`po` gives `error: <EXPR>:1:1: error: use of unresolved identifier`

I have this problem with po in the console where trying to output a function works in itself, but outputting a variable or constant doesn't.

As you can see here, although you'd think the var/let holds the content of bar.boy(), Swift somehow can't find it...

So it turns out there was probably a bug in the past that when you were adding a Swift file it would add/ask a Bridging header, but it wouldn't add that line to your project

SWIFT_OPTIMIZATION_LEVEL = "-Onone";

which means you'd stay in this state

resulting in error: <EXPR>:1:1: error: use of unresolved identifier!

I could only find that out because I moved around files in my project and when I added ObjC files to the project, it asked me about a Bridging header (although I had one already!) and luckily added that SWIFT_OPTIMIZATION_LEVEL. One could consider this is a bug to consider the default value is fastest, but then again I guess this was only a bug in the past and got fixed now.

Still, I fixed now it might be a bug the other way around, if it add none in the release build. I can't test this right now because for testing this I only had a Debug build. I'll leave that as an exercise :) for Apple's Engineers.

I set Swift Complier to "-O"

SWIFT_OPTIMIZATION_LEVEL = "-O";

and set it back to "-Onone".

SWIFT_OPTIMIZATION_LEVEL = "-Onone";

Then it works.

Fixed after setting:

Optimization Level = None[-Onone] under Swift Compiler - Code Generation

Note that setting Optimization Level under Apple LLVM 8.0 - Code Generation has no effect

I bet that bug is due to the fact that foo has been optimized out during compilation and it's symbol does not exist anymore in the compiled code (even if it shouldn't have in debug and it's still an LLDB bug)

Probably if you add some usage of foo in the next lines (even a println) its symbol will hopefully be kept in the IR and you'll be able to po foo

(I agree that that's still a bug but at least if it works you'll have a workaround and some sense of explanation)

I encountered a similar issue but I already had the correct configuration, all optimisations set to None. However I still didn't get any values.

After some further digging I found out that the issue originated from Xcode being unable to the resolve the types:

(lldb) frame variable self
<could not resolve type>

That led me to this question: https://stackoverflow.com/questions/41037921/xcode-8-debugger-could-not-resolve-type where the issue is described and the bridging header seems to cause issues.

With my project not having any bridging headers I studied the build settings once more and found this setting

This was initally set to YES. After changing the it to NO symbols are working again.

SWIFT_INSTALL_OBJC_HEADER = NO

If your project is using Swift, there are two separate "Optimization Level" settings in the project/target configuration. Its not only "SWIFT_OPTIMIZATION_LEVEL". Check this link: https://stackoverflow.com/a/32984193/2060180

I'll leave it here in case it's useful to someone.

For those who are using Swift framework in an Objective-c project, and wanna debug the Swift source files in that project: (In my case, I have a mixed-language module which managed by Cocoapods, I need to debug the swift module in my Objective-c Example project)

It works for me after I added an Empty Swift file in my Objective-c project.

Otherwise, those swift compiler options won't show up in the Build Settings.