[Parse] Add an attribute for typeEraser.

[hborla]

This will be used for compiler-driven type erasure for dynamic replacement of functions with an opaque return type. For now, just parse the attribute and ignore it.

[hborla]

@swift-ci please smoke test

[hborla]

@swift-ci please smoke test

[omochi]

Is not spelling typeErasure ?

I found a word type erasure in this document.

Prefixes and Suffixes
Any is used as a prefix to denote "type erasure," e.g. AnySequence wraps any sequence with element type T, conforms to SequenceType itself, and forwards all operations to the wrapped sequence. When handling the wrapper, the specific type of the wrapped sequence is fully hidden.

https://github.com/apple/swift/blob/master/docs/StdlibAPIGuidelines.rst#prefixes-and-suffixes

[hborla]

@omochi The spelling "type eraser" is intentional to describe the type that implements type erasure. For example, the protocol Sequence could specify that its type eraser is AnySequence

@_typeEraser(AnySequence)
protocol Sequence {

[omochi]

@hborla Sorry for my ambiguous sentences.
I talk about spelling is whether erasure or eraser.

[hborla]

@omochi Yes, the spelling is intentional. The type eraser is the type that implements type erasure.

[omochi]

@hborla

The type eraser is the type that implements type erasure.

I finally understand what you say 🙂
Thank you.