From f661d9429f0fb68b573019c9a14d0815ae0baa8a Mon Sep 17 00:00:00 2001
From: Christian Schwarz <me@cschwarz.com>
Date: Thu, 25 Mar 2021 22:36:01 +0100
Subject: [PATCH] pruning/keep_last_n: correctly handle the case where `count`
 > matching snaps

fixes #446
---
 pruning/keep_last_n.go      |  7 ++++++-
 pruning/keep_last_n_test.go | 13 +++++++++++++
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/pruning/keep_last_n.go b/pruning/keep_last_n.go
index 6bd7e2d..023568d 100644
--- a/pruning/keep_last_n.go
+++ b/pruning/keep_last_n.go
@@ -57,6 +57,11 @@ func (k KeepLastN) KeepRule(snaps []Snapshot) (destroyList []Snapshot) {
 		// then lexicographically descending (e.g. b, a)
 		return strings.Compare(matching[i].Name(), matching[j].Name()) == 1
 	})
-	destroyList = append(destroyList, matching[k.n:]...)
+
+	n := k.n
+	if n > len(matching) {
+		n = len(matching)
+	}
+	destroyList = append(destroyList, matching[n:]...)
 	return destroyList
 }
diff --git a/pruning/keep_last_n_test.go b/pruning/keep_last_n_test.go
index c96bbb9..4283e3e 100644
--- a/pruning/keep_last_n_test.go
+++ b/pruning/keep_last_n_test.go
@@ -83,6 +83,19 @@ func TestKeepLastN(t *testing.T) {
 				"b1": true,
 			},
 		},
+		"keep_more_than_matching": {
+			inputs: []Snapshot{
+				stubSnap{"a1", false, o(10)},
+				stubSnap{"b1", false, o(11)},
+				stubSnap{"a2", false, o(12)},
+			},
+			rules: []KeepRule{
+				MustKeepLastN(3, "a"),
+			},
+			expDestroy: map[string]bool{
+				"b1": true,
+			},
+		},
 	}
 
 	testTable(tcs, t)