Rust Tracing Practices

Event Recording

• Use level-specific macros for appropriate visibility: info!, debug!, trace!, warn!, error!
• Provide structured data as named arguments to facilitate automated processing and filtering
• Prefer lowercase log-message prose while preserving identifier and acronym spelling
• Record ordinary error values with Display, using %error or error = %error
• Record an error_stack::Report<Context> with Debug, using ?report or error = ?report on the complete report rather than its current_context() alone
• Keep public-response sanitization separate from diagnostic reporting. Debug formatting does not itself redact sensitive data
• Include relevant context through key-value pairs

These fragments assume a local user. Their error events are alternatives: e is an ordinary error value, and report is an error_stack::Report<_>.

tracing::info!(user_id = user.id, action = "login", "user logged in successfully");
tracing::error!(error = %e, user_id = user.id, "failed to authenticate user");
tracing::error!(error = ?report, user_id = user.id, "failed to authenticate user");

A report's plain Display stops after the first context and omits attachments. Its Debug formatter traverses the frames and renders printable attachments or installed hook output.

Instrumentation

• Apply the #[tracing::instrument] attribute to functions to automatically create trace spans
• When an error return merits an automatic event, use err for an ordinary error and err(Debug) for an error_stack::Report<Context>
• Exclude sensitive or large parameters using skip(password) or skip_all
• Add custom context fields with fields(request_id = req.id())

#[tracing::instrument(level = "debug", err, skip(password), fields(user_id = user.id))]
async fn authenticate_user(user: &User, password: &[u8]) -> Result<AuthToken, AuthError> {
    // Implementation
}