failEqualSlices

fn failEqualSlices(
    comptime T: type,
    expected: []const T,
    actual: []const T,
    diff_index: usize,
    w: *Io.Writer,
    terminal_mode: Io.Terminal.Mode,
) !void {
    try w.print("slices differ. first difference occurs at index {d} (0x{X})\n", .{ diff_index, diff_index });

    // TODO: Should this be configurable by the caller?
    const max_lines: usize = 16;
    const max_window_size: usize = if (T == u8) max_lines * 16 else max_lines;

    // Print a maximum of max_window_size items of each input, starting just before the
    // first difference to give a bit of context.
    var window_start: usize = 0;
    if (@max(actual.len, expected.len) > max_window_size) {
        const alignment = if (T == u8) 16 else 2;
        window_start = std.mem.alignBackward(usize, diff_index - @min(diff_index, alignment), alignment);
    }
    const expected_window = expected[window_start..@min(expected.len, window_start + max_window_size)];
    const expected_truncated = window_start + expected_window.len < expected.len;
    const actual_window = actual[window_start..@min(actual.len, window_start + max_window_size)];
    const actual_truncated = window_start + actual_window.len < actual.len;

    var differ = if (T == u8) BytesDiffer{
        .expected = expected_window,
        .actual = actual_window,
        .terminal_mode = terminal_mode,
    } else SliceDiffer(T){
        .start_index = window_start,
        .expected = expected_window,
        .actual = actual_window,
        .terminal_mode = terminal_mode,
    };

    // Print indexes as hex for slices of u8 since it's more likely to be binary data where
    // that is usually useful.
    const index_fmt = if (T == u8) "0x{X}" else "{}";

    try w.print("\n============ expected this output: =============  len: {} (0x{X})\n\n", .{ expected.len, expected.len });
    if (window_start > 0) {
        if (T == u8) {
            try w.print("... truncated, start index: " ++ index_fmt ++ " ...\n", .{window_start});
        } else {
            try w.print("... truncated ...\n", .{});
        }
    }
    differ.write(w) catch {};
    if (expected_truncated) {
        const end_offset = window_start + expected_window.len;
        const num_missing_items = expected.len - (window_start + expected_window.len);
        if (T == u8) {
            try w.print("... truncated, indexes [" ++ index_fmt ++ "..] not shown, remaining bytes: " ++ index_fmt ++ " ...\n", .{ end_offset, num_missing_items });
        } else {
            try w.print("... truncated, remaining items: " ++ index_fmt ++ " ...\n", .{num_missing_items});
        }
    }

    // now reverse expected/actual and print again
    differ.expected = actual_window;
    differ.actual = expected_window;
    try w.print("\n============= instead found this: ==============  len: {} (0x{X})\n\n", .{ actual.len, actual.len });
    if (window_start > 0) {
        if (T == u8) {
            try w.print("... truncated, start index: " ++ index_fmt ++ " ...\n", .{window_start});
        } else {
            try w.print("... truncated ...\n", .{});
        }
    }
    differ.write(w) catch {};
    if (actual_truncated) {
        const end_offset = window_start + actual_window.len;
        const num_missing_items = actual.len - (window_start + actual_window.len);
        if (T == u8) {
            try w.print("... truncated, indexes [" ++ index_fmt ++ "..] not shown, remaining bytes: " ++ index_fmt ++ " ...\n", .{ end_offset, num_missing_items });
        } else {
            try w.print("... truncated, remaining items: " ++ index_fmt ++ " ...\n", .{num_missing_items});
        }
    }
    try w.print("\n================================================\n\n", .{});

    return error.TestExpectedEqual;
}