fmt: Missing space between multiple values for the same key on a span

[bazaah]

Version

tracing v0.1.13
│ ├── tracing-attributes v0.1.7
│ └── tracing-core v0.1.10
└── tracing-subscriber v0.2.3
├── tracing-core v0.1.10 ()
├── tracing-log v0.1.1
│ └── tracing-core v0.1.10 ()
└── tracing-serde v0.1.1
└── tracing-core v0.1.10 (*)

Platform

Linux elysium 5.5.6-arch1-1 #1 SMP PREEMPT Mon, 24 Feb 2020 12:20:16 +0000 x86_64 GNU/Linux

Crates

tracing
tracing-subscriber

Description

When repeatedly record()ing values to the same span key, a space between each KV pair is missing.
MVP:

use {
    tracing::{info, info_span},
    tracing_subscriber::FmtSubscriber,
};

fn main() {
    let subscriber = FmtSubscriber::builder().finish();
    tracing::subscriber::set_global_default(subscriber).expect("setting default subscriber failed");

    let span = info_span!("debug", happy = true);
    let _grd = span.enter();
    span.record("happy", &false);

    info!("hello world");
}

The expected result: <DATE> INFO debug{happy=true happy=false}: <FILE>: hello world

The actual output: <DATE> INFO debug{happy=truehappy=false}: <FILE>: hello world

Note the lack of a space between 'true' and 'happy'

[hawkw]

Thanks for reporting & providing a minimal reproduction! This definitely looks like a bug.

[hawkw]

I think fixing this should be relatively straight-forward. Here is the code where we are recording a new value into a span that already has formatted fields:

tracing/tracing-subscriber/src/fmt/fmt_layer.rs

Lines 462 to 465 in d0a3bdd

	if let Some(FormattedFields { ref mut fields, .. }) =
	extensions.get_mut::<FormattedFields<N>>()
	{
	let _ = self.fmt_fields.format_fields(fields, values);

We can check here if the formatted fields string is non-empty. If it is, we can append a ' ' before recording the field.

If anyone is interested in looking into this, it's probably a pretty good first issue. I'm happy to provide further advice, too!