subscriber: expose access to event scope in FmtContext
#1728
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Motivation
Currently,
tracing_subscriber::fmt
'sFmtContext
type is missing thespan_scope
,event_span
, andevent_scope
methods thatContext
provides. This is a shame; these will make it much easier for users
implementing formatters to iterate over the scope of the event being
formatted correctly. We should expose those methods.
Solution
This branch adds new methods to
FmtContext
, most of which forward tothe similarly-named
Context
methods. However, because aFmtContext
is only constructed when formatting an event, we can also make the event
scope methods a little more ergonomic by storing a ref to the span being
formatted and automatically passing it to
Context::event_scope
andContext::event_span
. This means theFmtContext
can just always returnthe current event's scope without the user having to pass it in.