Swift Testing Macros - empty MacroExpansionContext.lexicalContext

[adammcarter]

Description

Following a discussion here:

https://forums.swift.org/t/generate-swift-testing-code-with-macros/77883

And further DMs to diagnose the issue (quote and credit to @grynspan):

I took a look and this appears it may be a bug in the compiler's macros implementation. There is a MacroExpansionContext.lexicalContext property available to the expansion of @Test that we use to determine if a test is a member of a type or not (and therefore whether thunk functions we emit need the static keyword or not), but it appears to be empty in the context of expanding @SnapshotTest. Please file a bug against the swift or swift-syntax repo?

I was able to get the code to compile by changing the macro expansion so it emitted the @Test function into a structure. This isn't ideal because it will cause the test function to be nested in a suite with an inscrutible name (generated by MacroExpansionContext.makeUniqueName()), but it does allow the macro expansion to compile successfully.

Happy to post more on this, but I think that quote above should give enough explanation.

I've also attached example project as a quick way to see this error and hopefully help diagnose the issue

SnapshotSuite.zip

Steps to Reproduce

No response

[ahoppen]

Synced to Apple’s issue tracker as rdar://144920985

[ahoppen]

Sounds like a bug in macros during compilation, so moving this to the compiler repo.