Question : how to use debug!(); ?

[stephan57160]

I'm currently trying to play with flapigen internals, let's say, for some experiment.

I'm sure it's a rookie question, but how to use debug!() and mainly, how to see its output ? Is there anything we have to initialise ? I suppose there is something to add in my library's build.rs, right ?

[stephan57160]

I mean ... I saw a couple of debug!() in flapigen code itself. How to use this ? Is there any 'debug' log file ?

[Dushistov]

There are no something special. It is the same old log crate as everywhere. You need register your logging implementation (for example env_logger ) in start of main and force it to output.

For example in cpp_tests: https://github.com/Dushistov/flapigen-rs/blob/b6b10fe44c745730beb1ac7e7a2fa87826b96823/cpp_tests/build.rs#L6

So you need to run build with RUST_LOG=debug to see debug output, details you can find in env_logger documentation. There are only one specific thing for build scripts, you get build script stdout/stderr in case of error, so if all OK, then RUST_LOG=debug cargo build prints nothing, even you have thounds of debug!, to see stdout/stderr you need RUST_LOG=debug cargo build -vv

[stephan57160]

OK. Thx. Found it.

For those who will read this, in my build.rs:

fn main() {
    env_logger::init();
    debug!("Stephan's log sample");
    debug!("Stephan's log sample"); // twice !
    debug!("Another log exmple");

    let profile = std::env::var("PROFILE").unwrap();

With a

cargo clean
export RUST_LOG=debug ; cargo build

nothing happens on stdout.

But one can find the logs in target/debug/build/MyLibrary-xxx/stderr:

DEBUG:<unknown>: Stephan's log sample
DEBUG:<unknown>: Stephan's log sample
DEBUG:<unknown>: Another log exmple
...

Note Do not forget to clean, else, build.rs is not executed if previous build is successful.

[Dushistov]

nothing happens on stdout.

As I wrote before you need "-vv" to see stdout of build script.

Do not forget to clean,

this is overkill, you need just touch path/to/build.rs