Umbrella: Chopping Block

I wanted to create a list of things whose existence makes React bigger and more complicated than necessary. This makes them more likely to need to be deprecated and actually removed in a future version. No clue of when this will happen and what the recommended upgrade path will be so don't take this issue as advice that you should move away from them until there's clear upgrade advice. You might make it worse by doing so. (This has some overlap with https://github.com/facebook/react/issues/9475 but those seem more longer term.) - [ ] __Unsafe Life Cycles without UNSAFE prefix__ - We'll keep the ones prefixed UNSAFE indefinitely but the original ones will likely be deprecated and removed. - [ ] __Legacy context__ - `.contextTypes`, `.childContextTypes`, `getChildContext` - The old context is full of edge cases for when it is accidentally supposed to work and the way it is designed requires all React code to become slower just to support this feature. - [ ] __String refs__ - This requires current owner to be exposed at runtime. While it is likely that some form of owner will remain, this particular semantics is likely not what we want out of it. So rather than having two owners, we should just remove this feature. It also requires an extra field on every ReactElement which is otherwise not needed. - [ ] __Module pattern components__ - This is a little used feature that lets you return a class instance from a regular function without extending `React.Component`. This is not that useful. In practice the ecosystem has moved around ES class like usage, and other language compiling to JS tries to comply with that model as well. The existence of this feature means that we don't know that something is a functional component by just testing if it's a function that is not extending `React.Component`. Instead we have to do some extra feature testing for every functional component there is. It also prevents us from passing the ref as the second argument by default for all functi…