From d3e827d371ac2e6bb68c81d992f99ccd4b1b2cf1 Mon Sep 17 00:00:00 2001
From: Deleplace <deleplace@google.com>
Date: Thu, 22 Feb 2024 23:44:31 +0100
Subject: [PATCH] slices: Delete clears the tail when j == len(s)

Fixes #65669

Change-Id: Ifd2011dd604fef399e4352b804fc2f6a9e74096e
Reviewed-on: https://go-review.googlesource.com/c/go/+/566237
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Keith Randall <khr@google.com>
Auto-Submit: Keith Randall <khr@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@golang.org>
---
 src/slices/slices.go      |  6 +++++-
 src/slices/slices_test.go | 13 +++++++++++++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/src/slices/slices.go b/src/slices/slices.go
index b0f048a6566..3e01eb2fb77 100644
--- a/src/slices/slices.go
+++ b/src/slices/slices.go
@@ -258,7 +258,11 @@ func Replace[S ~[]E, E any](s S, i, j int, v ...E) S {
 		return Insert(s, i, v...)
 	}
 	if j == len(s) {
-		return append(s[:i], v...)
+		s2 := append(s[:i], v...)
+		if len(s2) < len(s) {
+			clear(s[len(s2):len(s)]) // zero/nil out the obsolete elements, for GC
+		}
+		return s2
 	}
 
 	tot := len(s[:i]) + len(v) + len(s[j:])
diff --git a/src/slices/slices_test.go b/src/slices/slices_test.go
index 31d59abe17b..4b5f0355df2 100644
--- a/src/slices/slices_test.go
+++ b/src/slices/slices_test.go
@@ -1120,6 +1120,19 @@ func TestReplaceOverlap(t *testing.T) {
 	}
 }
 
+func TestReplaceEndClearTail(t *testing.T) {
+	s := []int{11, 22, 33}
+	v := []int{99}
+	// case when j == len(s)
+	i, j := 1, 3
+	s = Replace(s, i, j, v...)
+
+	x := s[:3][2]
+	if want := 0; x != want {
+		t.Errorf("TestReplaceEndClearTail: obsolete element is %d, want %d", x, want)
+	}
+}
+
 func BenchmarkReplace(b *testing.B) {
 	cases := []struct {
 		name string