instrument macro doesn't allow declaration of fields that have a period . in their name

[glademiller]

Feature Request

Motivation

I would like to set http.status_code to empty in order to be able to record the value later the most convenient way to do this would be with the macro.

Proposal

Allow
#[tracing::instrument(fields(http.status_code = ...))]

Alternatives

Allow recording of fields without declaring them upfront.

[hawkw]

This was implemented in #672. However, it has yet to be released as that PR also causes instrument to reject unrecognized input that it did not previously reject, which we think may constitute a breaking change (#773 (comment)). Stay tuned, though --- I'm planning on trying to make some additional changes to make that change backwards compatible.

[glademiller]

@hawkw awesome thanks for the update. Would this also allow for declaring the value on that field in the macro to be tracing::field::Empty? I suppose I can always just put another dummy value but being able to use Empty would more clearly communicate my intent.

Edit: I should have read through the linked comments first it looks like you are working through arbitrary expressions etc.

[hawkw]

Yup, that's right. :)

Currently, field names with no value in instrument are mapped to tracing::field::Empty, which is what that PR does as well, for backwards-compatibility (although you will also be able to use Empty explicitly as well when #672 is published) . However, in tracing-attributes 0.2, we want to change this so that instrument supports the same local variable shorthand as the function-like tracing macros, so you will need to use Empty explicitly instead, the same as all the other macros.