Drop read/write/close LibcShims and use the platform APIs directly from the SwiftPrivate module

[kubamracek]

This was attempted before by @mikeash in #20194, later reverted in #20372. I'd like to try again -- the goal is to avoid depending on read/write/close APIs in libswiftCore.

[compnerd]

I really like this change, but one minor question, is the renaming of read, write, close required for something or can we just use the regular libc names?

[mikeash]

Do you know if the problem that prompted #20372 is resolved, or is this part of finding out?

[kubamracek]

@swift-ci please test

[kubamracek]

Do you know if the problem that prompted #20372 is resolved, or is this part of finding out?

This is part of figuring that out, yes :)

[kubamracek]

@swift-ci please test

[kubamracek]

preset=stdlib_S_standalone_minimal_macho_x86_64,build,test
@swift-ci please test with toolchain and preset

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - 0209a88

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - 0209a88

[kubamracek]

@swift-ci please test macOS platform

[kubamracek]

@swift-ci please test Linux platform

[kubamracek]

@swift-ci please test

[kubamracek]

preset=stdlib_S_standalone_minimal_macho_x86_64,build,test
@swift-ci please test with toolchain and preset

[kubamracek]

Note that I have now reproduced the scenario that led to the revert last time (#20372, rdar://problem/45817565) and the build failure no longer occurs -- I believe this is due some recent work by Eric. So let's go forward with this change!

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - 0209a88

[kubamracek]

I really like this change, but one minor question, is the renaming of read, write, close required for something or can we just use the regular libc names?

I did the "rename" to avoid the name clash with methods called read/write/close on the structs defined in IO.swift. This felt like a less invasive solution compared to renaming of the methods, but I can easily do it the other way if you'd prefer that. @compnerd

[compnerd]

I assume that the "do it the other way" is mostly a typealias in the appropriate section or explicitly naming references to calls to the internal function. I think that is kinda nicer, but I'm not too concerned either way. To a certain extent it is about style, and I'm not convinced that this particular bit of style impacts much.

[kubamracek]

preset=stdlib_S_standalone_minimal_macho_x86_64,build,test
@swift-ci please test with toolchain and preset