From f5954dad8356c05c294630f19609c343d65ea544 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Micha=C3=ABl=20Larouche?= <michael.larouche@gmail.com>
Date: Tue, 25 Feb 2020 15:07:35 -0500
Subject: [PATCH] Fix crash when freeing empty string as null-terminated
 sentinel

---
 lib/std/mem.zig | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/lib/std/mem.zig b/lib/std/mem.zig
index 391d587dbc..4da7829570 100644
--- a/lib/std/mem.zig
+++ b/lib/std/mem.zig
@@ -1780,10 +1780,11 @@ fn SliceAsBytesReturnType(comptime sliceType: type) type {
 
 pub fn sliceAsBytes(slice: var) SliceAsBytesReturnType(@TypeOf(slice)) {
     const actualSlice = if (comptime trait.isPtrTo(.Array)(@TypeOf(slice))) slice[0..] else slice;
+    const actualSliceTypeInfo = @typeInfo(@TypeOf(actualSlice)).Pointer;
 
     // let's not give an undefined pointer to @ptrCast
     // it may be equal to zero and fail a null check
-    if (actualSlice.len == 0) {
+    if (actualSlice.len == 0 and actualSliceTypeInfo.sentinel == null) {
         return &[0]u8{};
     }
 
@@ -1805,6 +1806,12 @@ test "sliceAsBytes" {
     }));
 }
 
+test "sliceAsBytes with sentinel slice" {
+    const empty_string:[:0]const u8 = "";
+    const bytes = sliceAsBytes(empty_string);
+    testing.expect(bytes.len == 0);
+}
+
 test "sliceAsBytes packed struct at runtime and comptime" {
     const Foo = packed struct {
         a: u4,
@@ -1941,3 +1948,8 @@ test "isAligned" {
     testing.expect(!isAligned(4, 8));
     testing.expect(!isAligned(4, 16));
 }
+
+test "freeing empty string with null-terminated sentinel" {
+    const empty_string = try dupeZ(testing.allocator, u8, "");
+    testing.allocator.free(empty_string);
+}