log/slog: arg to Record.Attrs should return bool

[jba]

The Record.Attrs method currently accepts an argument of type func(Attr).
For future consistency with iteration over func values, it should accept func(Attr) bool.

[jba]

Returning a bool is also useful if the Handler wants to look for a particular Attr. For example, some handlers might want to extract an error if there is one and treat it specially.

/cc @ianthehat

Original proposal: #56345

[ianthehat]

Yes, my use cases were things like detecting a specific attribute key to indicate a message type (operating like a mux to underlying handlers), and detecting specific error types to filter out messages that were not interesting. In both cases the attribute in question will be first by convention, but I have to scan the whole list anyway using .Attrs right now.

[rsc]

This proposal has been added to the active column of the proposals project
and will now be reviewed at the weekly proposal review meetings.
— rsc for the proposal review group

[rsc]

Based on the discussion above, this proposal seems like a likely accept.
— rsc for the proposal review group

[gopherbot]

Change https://go.dev/cl/484096 mentions this issue: log/slog: function argument to Record.Attrs returns bool

[rsc]

No change in consensus, so accepted. 🎉
This issue now tracks the work of implementing the proposal.
— rsc for the proposal review group