Pre-apply the bootstrapping ConfChange entries.

This eliminates the need to fake an ApplyConfChange call before Campaign
in tests.

Fixes #1856.

raft/node.go

@@ -150,6 +150,18 @@ func StartNode(id uint64, peers []Peer, election, heartbeat int, storage Storage
 	// TODO(bdarnell): These entries are still unstable; do we need to preserve
 	// the invariant that committed < unstable?
 	r.raftLog.committed = r.raftLog.lastIndex()
+	// Now apply them, mainly so that the application can call Campaign
+	// immediately after StartNode in tests. Note that these nodes will
+	// be added to raft twice: here and when the application's Ready
+	// loop calls ApplyConfChange. The calls to addNode must come after
+	// all calls to raftLog.append so progress.next is set after these
+	// bootstrapping entries (it is an error if we try to append these
+	// entries since they have already been committed).
+	// We do not set raftLog.applied so the application will be able
+	// to observe all conf changes via Ready.CommittedEntries.
+	for _, peer := range peers {
+		r.addNode(peer.ID)
+	}
 
 	go n.run(r)
 	return &n

raft/node_test.go

@@ -324,7 +324,6 @@ func TestNodeStart(t *testing.T) {
 	}
 	storage := NewMemoryStorage()
 	n := StartNode(1, []Peer{{ID: 1}}, 10, 1, storage)
-	n.ApplyConfChange(cc)
 	n.Campaign(ctx)
 	g := <-n.Ready()
 	if !reflect.DeepEqual(g, wants[0]) {
@@ -421,7 +420,6 @@ func TestNodeAdvance(t *testing.T) {
 
 	storage := NewMemoryStorage()
 	n := StartNode(1, []Peer{{ID: 1}}, 10, 1, storage)
-	n.ApplyConfChange(raftpb.ConfChange{Type: raftpb.ConfChangeAddNode, NodeID: 1})
 	n.Campaign(ctx)
 	<-n.Ready()
 	n.Propose(ctx, []byte("foo"))