From @jkeenan

On Sun, 03 Sep 2017 03:02:20 GMT, jkeenan wrote:

On Thu, 10 Oct 2013 11:14:24 GMT, smylers@stripey.com wrote:

This is a bug report for perl from smylers@stripey.com,
generated with the help of perlbug 1.39 running under perl 5.19.5.

-----------------------------------------------------------------

In the Perl debugger commands written like the following used to
work,
but now throw errors:

p@ARGV
x@ARGV
x\@ARGV
x\%INC

They still work if you type a space between the command letter and
the
punctuation character which starts its argument, but they used to
work
without the space too.

It only seems to be the single-letter debugger commands that are
affected. print@ARGV and so on still works without spaces.

The error message in blead is:

DB<72> x\@ARGV
Backslash found where operator expected at (eval
8)[lib/perl5db.pl:732] line 2, near "x\"
at (eval 8)[lib/perl5db.pl:732] line 2.
eval 'no strict; ($@, $!, $^E, $,, $/, $\\, $^W) = @DB::saved;package
main; $^D = $^D | $DB::db_stop;
x\\@ARGV;
' called at lib/perl5db.pl line 732
DB::eval called at lib/perl5db.pl line 3091
DB::DB called at -e line 1
syntax error at (eval 8)[lib/perl5db.pl:732] line 2, near "x\"

This is it working in v5.14.3:

DB<72> x\@ARGV
0 ARRAY(0x2267d18)
empty array

I haven't tried to narrow it down any further, mainly cos I don't
know
how to come up with a non-interactive way of demonstrating the
change.

I have confirmed the regression. It is still present in blead
(5.27.3).

However, we should first ask: Is this a bug? That is, was the fact
that we once could use the 'p' and 'x' commands in the debugger
without a subsequent wordspace intentional or accidental?

Note: I'm not saying this should not be fixed. I simply think the
question should be faced.

Use of perlbrew to get various versions of perl shows roughly when the
regression occurred:

#####
good perlbrew use perl-5.16.3 Loading DB routines from perl5db.pl
version 1.37
bad perlbrew use perl-5.18.4 Loading DB routines from perl5db.pl
version 1.39_11
#####

Which means that the problem occurred roughly between these two
commits:

#####
commit 68cd360
Author: Jesse Vincent <jesse@bestpractical.com>
Date: Tue Apr 24 19:02:34 2012 -0400
-$VERSION = '1.36';
+$VERSION = '1.37';

commit 1799399
Author: Ricardo Signes <rjbs@cpan.org>
AuthorDate: Fri Jun 7 11:51:45 2013 -0400
Commit: Ricardo Signes <rjbs@cpan.org>
CommitDate: Fri Jun 7 11:51:45 2013 -0400

version bumps and perldelta for debugger depth
-$VERSION = '1.39_10';
+$VERSION = '1.40';
#####

There was a lot of work being done on the debugger during this period.
The diff is large enough that I'm attaching it gzipped first.

I don't know how to bisect a debugger problem. But I was able to
create a branch based on perl-5.16.3 (jkeenan/120174-starting-from-
5.16.3) in which I wrote some tests for the problem with passed.
Those same tests, when added to a branch based on blead (5.27.3)
(jkeenan/120174-starting-from-5.27.3), fail. Hence, the tests --
which, I concede, are rough, as I'm not familiar with the tests in
lib/perl5db.t -- can be used as regression tests once the problem is
corrected (assuming we want to correct it).

I have figured out how to bisect a debugger problem.

The problems with the 'x' command first appeared in this commit:

#####
$ git show --format=fuller d478d7a |cat
commit d478d7a
Author: Shlomi Fish <shlomif@shlomifish.org>
AuthorDate: Sun Oct 14 12:56:53 2012 +0200
Commit: Ricardo Signes <rjbs@cpan.org>
CommitDate: Mon Nov 12 09:18:40 2012 -0500

Add more commands to the lookup table.

Inline Patch

diff --git a/lib/perl5db.pl b/lib/perl5db.pl
index c9844fd..ed34703 100644
--- a/lib/perl5db.pl
+++ b/lib/perl5db.pl
@@ -2423,7 +2423,15 @@ sub _DB__at_end_of_every_command {
 # 's' is subroutine.
 my %cmd_lookup =
 (
-    'q' => { t => 'm', v => '_handle_q_command' },
+    '.' => { t => 's', v => \&_DB__handle_dot_command, },
+    'f' => { t => 's', v => \&_DB__handle_f_command, },
+    'm' => { t => 's', v => \&_DB__handle_m_command, },
+    'q' => { t => 'm', v => '_handle_q_command', },
+    'S' => { t => 'm', v => '_handle_S_command', },
+    't' => { t => 'm', v => '_handle_t_command', },
+    'x' => { t => 'm', v => '_handle_x_command', },
+    (map { $_ => { t => 'm', v => '_handle_V_command_and_X_command', }, }
+        ('X', 'V')),
 );
 
 sub DB {
@@ -2763,16 +2771,12 @@ If level is specified, set C<$trace_to_depth>.
 
 =cut
 
-                $obj->_handle_t_command;
-
 =head4 C<S> - list subroutines matching/not matching a pattern
 
 Walks through C<%sub>, checking to see whether or not to print the name.
 
 =cut
 
-                $obj->_handle_S_command;
-
 =head4 C<X> - list variables in current package
 
 Since the C<V> command actually processes this, just change this to the
@@ -2784,8 +2788,6 @@ Uses C<dumpvar.pl> to dump out the current values for selected variables.
 
 =cut
 
-                $obj->_handle_V_command_and_X_command;
-
 =head4 C<x> - evaluate and print an expression
 
 Hands the expression off to C<DB::eval>, setting it up to print the value
@@ -2793,22 +2795,16 @@ via C<dumpvar.pl> instead of just printing it directly.
 
 =cut
 
-                $obj->_handle_x_command;
-
 =head4 C<m> - print methods
 
 Just uses C<DB::methods> to determine what methods are available.
 
 =cut
 
-                _DB__handle_m_command($obj);
-
 =head4 C<f> - switch files
 
 =cut
 
-                _DB__handle_f_command($obj);
-
 =head4 C<.> - return to last-executed line.
 
 We set C<$incr> to -1 to indicate that the debugger shouldn't move ahead,
@@ -2816,8 +2812,6 @@ and then we look up the line in the magical C<%dbline> hash.
 
 =cut
 
-                _DB__handle_dot_command($obj);
-
 =head4 C<-> - back one window
 
 We change C<$start> to be one window back; if we go back past the first line,

#####

The changes to the 'p' command first appeared at this commit:

#####
$ git show --format=fuller 8f144df |cat
commit 8f144df
Author: Shlomi Fish <shlomif@shlomifish.org>
AuthorDate: Sun Oct 14 13:22:45 2012 +0200
Commit: Ricardo Signes <rjbs@cpan.org>
CommitDate: Mon Nov 12 09:18:41 2012 -0500

Low hanging fruit is now in %cmd_lookup.

Inline Patch

diff --git a/lib/perl5db.pl b/lib/perl5db.pl
index d79be51..56b8d65 100644
--- a/lib/perl5db.pl
+++ b/lib/perl5db.pl
@@ -2425,20 +2425,32 @@ my %cmd_lookup =
 (
     '-' => { t => 'm', v => '_handle_dash_command', },
     '.' => { t => 's', v => \&_DB__handle_dot_command, },
+    '=' => { t => 'm', v => '_handle_equal_sign_command', },
+    'H' => { t => 'm', v => '_handle_H_command', },
     'S' => { t => 'm', v => '_handle_S_command', },
     'T' => { t => 'm', v => '_handle_T_command', },
+    'W' => { t => 'm', v => '_handle_W_command', },
     'c' => { t => 's', v => \&_DB__handle_c_command, },
     'f' => { t => 's', v => \&_DB__handle_f_command, },
     'm' => { t => 's', v => \&_DB__handle_m_command, },
     'n' => { t => 'm', v => '_handle_n_command', },
+    'p' => { t => 'm', v => '_handle_p_command', },
     'q' => { t => 'm', v => '_handle_q_command', },
     'r' => { t => 'm', v => '_handle_r_command', },
     's' => { t => 'm', v => '_handle_s_command', },
+    'save' => { t => 'm', v => '_handle_save_command', },
+    'source' => { t => 'm', v => '_handle_source_command', },
     't' => { t => 'm', v => '_handle_t_command', },
+    'w' => { t => 'm', v => '_handle_w_command', },
     'x' => { t => 'm', v => '_handle_x_command', },
     'y' => { t => 's', v => \&_DB__handle_y_command, },
     (map { $_ => { t => 'm', v => '_handle_V_command_and_X_command', }, }
         ('X', 'V')),
+    (map { $_ => { t => 'm', v => '_handle_enable_disable_commands', }, }
+        qw(enable disable)),
+    (map { $_ =>
+        { t => 's', v => \&_DB__handle_restart_and_rerun_commands, },
+        } qw(R rerun)),
 );
 
 sub DB {
@@ -2888,18 +2900,10 @@ Just calls C<DB::print_trace>.
 
 Just calls C<DB::cmd_w>.
 
-=cut
-
-                $obj->_handle_w_command;
-
 =head4 C<W> - watch-expression processing.
 
 Just calls C<DB::cmd_W>.
 
-=cut
-
-                $obj->_handle_W_command;
-
 =head4 C</> - search forward for a string in the source
 
 We take the argument and treat it as a pattern. If it turns out to be a
@@ -2963,10 +2967,6 @@ C<DB::system> to avoid problems with C<STDIN> and C<STDOUT>.
 
 Prints the contents of C<@hist> (if any).
 
-=cut
-
-                $obj->_handle_H_command;
-
 =head4 C<man, doc, perldoc> - look up documentation
 
 Just calls C<runman()> to print the appropriate document.
@@ -2980,36 +2980,19 @@ Just calls C<runman()> to print the appropriate document.
 Builds a C<print EXPR> expression in the C<$cmd>; this will get executed at
 the bottom of the loop.
 
-=cut
-
-                $obj->_handle_p_command;
-
 =head4 C<=> - define command alias
 
 Manipulates C<%alias> to add or list command aliases.
 
-=cut
-
-                # = - set up a command alias.
-                $obj->_handle_equal_sign_command;
-
 =head4 C<source> - read commands from a file.
 
 Opens a lexical filehandle and stacks it on C<@cmdfhs>; C<DB::readline> will
 pick it up.
 
-=cut
-
-                $obj->_handle_source_command;
-
 =head4 C<enable> C<disable> - enable or disable breakpoints
 
 This enables or disables breakpoints.
 
-=cut
-
-                $obj->_handle_enable_disable_commands;
-
 =head4 C<save> - send current history to a file
 
 Takes the complete history, (not the shrunken version you see with C<H>),
@@ -3017,11 +3000,6 @@ and saves it to the given filename, so it can be replayed using C<source>.
 
 Note that all C<^(save|source)>'s are commented out with a view to minimise recursion.
 
-=cut
-
-                # save source - write commands to a file for later use
-                $obj->_handle_save_command;
-
 =head4 C<R> - restart
 
 Restart the debugger session.
@@ -3030,12 +3008,6 @@ Restart the debugger session.
 
 Return to any given position in the B<true>-history list
 
-=cut
-
-                # R - restart execution.
-                # rerun - controlled restart execution.
-                _DB__handle_restart_and_rerun_commands($obj);
-
 =head4 C<|, ||> - pipe output through the pager.
 
 For C<|>, we save C<OUT> (the debugger's output filehandle) and C<STDOUT>

#####

Thank you very much.

--
James E Keenan (jkeenan@cpan.org)

Debugger command regression: Now requires more spaces #13342

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