json5: accept 'comment' fields in all JSON files

vdobler · vdobler · commit 7d59b1463cac · 2016-06-22T10:09:18.000+02:00
One complaint about the JSON5 format was that it has bad editor support. Well, actually
no editor support. Any valid JSON is valid JSON5 so you basically can use JSON as the
definition format for tests and suites, unfortunately you loose the ability to add
comments. In traditional JSON this is done by ignored fields, often just named 'comment'.
Unfortiunately the JSON5 decoder failes on unknown fields in a struct to prevent
ugly and hard to track bugs from typos.

This CL deliberately allows 'comment' everywhere in a JSON5 and won't fail if
the struct to unmarshal to has no such field. Such comments are just ignored.
diff --git a/internal/json5/decode.go b/internal/json5/decode.go
@@ -31,6 +31,8 @@ import (
 //   b) If a JSON field cannot be mapped to a field in a Go struct
 //      an error is created (the stdlib json silently ignores this
 //      fact). The error is of type &UnmarshalUnknownFieldError.
+//      There is one excpetion to this rule: A JSON5 field named
+//      "comment" is allowed everywhere and ignored.
 // So this Unmarshal provides 'strict' unmarshaling.
 //
 // Unmarshal uses the inverse of the encodings that
@@ -598,11 +600,16 @@ func (d *decodeState) object(v reflect.Value) {
 					subv = subv.Field(i)
 				}
 			} else {
-				d.saveError(&UnmarshalUnknownFieldError{
-					typ:    v.Type().Name(),
-					field:  string(key),
-					Offset: int64(start),
-				})
+				// Field is unknown in struct. Stdlib json ignores it.
+				// We fail as this probably is a typo. But we do
+				// ignore comments.
+				if !bytes.Equal(key, []byte("comment")) {
+					d.saveError(&UnmarshalUnknownFieldError{
+						typ:    v.Type().Name(),
+						field:  string(key),
+						Offset: int64(start),
+					})
+				}
 			}
 		}
 
diff --git a/internal/json5/decode_test.go b/internal/json5/decode_test.go
@@ -235,6 +235,7 @@ var unmarshalTests = []unmarshalTest{
 	{in: `{"x": 1}`, ptr: new(tx), out: tx{},
 		err: &UnmarshalUnknownFieldError{"tx", "x", 1}},
 	{in: `{"F1":1,"F2":2,"F3":3}`, ptr: new(V), out: V{F1: float64(1), F2: int32(2), F3: Number("3")}},
+	{in: `{"F1":1,"comment":"foo","F2":2,"F3":3}`, ptr: new(V), out: V{F1: float64(1), F2: int32(2), F3: Number("3")}},
 	{in: `{"F1":1,"F2":2,"F3":3}`, ptr: new(V), out: V{F1: Number("1"), F2: int32(2), F3: Number("3")}, useNumber: true},
 	{in: `{"k1":1,"k2":"s","k3":[1,2.0,3e-3],"k4":{"kk1":"s","kk2":2}}`, ptr: new(interface{}), out: ifaceNumAsFloat64},
 	{in: `{"k1":1,"k2":"s","k3":[1,2.0,3e-3],"k4":{"kk1":"s","kk2":2}}`, ptr: new(interface{}), out: ifaceNumAsNumber, useNumber: true},
