[SR-15432] Hashable synthesis should add nonisolated keyword for conforming actors

[WowbaggersLiquidLunch]

Previous ID	SR-15432
Radar	rdar://problem/85004437
Original Reporter	@WowbaggersLiquidLunch
Type	New Feature
Status	Closed
Resolution	Done

Additional Detail from JIRA

Votes	0
Component/s	Compiler, Standard Library
Labels	New Feature
Assignee	@ktoso
Priority	Medium

md5: bed5a89f4e803a1b4d508284ed284e0f

Issue Description:

relevant forum thread: https://forums.swift.org/t/hashable-actors/53199

When an actor satisfies a synchronous requirement (such as Hashable’s hash(into:) and hashValue), the witness must be nonisolated. This presents a problem for Hashable conformance:

Since Swift 4.2, the user implements either the Hasher-based hash(into:) or the deprecated hashValue, and the compiler synthesises the other that uses the user-implemented one (see the Source Compatibility section of SE-206). Because currently the synthesised code doesn’t have “nonisolated” keyword when the conforming type is an actor, the user is prompted with a warning that asks them to add “nonisolated” to the compiler-synthesised part. This results in the user having to implement both parts of the conformance. In addition to negating the benefits of having automatic Hashable synthesis, for someone not familiar with how hash(into:) and hashValue work together, it can lead to incorrect implementation.

[ktoso]

Hmmm, this sounds off.. I implemented Hashable on actors and seemed to work... we'll look into it, thanks

@swift-ci create

[DougGregor]

#38620

[WowbaggersLiquidLunch]

Just tested it, and can confirm that this has been fixed in the trunk.