Reading sourcecode at parsing/compilation (CHECK) time?

LanX has asked for the wisdom of the Perl Monks concerning the following question:

motivation

An old trick is that when seeking the DATA filehandle to the beginning it's possible to read the sourcecode even before __DATA__ starts.

But with source in multiple files, modules and packages this becomes hairy.

approach

I was looking for a possibility to grab the source right away when its parsed.

Thats why I extended this example code from Attribute::Handlers to access DATA when CHECKing and print the line of the sub foo1() declaration:

package LoudDecl;
use Attribute::Handlers;
no warnings;
sub Loud :ATTR {
  my ($package, $symbol, $referent, $attr, $data, $phase, $filename
      , $linenum) = @_;
  print STDERR
    ref($referent), " ",
      *{$symbol}{NAME}, " ",
    "($referent) ", "was just declared ",
      "and ascribed the ${attr} attribute ",
        "with data ($data)\n",
          "in phase $phase\n",
        "in file $filename at line $linenum\n";
  
  my $tell=tell DATA;
  seek DATA,0,0;
  
  while (<DATA>) {print "> $_" if $.==$linenum  };
  seek DATA,$tell,0;
}
  
sub foo1 :Loud {print "HAHA"};
  
__DATA__
  
huhu
[download]

problem

well it works but I get a weird error from Attribut::Handlers, which only goes away after commenting out the while(<DATA>) line. I'm confused...

OUTPUT

 CODE foo1 (CODE(0x8eba020)) was just declared and ascribed the Loud a
+ttribute with data ()
in phase CHECK
in file /home/lanx/perl/exp/tell.pl at line 23
> sub foo1 :Loud {print "HAHA"};
Can't use an undefined value as an ARRAY reference at /usr/share/perl/
+5.10/Attribute/Handlers.pm line 185, <DATA> line 31.
INIT failed--call queue aborted, <DATA> line 31.
Can't use an undefined value as an ARRAY reference at /usr/share/perl/
+5.10/Attribute/Handlers.pm line 185, <DATA> line 31.
END failed--call queue aborted, <DATA> line 31.
[download]

question

What's going on, what can I do alternatively?

Cheers Rolf

UPDATE: I have the same error when directly opening the source file... it seems Attribute::Handlers is buggy...

Comment on Reading sourcecode at parsing/compilation (CHECK) time? Select or Download Code

Replies are listed 'Best First'.
Re: Reading sourcecode at parsing/compilation (CHECK) time? ($_) by tye (Sage) on Apr 04, 2010 at 03:34 UTC
You are clobbering `$_`. Put `local($_);` before your `while()` loop. - tye	[reply] [d/l] [select]
Re^2: Reading sourcecode at parsing/compilation (CHECK) time? ($_) by LanX (Saint) on Apr 04, 2010 at 10:51 UTC
thanks, switching to a lexical loop variable solved the problem! Silly me... I don't know why I was expecting that a core module either treats `$_` safely when calling foreign code or documents warnings about possible side effects... Cheers Rolf PS: maybe the author should take a look into PBP? (SCNR ;)	[reply] [d/l]
Re^3: Reading sourcecode at parsing/compilation (CHECK) time? (Ticket) by LanX (Saint) on Apr 04, 2010 at 13:14 UTC
> ... I was expecting that a core module either treats $_ safely when calling foreign code ... I filed a bug report for Attribute::Handlers with an attached diff which solves this issue. http://rt.perl.org/rt3/Ticket/Display.html?id=74052 Cheers Rolf UPDATE: wow already resolved at the following day! Steffen Müller++	[reply]
Re^4: Reading sourcecode at parsing/compilation (CHECK) time? (Ticket) by Anonymous Monk on Apr 05, 2010 at 14:26 UTC
Re^5: Reading sourcecode at parsing/compilation (CHECK) time? (Ticket) by LanX (Saint) on Apr 05, 2010 at 14:48 UTC
Re: Reading sourcecode at parsing/compilation (CHECK) time? by LanX (Saint) on Apr 03, 2010 at 14:59 UTC
hmm ... this workaround helps caching a snapshot of the source of the corresponding file (path is in $0) and bypasses the problems of Attribute::Handlers. `UNITCHECK { my $pos=tell DATA; seek DATA,0,0; $main::SOURCE{$0}=[<DATA>]; seek DATA,$pos,0; }` [download] works fine I can access the hash `%main::SOURCE` from everywhere, but ATM I'll have to include this block in any module I wanna process. Is there a global option to automatically include an UNITCHECK in any compiled file? UPDATE: Hmm ...or maybe I could gather all processed filenames so far from %INC, which I may process in one global CHECK block... Cheers Rolf	[reply] [d/l] [select]
Re: Reading sourcecode at parsing/compilation (CHECK) time? by LanX (Saint) on Apr 04, 2010 at 00:21 UTC
very strange ... replacing the `while(<DATA>)...` code in the attribute handler with `my $pos=tell DATA; seek DATA,0,0; my @src=<DATA>; print "> $src[$linenum-1]\n"; seek DATA,$pos,0;` [download] works fine! `while(<DATA>)` seems to have a special magic causing trouble... BUT if the `__DATA__` literal is missing at the end of the code, there doesn't seem to be any open file handle for the source code... Seems like explicitely opening and closing the file path seems the only way to go... Cheers Rolf	[reply] [d/l] [select]