gistfile1.txt

Line limit counting problem in $*ARGFILES.lines method

When passing a line count argument to the .lines method, it mis-counts the lines

For the examples, consider this input file:

  $ cat file
  A
  B

Examples:

  perl6 -e 'say $*ARGFILES.lines'    file file  #=> (A B A B)
  perl6 -e 'say $*ARGFILES.lines(1)' file file  #=> (A)
  perl6 -e 'say $*ARGFILES.lines(2)' file file  #=> (A B)
  perl6 -e 'say $*ARGFILES.lines(3)' file file  #=> (A B)      <-- WRONG
  perl6 -e 'say $*ARGFILES.lines(4)' file file  #=> (A B A)    <-- WRONG
  
  say IO::ArgFiles.new(:args(<file file>.Array)).lines     #=> (A B A B)
  say IO::ArgFiles.new(:args(<file file>.Array)).lines(1)  #=> (A)
  say IO::ArgFiles.new(:args(<file file>.Array)).lines(2)  #=> (A B)
  say IO::ArgFiles.new(:args(<file file>.Array)).lines(3)  #=> (A B)      <-- WRONG
  say IO::ArgFiles.new(:args(<file file>.Array)).lines(4)  #=> (A B A)    <-- WRONG

Inserting /dev/null in the middle of the argument list to illustrate the problem

  perl6 -e 'say $*ARGFILES.lines(5)' file /dev/null file  #=> (A B A)
  
  say IO::ArgFiles.new(:args(<file /dev/null file>.Array)).lines(5)  #=> (A B A)

$*ARGFILES is created from IO::ArgFiles.new(:args(@*ARGS))
I think the problem is inside the method lines($limit=*) of the rakudo/src/core/IO/ArgFiles.pm file
method pull-one of the Seq calls itself recursively when it reaches the end of a file
$!limit should only be decremented when an actual line is returned

Suggested fix:

--- rakudo-2016.11/src/core/IO/ArgFiles.pm.orig 2016-11-21 16:56:02.843748043 -0200
+++ rakudo-2016.11/src/core/IO/ArgFiles.pm      2016-11-21 16:56:24.508748604 -0200
@@ -103,7 +103,7 @@
             }
 
             method pull-one() {
-                return IterationEnd if $!limit-- <= 0;
+                return IterationEnd if $!limit <= 0;
                 my \value = $!iter.pull-one;
                 if value =:= IterationEnd {
                     my $io = $!next-io.();
@@ -114,6 +114,7 @@
                 }
                 else {
                     $!ins++;
+                    $!limit--;
                     value;
                 }
             }