Bad output message when using with_timer() API

[jaudiger]

Bug Report

Version

├── tracing v0.1.29 (*)
├── tracing-subscriber v0.3.6
│   ├── tracing-core v0.1.21 (*)
│   ├── tracing-log v0.1.2
│   │   └── tracing-core v0.1.21 (*)
│   └── tracing-serde v0.1.2
│       └── tracing-core v0.1.21 (*)
│   └── tracing v0.1.29 (*)

Platform

Linux 0533f12981cc 5.15.15-200.fc35.x86_64 #1 SMP Sun Jan 16 17:37:06 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux

Crates

tracing-subscriber

Description

I tried to create a configurable subscriber based on configuration input, but I encountered an issue that block me.

I tried this code:

let timer = UtcTime::new(format_description!(
    "[year]-[month]-[day] [hour]:[minute]:[second].[subsecond digits:3]"
));

let mut subscriber_builder = tracing_subscriber::fmt()
    .with_max_level(Level::INFO);

   // For demonstration purpose
    if true {
        subscriber_builder = subscriber_builder.with_timer(timer);
    }

tracing::subscriber::set_global_default( subscriber_builder.finish())
    .with_context(|| "Failed to initialize the logging library")?;

I expected to build the code as it's possible with the following code:

let subscriber = tracing_subscriber::fmt()
    .with_max_level(Level::INFO)
    .with_timer(timer)
    .finish();

tracing::subscriber::set_global_default(subscriber)
    .with_context(|| "Failed to initialize the logging library")?;

Instead, this happened:

error[E0308]: mismatched types
  --> src/application/tracing/tracing.rs:86:76
   |
86 |                         subscriber_builder = subscriber_builder.with_timer(timer);
   |                                                                            ^^^^^ expected struct `tracing_subscriber::fmt::time::SystemTime`, found struct `UtcTime`
   |
   = note: expected struct `tracing_subscriber::fmt::time::SystemTime`
              found struct `UtcTime<&[FormatItem<'_>]>`

For more information about this error, try `rustc --explain E0308`.

[hawkw]

The issue is that SystemTime and UtcTime are different types, so you are changing the type of the subscriber when you change the timer to UtcTime. Try something like this instead:

let timer = UtcTime::new(format_description!(
    "[year]-[month]-[day] [hour]:[minute]:[second].[subsecond digits:3]"
));

let mut subscriber_builder = tracing_subscriber::fmt()
    .with_max_level(Level::INFO);

if true {
    let subscriber = subscriber_builder
        .with_timer(timer)
        .finish();
    tracing::subscriber::set_global_default(subscriber)
} else {
    tracing::subscriber::set_global_default(subscriber_builder.finish())
}
    .with_context(|| "Failed to initialize the logging library")?;