>("pubsub onPublish")