Here's the test program:

import std.stdio;
void main() {
        foreach (line; stdin.byLine()) {
                writeln("Got input line: ", line);
        }
}

When the program is run on an empty input (e.g., running 'echo -n | program' in the shell, or hitting ctrl-D once the program starts up, or piping an empty file to the program), an assertion fails:

core.exception.AssertError@/usr/include/d2/4.6/std/stdio.d(989): Bug in File.readln

It appears that the problem is caused by one of two things:

(1) ByLine.empty() assuming that as long as a file is open it will have at least 1 line, but this is not true when the input is 0 bytes.

(2) stdin.readln() returns null if the input has 0 bytes, instead of a line of 0 length (which is what it does at EOF if the input is *not* empty).