DEV-only requires in FB bundles

[gaearon]

I see ReactDOMFiber-prod starts with

var invariant = require("fbjs/lib/invariant"), EventListener = require("fbjs/lib/EventListener"), React = require("React"), warning = require("fbjs/lib/warning"), ExecutionEnvironment = require("fbjs/lib/ExecutionEnvironment");

require("fbjs/lib/camelizeStyleName");

var hyphenateStyleName = require("fbjs/lib/hyphenateStyleName"), memoizeStringOnly = require("fbjs/lib/memoizeStringOnly");

require("prop-types");

var emptyFunction = require("fbjs/lib/emptyFunction"), containsNode = require("fbjs/lib/containsNode"), focusNode = require("fbjs/lib/focusNode"), getActiveElement = require("fbjs/lib/getActiveElement"), shallowEqual = require("fbjs/lib/shallowEqual");

require("prop-types/checkPropTypes");

Notice how require("prop-types") shouldn't be there. We probably require it and then don’t use it in PROD. We need some mechanism to express a module is pure from side effects, and have Rollup DCE this require.

[gaearon]

Preliminary conclusion: we decided that we’d write a Babel plugin that removes require/imports that are not referenced and fall into a whitelist of known modules without side effects. This seems easier than hooking into Rollup.

[gaearon]

Not a problem anymore.

"use strict";
var invariant = require("fbjs/lib/invariant"),
  React = require("React"),
  ExecutionEnvironment = require("fbjs/lib/ExecutionEnvironment"),
  emptyFunction = require("fbjs/lib/emptyFunction"),
  getActiveElement = require("fbjs/lib/getActiveElement"),
  shallowEqual = require("fbjs/lib/shallowEqual"),
  containsNode = require("fbjs/lib/containsNode"),
  emptyObject = require("fbjs/lib/emptyObject"),
  TouchEventUtils = require("fbjs/lib/TouchEventUtils");

I probably fixed it in #11389, specifically in 1bd389f.