Function init_tracing 

pub fn init_tracing(log: &LogSettings) -> Result<(), ConfigError>

Install a tracing-subscriber using log.

When RUST_LOG is set, it is used as the filter. Otherwise log.level is used. log.json selects JSON versus the default text formatter.

Errors

Returns ConfigError::InvalidFilter if the chosen filter cannot be parsed, or ConfigError::Tracing if a global subscriber is already installed.