encoding/json/v2: remove `unknown` tag option and DiscardUnknownMembers

WARNING: This commit contains breaking changes
for those already using GOEXPERIMENT=jsonv2.

This removes support for the `unknown` tag option and
the DiscardUnknownMembers marshal option.

The `unknown` tag option semantics are a bit too subtle
even for experienced Go programmers to understand.
Remove support for it. The exact same feature (or something similar)
can be added back into a future release of json/v2.

We already support the `inline` tag option,
which can handle most cases of what someone might want to do
with unknown fields (such as preserve them).

Fixes #77271
Updates #76444

Change-Id: I875952f0755e58aac4c571869b2cdb56e75cfda9
Reviewed-on: https://go-review.googlesource.com/c/go/+/741320
Reviewed-by: Damien Neil <dneil@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
8 files changed
tree: f52aba650a85b15a0a009df469e37c4c4ad76b13
  1. .github/
  2. api/
  3. doc/
  4. lib/
  5. misc/
  6. src/
  7. test/
  8. .gitattributes
  9. .gitignore
  10. codereview.cfg
  11. CONTRIBUTING.md
  12. go.env
  13. LICENSE
  14. PATENTS
  15. README.md
  16. SECURITY.md
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