fmt: add with_event_name configuration option

[CreditWorthy]

Fixes #2774

Motivation

Event names set with event!(name: "...", ...) are currently not shown in the output. Users sometimes want to see custom event names, like how span names are displayed.

Solution

Added with_event_name() option to control display of event name:

• Shows custom event name when enabled
• Hides verbose default names like "event src/main.rs:123"
• Disabled by default

Example:

tracing_subscriber::fmt()
    .with_event_name(true)
    .init();

event!(name: "user_login", Level::INFO, "User logged in");
// Output: 2024-01-01 INFO app: user_login: User logged in

event!(Level::INFO, "Regular event");
// Output: 2024-01-01 INFO app: Regular event (no event name shown)

[kaffarell]

I find it a bit weird that enabling the option can still cause the name field to not be shown. Maybe as an alternative to this PR we could consider always showing the name field in the Full format when it is not the default value?

[CreditWorthy]

Hey, thank you for the feedback! :D

Just to wanted to make sure I understand correctly - you're suggesting that in the Full formatter, we should automatically show custom event names (when they're different from the default), without requiring a configuration option? This would be only in the full formatter not the compact?

So:

• event!(name: "user_login", ...) → shows "user_login:"
• tracing::info!(...) → shows nothing (hides default name)
• Then we can just remove with_event_name() method

@kaffarell

[kaffarell]

Yep, that's what I thought. But maybe someone else wants to chime in -- @davidbarsky what do you think?

[CreditWorthy]

Hey, just wondering what am post to do now?

[cijothomas]

@hawkw @davidbarsky Could you review this PR and take it forward? We are really looking forward to using this from OpenTelemetry and OpenTelemetry-Arrow projects!

[cijothomas]

@hds Could you help review/merge?