[WIP] [Parse] Add _pointer_bit_width platform condition

[xwu]

Instead of explicitly listing each platform when testing for the native word size (which, per documentation, is the bit width of Int), add an explicit (underscored) platform conditional.

This supersedes the solution discussed in #14386 and #14409.

[xwu]

@swift-ci Please smoke test Linux platform

[jrose-apple]

At the same time as I objected to the other PR, I'm leery of adding this even as an underscored condition because people will start using it. Seems like someone should just take this through Evolution.

[xwu]

@swift-ci Please clean smoke test Linux platform

[xwu]

@jrose-apple I see your point. I think if there's broad consensus that this is necessary for the stdlib, however, then an underscored condition wouldn't be terrible as long as we intend to make it public eventually anyway.

At the moment I'm rather flummoxed by the technical issue that this seemingly straightforward addition doesn't seem to work. I wonder if it's the integer values that aren't being parsed correctly.

[jrose-apple]

At the moment I'm rather flummoxed by the technical issue that this seemingly straightforward addition doesn't seem to work. I wonder if it's the integer values that aren't being parsed correctly.

Yeah, the current grammar for platform conditions always expects a single identifier as the argument. You could use _32 and _64 for now, which not only sidesteps the implementation issue but matches _runtime(_ObjC).

[xwu]

@swift-ci Please smoke test Linux platform

[xwu]

Cf. __POINTER_WIDTH__ in Clang, getArchPointerBitWidth in LLVM, target_pointer_width in Rust.

[xwu]

@swift-ci Please smoke test OS X platform

[CodaFi]

@xwu If you still want to pursue this, could you rebase it and take it through evolution?

Also, if you wouldn't mind adding a Parse test for a bogus condition value.

[CodaFi]

Alright, it's been 4 months without a reply. I'm closing this due to age and inactivity.

[xwu]

It's entirely slipped my mind. Will revisit this topic later in the year, time permitting. Thanks @CodaFi!