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[SR-7147] Compiler crash (Illegal instruction 4) when working with protocols. #49695

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swift-ci opened this issue Mar 8, 2018 · 3 comments
Closed

[SR-7147] Compiler crash (Illegal instruction 4) when working with protocols. #49695

swift-ci opened this issue Mar 8, 2018 · 3 comments
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself crash Bug: A crash, i.e., an abnormal termination of software

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@swift-ci
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swift-ci commented Mar 8, 2018

Previous ID SR-7147
Radar None
Original Reporter marcusrossel (JIRA User)
Type Bug
Status Resolved
Resolution Done
Environment

  • XCode Version 9.2 (9C40b)

  • in a standard command-line project

  • on a 2017 MacBook Pro

  • High Sierra Version 10.13.3 (17D102).

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

md5: 438c31914626374ed2849a24c550f4b2

Issue Description:

The code below causes the compiler to emit the following:

warning: redundant conformance constraint 'G2': 'P2'
extension S where G2 == C<S.A2ofG2>
                     ^

Command failed due to signal: Illegal instruction: 4

Code:

protocol P1 { associatedtype A1 }

protocol P2 { associatedtype A2: P1 }

class C<G1: P1>: P2 { typealias A2 = G1 }

struct S<G2: P2> { typealias A2ofG2 = G2.A2 }

extension S where G2 == C<S.A2ofG2> { }
@belkadan
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belkadan commented Mar 9, 2018

Fixed in Swift 4.1!

<stdin>:9:22: error: same-type constraint 'G2' == 'C<G2.A2>' is recursive
extension S where G2 == C<S.A2ofG2> { }
                     ^

@swift-ci
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Comment by Marcus Rossel (JIRA)

Thanks @belkadan! Nice to see the error message fixed.

Please redirect me, if this is the wrong place to ask this...

I was actually assuming that the code shouldn't produce an error at all ^^

What mechanism is there then to constrain `S.G2` to be of type `C`, while still keeping `C.A1` generic?

Perhaps this isn't possible, because the generic `G2` can't only be partially specified? And if so... Is it desired not to allow this, or is this a current limitation of generics?

@belkadan
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I don't think we have a way to spell that yet; it'd be something like

extension <A2ofG2> S where G2 == C<A2ofG2> { }

But I think you can fake it if you only want to put methods in the extension:

extension S {
  func foo<A2ofG2>() where G2 == C<A2ofG2> { }
}

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
@AnthonyLatsis AnthonyLatsis added the crash Bug: A crash, i.e., an abnormal termination of software label Dec 12, 2022
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself crash Bug: A crash, i.e., an abnormal termination of software
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@belkadan @swift-ci @AnthonyLatsis