External macro implementation type could not be found #3419

MiguelG97 · 2024-09-30T02:09:26Z

MiguelG97
Sep 30, 2024

Description

Can someone guide me on how to set up my project to not have the following issues when implementing TCA?
Github repo:

External macro implementation type 'ComposableArchitectureMacros.ReducerMacro' could not be found for macro 'Reducer()

External macro implementation type 'ComposableArchitectureMacros.ObservableStateMacro' could not be found for macro 'ObservableState()'

External macro implementation type 'ComposableArchitectureMacros.ReducerMacro' could not be found for macro 'Reducer()'

Checklist

I have determined whether this bug is also reproducible in a vanilla SwiftUI project.
If possible, I've reproduced the issue using the main branch of this package.
This issue hasn't been addressed in an existing GitHub issue or discussion.

Expected behavior

xcode to not throw errors

Actual behavior

xcode is throwing errors

Reproducing project

Github repo:

All I did is installed the TCA package through SPM.
Once finished I added the library to my target project.
Then, when trying to implement the code a bunch of messages show up:

import ComposableArchitecture

@Reducer
struct LayoutSlice {
    
    @ObservableState
    struct State{
        var isLandScape = false
    }
    
    enum Action{
        case setLandScape
    }
    
    var body: some ReducerOf<Self>{
        Reduce{ state, action in
            switch action{
            case .setLandScape:
                state.isLandScape = true
                return .none
            }
        }
        
    }
}

The Composable Architecture version information

1.15.0

Destination operating system

IOS 17.5

Xcode version information

No response

Swift Compiler version information

No response

mbrandonw · 2024-09-30T14:16:09Z

mbrandonw
Sep 30, 2024
Maintainer

Hi @MiguelG97, this project builds just fine for me without any errors. There is a chance you have not enabled macros for your project. In the build errors for your project you may see a number of errors like this:

If you enable all of those it should work fine.

Since this isn't an issue with the library I am going to convert it to a discussion. Please feel free to continue the conversation over there!

1 reply

MiguelG97 Oct 4, 2024
Author

That's strange, I remind enabling all macros.
I appreciate your response anyways

JeromeTonnelierOgury · 2024-10-21T07:18:15Z

JeromeTonnelierOgury
Oct 21, 2024

Hi!
For some reasons, I've got the same behavior, but the weirdest thing is that the project compiles and works.
I tried to remove TCA and add it again (so that I can enable macros when Xcode asks me to), but the errors keep coming back. Basically, after doing that, if I don't touch anything, I have no error. But as soon as I add event just a line break in a reducer, all errors comes back :-/
I tried to remove all cache/derived data and start again, same result.
What's rellay annoying is that when there is an actual error, I just can't find it. One example os error would be ...MobileMenuView/MobileMenuFeature.swift:24:8 External macro implementation type 'ComposableArchitectureMacros.ReducerMacro' could not be found for macro 'Reducer()'; No such file or directory
Any idea ? It's a pretty big project with Cocoapods, SMP (both local and github hosted).
Thanks 🙏

11 replies

usiddiqui-google Nov 6, 2024

For us, the issue turned out to using Swift 6 in the swift-syntax package while our project was still on Swift 5. So updating it from package(url: "https://github.com/swiftlang/swift-syntax.git", exact: "600.0.1") to .package(url: "https://github.com/swiftlang/swift-syntax.git", exact: "510.0.2"), followed by deleting derived data and rebuilding packages fixed the issue.

usiddiqui-google Nov 6, 2024

@mbrandonw lmk if its worth adding it here? I will do a PR.
https://pointfreeco.github.io/swift-composable-architecture/main/documentation/composablearchitecture/reducer/#Error-External-macro-implementation--could-not-be-found

mbrandonw Nov 6, 2024
Maintainer

Hi @usiddiqui-google, that seems very surprising. I believe this is an Xcode bug and that the version of Swift Syntax can't really have any impact on this. I would be happy to update the docs, but first I would want to see conclusive evidence that it does indeed fix the problem.

davidmorra Jan 2, 2025

Hi @JeromeTonnelierOgury, do you have custom build configurations? For example, something other than the default Debug and Release configurations? That can cause this problem.

Personally I don't think custom configurations are useful because it seems that Xcode has a lot of problems with it, but if it's too much trouble to change back then you could at least try adding back the default Debug and Release ones. Though I'm not sure if that's enough to get the project back into good shape.

I had the exact same problem with the latest version. Everything works and builds, but that macro errors don't disappear. Indeed problem was in the custom configuration. Once i switched to the default configuration errors disappear.
Thanks!

medef00 Apr 27, 2025

For us, the issue turned out to using Swift 6 in the swift-syntax package while our project was still on Swift 5. So updating it from package(url: "https://github.com/swiftlang/swift-syntax.git", exact: "600.0.1") to .package(url: "https://github.com/swiftlang/swift-syntax.git", exact: "510.0.2"), followed by deleting derived data and rebuilding packages fixed the issue.

Doesn't work for me. Project Swift 6, swift-syntax 600.0.1 🥲

danscan · 2025-03-18T23:56:13Z

danscan
Mar 18, 2025

For posterity: After fighting with this issue for HOURS, I was creating a simple repro project to post here, and I figured out it goes away if you just do a CMD+B build 🙃

2 replies

mbrandonw Mar 19, 2025
Maintainer

The main reason this happens is because the macros have not been built in order for Xcode to understand what @Reducer means. So it's always a good idea to do a full build before working on the app.

VladimirCreator Jun 17, 2025

It really helped…

rt12379 · 2025-05-31T03:16:45Z

rt12379
May 31, 2025

I am trying to build a project with TCA using Azure pipelines, but the build fails with the same error.
The strange thing is that on Xcode I get the same error but can still build.
The project is on swift 5 but the method of setting the swift-syntax version to 510.0.2 did not work.
I am using Custom configuration, which I think is fine for the CI build pipeline. Has anyone solved this error on Azure pipelines?

0 replies

External macro implementation type could not be found #3419

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Description

Checklist

Expected behavior

Actual behavior

Reproducing project

The Composable Architecture version information

Destination operating system

Xcode version information

Swift Compiler version information

Replies: 4 comments · 14 replies

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mbrandonw Sep 30, 2024 Maintainer

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MiguelG97 Oct 4, 2024 Author

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mbrandonw Nov 6, 2024 Maintainer

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mbrandonw Mar 19, 2025 Maintainer

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Replies: 4 comments 14 replies

mbrandonw
Sep 30, 2024
Maintainer

MiguelG97 Oct 4, 2024
Author

mbrandonw Nov 6, 2024
Maintainer

mbrandonw Mar 19, 2025
Maintainer