fmt: weird formatting with targets disabled

[hawkw]

Bug Report

Crates

• tracing-subscriber

Description

When configuring a formatter with

    .with_target(false)

events are formatted with a second space and colon following the span context, like this:

This doesn't look great. We should fix it.

The issue is in this code:

tracing/tracing-subscriber/src/fmt/format/mod.rs

Lines 311 to 321 in fc3ab4c

	write!(
	writer,
	"{} {}{}: ",
	fmt_level,
	fmt_ctx,
	if self.display_target {
	meta.target()
	} else {
	""
	}
	)?;

Notice how the : is part of the format string, so it's always output, even when we don't print a target.

We should change this so that when display_targets is not set, we don't include the : . We could do that by putting the if around the write! macro, instead, and having two separate format specs depending on whether or not we're including a target.