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[SR-15916] @MainActor-isolated default arguments for @MainActor-isolated functions #58177

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groue opened this issue Feb 26, 2022 · 8 comments · Fixed by #68794 or #70257
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[SR-15916] @MainActor-isolated default arguments for @MainActor-isolated functions #58177

groue opened this issue Feb 26, 2022 · 8 comments · Fixed by #68794 or #70257
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@hborla
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actor isolation Feature → concurrency: Actor isolation actor Feature → concurrency: `actor` declarations bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself concurrency Feature: umbrella label for concurrency language features default arguments Feature: default arguments for value parameters type checker Area → compiler: Semantic analysis unexpected error Bug: Unexpected error

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@groue
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groue commented Feb 26, 2022

Previous ID SR-15916
Radar None
Original Reporter @groue
Type Bug
Environment

Xcode 13.3 beta 3 (13E5104i)

Additional Detail from JIRA
Votes 2
Component/s Compiler
Labels Bug
Assignee None
Priority Medium

md5: 618b69843e92ff0edf9587c87894767b

Issue Description:

Hello,

The following snippet does not compile:

@MainActor class Foo { }

// error: call to main actor-isolated initializer 'init()' in a synchronous nonisolated context
// @MainActor func f(foo: Foo = Foo()) { }
//                               ^
// note: calls to initializer 'init()' from outside of its actor context are implicitly asynchronous
// @MainActor class Foo {
//                  ^
@MainActor func f(foo: Foo = Foo()) { }

It should compile, since everything in the declaration of the f function is MainActor-isolated.
@groue
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groue commented Feb 27, 2022

Related thread: https://forums.swift.org/t/using-mainactor-values-in-initializer-default-arguments/52694

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
@alberussoftware
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Such an annoying bug. Are there any rough plans for when it will be fixed? @ktoso @DougGregor

@AnthonyLatsis AnthonyLatsis added concurrency Feature: umbrella label for concurrency language features type checker Area → compiler: Semantic analysis actor Feature → concurrency: `actor` declarations swift 5.9 default arguments Feature: default arguments for value parameters actor isolation Feature → concurrency: Actor isolation unexpected error Bug: Unexpected error labels May 2, 2023
@AnthonyLatsis AnthonyLatsis mentioned this issue May 2, 2023
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@vykut
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vykut commented Jun 15, 2023

@AnthonyLatsis are there plans to fix this bug in Swift 5.9?

@AnthonyLatsis
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I have a feeling fixing this might warrant a formal evolution proposal that outlines the semantics and restrictions for public approval, so I suppose not, but we should really ask the concurrency experts (@ktoso or @DougGregor ping).

@ktoso ktoso changed the title [SR-15916] Not implemented: @MainActor-isolated default arguments for @MainActor-isolated functions [SR-15916] @MainActor-isolated default arguments for @MainActor-isolated functions Jul 13, 2023
@ktoso
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ktoso commented Jul 13, 2023

Might need a mini proposal, let me track it with a radar. rdar://112171197

@hborla FYI

@ktoso ktoso removed the swift 5.9 label Jul 13, 2023
@hborla hborla self-assigned this Sep 29, 2023
@hborla hborla mentioned this issue Sep 27, 2023
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@hborla
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hborla commented Sep 29, 2023

I have a draft implementation of this at #68794. I'm also working on a proposal to detail the semantics. I'm thinking we want similar rules for default value expressions of (global-)actor-isolated instance properties.

@hborla
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hborla commented Oct 6, 2023

Here's the pitch thread, in case anybody would like to participate in the discussion: https://forums.swift.org/t/pitch-isolated-default-value-expressions/67714

I'm also going to reopen this - it was automatically closed when I merged my implementation PR, but the feature is behind an experimental feature flag.

@hborla hborla reopened this Oct 6, 2023
@hborla
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hborla commented Jan 23, 2024

The given example compiles under -strict-concurrency=complete in Swift 5.10. This is resolved by #70839

@hborla hborla closed this as completed Jan 23, 2024
This was referenced Jan 24, 2024
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Labels
actor isolation Feature → concurrency: Actor isolation actor Feature → concurrency: `actor` declarations bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself concurrency Feature: umbrella label for concurrency language features default arguments Feature: default arguments for value parameters type checker Area → compiler: Semantic analysis unexpected error Bug: Unexpected error
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@groue @ktoso @hborla @AnthonyLatsis @vykut @alberussoftware