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[SR-7370] Generic class conforming to @objc protocol fails assertion: "extended objc class doesn't have constant metadata?" #49918

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purpleblues opened this issue Apr 6, 2018 · 7 comments
Closed

[SR-7370] Generic class conforming to @objc protocol fails assertion: "extended objc class doesn't have constant metadata?" #49918

purpleblues opened this issue Apr 6, 2018 · 7 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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@purpleblues
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Previous ID SR-7370
Radar rdar://problem/39239512
Original Reporter @purpleblues
Type Bug
Status Resolved
Resolution Done
Environment

Xcode 9.3(9E145), Swift 4.1

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

md5: f39162a34c6102d121b7a4579f00b4fb

cloned to:

  • SR-7372 Reject conditional conformances of @objc protocols

is duplicated by:

  • SR-857 Extensions to generic classes cannot implement Objective-C protocols

Issue Description:

import Foundation

public class FooClass<T> {

}

@objc protocol BarProtocol {

}

extension FooClass: BarProtocol where T: BarProtocol {
    
}

When the protocol used with conditional conformance for the placeholder type of generic class (T in this case) is marked @objc, the code causes Segmentation fault: 11 with error message containing call stack like below.

0  swift                    0x000000010d0deffa PrintStackTraceSignalHandler(void*) + 42
1  swift                    0x000000010d0de3b6 SignalHandler(int) + 966
2  libsystem_platform.dylib 0x00007fff513a1f5a _sigtramp + 26
3  libsystem_platform.dylib 0x00007fa4e556fda5 _sigtramp + 2484919909
4  swift                    0x0000000109cb7016 clang::CodeGen::ConstantAggregateBuilderBase::finishStruct(llvm::StructType*) + 150
5  swift                    0x00000001097e04e5 llvm::Constant* (anonymous namespace)::ClassDataBuilder::buildGlobalVariable<swift::irgen::ConstantStructBuilder>(swift::irgen::ConstantStructBuilder&, llvm::StringRef) + 597
6  swift                    0x00000001097e4942 swift::irgen::emitCategoryData(swift::irgen::IRGenModule&, swift::ExtensionDecl*) + 2418
7  swift                    0x00000001097eb3e7 swift::irgen::IRGenModule::emitGlobalDecl(swift::Decl*) + 887
8  swift                    0x00000001097eaf95 swift::irgen::IRGenModule::emitSourceFile(swift::SourceFile&, unsigned int) + 133
9  swift                    0x00000001098e353e performIRGeneration(swift::IRGenOptions&, swift::ModuleDecl*, std::__1::unique_ptr<swift::SILModule, std::__1::default_delete<swift::SILModule> >, llvm::StringRef, llvm::LLVMContext&, swift::SourceFile*, llvm::GlobalVariable**, unsigned int) + 1422
10 swift                    0x000000010973edce performCompile(swift::CompilerInstance&, swift::CompilerInvocation&, llvm::ArrayRef<char const*>, int&, swift::FrontendObserver*, swift::UnifiedStatsReporter*) + 38110
11 swift                    0x0000000109733e64 swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*) + 7908
12 swift                    0x00000001096e88b5 main + 18917
13 libdyld.dylib            0x00007fff51093015 start + 1

The issue disappears when @objc is removed from the protocol
@belkadan
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belkadan commented Apr 6, 2018

With assertions:

Assertion failed: (metadata && "extended objc class doesn't have constant metadata?"), function emitCategory, file /Volumes/Data/swift-public/swift/lib/IRGen/GenClass.cpp, line 1322.

I don't think conditional conformances to @objc protocols should be accepted, but even dropping that part causes the assertion failure for me. I'll clone out a separate bug for that.

@swift-ci create

@huonw
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Mannequin

huonw mannequin commented Apr 9, 2018

By "dropping that part", I think @belkadan means removing the where T: BarProtocol since just extension FooClass: BarProtocol triggers the same assertion. @jckarter, thoughts?

@jckarter
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jckarter commented Apr 9, 2018

I think that's a dup of another issue, where we haven't really implemented adding ObjC methods or protocol extensions for generic classes, since there's no single class object to generate a "category" for.

@huonw
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Mannequin

huonw mannequin commented Apr 10, 2018

Ah, thanks! I think I found it. It does appear to be resolved if the (non-conditional) conformance is moved to the type declaration instead of the extension.

@huonw
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Mannequin

huonw mannequin commented Apr 10, 2018

Actually, I changed my mind: the example in that issue gives a diagnostic "@objc is not supported within extensions of generic classes or classes that inherit from generic classes", but that's only because the protocol defines a requirement. We should have an error for this case too.

@huonw
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Mannequin

huonw mannequin commented Apr 10, 2018

#15842

@huonw
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Mannequin

huonw mannequin commented Apr 13, 2018

db8b98b

@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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@jckarter @belkadan @purpleblues @AnthonyLatsis