From ac1149a3f50e5b74f5c7129f26039af0f14807bb Mon Sep 17 00:00:00 2001
From: Ben Johnson <benbjohnson@yahoo.com>
Date: Mon, 2 Feb 2015 08:27:34 -0700
Subject: [PATCH] Persist sequence-only changes.

This commit fixes a bug where only calling NextSequence() on a Bucket does not cause the Bucket to be
peristed. The simple fix is to simply materialize the root node so that the bucket is flushed out
during commit.

Thanks to Matthew Dawson (@MJDSys) for reporting.

https://github.com/boltdb/bolt/issues/296
---
 bucket.go      |  6 ++++++
 bucket_test.go | 27 +++++++++++++++++++++++++++
 db.go          |  9 ++-------
 db_test.go     |  3 +++
 4 files changed, 38 insertions(+), 7 deletions(-)

diff --git a/bucket.go b/bucket.go
index 28832fc..470689b 100644
--- a/bucket.go
+++ b/bucket.go
@@ -332,6 +332,12 @@ func (b *Bucket) NextSequence() (uint64, error) {
 		return 0, ErrTxNotWritable
 	}
 
+	// Materialize the root node if it hasn't been already so that the
+	// bucket will be saved during commit.
+	if b.rootNode == nil {
+		_ = b.node(b.root, nil)
+	}
+
 	// Increment and return the sequence.
 	b.bucket.sequence++
 	return b.bucket.sequence, nil
diff --git a/bucket_test.go b/bucket_test.go
index 90e704a..883fa03 100644
--- a/bucket_test.go
+++ b/bucket_test.go
@@ -490,6 +490,33 @@ func TestBucket_NextSequence(t *testing.T) {
 	})
 }
 
+// Ensure that a bucket will persist an autoincrementing sequence even if its
+// the only thing updated on the bucket.
+// https://github.com/boltdb/bolt/issues/296
+func TestBucket_NextSequence_Persist(t *testing.T) {
+	db := NewTestDB()
+	defer db.Close()
+	db.Update(func(tx *bolt.Tx) error {
+		_, _ = tx.CreateBucket([]byte("widgets"))
+		return nil
+	})
+
+	db.Update(func(tx *bolt.Tx) error {
+		_, _ = tx.Bucket([]byte("widgets")).NextSequence()
+		return nil
+	})
+
+	db.Update(func(tx *bolt.Tx) error {
+		seq, err := tx.Bucket([]byte("widgets")).NextSequence()
+		if err != nil {
+			t.Fatalf("unexpected error: %s", err)
+		} else if seq != 2 {
+			t.Fatalf("unexpected sequence: %d", seq)
+		}
+		return nil
+	})
+}
+
 // Ensure that retrieving the next sequence on a read-only bucket returns an error.
 func TestBucket_NextSequence_ReadOnly(t *testing.T) {
 	db := NewTestDB()
diff --git a/db.go b/db.go
index ae135ef..773620d 100644
--- a/db.go
+++ b/db.go
@@ -694,13 +694,8 @@ func _assert(condition bool, msg string, v ...interface{}) {
 	}
 }
 
-func warn(v ...interface{}) {
-	fmt.Fprintln(os.Stderr, v...)
-}
-
-func warnf(msg string, v ...interface{}) {
-	fmt.Fprintf(os.Stderr, msg+"\n", v...)
-}
+func warn(v ...interface{})              { fmt.Fprintln(os.Stderr, v...) }
+func warnf(msg string, v ...interface{}) { fmt.Fprintf(os.Stderr, msg+"\n", v...) }
 
 func printstack() {
 	stack := strings.Join(strings.Split(string(debug.Stack()), "\n")[2:], "\n")
diff --git a/db_test.go b/db_test.go
index 7ba5ce8..4f05ad9 100644
--- a/db_test.go
+++ b/db_test.go
@@ -696,3 +696,6 @@ func fileSize(path string) int64 {
 	}
 	return fi.Size()
 }
+
+func warn(v ...interface{})              { fmt.Fprintln(os.Stderr, v...) }
+func warnf(msg string, v ...interface{}) { fmt.Fprintf(os.Stderr, msg+"\n", v...) }