From ee5af46172e64eceddb56018de8ea850fe0a6cae Mon Sep 17 00:00:00 2001 From: Joe Tsai Date: Sat, 11 Oct 2025 11:57:46 -0700 Subject: 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 Reviewed-by: Dmitri Shuralyov Reviewed-by: Damien Neil --- src/encoding/json/v2_decode_test.go | 28 ++++++++++++++++++++++++++++ 1 file changed, 28 insertions(+) (limited to 'src/encoding/json/v2_decode_test.go') diff --git a/src/encoding/json/v2_decode_test.go b/src/encoding/json/v2_decode_test.go index 28c57ec8bf..26b4448721 100644 --- a/src/encoding/json/v2_decode_test.go +++ b/src/encoding/json/v2_decode_test.go @@ -2363,6 +2363,34 @@ func TestUnmarshalTypeError(t *testing.T) { } } +func TestUnmarshalTypeErrorMessage(t *testing.T) { + err := &UnmarshalTypeError{ + Value: "number 5", + Type: reflect.TypeFor[int](), + Offset: 1234, + Struct: "Root", + } + + for _, tt := range []struct { + field string + want string + }{ + {"", "json: cannot unmarshal number 5 into Go struct field Root. of type int"}, + {"1", "json: cannot unmarshal number 5 into Root.1 of type int"}, + {"foo", "json: cannot unmarshal number 5 into Go struct field Root.foo of type int"}, + {"foo.1", "json: cannot unmarshal number 5 into Root.foo.1 of type int"}, + {"foo.bar", "json: cannot unmarshal number 5 into Go struct field Root.foo.bar of type int"}, + {"foo.bar.1", "json: cannot unmarshal number 5 into Root.foo.bar.1 of type int"}, + {"foo.bar.baz", "json: cannot unmarshal number 5 into Go struct field Root.foo.bar.baz of type int"}, + } { + err.Field = tt.field + got := err.Error() + if got != tt.want { + t.Errorf("Error:\n\tgot: %v\n\twant: %v", got, tt.want) + } + } +} + func TestUnmarshalSyntax(t *testing.T) { var x any tests := []struct { -- cgit v1.3