contextjson120: Add context to decode error message

common/json/internal/contextjson_120/decode.go

@@ -217,6 +217,7 @@ type decodeState struct {
 	savedError            error
 	useNumber             bool
 	disallowUnknownFields bool
+	context               *decodeContext
 }
 
 // readIndex returns the position of the last byte read.
@@ -245,7 +246,11 @@ func (d *decodeState) init(data []byte) *decodeState {
 // for reporting at the end of the unmarshal.
 func (d *decodeState) saveError(err error) {
 	if d.savedError == nil {
-		d.savedError = d.addErrorContext(err)
+		if d.context != nil {
+			d.savedError = d.addErrorContext(&contextError{err, d.formatContext(), d.context.key == ""})
+		} else {
+			d.savedError = d.addErrorContext(err)
+		}
 	}
 }
 
@@ -504,7 +509,11 @@ func (d *decodeState) array(v reflect.Value) error {
 	if u != nil {
 		start := d.readIndex()
 		d.skip()
-		return u.UnmarshalJSON(d.data[start:d.off])
+		err := u.UnmarshalJSON(d.data[start:d.off])
+		if err != nil {
+			d.saveError(err)
+		}
+		return nil
 	}
 	if ut != nil {
 		d.saveError(&UnmarshalTypeError{Value: "array", Type: v.Type(), Offset: int64(d.off)})
@@ -533,6 +542,7 @@ func (d *decodeState) array(v reflect.Value) error {
 	}
 
 	i := 0
+	d.context = &decodeContext{parent: d.context}
 	for {
 		// Look ahead for ] - can only happen on first iteration.
 		d.scanWhile(scanSkipSpace)
@@ -580,8 +590,11 @@ func (d *decodeState) array(v reflect.Value) error {
 		if d.opcode != scanArrayValue {
 			panic(phasePanicMsg)
 		}
+		d.context.index++
 	}
 
+	d.context = d.context.parent
+
 	if i < v.Len() {
 		if v.Kind() == reflect.Array {
 			// Array. Zero the rest.
@@ -612,7 +625,11 @@ func (d *decodeState) object(v reflect.Value) error {
 	if u != nil {
 		start := d.readIndex()
 		d.skip()
-		return u.UnmarshalJSON(d.data[start:d.off])
+		err := u.UnmarshalJSON(d.data[start:d.off])
+		if err != nil {
+			d.saveError(err)
+		}
+		return nil
 	}
 	if ut != nil {
 		d.saveError(&UnmarshalTypeError{Value: "object", Type: v.Type(), Offset: int64(d.off)})
@@ -668,6 +685,7 @@ func (d *decodeState) object(v reflect.Value) error {
 		origErrorContext = *d.errorContext
 	}
 
+	d.context = &decodeContext{parent: d.context}
 	for {
 		// Read opening " of string key or closing }.
 		d.scanWhile(scanSkipSpace)
@@ -687,6 +705,7 @@ func (d *decodeState) object(v reflect.Value) error {
 		if !ok {
 			panic(phasePanicMsg)
 		}
+		d.context.key = string(key)
 
 		// Figure out field corresponding to key.
 		var subv reflect.Value
@@ -749,6 +768,7 @@ func (d *decodeState) object(v reflect.Value) error {
 			} else if d.disallowUnknownFields {
 				d.saveError(fmt.Errorf("json: unknown field %q", key))
 			}
+			d.context.index++
 		}
 
 		// Read : before value.
@@ -838,6 +858,7 @@ func (d *decodeState) object(v reflect.Value) error {
 			panic(phasePanicMsg)
 		}
 	}
+	d.context = d.context.parent
 	return nil
 }
 
@@ -871,7 +892,11 @@ func (d *decodeState) literalStore(item []byte, v reflect.Value, fromQuoted bool
 	isNull := item[0] == 'n' // null
 	u, ut, pv := indirect(v, isNull)
 	if u != nil {
-		return u.UnmarshalJSON(item)
+		err := u.UnmarshalJSON(item)
+		if err != nil {
+			d.saveError(err)
+		}
+		return nil
 	}
 	if ut != nil {
 		if item[0] != '"' {
@@ -1059,6 +1084,7 @@ func (d *decodeState) valueInterface() (val any) {
 // arrayInterface is like array but returns []interface{}.
 func (d *decodeState) arrayInterface() []any {
 	v := make([]any, 0)
+	d.context = &decodeContext{parent: d.context}
 	for {
 		// Look ahead for ] - can only happen on first iteration.
 		d.scanWhile(scanSkipSpace)
@@ -1078,13 +1104,16 @@ func (d *decodeState) arrayInterface() []any {
 		if d.opcode != scanArrayValue {
 			panic(phasePanicMsg)
 		}
+		d.context.index++
 	}
+	d.context = d.context.parent
 	return v
 }
 
 // objectInterface is like object but returns map[string]interface{}.
 func (d *decodeState) objectInterface() map[string]any {
 	m := make(map[string]any)
+	d.context = &decodeContext{parent: d.context}
 	for {
 		// Read opening " of string key or closing }.
 		d.scanWhile(scanSkipSpace)
@@ -1104,6 +1133,7 @@ func (d *decodeState) objectInterface() map[string]any {
 		if !ok {
 			panic(phasePanicMsg)
 		}
+		d.context.key = key
 
 		// Read : before value.
 		if d.opcode == scanSkipSpace {
@@ -1127,7 +1157,9 @@ func (d *decodeState) objectInterface() map[string]any {
 		if d.opcode != scanObjectValue {
 			panic(phasePanicMsg)
 		}
+		d.context.index++
 	}
+	d.context = d.context.parent
 	return m
 }
 

common/json/internal/contextjson_120/decode_context.go

@@ -0,0 +1,49 @@
+package json
+
+import "strconv"
+
+type decodeContext struct {
+	parent *decodeContext
+	index  int
+	key    string
+}
+
+func (d *decodeState) formatContext() string {
+	var description string
+	context := d.context
+	var appendDot bool
+	for context != nil {
+		if appendDot {
+			description = "." + description
+		}
+		if context.key != "" {
+			description = context.key + description
+			appendDot = true
+		} else {
+			description = "[" + strconv.Itoa(context.index) + "]" + description
+			appendDot = false
+		}
+		context = context.parent
+	}
+	return description
+}
+
+type contextError struct {
+	parent  error
+	context string
+	index   bool
+}
+
+func (c *contextError) Unwrap() error {
+	return c.parent
+}
+
+func (c *contextError) Error() string {
+	//goland:noinspection GoTypeAssertionOnErrors
+	switch c.parent.(type) {
+	case *contextError:
+		return c.context + "." + c.parent.Error()
+	default:
+		return c.context + ": " + c.parent.Error()
+	}
+}