Update

vendor/github.com/go-json-experiment/json/fields.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build !goexperiment.jsonv2 || !go1.25
+
 package json
 
 import (
@@ -402,6 +404,7 @@ type fieldOptions struct {
 // the JSON member name and other features.
 func parseFieldOptions(sf reflect.StructField) (out fieldOptions, ignored bool, err error) {
 	tag, hasTag := sf.Tag.Lookup("json")
+	tagOrig := tag
 
 	// Check whether this field is explicitly ignored.
 	if tag == "-" {
@@ -451,6 +454,13 @@ func parseFieldOptions(sf reflect.StructField) (out fieldOptions, ignored bool,
 			err = cmp.Or(err, fmt.Errorf("Go struct field %s has JSON object name %q with invalid UTF-8", sf.Name, name))
 			name = string([]rune(name)) // replace invalid UTF-8 with utf8.RuneError
 		}
+		if name == "-" && tag[0] == '-' {
+			defer func() { // defer to let other errors take precedence
+				err = cmp.Or(err, fmt.Errorf("Go struct field %s has JSON object name %q; either "+
+					"use `json:\"-\"` to ignore the field or "+
+					"use `json:\"'-'%s` to specify %q as the name", sf.Name, out.name, strings.TrimPrefix(strconv.Quote(tagOrig), `"-`), name))
+			}()
+		}
 		if err2 == nil {
 			out.hasName = true
 			out.name = name