journald: Do not log additional string data in Debug representation

[swsnr]

Bug Report

Follow up from #1709 (comment)

Description

tracing-journald currently logs additional string fields in their Debug representation, i.e. this code

info!(foo="foo", "test")

writes FOO="foo" to the journal, i.e. with extra quotes from format!("{:?}").

I expected FOO=foo, i.e. a regular string.

[swsnr]

@Ralith You've said over in the merge request that this is intended because it helps distinguish between 1 as a number, and 1 as a string, which one couldn't if strings were logged directly.

I understand the motivation, but my concern is that this effectively requires downstream consumers of the journal to "unparse" Rust's Debug representation in order to get the original string back out.

It also seems rather unusual to add extra formatting to field values, as far as I can see: The slog implementation uses Display, not Debug, and I superficially (my C's a bit rusty 😉 ) checked Glib's structured logging code, and it seems to treat all fields as strings upfront, unless they contain internal NULs.

[Ralith]

On review I think I agree; the common case (especially in idiomatic journald clients) of working with strings trumps the rather weird case of meaningfully dynamically-typed fields. I'd be happy to approve a fix.

[swsnr]

I'll make a MR after the tests are merged.

We can also have a flag, similar to the field prefix, to toggle between the literal and the debug representation of strings, if you like 🙂

[Ralith]

Eh, I'd rather avoid the complexity.

[swsnr]

Absolutely fine with me 🙂 I'll make a merge request after #1709

@Ralith Thanks for your great support and your help 🙏

[Ralith]

Thanks for the contributions!