Fix RCTLinkingManager Swift representation (take 2!)

[radex]

Summary

The fix in #22764, unfortunately, does not work (at least not in Xcode 10.2 / Swift 5 mode). __has_include(<UIKitCore/UIUserActivity.h>) confuses the ObjC→Swift header converter and makes everything be Any (again, causing a crash at runtime).

This condition was added by @cpojer , so I assume it is important for Facebook tooling, but perhaps there's a different way to satisfy this?

Changelog

[CATEGORY] [TYPE] - Message

Test Plan

[pull-bot]

Messages

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[radex]

Will include a changeling — but for now, I'm waiting for @cpojer's feedback – details above :)

[cpojer]

Yeah I had to make this change at FB, otherwise it would break and not work. We use this check in other places of the codebase so I thought it is fine here too. I'm open to other suggestions.

[radex]

OK, I have one idea in mind — will test it and let you know

[cpojer]

@radex did you have a chance to get back to this?

[radex]

Not quite :( I'm stuck with this — for some reason, the swift headers converter gets very confused by __has_include...

Can you give me a little more information about how the lack of __has_include is a problem with Facebook's internal tooling? Is it related to BUCK?

Perhaps there's some preprocessor flag that's passed in Facebook builds that are not applicable to open-source builds (e.g. FACEBOOK)? If so, maybe I could use a hack like this:

#ifdef FACEBOOK
#define xcode10_headers_available __has_include......
#elseif
#define xcode10_headers_available true
#endif

[cpojer]

There is some build system stuff going on where I specifically need to test for that file to make something pass internally. I'm sorry I can't share more details than that :(

[RubenSandwich]

@radex Can you share a working example of this crash? I have some time and want to help you out here.

[cpojer]

We are trying to fix this internally, a commit should hopefully land and sync out to GitHub soon removing the __has_include.