lib/model: Don't set ignore bit when it's already set

This adds a metric for "committed items" to the database instance that I
use in the test code, and a couple of tests that ensure that scans that
don't change anything also don't commit anything.

There was a case in the scanner where we set the invalid bit on files
that are ignored, even though they were already ignored and had the
invalid bit set. I had assumed this would result in an extra database
commit, but it was in fact filtered out by the Set... Anyway, I think we
can save some work on not pushing that change to the Set at all.

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3298

lib/db/leveldb_transactions.go

@@ -8,6 +8,7 @@ package db
 
 import (
 	"bytes"
+	"sync/atomic"
 
 	"github.com/syncthing/syncthing/lib/protocol"
 	"github.com/syndtr/goleveldb/leveldb"
@@ -55,21 +56,24 @@ func (db *Instance) newReadWriteTransaction() readWriteTransaction {
 }
 
 func (t readWriteTransaction) close() {
-	if err := t.db.Write(t.Batch, nil); err != nil {
-		panic(err)
-	}
+	t.flush()
 	t.readOnlyTransaction.close()
 }
 
 func (t readWriteTransaction) checkFlush() {
 	if t.Batch.Len() > batchFlushSize {
-		if err := t.db.Write(t.Batch, nil); err != nil {
-			panic(err)
-		}
+		t.flush()
 		t.Batch.Reset()
 	}
 }
 
+func (t readWriteTransaction) flush() {
+	if err := t.db.Write(t.Batch, nil); err != nil {
+		panic(err)
+	}
+	atomic.AddInt64(&t.db.committed, int64(t.Batch.Len()))
+}
+
 func (t readWriteTransaction) insertFile(folder, device []byte, file protocol.FileInfo) int64 {
 	l.Debugf("insert; folder=%q device=%v %v", folder, protocol.DeviceIDFromBytes(device), file)