New documentation for underscored attributes

typesanitizer · August 3, 2021, 1:29am

With help from many different people, we have some new documentation describing the semantics of different underscored attributes in one central place.

github.com

apple/swift/blob/main/docs/ReferenceGuides/UnderscoredAttributes.md

# Underscored Attributes Reference

**WARNING:** This information is provided primarily for compiler and standard
library developers. Usage of these attributes outside of the Swift monorepo
is STRONGLY DISCOURAGED.

The Swift reference has a chapter discussing [stable attributes][Attributes].
This document is intended to serve as a counterpart describing underscored
attributes, whose semantics are subject to change and most likely need to
go through the Swift evolution process before being stabilized.

[Attributes]: https://docs.swift.org/swift-book/ReferenceManual/Attributes.html

The attributes are organized in alphabetical order.

## `@_alignment(numericValue)`

Allows controlling the alignment of a type.

The alignment value specified must be a power of two, and cannot be less

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In case there are some attributes which you didn't quite understand, this is a good place to look. In case you think you know all the attributes, you may still want to take a look, maybe there are some "top secret" attributes that you didn't know about. Of course, it may not be perfect right now, please feel free to submit a PR if you see a mistake. If you have questions or suggestions, feel free to ask/comment here.

Also, if you're adding new attributes, please document them in this doc.

typesanitizer · August 3, 2021, 5:58am

As one does, I noticed some gaps and inconsistencies after landing the PR. [docs] Make some corrections and additions to UnderscoredAttributes.md by varungandhi-apple · Pull Request #38729 · apple/swift · GitHub