Parsing an Expr fails with embedded macros in expression position

[dhardy]

As in the title, let expr: Expr = input.parse()?; fails on content containing a macro.

I'm not actually sure whether this should be supported, though it works for declarative macros.

Related: rust-lang/rust#54727 (procedural macros can't currently be used in expression position; though declarative macros can be).

[dtolnay]

You may need to enable the "full" feature if you are parsing expressions: https://github.com/dtolnay/syn#optional-features. By default we only parse the basic subset of expressions that typically appear as array lengths.

For procedural macros in expression position check out https://github.com/dtolnay/proc-macro-hack.

[dhardy]

Oh, was wondering whether I should try that, but didn't think a feature combination would allow only limited parsing. Will do.

Awesome! Thanks for all the hacks around macros. I'm currently using nightly-only and only at the proof-of-concept stage, so just using the nightly feature flag.