Add Backoff.ErrCause()

[pracucci]

What this PR does:

In this PR I propose a add Backoff.ErrCause() which is like Backoff.Err() but returns the context cause if backoff is terminated because the context has been canceled.

Which issue(s) this PR fixes:

N/A

Checklist

• Tests updated
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX]

[pracucci]

I just realised we require golang 1.20 in dskit. Damn this repo lives in the past!

[aknuds1]

LGTM - except I guess we need to increase the minimum Go version to 1.21. Does anything hinder us from doing so?

[pstibrany]

If there are objections to this change, then an alternative may be adding another function Backoff.ErrCause() which is like Err() but returns the context cause instead.

This seems like safer option to me, to avoid breaking changes to clients using Backoff today.

[simonswine]

If there are objections to this change, then an alternative may be adding another function Backoff.ErrCause() which is like Err() but returns the context cause instead.

This seems like safer option to me, to avoid breaking changes to clients using Backoff today.

I would agree with @pstibrany: A subtle breaking change like this will not come up when randomly upgrading the dskit package, and not too sure that everyone fully check the diff between go mod updates.

I could also think of something that would at least make the errors.Is still work by wrapping the cause: https://go.dev/play/p/tT6qg_rnDxd, but still prefer the simplicity of a separate method.

[pracucci]

Thanks for the feedback. Switching to draft cause it requires golang 1.21 anyway, so we would need to upgrade first.

[pracucci]

Thanks for the feedback people. I've added Backoff.ErrCause() instead, so that this PR is not a breaking change. Still blocked on #540 tho.

[pracucci]

Still blocked on #540 tho.

I merged #540

[simonswine]

LGTM