std.Io.takeDelimiter tosses too many characters

[pancelor]

Zig Version

0.16.0-dev.164+bc7955306

Steps to Reproduce and Observed Behavior

This test fails:

const std = @import("std");
test {
    var r: std.Io.Reader = .fixed("abc\ndef");

    try std.testing.expectEqualStrings("abc", try r.takeDelimiter('\n') orelse "null");
    try std.testing.expectEqualStrings("def", try r.takeDelimiter('\n') orelse "null");
    try std.testing.expectEqual(null, r.takeDelimiter('\n'));
}

Result of zig build test:

error: 'main.test_0' failed: ====== expected this output: =========
def␃

======== instead found this: =========
ef␃

Expected Behavior

The test should pass