add test case

mutable_tree_test.go

@@ -3,6 +3,9 @@ package iavl
 import (
 	"bytes"
 	"fmt"
+	"io/ioutil"
+	"math/rand"
+	"os"
 	"runtime"
 	"testing"
 
@@ -263,3 +266,65 @@ func BenchmarkMutableTree_Set(b *testing.B) {
 		t.Set(randBytes(10), []byte{})
 	}
 }
+
+func TestDeleteVersion_issue261(t *testing.T) {
+	makeVersions := func(t *testing.T, mainDB db.DB, versions int, keepEvery int64) {
+		// We set the same RNG for every run, which of course means we'll be regenerating the
+		// same keys and values.
+		r := rand.New(rand.NewSource(49872768940))
+
+		// This follows SDK behavior.
+		keepRecent := int64(1)
+		if keepEvery == 1 {
+			keepRecent = 0
+		}
+
+		tree, err := NewMutableTreeWithOpts(mainDB, db.NewMemDB(), 0, &Options{
+			KeepEvery:  keepEvery,
+			KeepRecent: keepRecent,
+		})
+		require.NoError(t, err)
+
+		version, err := tree.LoadVersion(0)
+		require.NoError(t, err)
+		t.Logf("Loaded version %v\n", version)
+
+		// Create new versions
+		for v := 0; v < versions; v++ {
+			for i := 0; i < 4096; i++ {
+				key := []byte(fmt.Sprintf("%v", r.Intn(65536)))
+				value := []byte(fmt.Sprintf("%v", r.Intn(1<<20)))
+				tree.Set(key, value)
+			}
+
+			_, version, err = tree.SaveVersion()
+			require.NoError(t, err)
+			t.Logf("Saved version %v\n", version)
+
+			// Delete the previous keepEvery version if it's a multiple of KeepEvery. This follows
+			// SDK pruning behavior.
+			if version%keepEvery == 0 && version > keepEvery {
+				err = tree.DeleteVersion(version - keepEvery)
+				require.NoError(t, err)
+				t.Logf("Deleted version %v\n", version-keepEvery)
+			}
+		}
+	}
+
+	// Use the same on-disk database for all runs.
+	tempdir, err := ioutil.TempDir("", "iavl")
+	require.NoError(t, err)
+	defer os.RemoveAll(tempdir)
+
+	levelDB, err := db.NewGoLevelDB("pruning", "")
+	require.NoError(t, err)
+
+	// First, create 12 versions and persist every 5 versions to disk, deleting the previous
+	// persisted version.
+	makeVersions(t, levelDB, 12, 5)
+
+	// Now, create another 12 versions and persist every 5 versions to disk, deleting the previous
+	// persisted one. This will load version 10 (the last persisted one) and generate new versions
+	// from that. In the original issue, this panics after version 10 has been deleted.
+	makeVersions(t, levelDB, 12, 5)
+}