Xcode reports a "module not found" error even though the module is one of the target dependencies

[crazytonyli]

Description

Mix.zip is an example Swift package.

There are three targets in this package:

• MixCore is implemented in Swift.
• MixObjC depends on MixCore and is implemented in Objective-C.
• Mix depends on both above targets and is implemented in Swift.

Expected behavior

Mix scheme can be built successfully.

Actual behavior

Mix scheme can't be built.

Steps to reproduce

1. Open this project in Xcode.
2. MixObjC scheme can be built successfully.
3. Xcode reports an error when building Mix scheme: "module not found" error in MixObjc/ObjC.h.

Swift Package Manager version/commit hash

Release 5.7

Swift & OS version (output of swift --version && uname -a)

swift-driver version: 1.62.15 Apple Swift version 5.7.1 (swiftlang-5.7.1.135.3 clang-1400.0.29.51)
Target: arm64-apple-macosx12.0
Darwin A8C-MBP.local 21.6.0 Darwin Kernel Version 21.6.0: Thu Sep 29 20:13:56 PDT 2022; root:xnu-8020.240.7~1/RELEASE_ARM64_T6000 arm64

[neonichu]

Looks like in Xcode, there's no -fmodule-map-path being passed to MixCore.modulemap when building the "Mix" target, but the package appears to build with swift build. cc @abertelrud

[crazytonyli]

BTW, I have reported this issue on Feedback Assistant, ID: FB12110253.

[Kjuly]

Just happened to be in the same situation, and found out why.

As "Importing Swift into Objective-C" said:

When declarations in an Objective-C header file refer to a Swift class or protocol that comes from the same target, importing the generated header creates a cyclical reference. To avoid this, use a forward declaration of the Swift class or protocol to reference it in an Objective-C interface.

Therefore, it's better to avoid importing MixObjC in the .h file:

#import <Foundation/Foundation.h>

@import MixCore; // HERE: Replace it with `@class MixCoreClass;`

@interface MixObjC: NSObject

@property (nonatomic, strong) MixCoreClass *core;
@property (nonatomic, assign) int value;

@end

---

This will solve your "module not found" error. However, you will get another error when you import the MixObjC into a Swift file to access the property core:

Value of type 'MixObjC' has no member 'core'

This issue occurs in a situation of such package dependencies:

Mix (Swift)
-- MixObjC (Objective-C)
---- MixCore (Swift)

Which was mentioned in this thread: "[SR-1549] Swift member of Objective-C class not exposed to Swift".