Fix code generation for macro calls that store args in variables.

[rfk]

This fixes #498 for me locally. I don't know enough about the codebase to know how to write a good test for this or whether there's a cleaner way to fix it. But I'll be happy to polish this up a bit if you can give me a few pointers.

[djc]

Thanks for fixing this! The fix itself seems fine.

There are integration tests in the testing crate, should be easy to copy your reproducer in there. Probably put this in the macro module.

(Maybe also shorten the commit message little bit so it fits in one line?)

[rfk]

There are integration tests in the testing crate, should be easy to copy your reproducer in there.
Probably put this in the macro module.

Sounds good, I should be able to make time to revisit this in the next couple of days.

[rfk]

Updated with a test (which I confirmed fails on current main) and a briefer commit message.

[djc]

Thanks!