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[SR-11128] Protocol stubs include __consuming and __owned #53524

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beccadax opened this issue Jul 14, 2019 · 7 comments
Open

[SR-11128] Protocol stubs include __consuming and __owned #53524

beccadax opened this issue Jul 14, 2019 · 7 comments
Labels
bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself diagnostics QoI Bug: Diagnostics Quality of Implementation

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@beccadax
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Previous ID SR-11128
Radar None
Original Reporter @beccadax
Type Bug
Environment

Reproduced in Xcode 11 beta 3 and Swift Development Snapshot 2019-07-11 (a)

Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Bug, DiagnosticsQoI
Assignee None
Priority Medium

md5: b4e61ffcb5ec292d8f0f34fef152663e

Issue Description:

When Swift offers to apply protocol stubs in Xcode, the fix-it produced may include the __consuming and __owned modifiers, which are not currently a supported part of the language and are not intended to be used in most conformances even once they are officially added.

Steps To Reproduce:
Although this is a compiler bug, the printed form of compiler diagnostics doesn't display fix-its in sufficient detail to easily demonstrate it. It's most easily reproduced in an Xcode with an appropriate toolchain:

1. Create a new Xcode project with this code in a Swift source file:

struct MyType: Hashable {
  typealias Element = Int
}
extension MyType: SetAlgebra {}

2. Build it.
3. Click the error badge on the extension line, then click the “Fix” button to apply the fix-it.

Results:
Some of the stubbed declarations include __consuming and/or __owned modifiers, such as:

__consuming func union(_ other: __owned MyType) -> MyType

I would not expect Swift to suggest these modifiers, since they aren’t officially part of the language. Instead I would expect it to drop these keywords:

func union(_ other: MyType) -> MyType

Even after we fully support move-only types, I would expect the protocol stubs for a non-move-only conformance to remove unnecessary move-only–related modifiers so that users don't need to worry about this complexity.
@beccadax
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In later work on my project, I realized that mutating is not treated as compatible with __consuming in copyable (i.e. currently all) types. This seems…less than ideal.

@belkadan
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Can you file a separate bug for "mutating implementations should satisfy consuming requirements"?

I think there's a Radar for the protocol stubs one, too.

@beccadax
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We talked and we don't actually think mutating methods should satisfy __consuming requirements; however, dropping __consuming should be (and is) supported. So the bug here is merely that the compiler should drop these attributes if you aren't conforming a move-only type.

@theblixguy
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Just to clarify, do we always want to drop __consuming and __owned when printing stubs or only when the type is not move-only? Also, since only functions can have the __consuming attribute (correct me if I am wrong), should we add a check before printing it?

@belkadan
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We don't have any such thing as "move-only types" yet. And I think you meant "only structs and enums" rather than "only functions", right?

@theblixguy
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I meant functions, because if you add **consuming ** to anything other than a func then the compiler throws an error: "__consuming may only be used on 'func' declarations" (unless I am doing something wrong!). To fix this, I was thinking of setting SkipUnderscoredKeywords=true in printRequirementStub().

@belkadan
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The point of protocol stubs is to match what was written in a protocol's requirements, though. If someone put __consuming on a non-function in a protocol, they already would have gotten an error.

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself diagnostics QoI Bug: Diagnostics Quality of Implementation
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@belkadan @beccadax @theblixguy