From a690b5762480ae80ef4264402fcfa8d84b57339a Mon Sep 17 00:00:00 2001
From: Jamie Liu <jamieliu@google.com>
Date: Wed, 4 Mar 2020 14:29:11 -0800
Subject: Ensure that safemem.BlockSeqOf(safemem.Block{}) produces an empty
 BlockSeq.

PiperOrigin-RevId: 298941855
---
 pkg/safemem/seq_test.go   | 21 +++++++++++++++++++++
 pkg/safemem/seq_unsafe.go |  3 +++
 2 files changed, 24 insertions(+)

(limited to 'pkg/safemem')

diff --git a/pkg/safemem/seq_test.go b/pkg/safemem/seq_test.go
index eba4bb535..de34005e9 100644
--- a/pkg/safemem/seq_test.go
+++ b/pkg/safemem/seq_test.go
@@ -20,6 +20,27 @@ import (
 	"testing"
 )
 
+func TestBlockSeqOfEmptyBlock(t *testing.T) {
+	bs := BlockSeqOf(Block{})
+	if !bs.IsEmpty() {
+		t.Errorf("BlockSeqOf(Block{}).IsEmpty(): got false, wanted true; BlockSeq is %v", bs)
+	}
+}
+
+func TestBlockSeqOfNonemptyBlock(t *testing.T) {
+	b := BlockFromSafeSlice(make([]byte, 1))
+	bs := BlockSeqOf(b)
+	if bs.IsEmpty() {
+		t.Fatalf("BlockSeqOf(non-empty Block).IsEmpty(): got true, wanted false; BlockSeq is %v", bs)
+	}
+	if head := bs.Head(); head != b {
+		t.Fatalf("BlockSeqOf(non-empty Block).Head(): got %v, wanted %v", head, b)
+	}
+	if tail := bs.Tail(); !tail.IsEmpty() {
+		t.Fatalf("BlockSeqOf(non-empty Block).Tail().IsEmpty(): got false, wanted true: tail is %v", tail)
+	}
+}
+
 type blockSeqTest struct {
 	desc string
 
diff --git a/pkg/safemem/seq_unsafe.go b/pkg/safemem/seq_unsafe.go
index dcdfc9600..f5f0574f8 100644
--- a/pkg/safemem/seq_unsafe.go
+++ b/pkg/safemem/seq_unsafe.go
@@ -56,6 +56,9 @@ type BlockSeq struct {
 
 // BlockSeqOf returns a BlockSeq representing the single Block b.
 func BlockSeqOf(b Block) BlockSeq {
+	if b.length == 0 {
+		return BlockSeq{}
+	}
 	bs := BlockSeq{
 		data:   b.start,
 		length: -1,
-- 
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