Allow iOS PlatformColor strings to be ObjC or Swift UIColor selectors

[tom-un]

Summary

Per discussion in react-native-community/releases#186 the iOS PlatformColor() function is documented to use the semantic color names provided by the system. The referenced HIG documentation itself links to the UIColor documentation for semantic colors names. However, these names differ depending on if you are viewing the new Swift API docs or the Objective C docs. The current Objective C implementation in react-native assumes Objective C UIColor selector names that are suffixed 'Color'. But in Swift, Apple provides a Swift Extension on UIColor that makes aliases without the the 'Color' suffix and then makes the original selectors invalid presumably via NS_UNAVAILABLE_SWIFT.

Since both selector names are valid depending on if you are using Objective C or Swift, let's make both forms be legal for PlatformColor(). In RCTConvert.m there is a dictionary of legal selector names. The code already supports the ability to have names be aliases of other selectors via a RCTSelector metadata key. The change adds code to the initialization of the map: it iterates over the keys in the map, which are all ObjC style UIColor selectors, and creates aliases by duplicating the entries, creating key names by stripping off the ObjC "Color" suffix, adds the RCTSelector key referring to the original and then appends these new Swift aliases to the map.

Changelog

[iOS] [Changed] - Allow iOS PlatformColor strings to be ObjC or Swift UIColor selectors

Test Plan

The PlatformColorExample.js is updated to use the new, shorter Swift selector names. There are still other examples in the same file and in unit tests that exercise the ObjC selector names.

[analysis-bot]

Platform	Engine	Arch	Size (bytes)	Diff
android	hermes	arm64-v8a	6,760,906	-80
android	hermes	armeabi-v7a	6,407,914	-84
android	hermes	x86	7,143,116	-84
android	hermes	x86_64	7,033,841	-83
android	jsc	arm64-v8a	8,929,410	-5
android	jsc	armeabi-v7a	8,568,795	-35
android	jsc	x86	8,754,733	-6
android	jsc	x86_64	9,331,071	-24

Base commit: 7701275

[analysis-bot]

Platform	Engine	Arch	Size (bytes)	Diff
ios	-	universal	10,660,064	9,850,496

Base commit: 7701275

[elicwhite]

Do you want to keep any examples that include the Color suffix? And / or maybe have an automated test that verifies both ways work?

[tom-un]

As I said in the Test notes, there still are ObjC examples later in this file and in unit tests

[elicwhite]

Ah, whoops. I should read better :D

[facebook-github-bot]

@TheSavior has imported this pull request. If you are a Facebook employee, you can view this diff on Phabricator.

[react-native-bot]

This pull request was successfully merged by @tom-un in 25793ea.

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[alloy]

Seems like this code could have been slightly simpler/faster if it had been reversed, i.e. manually add them all without the Color suffix and then alias them by appending the suffix. Not a huge deal [on its own], though, as this map is cached.

[tom-un]

If reversed, it would mean having to add an explicit RCTSelector for each entry -- which is more error prone for maintenance. I like it this way because the table is more truthy to ObjC which is the native language of the RN implementation itself.