Hello, wise monks. I believe the code below demonstrates a perl bug, but before reporting it as such, I'd like to run it by the perl cognoscenti, and make sure I'm not doing something foolish. I am running perl v5.22.2 on i686-linux.

The bug is a warning perl emits that seems completely inapplicable, A precise interaction of a number of components seems to trigger it; I've not found a way to further pare down the code snippet below and still trigger the bug. In particular:

• it only happens when input comes from a file; I cannot reproduce it by redirecting stdin, using a DATA block, or any other of the usual means of crafting an example that doesn't rely on external files
• the input-file encoding must be specified as iso-8859-1, even if the input file contains only the ASCII subset of this character set
• smartmatch must be activated, even though this code snippet doesn't use it
• the regular expression is not the simplest way to express this particular match, but all its components seem necessary for the bug to show up

Here is my code:

#!/usr/bin/perl

use experimental 'smartmatch';
use open ':encoding(iso-8859-1)';
use POSIX 'locale_h';
use locale ':ctype';
setlocale(LC_CTYPE, 'en_US.iso88591');

open (FILE, '< s2') || die "Cannot open\n";

while (<FILE>) {
  chomp;
  print "--$_--\n";
  print "ends with x and optional y or z\n" if /x(y|z)?$/;
}
close (FILE);
[download]

and here is a sample input file (filename "s2" hard-coded in the the perl code) with one line that passes unremarked, and one line that triggers the bug:

flee
flex
[download]

When I run the code, I see:

--flee--
--flex--
Wide character (U+FFFD) in pattern match (m//) at ./fmin line 14, <FIL
+E> line 2.
ends with x and optional y or z
[download]

The reported U+FFFD, of course, appears nowhere in the perl code or the input file, so I don't know where it's coming from, hence why I'm pretty sure it's a perl bug rather than something I'm doing wrong. Any insight appreciated!

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