errors, fmt: add support for wrapping multiple errors
An error which implements an "Unwrap() []error" method wraps all the
non-nil errors in the returned []error.
We replace the concept of the "error chain" inspected by errors.Is
and errors.As with the "error tree". Is and As perform a pre-order,
depth-first traversal of an error's tree. As returns the first
matching result, if any.
The new errors.Join function returns an error wrapping a list of errors.
The fmt.Errorf function now supports multiple instances of the %w verb.
For #53435.
Change-Id: Ib7402e70b68e28af8f201d2b66bd8e87ccfb5283
Reviewed-on: https://go-review.googlesource.com/c/go/+/432898 Reviewed-by: Cherry Mui <cherryyz@google.com> Reviewed-by: Rob Pike <r@golang.org>
Run-TryBot: Damien Neil <dneil@google.com> Reviewed-by: Joseph Tsai <joetsai@digital-static.net>