Remove empty fields from /sync response (#2755)

First attempt at removing empty fields from `/sync` responses. Needs
https://github.com/matrix-org/sytest/pull/1298 to keep Sytest happy.

Co-authored-by: Neil Alexander <neilalexander@users.noreply.github.com>

syncapi/streams/stream_accountdata.go

@@ -90,9 +90,9 @@ func (p *AccountDataStreamProvider) IncrementalSync(
 				}
 			} else {
 				if roomData, ok := dataRes.RoomAccountData[roomID][dataType]; ok {
-					joinData := *types.NewJoinResponse()
-					if existing, ok := req.Response.Rooms.Join[roomID]; ok {
-						joinData = existing
+					joinData, ok := req.Response.Rooms.Join[roomID]
+					if !ok {
+						joinData = types.NewJoinResponse()
 					}
 					joinData.AccountData.Events = append(
 						joinData.AccountData.Events,

syncapi/streams/stream_invite.go

@@ -65,7 +65,7 @@ func (p *InviteStreamProvider) IncrementalSync(
 			continue
 		}
 		ir := types.NewInviteResponse(inviteEvent)
-		req.Response.Rooms.Invite[roomID] = *ir
+		req.Response.Rooms.Invite[roomID] = ir
 	}
 
 	// When doing an initial sync, we don't want to add retired invites, as this
@@ -87,7 +87,7 @@ func (p *InviteStreamProvider) IncrementalSync(
 				Type:           "m.room.member",
 				Content:        gomatrixserverlib.RawJSON(`{"membership":"leave"}`),
 			})
-			req.Response.Rooms.Leave[roomID] = *lr
+			req.Response.Rooms.Leave[roomID] = lr
 		}
 	}
 

syncapi/streams/stream_pdu.go

@@ -106,7 +106,7 @@ func (p *PDUStreamProvider) CompleteSync(
 			}
 			continue
 		}
-		req.Response.Rooms.Join[roomID] = *jr
+		req.Response.Rooms.Join[roomID] = jr
 		req.Rooms[roomID] = gomatrixserverlib.Join
 	}
 
@@ -129,7 +129,7 @@ func (p *PDUStreamProvider) CompleteSync(
 				}
 				continue
 			}
-			req.Response.Rooms.Peek[peek.RoomID] = *jr
+			req.Response.Rooms.Peek[peek.RoomID] = jr
 		}
 	}
 
@@ -320,7 +320,7 @@ func (p *PDUStreamProvider) addRoomDeltaToResponse(
 		// didn't "remove" events, return that the response is limited.
 		jr.Timeline.Limited = limited && len(events) == len(recentEvents)
 		jr.State.Events = gomatrixserverlib.HeaderedToClientEvents(delta.StateEvents, gomatrixserverlib.FormatSync)
-		res.Rooms.Join[delta.RoomID] = *jr
+		res.Rooms.Join[delta.RoomID] = jr
 
 	case gomatrixserverlib.Peek:
 		jr := types.NewJoinResponse()
@@ -329,7 +329,7 @@ func (p *PDUStreamProvider) addRoomDeltaToResponse(
 		jr.Timeline.Events = gomatrixserverlib.HeaderedToClientEvents(recentEvents, gomatrixserverlib.FormatSync)
 		jr.Timeline.Limited = limited
 		jr.State.Events = gomatrixserverlib.HeaderedToClientEvents(delta.StateEvents, gomatrixserverlib.FormatSync)
-		res.Rooms.Peek[delta.RoomID] = *jr
+		res.Rooms.Peek[delta.RoomID] = jr
 
 	case gomatrixserverlib.Leave:
 		fallthrough // transitions to leave are the same as ban
@@ -342,7 +342,7 @@ func (p *PDUStreamProvider) addRoomDeltaToResponse(
 		// didn't "remove" events, return that the response is limited.
 		lr.Timeline.Limited = limited && len(events) == len(recentEvents)
 		lr.State.Events = gomatrixserverlib.HeaderedToClientEvents(delta.StateEvents, gomatrixserverlib.FormatSync)
-		res.Rooms.Leave[delta.RoomID] = *lr
+		res.Rooms.Leave[delta.RoomID] = lr
 	}
 
 	return latestPosition, nil

syncapi/streams/stream_receipt.go

@@ -4,9 +4,10 @@ import (
 	"context"
 	"encoding/json"
 
+	"github.com/matrix-org/gomatrixserverlib"
+
 	"github.com/matrix-org/dendrite/syncapi/storage"
 	"github.com/matrix-org/dendrite/syncapi/types"
-	"github.com/matrix-org/gomatrixserverlib"
 )
 
 type ReceiptStreamProvider struct {
@@ -76,7 +77,7 @@ func (p *ReceiptStreamProvider) IncrementalSync(
 			continue
 		}
 
-		jr := *types.NewJoinResponse()
+		jr := types.NewJoinResponse()
 		if existing, ok := req.Response.Rooms.Join[roomID]; ok {
 			jr = existing
 		}

syncapi/streams/stream_typing.go

@@ -4,10 +4,11 @@ import (
 	"context"
 	"encoding/json"
 
+	"github.com/matrix-org/gomatrixserverlib"
+
 	"github.com/matrix-org/dendrite/internal/caching"
 	"github.com/matrix-org/dendrite/syncapi/storage"
 	"github.com/matrix-org/dendrite/syncapi/types"
-	"github.com/matrix-org/gomatrixserverlib"
 )
 
 type TypingStreamProvider struct {
@@ -35,9 +36,9 @@ func (p *TypingStreamProvider) IncrementalSync(
 			continue
 		}
 
-		jr := *types.NewJoinResponse()
-		if existing, ok := req.Response.Rooms.Join[roomID]; ok {
-			jr = existing
+		jr, ok := req.Response.Rooms.Join[roomID]
+		if !ok {
+			jr = types.NewJoinResponse()
 		}
 
 		if users, updated := p.EDUCache.GetTypingUsersIfUpdatedAfter(