The following will make non-blocking logs. Note for these logs to be output, you need to "drain" them. See how to do that in the cortex-m-funnel crate. This doesn't apply for std.

info!("log {}", a_value);
warn!("log {}", a_value);
debug!("log {}", a_value);
error!("log {}", a_value);

The following will log and block until all information has been output.

blocking::info!("log {}", a_value);
blocking::warn!("log {}", a_value);
blocking::debug!("log {}", a_value);
blocking::error!("log {}", a_value);

Configuring

By default, all logs are turned off. You can use the following features to enable them.

all
info
warn
debug
error

Enabling/disabling logs at crate level

A crate can generate a wrapper around the log API and use default feature flags to enable/disable them, independent of other crates using logging.

Usage:

logging::add!(my_logger);
// ...
fn my_crate_function(arg: u32){
    my_logger::info!("arg = {}", arg);
}

Cargo.toml:

[features]
log-all = []
log-none = []
log-info = []
log-debug = []
log-warn = []
log-error = []

Now logs can be enabled or disabled in this sub crate by passing a feature flag, e.g. mycrate/log-all or mycrate/log-debug.

Testing

You will need to change your --target based on what your machine is. See rustc --Vv to see your target triple string.

cargo test --features std,all --target $(rustc -Vv | awk 'NR==5{print $2}') -- --nocapture