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[SR-2345] Linker Error: Nested classes are hidden from the Linker when calling class methods from Objective-C #44952

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swift-ci opened this issue Aug 15, 2016 · 7 comments
Closed

[SR-2345] Linker Error: Nested classes are hidden from the Linker when calling class methods from Objective-C #44952

swift-ci opened this issue Aug 15, 2016 · 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 regression swift 3.0

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@swift-ci
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Previous ID SR-2345
Radar None
Original Reporter fbartho (JIRA User)
Type Bug
Status Resolved
Resolution Duplicate
Environment

Occurs in (Swift3):

  • Version 8.0 beta 6 (8S201h)

  • beta 5

  • (not verified in other beta versions)

macOS 10.11.6

Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Bug, 3.0Regression
Assignee None
Priority Medium

md5: f887ae0d676991544eca9354bd94d1b3

duplicates:

  • SR-2267 Nested Swift classes fail to link for Objective-C

Issue Description:

Scenario:

@objc(A)
public class ASwift: NSObject {
    public class func factory() -> ASwift {
        return ASwift()
    }
}

public extension ASwift {
    @objc(B)
    public class BSwift: NSObject {
        public class func factory() -> BSwift {
            return BSwift()
        }
    }
}

In Objective-C:

// Import your bridging header somewhere

A* a = [A factory]; // No problems
B* b = [B factory]; // Linker error "can't find B used in file.o"

B* b2 = [NSClassFromString(@"B") factory]; // Works

If you examine the -Swift.h bridging header, your classes & methods are properly exposed

Expectation:

  • no linker errors, no need to call NSClassFromString

Workarounds:

  • Call Swift-defined accessible class's method to return an AnyClass reference to bounce into the unaccessible class.

  • Call Swift-defined non-class functions to bounce into the class method.

  • Call NSClassFromString to get the class reference. No longer works as of Beta6

  • Create a top-level unnested Swift subclass of your class and reference that when calling class methods.
@lilyball
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lilyball mannequin commented Aug 15, 2016

This issue does not reproduce with Xcode 7.3.1.

@lilyball
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lilyball mannequin commented Aug 15, 2016

The linker error in question:

Undefined symbols for architecture x86_64:
  "_OBJC_CLASS_$_B", referenced from:
      objc-class-ref in File.o
ld: symbol(s) not found for architecture x86_64

@lilyball
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Mannequin

lilyball mannequin commented Aug 15, 2016

If I run nm on the .o file generated from the Swift file, I see the following:

00000000000007c8 S _OBJC_CLASS_$_A
                 U _OBJC_CLASS_$_NSObject
00000000000004b8 D _OBJC_METACLASS_$_A
00000000000004e0 D _OBJC_METACLASS_$_B
                 U _OBJC_METACLASS_$_NSObject

So we're creating the metaclass runtime info for B but not the class info.

@swift-ci
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Comment by Frederic Barthelemy (JIRA)

My NSClassFromString workaround appears to no longer work for Beta6, updated description after testing the top-level unnested class bounce strategy.

@swift-ci
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Comment by Frederic Barthelemy (JIRA)

I spoke too soon. Using a top level subclass of the nested class doesn't work either. It leads to a similar linker error as above. 🙁

@swift-ci
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Comment by Frederic Barthelemy (JIRA)

Function bound to a top-level class can return the class appears to work in Beta6:

public extension A {
    public class func A.B_LinkerBypass() -> AnyClass {
        return A.B.classForCoder()
    }
}

@swift-ci
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swift-ci commented Dec 1, 2016

Comment by James Richard (JIRA)

Just ran into this bug in an obscure way. We don't directly use our nested class via Obj-C code, but we were encoding one into an archive file. Upon unarchiving the Obj-C runtime would search for the class. It'd fail as the symbols aren't there, so we were getting this error:

cannot decode object of class ([REDACTED]) for key (NS.objects); the class may be defined in source code or a library that is not linked

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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Labels
bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself regression swift 3.0
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@swift-ci @AnthonyLatsis