[Issue 7374] New: stdin.byLine() throws AssertError on empty input

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=7374

           Summary: stdin.byLine() throws AssertError on empty input
           Product: D
           Version: D2
          Platform: x86_64
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Phobos
        AssignedTo: nobody at puremagic.com
        ReportedBy: hsteoh at quickfur.ath.cx


--- Comment #0 from hsteoh at quickfur.ath.cx 2012-01-26 12:16:45 PST ---
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).

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