std.mem.bytesAsSlice: fix to support zero-bytes sized types

also added a test for json parsing of zero sized type

lib/std/json/static_test.zig

@@ -925,3 +925,19 @@ test "parse at comptime" {
     };
     comptime testing.expectEqual(@as(u64, 9999), config.uptime) catch unreachable;
 }
+
+test "parse with zero-bit field" {
+    const str =
+        \\{
+        \\    "a": ["a", "a"],
+        \\    "b": "a"
+        \\}
+    ;
+    const ZeroSizedEnum = enum { a };
+    try testing.expectEqual(0, @sizeOf(ZeroSizedEnum));
+
+    const Inner = struct { a: []const ZeroSizedEnum, b: ZeroSizedEnum };
+    const expected: Inner = .{ .a = &.{ .a, .a }, .b = .a };
+
+    try testAllParseFunctions(Inner, expected, str);
+}

lib/std/mem.zig

@@ -4219,10 +4219,11 @@ fn BytesAsSliceReturnType(comptime T: type, comptime bytesType: type) type {
 
 /// Given a slice of bytes, returns a slice of the specified type
 /// backed by those bytes, preserving pointer attributes.
+/// If `T` is zero-bytes sized, the returned slice has a len of zero.
 pub fn bytesAsSlice(comptime T: type, bytes: anytype) BytesAsSliceReturnType(T, @TypeOf(bytes)) {
     // let's not give an undefined pointer to @ptrCast
     // it may be equal to zero and fail a null check
-    if (bytes.len == 0) {
+    if (bytes.len == 0 or @sizeOf(T) == 0) {
         return &[0]T{};
     }
 
@@ -4300,6 +4301,19 @@ test "bytesAsSlice preserves pointer attributes" {
     try testing.expectEqual(in.alignment, out.alignment);
 }
 
+test "bytesAsSlice with zero-bit element type" {
+    {
+        const bytes = [_]u8{};
+        const slice = bytesAsSlice(void, &bytes);
+        try testing.expectEqual(0, slice.len);
+    }
+    {
+        const bytes = [_]u8{ 0x01, 0x02, 0x03, 0x04 };
+        const slice = bytesAsSlice(u0, &bytes);
+        try testing.expectEqual(0, slice.len);
+    }
+}
+
 fn SliceAsBytesReturnType(comptime Slice: type) type {
     return CopyPtrAttrs(Slice, .slice, u8);
 }