function getBaseConfig() {
  return {
    parser: 'hermes-eslint',
    parserOptions: {
      ecmaVersion: 6,
      sourceType: 'module',
    },

    plugins: [
      'babel',
      'ft-flow',
      'jsx-a11y',
      'react',
    ],

    // Tries to match the jshint configuration as closely as possible, with the
    // exeception of a few things that jshint doesn't check, but that we really
    // shouldn't be using anyways.
    //
    // Things that jshint checked for are errors, new rules are warnings.
    //
    // If you update eslint, be sure to check the changelog to figure out what
    // rules to add/remove to/from this list.
    rules: {
      // Possible Errors <http://eslint.org/docs/rules/#possible-errors>

      // Forked and moved to fb-www/comma-dangle
      'comma-dangle': OFF,
      // equivalent to jshint boss
      'no-cond-assign': OFF,
      // equivalent to jshint devel
      'no-console': [WARNING, {
        allow: ['warn', 'error', 'time', 'timeEnd', 'timeStamp'],
      }],
      // prohibits things like `while (true)`
      'no-constant-condition': OFF,
      // we need to be able to match these
      'no-control-regex': OFF,
      // equivalent to jshint debug
      'no-debugger': ERROR,
      // equivalent to jshint W004
      'no-dupe-args': ERROR,
      // syntax error in strict mode, almost certainly unintended in any case
      'no-dupe-keys': ERROR,
      // almost certainly a bug
      'no-duplicate-case': WARNING,
      // almost certainly a bug
      'no-empty-character-class': WARNING,
      // would warn on uncommented empty `catch (ex) {}` blocks
      'no-empty': OFF,
      // can cause subtle bugs in IE 8, and we shouldn't do this anyways
      'no-ex-assign': WARNING,
      // we shouldn't do this anyways
      'no-extra-boolean-cast': WARNING,
      // parens may be used to improve clarity, equivalent to jshint W068
      'no-extra-parens': [WARNING, 'functions'],
      // equivalent to jshint W032
      'no-extra-semi': WARNING,
      // a function delaration shouldn't be rewritable
      'no-func-assign': ERROR,
      // babel and es6 allow block-scoped functions
      'no-inner-declarations': OFF,
      // will cause a runtime error
      'no-invalid-regexp': WARNING,
      // disallow non-space or tab whitespace characters
      'no-irregular-whitespace': WARNING,
      // write `if (!(a in b))`, not `if (!a in b)`, equivalent to jshint W007
      'no-negated-in-lhs': ERROR,
      // will cause a runtime error
      'no-obj-calls': ERROR,
      // improves legibility
      'no-regex-spaces': WARNING,
      // equivalent to jshint elision
      'no-sparse-arrays': ERROR,
      // equivalent to jshint W027
      'no-unreachable': ERROR,
      // equivalent to jshint use-isnan
      'use-isnan': ERROR,
      // probably too noisy ATM
      'valid-jsdoc': OFF,
      // equivalent to jshint notypeof
      'valid-typeof': ERROR,
      // we already require semicolons
      'no-unexpected-multiline': OFF,

      // Best Practices <http://eslint.org/docs/rules/#best-practices>

      // probably a bug, we shouldn't actually even use this yet, because of IE8
      'accessor-pairs': [WARNING, {setWithoutGet: true}],
      // probably too noisy ATM
      'block-scoped-var': OFF,
      // cyclomatic complexity, we're too far gone
      'complexity': OFF,
      // require return statements to either always or never specify values
      'consistent-return': WARNING,
      // style guide: Always use brackets, even when optional.
      'curly': [WARNING, 'all'],
      // we don't do this/care about this
      'default-case': OFF,
      // disabled in favor of our temporary fork
      'dot-notation': OFF,
      // we don't do this/care about this, but probably should eventually
      'dot-location': OFF,
      // disabled as it's too noisy ATM
      'eqeqeq': [OFF, 'allow-null'],
      // we don't do this/care about this, equivalent to jshint forin
      'guard-for-in': OFF,
      // we have too many internal examples/tools using this
      'no-alert': OFF,
      // incompatible with 'use strict' equivalent to jshint noarg
      'no-caller': ERROR,
      // we don't care about this right now, but might later
      'no-case-declarations': OFF,
      // we don't do this/care about this
      'no-div-regex': OFF,
      // we don't do this/care about this
      'no-else-return': OFF,
      // avoid mistaken variables when destructuring
      'no-empty-pattern': WARNING,
      // see eqeqeq: we explicitly allow this, equivalent to jshint eqnull
      'no-eq-null': OFF,
      // equivalent to jshint evil
      'no-eval': ERROR,
      // should only be triggered on polyfills, which we can fix case-by-case
      'no-extend-native': WARNING,
      // might be a sign of a bug
      'no-extra-bind': WARNING,
      // equivalent to jshint W089
      'no-fallthrough': WARNING,
      // equivalent to jshint W008
      'no-floating-decimal': ERROR,
      // implicit coercion is often idiomatic
      'no-implicit-coercion': OFF,
      // equivalent to jshint evil/W066
      'no-implied-eval': ERROR,
      // will likely create more signal than noise
      'no-invalid-this': OFF,
      // babel should handle this fine
      'no-iterator': OFF,
      // Should be effectively equivalent to jshint W028 - allowing the use
      // of labels in very specific situations. ESLint no-empty-labels was
      // deprecated.
      'no-labels': [ERROR, {allowLoop: true, allowSwitch: true}],
      // lone blocks create no scope, will ignore blocks with let/const
      'no-lone-blocks': WARNING,
      // equivalent to jshint loopfunc
      'no-loop-func': OFF,
      // we surely have these, don't bother with it
      'no-magic-numbers': OFF,
      // we may use this for alignment in some places
      'no-multi-spaces': OFF,
      // equivalent to jshint multistr, consider using es6 template strings
      'no-multi-str': ERROR,
      // equivalent to jshint W02OFF, similar to no-extend-native
      'no-native-reassign': ERROR,
      // equivalent to jshint evil/W054
      'no-new-func': ERROR,
      // don't use constructors for side-effects, equivalent to jshint nonew
      'no-new': WARNING,
      // very limited uses, mostly in third_party
      'no-new-wrappers': WARNING,
      // deprecated in ES5, but we still use it in some places
      'no-octal-escape': WARNING,
      // deprecated in ES5, may cause unexpected behavior
      'no-octal': WARNING,
      // treats function parameters as constants, probably too noisy ATM
      'no-param-reassign': OFF,
      // only relevant to node code
      'no-process-env': OFF,
      // deprecated in ES3.WARNING, equivalent to jshint proto
      'no-proto': ERROR,
      // jshint doesn't catch this, but this is inexcusable
      'no-redeclare': WARNING,
      // equivalent to jshint boss
      'no-return-assign': OFF,
      // equivalent to jshint scripturl
      'no-script-url': ERROR,
      // not in jshint, but is in jslint, and is almost certainly a mistake
      'no-self-compare': WARNING,
      // there are very limited valid use-cases for this
      'no-sequences': WARNING,
      // we're already pretty good about this, and it hides stack traces
      'no-throw-literal': ERROR,
      // breaks on `foo && foo.bar()` expression statements, which are common
      'no-unused-expressions': OFF,
      // disallow unnecessary .call() and .apply()
      'no-useless-call': WARNING,
      // disallow concatenating string literals
      'no-useless-concat': WARNING,
      // this has valid use-cases, eg. to circumvent no-unused-expressions
      'no-void': OFF,
      // this journey is 1% finished (allow TODO comments)
      'no-warning-comments': OFF,
      // equivalent to jshint withstmt
      'no-with': OFF,
      // require radix argument in parseInt, we do this in most places already
      'radix': WARNING,
      // we don't do this/care about this
      'vars-on-top': OFF,
      // equivalent to jshint immed
      'wrap-iife': OFF,
      // probably too noisy ATM
      'yoda': OFF,

      // Strict Mode <http://eslint.org/docs/rules/#strict-mode>
      // jshint wasn't checking this, and the compiler should add this anyways
      'strict': OFF,

      // Variables <http://eslint.org/docs/rules/#variables>
      // we don't do this/care about this
      'init-declarations': OFF,
      // equivalent to jshint W002, catches an IE8 bug
      'no-catch-shadow': ERROR,
      // equivalent to jshint W051, is a strict mode violation
      'no-delete-var': ERROR,
      // we should avoid labels anyways
      'no-label-var': WARNING,
      // redefining undefined, NaN, Infinity, arguments, and eval is bad, mkay?
      'no-shadow-restricted-names': WARNING,
      // a definite code-smell, but probably too noisy
      'no-shadow': OFF,
      // it's nice to be explicit sometimes: `let foo = undefined;`
      'no-undef-init': OFF,
      // equivalent to jshint undef, turned into an error in getConfig
      'no-undef': WARNING,
      // using undefined is safe because we enforce no-shadow-restricted-names
      'no-undefined': OFF,
      // equivalent to jshint unused
      'no-unused-vars': [WARNING, {args: 'none', varsIgnorePattern: '^_'}],
      // too noisy
      'no-use-before-define': OFF,

      // Node.js <http://eslint.org/docs/rules/#nodejs>
      // TODO: turn some of these on in places where we lint node code
      'callback-return': OFF,
      'global-require': OFF,
      'handle-callback-err': OFF,
      'no-mixed-requires': OFF,
      'no-new-require': OFF,
      'no-path-concat': OFF,
      'no-process-exit': OFF,
      'no-restricted-modules': OFF,
      'no-sync': OFF,

      // Stylistic Issues <http://eslint.org/docs/rules/#stylistic-issues>
      // See also: https://our.intern.facebook.com/intern/dex/style-guide/
      'array-bracket-spacing': WARNING,
      // TODO: enable this with consensus on single line blocks
      'block-spacing': OFF,
      'brace-style': [WARNING, '1tbs', {allowSingleLine: true}],
      // too noisy at the moment, and jshint didn't check it
      'camelcase': [OFF, {properties: 'always'}],
      'comma-spacing': [WARNING, {before: false, after: true}],
      // jshint had laxcomma, but that was against our style guide
      'comma-style': [WARNING, 'last'],
      'computed-property-spacing': [WARNING, 'never'],
      // we may use more contextually relevant names for this than self
      'consistent-this': [OFF, 'self'],
      // should be handled by a generic TXT linter instead
      'eol-last': OFF,
      'func-names': OFF,
      // too noisy ATM
      'func-style': [OFF, 'declaration'],
      // no way we could enforce min/max lengths or patterns for vars
      'id-length': OFF,
      'id-match': OFF,
      // we weren't enforcing this with jshint, so erroring would be too noisy
      'indent': [WARNING, INDENT_SIZE, {SwitchCase: 1}],
      // we use single quotes for JS literals, double quotes for JSX literals
      'jsx-quotes': [WARNING, 'prefer-double'],
      // we may use extra spaces for alignment
      'key-spacing': [OFF, {beforeColon: false, afterColon: true}],
      'keyword-spacing': [WARNING],
      'lines-around-comment': OFF,
      // should be handled by a generic TXT linter instead
      'linebreak-style': [OFF, 'unix'],
      'max-depth': OFF,
      'max-len': [WARNING, 80, INDENT_SIZE,
        {'ignorePattern': maxLenIgnorePattern, 'ignoreUrls': true},
      ],
      'max-nested-callbacks': OFF,
      'max-params': OFF,
      'max-statements': OFF,
      // https://facebook.com/groups/995898333776940/1027358627297577
      'new-cap': OFF,
      // equivalent to jshint W058
      'new-parens': ERROR,
      'newline-after-var': OFF,
      'no-array-constructor': ERROR,
      'no-bitwise': WARNING,
      'no-continue': OFF,
      'no-inline-comments': OFF,
      // doesn't play well with `if (__DEV__) {}`
      'no-lonely-if': OFF,
      // stopgap, irrelevant if we can eventually turn `indent` on to error
      'no-mixed-spaces-and-tabs': ERROR,
      // don't care
      'no-multiple-empty-lines': OFF,
      'no-negated-condition': OFF,
      // we do this a bunch of places, and it's less bad with proper indentation
      'no-nested-ternary': OFF,
      // similar to FacebookWebJSLintLinter's checkPhpStyleArray
      'no-new-object': WARNING,
      'no-plusplus': OFF,
      'no-restricted-syntax': OFF,
      'no-spaced-func': WARNING,
      'no-ternary': OFF,
      // should be handled by a generic TXT linter instead
      'no-trailing-spaces': OFF,
      // we use this for private/protected identifiers
      'no-underscore-dangle': OFF,
      // disallow `let isYes = answer === 1 ? true : false;`
      'no-unneeded-ternary': WARNING,
      // too noisy ATM
      'object-curly-spacing': OFF,
      // makes indentation warnings clearer
      'one-var': [WARNING, {initialized: 'never'}],
      // prefer `x += 4` over `x = x + 4`
      'operator-assignment': [WARNING, 'always'],
      // equivalent to jshint laxbreak
      'operator-linebreak': OFF,
      'padded-blocks': OFF,
      // probably too noisy on pre-ES5 code
      'quote-props': [OFF, 'as-needed'],
      'quotes': [
        WARNING,
        'single',
        {
          avoidEscape: true,
          allowTemplateLiterals: true,
        },
      ],
      'require-jsdoc': OFF,
      'semi-spacing': [WARNING, {before: false, after: true}],
      // equivalent to jshint asi/W032
      'semi': [WARNING, 'always'],
      'sort-vars': OFF,
      // require `if () {` instead of `if (){`
      'space-before-blocks': [WARNING, 'always'],
      // require `function foo()` instead of `function foo ()`
      'space-before-function-paren': [
        WARNING,
        {anonymous: 'never', named: 'never'},
      ],
      // incompatible with our legacy inline type annotations
      'space-in-parens': [OFF, 'never'],
      'space-infix-ops': [WARNING, {int32Hint: true}],
      'space-unary-ops': [WARNING, {words: true, nonwords: false}],
      // TODO: Figure out a way to do this that doesn't break typechecks
      // or wait for https://github.com/eslint/eslint/issues/2897
      'spaced-comment':
        [OFF, 'always', {exceptions: ['jshint', 'jslint', 'eslint', 'global']}],
      'wrap-regex': OFF,

      // ECMAScript 6 <http://eslint.org/docs/rules/#ecmascript-6>
      'arrow-body-style': OFF,
      // Forked to fb-www/arrow-parens to fix issues with flow and add fixer
      'arrow-parens': OFF,
      // tbgs finds *very few* places where we don't put spaces around =>
      'arrow-spacing': [WARNING, {before: true, after: true}],
      // violation of the ES6 spec, won't transform
      'constructor-super': ERROR,
      // https://github.com/babel/babel-eslint#known-issues
      'generator-star-spacing': OFF,
      'no-class-assign': WARNING,
      'no-confusing-arrow': OFF,
      // this is a runtime error
      'no-const-assign': ERROR,
      'no-dupe-class-members': ERROR,
      // violation of the ES6 spec, won't transform, `this` is part of the TDZ
      'no-this-before-super': ERROR,
      'no-useless-computed-key': WARNING,
      // we have way too much ES3 & ES5 code
      'no-var': OFF,
      'object-shorthand': OFF,
      'prefer-const': OFF,
      'prefer-spread': OFF,
      // we don't support/polyfill this yet
      'prefer-reflect': OFF,
      'prefer-template': OFF,
      // there are legitimate use-cases for an empty generator
      'require-yield': OFF,

      // eslint-plugin-babel <https://github.com/babel/eslint-plugin-babel>
      'babel/generator-star-spacing': OFF,
      'babel/new-cap': OFF,
      'babel/array-bracket-spacing': OFF,
      'babel/object-curly-spacing': OFF,
      'babel/object-shorthand': OFF,
      'babel/arrow-parens': OFF,
      'babel/no-await-in-loop': OFF,
      'babel/flow-object-type': [WARNING, 'comma'],

      // eslint-plugin-react <https://github.com/yannickcr/eslint-plugin-react>
      // TODO: We're being extremely conservative here as we roll out eslint on
      // www. As we finish rollout, we can turn on more of these, and replace
      // some legacy regex rules in the process.
      'react/display-name': OFF,
      'react/forbid-prop-types': OFF,
      'react/jsx-boolean-value': OFF,
      'react/jsx-closing-bracket-location': OFF,
      'react/jsx-curly-spacing': OFF,
      'react/jsx-equals-spacing': WARNING,
      'react/jsx-filename-extension': OFF,
      'react/jsx-first-prop-new-line': OFF,
      'react/jsx-handler-names': OFF,
      'react/jsx-indent': OFF,
      'react/jsx-indent-props': OFF,
      'react/jsx-key': OFF,
      'react/jsx-max-props-per-line': OFF,
      'react/jsx-no-bind': OFF,
      'react/jsx-no-duplicate-props': ERROR,
      'react/jsx-no-literals': OFF,
      'react/jsx-no-target-blank': OFF,
      'react/jsx-no-undef': ERROR,
      'react/jsx-pascal-case': OFF,
      'react/jsx-sort-props': OFF,
      'react/jsx-space-before-closing': OFF,
      // forked to fb-www/jsx-uses-react
      'react/jsx-uses-react': OFF,
      'react/jsx-uses-vars': ERROR,
      'react/jsx-wrap-multilines': OFF,
      'react/no-comment-textnodes': OFF,
      'react/no-danger': OFF,
      'react/no-deprecated': OFF,
      'react/no-did-mount-set-state': OFF,
      'react/no-did-update-set-state': OFF,
      'react/no-direct-mutation-state': OFF,
      'react/no-is-mounted': WARNING,
      'react/no-multi-comp': OFF,
      'react/no-render-return-value': OFF,
      'react/no-set-state': OFF,
      'react/no-string-refs': OFF,
      'react/no-unknown-property': OFF,
      'react/prefer-es6-class': OFF,
      'react/prefer-stateless-function': OFF,
      'react/prop-types': OFF,
      // forked to fb-www/react-in-jsx-scope
      'react/react-in-jsx-scope': OFF,
      'react/require-extension': OFF,
      'react/require-optimization': OFF,
      'react/require-render-return': OFF,
      'react/self-closing-comp': OFF,
      'react/sort-comp': OFF,
      'react/sort-prop-types': OFF,

      // JSX Accessibility checks
      'jsx-a11y/accessible-emoji': OFF,
      'jsx-a11y/anchor-has-content': OFF,
      'jsx-a11y/aria-activedescendant-has-tabindex': OFF,
      'jsx-a11y/aria-props': WARNING,
      'jsx-a11y/aria-proptypes': OFF,
      'jsx-a11y/aria-role': WARNING,
      'jsx-a11y/aria-unsupported-elements': OFF,
      'jsx-a11y/click-events-have-key-events': OFF,
      'jsx-a11y/heading-has-content': OFF,
      'jsx-a11y/html-has-lang': OFF,
      'jsx-a11y/iframe-has-title': OFF,
      'jsx-a11y/img-has-alt': OFF,
      'jsx-a11y/img-redundant-alt': OFF,
      'jsx-a11y/interactive-supports-focus': [
        WARNING,
        {
          tabbable: [
            'button',
            'checkbox',
            'link',
            'searchbox',
            'spinbutton',
            'switch',
            'textbox',
          ],
        },
      ],
      'jsx-a11y/label-has-for': OFF,
      'jsx-a11y/lang': OFF,
      'jsx-a11y/mouse-events-have-key-events': OFF,
      'jsx-a11y/no-access-key': OFF,
      'jsx-a11y/no-autofocus': OFF,
      'jsx-a11y/no-distracting-elements': OFF,
      'jsx-a11y/no-interactive-element-to-noninteractive-role': [
        WARNING,
        {
          tr: ['none', 'presentation'],
        },
      ],
      'jsx-a11y/no-noninteractive-element-interactions': [
        WARNING,
        {
          handlers: ['onClick'],
        },
      ],
      'jsx-a11y/no-noninteractive-element-to-interactive-role': [
        WARNING,
        {
          ul: ['listbox', 'menu', 'menubar',
            'radiogroup', 'tablist', 'tree', 'treegrid'],
          ol: ['listbox', 'menu', 'menubar',
            'radiogroup', 'tablist', 'tree', 'treegrid'],
          li: ['menuitem', 'option', 'row', 'tab', 'treeitem'],
          table: ['grid'],
          td: ['gridcell'],
        },
      ],
      'jsx-a11y/no-noninteractive-tabindex': WARNING,
      'jsx-a11y/no-onchange': OFF,
      'jsx-a11y/no-redundant-roles': OFF,
      'jsx-a11y/no-static-element-interactions': [
        WARNING,
        {
          handlers: ['onClick'],
        },
      ],
      'jsx-a11y/role-has-required-aria-props': WARNING,
      'jsx-a11y/role-supports-aria-props': WARNING,
      'jsx-a11y/scope': OFF,
      'jsx-a11y/tabindex-no-positive': WARNING,

      // eslint-plugin-ft-flow
      // These don't actually result in warnings. Enabling them ensures they run
      // and mark variables as used, avoiding false positives with Flow
      // annotations.
      'ft-flow/define-flow-type': WARNING,
      'ft-flow/use-flow-type': WARNING,
    },

    // Defines a basic set of globals
    env: {
      browser: true,
      es6: true,
    },

    globals: shared.globals,

  };
}
This file resembles what we use for our internal configuration. Several changes
have been made to acoomodate the differences between our internal setup and
what we would expect to see in open source.

Internally we also lint each file individually, allowing use to use the file
path to selectively enable/disable pieces of the lint configuration. For
example, we don't actually want jest globals to be enabled all the time so
we only enable that when we know we're linting a test file. That isn't possible
here so we just always enable that.

We are also missing our growing library of custom rules. Many of those will
make their way out here soon, but it does mean we need to do some editing of
our configuration object.