gotipでencoding/json/v2を試す

go install golang.org/dl/gotip@latest
go download 665796

cd ~/anywhere/your/favorite/playground
# or
cd $(mktemp -d)
gotip mod init iikanji-no-namae

-- gopls from PATH, maybe maosn managed (= latest stable).
local lsCmd = { "gopls" }

if vim.env.GOPLS_PATH ~= nil and vim.env.GOPLS_PATH ~= "" then
  -- Can be changed arbitrarily, maybe latest unreleased.
  lsCmd = vim.env.GOPLS_PATH
end

return {
  cmd = lsCmd,
  settings = {
    gopls = { -- https://github.com/golang/tools/blob/master/gopls/doc/settings.md
      analyses = {
        ST1003 = true,
        fieldalignment = false,
        fillreturns = true,
        nilness = true,
        nonewvars = true,
        shadow = true,
        undeclaredname = true,
        unreachable = true,
        unusedparams = true,
        unusedwrite = true,
        useany = true,
      },
      codelenses = {
        generate = true, -- show the `go generate` lens.
        regenerate_cgo = true,
        test = true,
        tidy = true,
        upgrade_dependency = true,
        vendor = true,
      },
      hints = {
        assignVariableTypes = true,
        compositeLiteralFields = true,
        compositeLiteralTypes = true,
        constantValues = true,
        functionTypeParameters = true,
        parameterNames = true,
        rangeVariableTypes = true,
      },
      buildFlags = { "-tags", "integration" },
      completeUnimported = true,
      diagnosticsDelay = "500ms",
      gofumpt = true,
      matcher = "Fuzzy",
      semanticTokens = true,
      staticcheck = true,
      symbolMatcher = "fuzzy",
      -- I've used for a while with this option, and found it annoying.
      -- Great feature tho.
      -- usePlaceholders = true,
    },
  },
}

export PATH=$(gotip env GOROOT)/bin/:$PATH
export GOTOOLCHAIN=path

export GOEXPERIMENT=jsonv2

package main

import (
	"encoding/json/jsontext"
	"encoding/json/v2"
	"fmt"
	"time"
)

type A struct {
	Foo string    `json:"foo,omitzero"`
	Bar int       `json:"int,omitzero"`
	T   time.Time `json:"t,omitzero,format:RFC3339"`
}

func main() {
	a := A{
		Foo: "foo",
		Bar: 123,
		T:   time.Now(),
	}

	bin, err := json.Marshal(a, jsontext.WithIndent("    "))
	if err != nil {
		panic(err)
	}
	fmt.Println(string(bin))
}

$ go run .
{
    "foo": "foo",
    "int": 123,
    "t": "2025-05-11T14:48:17+09:00"
}