encoding/json: merge FieldStack if the error's Field exists.

When people return UnmarshalTypeError in UnmarshalJSON, we should append error's Field to FieldStack.

Fixes #68750

Change-Id: I0a5a9b259a1b569de1bebc815ec936c913e10469
GitHub-Last-Rev: 18796addc3fa0d367ba1a3f4bd268ca246890fe0
GitHub-Pull-Request: golang/go#68870
Reviewed-on: https://go-review.googlesource.com/c/go/+/605455
Reviewed-by: Carlos Amedee <carlos@golang.org>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

diff --git a/src/encoding/json/decode.go b/src/encoding/json/decode.go
index 69a1013b8598fe95e4a841661a69f6acd6a2cae3..19d4563e33f27a4c191aadaa35f6187c6eba9bc2 100644 (file)
--- a/src/encoding/json/decode.go
+++ b/src/encoding/json/decode.go
@@ -255,7 +255,11 @@ func (d *decodeState) addErrorContext(err error) error {
                switch err := err.(type) {
                case *UnmarshalTypeError:
                        err.Struct = d.errorContext.Struct.Name()
-                       err.Field = strings.Join(d.errorContext.FieldStack, ".")
+                       fieldStack := d.errorContext.FieldStack
+                       if err.Field != "" {
+                               fieldStack = append(fieldStack, err.Field)
+                       }
+                       err.Field = strings.Join(fieldStack, ".")
                }
        }
        return err

diff --git a/src/encoding/json/decode_test.go b/src/encoding/json/decode_test.go
index ed906950394d052dc61e4c4df9b7860e67400116..752825cffeac4f2327435d01e432cd681b52cca2 100644 (file)
--- a/src/encoding/json/decode_test.go
+++ b/src/encoding/json/decode_test.go
@@ -62,6 +62,21 @@ func (*SS) UnmarshalJSON(data []byte) error {
        return &UnmarshalTypeError{Value: "number", Type: reflect.TypeFor[SS]()}
 }
 
+type TAlias T
+
+func (tt *TAlias) UnmarshalJSON(data []byte) error {
+       t := T{}
+       if err := Unmarshal(data, &t); err != nil {
+               return err
+       }
+       *tt = TAlias(t)
+       return nil
+}
+
+type TOuter struct {
+       T TAlias
+}
+
 // ifaceNumAsFloat64/ifaceNumAsNumber are used to test unmarshaling with and
 // without UseNumber
 var ifaceNumAsFloat64 = map[string]any{
@@ -428,6 +443,7 @@ var unmarshalTests = []struct {
        {CaseName: Name(""), in: `{"x": 1}`, ptr: new(tx), out: tx{}},
        {CaseName: Name(""), in: `{"x": 1}`, ptr: new(tx), err: fmt.Errorf("json: unknown field \"x\""), disallowUnknownFields: true},
        {CaseName: Name(""), in: `{"S": 23}`, ptr: new(W), out: W{}, err: &UnmarshalTypeError{"number", reflect.TypeFor[SS](), 0, "W", "S"}},
+       {CaseName: Name(""), in: `{"T": {"X": 23}}`, ptr: new(TOuter), out: TOuter{}, err: &UnmarshalTypeError{"number", reflect.TypeFor[string](), 0, "TOuter", "T.X"}},
        {CaseName: Name(""), in: `{"F1":1,"F2":2,"F3":3}`, ptr: new(V), out: V{F1: float64(1), F2: int32(2), F3: Number("3")}},
        {CaseName: Name(""), in: `{"F1":1,"F2":2,"F3":3}`, ptr: new(V), out: V{F1: Number("1"), F2: int32(2), F3: Number("3")}, useNumber: true},
        {CaseName: Name(""), in: `{"k1":1,"k2":"s","k3":[1,2.0,3e-3],"k4":{"kk1":"s","kk2":2}}`, ptr: new(any), out: ifaceNumAsFloat64},