encoding/json: avoid misleading errors under goexperiment.jsonv2
The jsontext package represents the location of JSON errors
using a JSON Pointer (RFC 6901). This uses the JSON type system.
Unfortunately the v1 json.UnmarshalTypeError assumes a Go struct-based
mechanism for reporting the location of errors
(and has historically never been implemented correctly since
it was a weird mix of both JSON and Go namespaces; see #43126).
Trying to map a JSON Pointer into UnmarshalTypeError.{Struct,Field}
is difficult to get right without teaching jsontext
about the Go type system.
To reduce the probability of misleading errors,
check whether the last token looks like a JSON array index
and if so, elide the phrase "into Go struct field".
Fixes #74801
Change-Id: Id2088ffb9c339a9238ed38c90223d86a89422842
Reviewed-on: https://go-review.googlesource.com/c/go/+/710676
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Dmitri Shuralyov <dmitshur@google.com> Reviewed-by: Damien Neil <dneil@google.com>