Data.append now calls Data.count’s setter, which used to have a bug in previously shipped versions of the Foundation overlay (#28918).
To prevent working code from breaking when recompiled with the current version, avoid calling Data.count’s setter directly. Instead, extract its implementation (conveniently already packaged into a nested function) into a named method, marking it @_alwaysEmitIntoClient.
Data provides a settable `count` property. Its expected behavior is undocumented, but based on the implementation, it is intended to zero-extend (or truncate) the collection to the specified length.
This does not work correctly if we start with an empty Data and we try to increase the count by a small integer:
```
import Foundation
var d = Data()
d.count = 2
print(d.count) // ⟹ 0 ⁉️
d.count = 100
print(d.count) // ⟹ 100 ✓
```
It looks like this bug was introduced with the Data overhaul that shipped in Swift 5.
(This issue was uncovered by https://github.com/apple/swift/pull/28918.)
rdar://58134026
We want to enable overlays to import their shims as @_implementationOnly, so that the shims disappear from the public interface.
However, this isn’t possible when a shim is called from an @inlinable func, because then the existence (and definition) of the shim needs to be available to all callers of it.
Unfortunately Foundation’s Data has three instances where it calls _SwiftFoundationOverlayShims._withStackOrHeapBuffer within @inlinable code:
- Data.init<S: Sequence>(_: S)
- Data.append<S: Sequence>(contentsOf: S)
- Data.replaceSubrange<C: Collection>(_: Range<Int>, with: C)
Rewrite the first two to write sequence contents directly into the target Data instance (saving a memcpy and possibly a memory allocation).
In replaceSubrange, add fast paths for contiguous collection cases, falling back to a Swift version of _withStackOrHeapBuffer with a 32-byte inline buffer.
The expectation is that this will be an overall speedup in most cases, with the possible exception of replaceSubrange invocations with a large non-contiguous collection.
rdar://58132561
Old Swift and new Swift runtimes and overlays need to coexist in the same process. This means there must not be any classes which have the same ObjC runtime name in old and new, because the ObjC runtime doesn't like name collisions.
When possible without breaking source compatibility, classes were renamed in Swift, which results in a different ObjC name.
Public classes were renamed only on the ObjC side using the @_objcRuntimeName attribute.
This is similar to the work done in pull request #19295. That only renamed @objc classes. This renames all of the others, since even pure Swift classes still get an ObjC name.
rdar://problem/46646438
The SDK directory is now confusing as the Windows target also has a SDK
overlay. In order to make this more uniform, move the SDK directory to
Darwin which covers the fact that this covers the XNU family of OSes.
The Windows directory contains the SDK overlay for the Windows target.
