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[SR-10507] Dynamic cast to existential fails when conformance is added in extension in static library #52907

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ChristopherRogers opened this issue Apr 18, 2019 · 2 comments
Closed

[SR-10507] Dynamic cast to existential fails when conformance is added in extension in static library #52907

ChristopherRogers opened this issue Apr 18, 2019 · 2 comments
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself

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@ChristopherRogers
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Previous ID SR-10507
Radar rdar://problem/50169873
Original Reporter @ChristopherRogers
Type Bug
Status Resolved
Resolution Duplicate

Attachment: Download

Environment

Swift 5.0.1, macOS 10.14.4

Swift Development Snapshot toolchain, 2019-04-11

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

md5: 0cd9932cf7032fccdb1ff06896f91884

duplicates:

  • SR-6004 Static libraries don't automatically load extensions

Issue Description:

I've attached sample code & a build script to demonstrate the problem. All of the "My*.swift" files are a part of MyModule, which is built as a static library. main.swift is for an executable that will import MyModule.

MyClass conforms to MyProtocol via an extension, which is present in a separate file. Attempting to dynamically cast MyClass to MyProtocol will either fail or crash at runtime, depending on how the cast is performed.

Three ways to workaround this problem:

  1. Move the protocol conformance to the same file as the class definition

  2. Coerce MyClass to MyProtocol first before attempting to dynamically cast to MyProtocol

  3. Build MyModule as a dylib
@belkadan
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A fourth way that should work: explicitly pass -force_load libMyModule.a to the linker (possibly using -Xlinker if not invoking ld directly).

Thanks for the report. I think we have an old Radar that says this can happen, but it's valuable to know that someone hit it in the wild.

@belkadan
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Bob found it.

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
This issue was closed.
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself
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@ChristopherRogers @belkadan