Implement SE-0068: Expanding Swift Self to class members and value types

[joewillsher]

What's in this pull request?

Implementation start on SE-0068. This does not yet implement allowing Self to refer to the dynamic type in non final classes outside of function signatures, just expanding Self to value types.

Resolved bug number: (SR-1340)

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[joewillsher]

@tkremenek Here is a PR which implements most of SE-0068 for Swift 3

[tkremenek]

@swift-ci smoke test

[tkremenek]

@joewillsher thanks! Will have a couple people review this change.

[slavapestov]

What happens if you use Self inside a non-Self-returning class method? Does it still work?

[joewillsher]

I’m running tests on that updated version now — I can submit separately when it is ready.

[jrose-apple]

Nitpick: I don't think it's correct to say a nominal is "enclosing" when you're in an extension.

[jrose-apple]

getInnermostTypeContext()->getDeclaredTypeInContext()?

[joewillsher]

This was a refactor of a global static function, but I will remove it and replace it with that, thanks

[joewillsher]

@jrose-apple I have made a bunch of these changes as well as finish of the rest of the SE proposal implementation, but there are still a few issues.

[joewillsher]

Adding Self to dynamic contexts has proven difficult — it ends up hitting lots of SILGen edge cases when the DynamicSelfType and the concrete type get used interchangeably.

I’m going to have to look at changing the hasDynamicSelf mechanism on functions and figure out how to cannonicalise non-final-class's DynamicSelfType without all the special cases it has now.

I will close this PR now and will open a new one when that work is complete.

[jckarter]

@slavapestov and @rjmccall have some short- and long-term ideas for improving how Self types get lowered in SIL. The current representation is pretty bogus. You might want to coordinate with them.

[joewillsher]

Thanks Joe. Slava and John I would really appreciate some pointers here, this proposal requires some significant changes to this area and I’m not sure how to approach it. I’d be happy to work on implementing any ideas you have, thanks.

[jckarter]

I think the proposal as written is reasonable, but the compiler implementation needs a lot of work to live up to it.

[slavapestov]

@joewillsher I think a good start is to put 'Self' behind a staging flag for now.

Another thing to try is to give 'self' the dynamic 'Self' type in all class methods, not just those returning 'Self', again, guarding this with a staging flag. Presently, this will result in some optimizer regressions, but it might allow you to make more progress with the language change.