reflect/protoreflect: rename methods with Type suffix

The protobuf type system uses the word "descriptor" instead of "type".
We should avoid the "type" verbage when we aren't talking about Go types.
The old names are temporarily kept around for compatibility reasons.

Change-Id: Icc99c913528ead011f7a74aa8399d9c5ec6dc56e
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/172238
Reviewed-by: Herbie Ong <herbie@google.com>
Reviewed-by: Damien Neil <dneil@google.com>
diff --git a/encoding/jsonpb/decode.go b/encoding/jsonpb/decode.go
index 80700df..4b46ffc 100644
--- a/encoding/jsonpb/decode.go
+++ b/encoding/jsonpb/decode.go
@@ -242,7 +242,7 @@
 			}
 		} else {
 			// If field is a oneof, check if it has already been set.
-			if od := fd.OneofType(); od != nil {
+			if od := fd.Oneof(); od != nil {
 				idx := uint64(od.Index())
 				if seenOneofs.Has(idx) {
 					return errors.New("%v: oneof is already set", od.FullName())
@@ -276,12 +276,12 @@
 }
 
 func isKnownValue(fd pref.FieldDescriptor) bool {
-	md := fd.MessageType()
+	md := fd.Message()
 	return md != nil && md.FullName() == "google.protobuf.Value"
 }
 
 func isNullValue(fd pref.FieldDescriptor) bool {
-	ed := fd.EnumType()
+	ed := fd.Enum()
 	return ed != nil && ed.FullName() == "google.protobuf.NullValue"
 }
 
@@ -506,7 +506,7 @@
 	case json.String:
 		// Lookup EnumNumber based on name.
 		s := jval.String()
-		if enumVal := fd.EnumType().Values().ByName(pref.Name(s)); enumVal != nil {
+		if enumVal := fd.Enum().Values().ByName(pref.Name(s)); enumVal != nil {
 			return pref.ValueOf(enumVal.Number()), nil
 		}
 		return pref.Value{}, newError("invalid enum value %q", jval)
@@ -602,7 +602,7 @@
 		return unexpectedJSONError{jval}
 	}
 
-	fields := fd.MessageType().Fields()
+	fields := fd.Message().Fields()
 	keyDesc := fields.ByNumber(1)
 	valDesc := fields.ByNumber(2)
 
diff --git a/encoding/jsonpb/encode.go b/encoding/jsonpb/encode.go
index 2d2d626..9375091 100644
--- a/encoding/jsonpb/encode.go
+++ b/encoding/jsonpb/encode.go
@@ -178,19 +178,16 @@
 		}
 
 	case pref.EnumKind:
-		enumType := fd.EnumType()
-		num := val.Enum()
-
-		if enumType.FullName() == "google.protobuf.NullValue" {
+		if fd.Enum().FullName() == "google.protobuf.NullValue" {
 			o.encoder.WriteNull()
-		} else if desc := enumType.Values().ByNumber(num); desc != nil {
+		} else if desc := fd.Enum().Values().ByNumber(val.Enum()); desc != nil {
 			err := o.encoder.WriteString(string(desc.Name()))
 			if !nerr.Merge(err) {
 				return err
 			}
 		} else {
 			// Use numeric value if there is no enum value descriptor.
-			o.encoder.WriteInt(int64(num))
+			o.encoder.WriteInt(int64(val.Enum()))
 		}
 
 	case pref.MessageKind, pref.GroupKind:
@@ -229,7 +226,7 @@
 	o.encoder.StartObject()
 	defer o.encoder.EndObject()
 
-	msgFields := fd.MessageType().Fields()
+	msgFields := fd.Message().Fields()
 	keyType := msgFields.ByNumber(1)
 	valType := msgFields.ByNumber(2)
 
@@ -286,7 +283,7 @@
 		name := xt.FullName()
 		// If extended type is a MessageSet, set field name to be the message type name.
 		if isMessageSetExtension(xt) {
-			name = xt.MessageType().FullName()
+			name = xt.Message().FullName()
 		}
 
 		num := xt.Number()
@@ -328,13 +325,13 @@
 	if xt.Name() != "message_set_extension" {
 		return false
 	}
-	mt := xt.MessageType()
-	if mt == nil {
+	md := xt.Message()
+	if md == nil {
 		return false
 	}
-	if xt.FullName().Parent() != mt.FullName() {
+	if xt.FullName().Parent() != md.FullName() {
 		return false
 	}
-	xmt, ok := xt.ExtendedType().(interface{ IsMessageSet() bool })
-	return ok && xmt.IsMessageSet()
+	xmd, ok := xt.Extendee().(interface{ IsMessageSet() bool })
+	return ok && xmd.IsMessageSet()
 }