Macro failure only when depending on a project having bindgen as a build dependency.

[leoschwarz]

As a preamble this might very well be some issue hidden away somewhere and not actually a bug in bindgen, however tracing down the bug is proving to be really hard.

Source code

I setup a reduced (if you think it's worth the effort I can try minimize it further) example here: https://github.com/leoschwarz/bug_2018-03-28

Bindgen Invocation

None other than including it as build-dependency of the subcrate ext_crate.

Actual Results

Rustc fails with a long error message, where some macros lead to code with mismatched types.
If you leave away either the bindgen in ext_crate or the ext_crate dependency in the top level Cargo.toml the code compiles just fine.

Output:

rustc 1.26.0-nightly (9c9424de5 2018-03-27)

• cargo check: https://gist.github.com/leoschwarz/918266935b5624f32d5cc7d03280f45e
• RUSTFLAGS="-Z external-macro-backtrace" cargo check -vv: https://gist.github.com/leoschwarz/0c30bd71563d85ffed0fa30992aeff66

rustc 1.24.1 (d3ae9a9e0 2018-02-27)

• cargo check -vv: https://gist.github.com/leoschwarz/0a863147dba9d01b340e5715b7717fec

[emilio]

I suspect something is getting confused... Nom is pulled via bindgen -> cexpr, and probably you're peeking the wrong version or something? Looks really weird.

I can't look into it right now, but I'll try to take a look tomorrow if you haven't figured out.

I'd try to lock nom to a specific version or something. Also, does it happen with all rustc versions?

[leoschwarz]

Thanks. I've been able to narrow down the issue further, it's not a bindgen issue, sorry, however bindgen depends on nom with the verbose-errors feature which leads to the issue (nom has different error types with and without the flag) only occuring when I include bindgen. (However I did not assume that having a build dependency select certain features would also include the feature in libraries using it as normal dependency.)

So essentially the iso8601 crate has to be patched to work with verbose-errors or the feature should be disabled for that crate's nom. I'm not sure if the later is possible though.

Edit: Actually I'm not the first one bothered by this, see rust-bakery/nom#544.

[leoschwarz]

Closing as it is not actually a bug in bindgen, and is apparently fixed in nom 4.