log-to-defmt 0.1.0

A backend for log that emits through defmt
Documentation 
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#![no_std]
//! This is a logging adapter that acts as an implementation of the [log crate] and hands the
//! rendered messages off to the [defmt crate].
//!
//! Using this is generally not recommended: Once the log infrastructure is pulled into a project,
//! Rust's string formatting is brought in, avoiding which is a big part of the point of defmt.
//!
//! However, this can be useful during development, when debugging a particular library (that
//! optionally produces messages through log) on a platform for which a defmt output has already
//! been established.
//!
//! [log crate]: https://crates.io/crates/log
//! [defmt crate]: https://crates.io/crates/defmt
//!
//! ### Maturity
//!
//! The current implementation of this takes a huge amount of shortcuts: not only does it not
//! convert log levels, it also hardwires some to the most verbose level, discards lots of
//! information that would otherwise be available, and uses a fixed size buffer.
//!
//! Future iterations of this crate are expected to address these on demand; for example, this
//! could gain a build time configuration mechanism for the maximum expected length, or an `alloc`
//! feature that renders the log messages to a `Vec` instead of a `heapless::Vec` before handing
//! them off to defmt as a slice.
//!
//! The crate will likely introduce such features (altering its behavior) without declaring
//! breaking changes; users are advised to configure their error levels to match which messages
//! they expect to see.

/// Set up log output to be forwarded to defmt
///
/// If the global logger can not be set, this fails silently (in the API sense), but does report to
/// defmt.
pub fn setup() {
    struct DefmtLogger;

    impl log::Log for DefmtLogger {
        fn enabled(&self, _: &log::Metadata) -> bool {
            true
        }

        fn log(&self, record: &log::Record) {
            use core::fmt::Write;
            let mut rendered = heapless::Vec::<u8, 200>::new();
            match write!(rendered, "{}", record.args()) {
                Ok(()) => defmt::info!("{}", core::str::from_utf8(&rendered).unwrap()),
                Err(_) => defmt::info!(
                    "{:?}...",
                    core::str::from_utf8(&rendered).map_err(|_| "Truncated at UTF-8 boundary")
                ),
            }
        }

        fn flush(&self) {}
    }

    if log::set_logger(&DefmtLogger).is_err() {
        defmt::error!("Could not log::set_logger, continuing without output from there");
    } else {
        defmt::info!("Should be up now");
    }
    log::set_max_level(log::LevelFilter::Debug);
}