.eslintrc.js

module.exports = {
  root: true,
  parser: "@typescript-eslint/parser",
  plugins: [
    "@typescript-eslint",
  ],
  extends: [
    "eslint:recommended",
    "plugin:@typescript-eslint/eslint-recommended",
    "plugin:@typescript-eslint/recommended",
    "prettier"
  ],
  parserOptions: {
    ecmaVersion: 2020,
    sourceType: "module",
    ecmaFeatures: {},
  },

  // === General rules =========================================================

  rules: {
    // Omitted semicolons are hugely popular, yet within the compiler it makes
    // sense to be better safe than sorry.
    semi: "error",

    // Our code bases uses 2 spaces for indentation, and we enforce it here so
    // files don't mix spaces, tabs or different indentation levels.
    indent: [
      "error",
      2,
      {
        SwitchCase: 1,
        VariableDeclarator: "first",
        offsetTernaryExpressions: true,
        ignoredNodes: [
          // FIXME: something's odd here
          "ConditionalExpression > *",
          "ConditionalExpression > * > *",
          "ConditionalExpression > * > * > *",
        ],
      },
    ],

    // This is mostly visual style, making comments look uniform.
    "spaced-comment": [
      "error",
      "always",
      {
        markers: ["/"], // triple-slash
        exceptions: ["/"], // all slashes
      },
    ],

    // This tends to be annoying as it encourages developers to make everything
    // that is never reassigned a 'const', sometimes semantically incorrect so,
    // typically leading to huge diffs in follow-up PRs modifying affected code.
    "prefer-const": "off",

    // It is perfectly fine to declare top-level variables with `var`, yet this
    // rule doesn't provide configuration options that would help.
    "no-var": "off",

    // Quite often, dealing with multiple related cases at once or otherwise
    // falling through is exactly the point of using a switch.
    "no-fallthrough": "off",

    // Typical false-positives here are `do { ... } while (true)` statements or
    // similar, but the only option provided here is not checking any loops.
    "no-constant-condition": ["error", { checkLoops: false }],

    // Functions are nested in blocks occasionally, and there haven't been any
    // problems with this so far, so turning the check off.
    "no-inner-declarations": "off",

    // Quite common in scenarios where an iteration starts at `current = this`.
    "@typescript-eslint/no-this-alias": "off",

    // Disabled here, but enabled again for JavaScript files.
    "no-unused-vars": "off",

    // Disabled here, but enabled again for TypeScript files.
    "@typescript-eslint/no-unused-vars": "off",
  },
  overrides: [
    // === TypeScript rules ====================================================

    {
      files: ["**/assembly/**/*.ts"],
      rules: {
        // Enforcing to remove function parameters on stubs makes code less
        // maintainable, so we instead allow unused function parameters.
        "@typescript-eslint/no-unused-vars": [
          "warn",
          {
            vars: "local",
            varsIgnorePattern: "^_|^[A-Z](?:From|To)?$", // ignore type params
            args: "none",
            ignoreRestSiblings: false,
          },
        ],

        // Namespaces are quite useful in AssemblyScript
        "@typescript-eslint/no-namespace": "off",

        // There is actually codegen difference here
        "@typescript-eslint/no-array-constructor": "off",

        // Sometimes it can't be avoided to add a @ts-ignore
        "@typescript-eslint/ban-ts-comment": "off",

        // Utilized to achieve portability in some cases
        "@typescript-eslint/no-non-null-assertion": "off",
      },
    },

    // === Compiler rules (extends AssemblyScript rules) =======================

    {
      files: ["**/assembly/**/*.ts"],
      rules: {
        // There is an actual codegen difference here - TODO: revisit
        "no-cond-assign": "off",

        // Not all types can be omitted in AS yet - TODO: revisit
        "@typescript-eslint/no-inferrable-types": "off",

        // Used rarely to reference internals that are not user-visible
        "@typescript-eslint/triple-slash-reference": "off",

        // The compiler has its own `Function` class for example
        "no-shadow-restricted-names": "off",
        "@typescript-eslint/ban-types": "off",
      },
    },

    // === Standard Library rules (extends AssemblyScript rules) ===============

    {
      files: ["**/assembly/**/*.ts"],
      rules: {
        // We are implementing with --noLib, so we shadow all the time
        "no-shadow-restricted-names": "off",

        // Similarly, sometimes we need the return type to be String, not string
        "@typescript-eslint/ban-types": "off",
      },
    },

    // === Standard Definition rules (extends TypeScript rules) ================

    {
      files: ["**/assembly/**/*.d.ts"],
      rules: {
        // Often required to achieve compatibility with TypeScript
        "@typescript-eslint/no-explicit-any": "off",

        // Interfaces can be stubs here, i.e. not yet fully implemented
        "@typescript-eslint/no-empty-interface": "off",

        // Definitions make use of `object` to model rather unusual constraints
        "@typescript-eslint/ban-types": "off",
      },
    },

    // === Test rules (extends TypeScript rules) ===============================

    {
      files: ["**/assembly/__tests__/**/*.ts"],
      rules: {
        // Tests typically include unusual code patterns on purpose. This is
        // very likely not an extensive list, but covers what's there so far.
        "no-empty": "off",
        "no-cond-assign": "off",
        "no-compare-neg-zero": "off",
        "no-inner-declarations": "off",
        "no-constant-condition": "off",
        "use-isnan": "off",
        "@typescript-eslint/no-namespace": "off",
        "@typescript-eslint/no-unused-vars": "off",
        "@typescript-eslint/no-empty-function": "off",
        "@typescript-eslint/no-non-null-assertion": "off",
        "@typescript-eslint/no-extra-semi": "off",
        "@typescript-eslint/no-inferrable-types": "off",
        "@typescript-eslint/ban-types": "off",
        "@typescript-eslint/triple-slash-reference": "off",
        "@typescript-eslint/ban-ts-comment": "off",
        "@typescript-eslint/no-extra-non-null-assertion": "off",
        "@typescript-eslint/no-empty-interface": "off",
      },
    },
  ],
};