error: Couldn't IRGen expression, no additional error

You should better send a bug report to swift.org (bugs.swift.org), when you find such bugs. (Compiler should output an appropriate diagnostics even when your code has some flaws.)

Until the problem will be fixed, we cannot show you any workarounds as you are not showing any parts of your code.

I have the same problem like here for Xcode 10 GM and OS High Sierra 10.13.6, SWIFT 4.2

https://stackoverflow.com/questions/43977271/lldb-couldnt-irgen-expression

Thanks for clarifying. Frankly I have been missing some parts of your post.

The timestamp of the linked article shows they had some problems in Xcode 8.

So, I'm not sure the issue still exists or yours is another,

but sending a bug report, with enough info to reproduce the issue, would help Xcode team or LLDB team to fix it.

Have you all ready sent one?

By the way, multiposting is not considered to be a good manner and rarely helps someone to solve the issue.

@OOper thank you for your answer.

We found that the problem appears when an external framework is added to the UI Tests Target. We've created an example project with RxSwift.framework included which can be use to reproduce our issue (unfortunately i can not upload project file here). What do you think, where we should looking for solution? On bugs.swift.org or Radar?

Thanks in advance.

If you have an example project that reproduces the problem you should definitely file a bug and include that project. Even if you are doing something wrong, Xcode should be giving you diagnostics that guide you to a solution rather than this cryptic error!

Based on what’s been posted here so far I’m not sure if this is a Swift-specific problem or a bigger issue within Xcode. Given that, my recommendation is that you file your bug against Xcode, and lets the Xcode folks route it appropriately. You can do that here.

Please post your bug number, just for the record.

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Apple Developer Relations, Developer Technical Support, Core OS/Hardware

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Thanks, for your answer. I've created an https://bugreport.apple.com/web/?problemID=44635045

I don´t know the status of this, but we´re having the same issue. We reported a bug with a project that reproduces the issue

You can find it here: https://bugreport.apple.com/web/?problemID=49014360

Regards