How to include generated file written under OUT_DIR

[egrimley-arm]

Recent versions of protobuf-codegen seem to enable putting the generated .rs file under OUT_DIR (using cargo_out_dir), but it's unclear to me how to use the .rs file when it's under OUT_DIR. It does not seem to be possible to include! the file because of:

1. the inner attributes (#!allow(...), etc.): see include! macro fails if included file has top-level inner attributes rust-lang/rfcs#752

2. the documentation comment (//! Generated file from ...)

Sorry if this is in the documentation somewhere and I've missed it or if I'm just using the wrong combination of versions.

[egrimley-arm]

I haven't explicitly said how this could be "fixed". I suppose there are two things that could be done:

• Have an option for rust-protobuf to generate a .rs file without the inner attributes and without the documentation comment, so that it can be include!-ed.
• Find and document some work-around so that the .rs file as currently generated can be used after it has been written to OUT_DIR.

[matejcik]

faced the same problem. The solution seems to be to create your own mod.rs whose contents are:

include!(concat!(env!("OUT_DIR"), "/mod.rs"));

(this requires gen_mod_rs to be enabled, which is the default since version 3)

Rust somehow magically picks the rest of the modules from the outdir.

related original issues:
#117
#523
#525

[egrimley-arm]

Thank you, @matejcik . That's very helpful. I also found this useful example: https://github.com/jgarzik/rust-protobuf-example

However, there's one thing I don't understand yet: how cargo dependencies are tracked. With that rust-protobuf-example I found that any change to any file (even rust-protobuf-example/newdir/newfile, for example) results in a rebuild. But when I had a crate that was a dependency of a larger project I found I had to add my own println!("cargo:rerun-if-changed=..."):
https://github.com/veracruz-project/veracruz/blob/870db97945f9880cdbc8d3c4002fda64f2bb969d/transport-protocol/build.rs#L13-L15

But that's a different issue. I'll close this one.