.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",
  ],
  parserOptions: {
    ecmaVersion: 2020,
    sourceType: "module",
    ecmaFeatures: {}
  },
  globals: {
    "BigInt64Array": "readonly",
    "BigUint64Array": "readonly",
    "__non_webpack_require__": "readonly"
  },

  // === 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: [

    // === JavaScript rules ====================================================

    {
      env: {
        "browser": true,
        "amd": true,
        "node": true,
        "es6": true
      },
      files: [
        "**/*.js",
        "bin/*"
      ],
      rules: {
        // We are testing both ESM and UMD, so don't limit us.
        "@typescript-eslint/no-var-requires": "off",

        // This rule does not behave well in JS files.
        "@typescript-eslint/explicit-module-boundary-types": "off",

        // Enforcing to remove function parameters on stubs makes code less
        // maintainable, so we instead allow unused function parameters.
        "no-unused-vars": [
          "warn", {
            "vars": "local",
            "args": "none",
            "ignoreRestSiblings": false
          }
        ]
      }
    },

    // === TypeScript rules ====================================================

    {
      files: [
        "**/*.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
          }
        ]
      }
    },

    // === AssemblyScript rules (extends TypeScript rules) =====================

    {
      files: [
        "**/assembly/**/*.ts",
        "src/**/*.ts",
        "lib/parse/src/**/*.ts"
      ],
      rules: {
        // 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: [
        "src/**/*.ts",
        "std/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: [
        "std/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: [
        "std/**/*.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"
      }
    },

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

    {
      files: [
        "./index.d.ts",
        "./index.release.d.ts",
      ],
      rules: {
        // Our definitions are complicated, and all attempts to describe them
        // as modules have failed so far. As such, we re-export namespaces.
        "@typescript-eslint/no-namespace": "off",
        "@typescript-eslint/triple-slash-reference": "off"
      }
    },

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

    {
      files: [
        "./tests/compiler/**/*.ts",
        "./lib/loader/tests/assembly/**/*.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"
      }
    },
  ]
};