encoding/json: ignore embedded fields of pointers to unexported non-structs

https://golang.org/cl/33773 fixes the JSON marshaler to avoid serializing
embedded fields on unexported types of non-struct types. However, Go allows
embedding pointer to types, so the check for whether the field is a non-struct
type must first dereference the pointer to get at the underlying type.

Furthermore, due to a edge-case in the behavior of StructField.PkgPath not
being a reliable indicator of whether the field is unexported (see #21122),
we use our own logic to determine whether the field is exported or not.

The logic in this CL may be simplified depending on what happens in #21122.

Fixes #21121
Updates #21122

Change-Id: I8dfd1cdfac8a87950df294a566fb96dfd04fd749
Reviewed-on: https://go-review.googlesource.com/50711
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

1 files changed, 22 insertions, 1 deletions

diff --git a/src/encoding/json/encode.go b/src/encoding/json/encode.go
index 6fcea4735f..0371f0a24d 100644
--- a/src/encoding/json/encode.go
+++ b/src/encoding/json/encode.go
@@ -1093,7 +1093,22 @@ func typeFields(t reflect.Type) []field {
 			// Scan f.typ for fields to include.
 			for i := 0; i < f.typ.NumField(); i++ {
 				sf := f.typ.Field(i)
-				if sf.PkgPath != "" && (!sf.Anonymous || sf.Type.Kind() != reflect.Struct) { // unexported
+				if sf.Anonymous {
+					t := sf.Type
+					if t.Kind() == reflect.Ptr {
+						t = t.Elem()
+					}
+					// If embedded, StructField.PkgPath is not a reliable
+					// indicator of whether the field is exported.
+					// See https://golang.org/issue/21122
+					if !isExported(t.Name()) && t.Kind() != reflect.Struct {
+						// Ignore embedded fields of unexported non-struct types.
+						// Do not ignore embedded fields of unexported struct types
+						// since they may have exported fields.
+						continue
+					}
+				} else if sf.PkgPath != "" {
+					// Ignore unexported non-embedded fields.
 					continue
 				}
 				tag := sf.Tag.Get("json")
@@ -1211,6 +1226,12 @@ func typeFields(t reflect.Type) []field {
 	return fields
 }
 
+// isExported reports whether the identifier is exported.
+func isExported(id string) bool {
+	r, _ := utf8.DecodeRuneInString(id)
+	return unicode.IsUpper(r)
+}
+
 // dominantField looks through the fields, all of which are known to
 // have the same name, to find the single field that dominates the
 // others using Go's embedding rules, modified by the presence of