Compilation mode between "full" and "derive"

[alexcrichton]

I've often found that for proc_macro_attribute purposes you often need to parse the function signature, but nothing beyond that really needs to be parsed. Namely use cases like wasm-bindgen don't need a full expression parser and can get away with the body of a function being internally stored as TokenStream.

I'm curious if it would be possible to have an interemediate mode between "full" and "derive" which allows compiling syn a bit more quickly. Have others run across this sort of desire before?

[dtolnay]

I would be on board with more fine-grained knobs over what you want to support parsing. Do you know of any other attribute macros that would want function signatures only?

[dtolnay]

This is now handled by https://github.com/taiki-e/syn-mid.