in reply to right usage of #line ??

> Any idea or previous experience on this, are both welcome.

Just an idea: I seem to remember that perl5db.pl is using a hash to associate line numbers and op tree entries source lines for caching.

Line 3 will point to the #shebang line which has no conflicts (comments are never compiled)

Having multiple sequences of op-codes with the same line number is not only bad practice but a bug in my books.

PLEASE use a linenumber/file pointing to a reasonable code explaining what is happening.

The debugger will just show the static lines found in the file system.

It will not try to deparse your evaled code.

Cheers Rolf
(addicted to the Perl Programming Language and ☆☆☆☆ :)
Je suis Charlie!

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Re^2: right usage of #line ??
by jjmoka (Beadle) on Sep 10, 2015 at 07:19 UTC
    I'm delighted of the feedback. Thanks. It's not my main activity but I'm investigating this topic by a while. Now I found some workaround (fixing #line) so that I can have a quite effective remote debugging session. But I'm interested to fix it definitely and understand the problem. Besides starting to add a first question on this site ( here ), I then provided a more detailed question here but I got no solution.

    I'm just trying to use 2 old (and I so guess stable-enough) modules, mod_perl and Apache::DB. Even developed by the same author, Doug MacEachern, so I believe they should understand each other. I'm running them out of the box. MY code is only the 4 lines snipped shown, just to see them working as expected for the most simple case.

    So the lab is this:

    1. have Apache and mod_perl

    2. have module Apache::DB

    3. use the most simple httpd.conf. Mine is this

    4. excute Apache in not-forking mode httpd  -X -DPERLDB -f simple.httpd.conf

    5. point your browser to your snippet

    6. go to your new fresh debug prompt, arisen magically in the shell of point 4

    7. step-step-step-step ... till reaching the sub default_handler of mod_perl

    (all will happen inside mod_perl, the file ModPerl::RegistryCooker ) 
           A) sub default_handler {
          |
       B) |___| $rc = $self->convert_script_to_compiled_handler;
              |       |
              |       |___|  ....
       C)     |           | my $line = $self->get_mark_line;
       D)     |           | my $eval = join '' .....   <------ the joi
+n shown in my opening question above
       E)     |           | $rc = $self->compile(\$eval);
              |           |              |__
              |           |                 | ....
       F)     |           |                 |  eval $$eval;  <----- tr
+anslated in   return $self->error_check;
              |           |                 |
              |           |
       G)     |           | $self->cache_it;
              |
       H)     | $rc = $self->run;
              |              | ....
       I)     |              | eval { $cv->($r, @_) };  ------->   JUM
+P INTO USER CODE  (here #line will not be understood)

    [download]
    I much appreciate the work of sir MacEachern, as it's a complex matter, but it shouldn't be such a pain to turn them on, after having simplifed your code to 4 lines (shebang, and print CGI header included!, ... so 2 lines). Why that #line is so difficult to understand ? Moreover as already linked (here again) , I found some different opinion on how it should be used so the fixed #line 1 in mod_perl code is on a different choice..... that incidentally does not work so well :)
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      I found a working solution. I post it here, in case others will join this page from Google, one day. Instead of trying to fix the #line issue, I decided to work around those evals. The 'evaled' code is not properly stored in Symbol Tables (much on this can be found also on this site). As the problem is always on the first entering file, I made a wrapper.pl of 2 lines, giving the problem to it, and having my code clean: 
       require '/home/jjmoka/TEST/code/test2.pl'
 $DB::single=2;

      [download]
      This worked both for the simplest example, and for my real production use case (with the proper path in the require).
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