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[SR-13018] Type constraints are not honored when invoking method #55463

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mbrandonw opened this issue Jun 15, 2020 · 3 comments
Closed

[SR-13018] Type constraints are not honored when invoking method #55463

mbrandonw opened this issue Jun 15, 2020 · 3 comments

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@mbrandonw
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@mbrandonw mbrandonw commented Jun 15, 2020

Previous ID SR-13018
Radar rdar://problem/64953119
Original Reporter @mbrandonw
Type Bug
Status Resolved
Resolution Done
Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Bug, RunTimeCrash
Assignee @slavapestov
Priority Medium

md5: 2c03afa2034e8d179cd73102ecf6a551

Issue Description:

Consider the following method:

struct T<A> {
  func run<C>(_ c: C) where C: Collection, C.SubSequence == A {
    print(c[...] as! A)
  }
}

This should restrict the collection passed into `run` to be such that its subsequence matches the generic A.

For example, these following compile just fine:

// These should compile ✅
T<Substring>().run("")
T<Data>().run(Data())

However, there seem to be some situations where we can pass in a collection that does not match this constraint and yet it still compiles, and hence crashes at runtime:

// These should not but do⁉️
T<Substring>().run(Data())
T<Data>().run("")
@CodaFi
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@CodaFi CodaFi commented Jun 19, 2020

Ah, this is an impressive soundness hole. We're straight-up forming a generic signature with the wrong constraints.

Generic signature: <A, C where A == A.SubSequence, C : Collection>

@swift-ci create

@slavapestov
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@slavapestov slavapestov commented Aug 15, 2020

Here is a reduction:

protocol P {
  associatedtype A : P where A.A == A
}

func foo<X, Y>(_: X, _: Y) where X : P, Y : P, Y.A == X {}

@slavapestov
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@slavapestov slavapestov commented Apr 2, 2022

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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