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Aug 4, 2021
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[docs] Make some corrections and additions to UnderscoredAttributes.md #38729

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297bc92
[docs] Add documentation for _assemblyVision.
varungandhi-apple Aug 3, 2021
585ba57
[docs] Minor cleanup and consistency fixes in UnderscoredAttributes.md.
varungandhi-apple Aug 3, 2021
2c9358b
[docs] Add reference to documentation in Attr.def to nudge people.
varungandhi-apple Aug 3, 2021
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20 changes: 11 additions & 9 deletions docs/ReferenceGuides/UnderscoredAttributes.md
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Expand Up @@ -39,6 +39,14 @@ Most notably, default argument expressions are implicitly
`@_alwaysEmitIntoClient`, which means that adding a default argument to a
function which did not have one previously does not break ABI.

## `@_assemblyVision`

Forces emission of assembly vision remarks for a function or method, showing
where various runtime calls and performance impacting hazards are in the code
at source level after optimization.

Adding this attribute to a type leads to remarks being emitted for all methods.

## `@_borrowed`

Indicates that the [conservative access pattern](/docs/Lexicon.md#access-pattern)
Expand Down Expand Up @@ -95,15 +103,15 @@ extension Text {
}
```

## `@_dynamicReplacement(for:)`
## `@_dynamicReplacement(for: targetFunc(label:))`

Marks a function as the dynamic replacement for another `dynamic` function.
This is similar to method swizzling in other languages such as Objective-C,
except that the replacement happens at program start (or loading a shared
library), instead of at an arbitrary point in time.

For more details, see the forum post on
[Dynamic method replacement](https://forums.swift.org/t/dynamic-method-replacement/16619).
[dynamic method replacement](https://forums.swift.org/t/dynamic-method-replacement/16619).

## `@_distributedActorIndependent`

Expand Down Expand Up @@ -134,7 +142,7 @@ This attribute is most commonly used by overlays.

```swift
// module M
func f() {}
public func f() {}

// module N
@_exported import M
Expand Down Expand Up @@ -270,11 +278,6 @@ of the closure. This is different from the typical behavior, where the closure
may be runnable anywhere unless its type specifically declares that it will
run on a specific actor.

This new attribute can be used on parameters of `@Sendable async` type
to indicate that the closures arguments passed to such parameters
should inherit the actor context where they are formed, which is not
the normal behavior for `@Sendable` closures.

## `@_inheritsConvenienceInitializers`

An attribute that signals that a class declaration inherits its convenience
Expand All @@ -289,7 +292,6 @@ Indicates that a protocol is a marker protocol. Marker protocols represent some
meaningful property at compile-time but have no runtime representation.

For more details, see [SE-0302](https://github.com/apple/swift-evolution/blob/main/proposals/0302-concurrent-value-and-concurrent-closures.md#marker-protocols), which introduces marker protocols.

At the moment, the language only has one marker protocol: `Sendable`.

Fun fact: Rust has a very similar concept called
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3 changes: 3 additions & 0 deletions include/swift/AST/Attr.def
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Expand Up @@ -670,6 +670,9 @@ SIMPLE_DECL_ATTR(_assemblyVision, EmitAssemblyVisionRemarks,
ABIStableToAdd | ABIStableToRemove | APIStableToAdd | APIStableToRemove,
120)

// If you're adding a new underscored attribute here, please document it in
// docs/ReferenceGuides/UnderscoredAttributes.md.

#undef TYPE_ATTR
#undef DECL_ATTR_ALIAS
#undef CONTEXTUAL_DECL_ATTR_ALIAS
Expand Down