diagnostics.pm

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package diagnostics;

=head1 NAME

diagnostics, splain - produce verbose warning diagnostics

=head1 SYNOPSIS

Using the C<diagnostics> pragma:

    use diagnostics;
    use diagnostics -verbose;

    enable  diagnostics;
    disable diagnostics;

Using the C<splain> standalone filter program:

    perl program 2>diag.out
    splain [-v] [-p] diag.out

Using diagnostics to get stack traces from a misbehaving script:

    perl -Mdiagnostics=-traceonly my_script.pl

=head1 DESCRIPTION

=head2 The C<diagnostics> Pragma

This module extends the terse diagnostics normally emitted by both the
perl compiler and the perl interpreter (from running perl with a -w 
switch or C<use warnings>), augmenting them with the more
explicative and endearing descriptions found in L<perldiag>.  Like the
other pragmata, it affects the compilation phase of your program rather
than merely the execution phase.

To use in your program as a pragma, merely invoke

    use diagnostics;

at the start (or near the start) of your program.  (Note 
that this I<does> enable perl's B<-w> flag.)  Your whole
compilation will then be subject(ed :-) to the enhanced diagnostics.
These still go out B<STDERR>.

Due to the interaction between runtime and compiletime issues,
and because it's probably not a very good idea anyway,
you may not use C<no diagnostics> to turn them off at compiletime.
However, you may control their behaviour at runtime using the 
disable() and enable() methods to turn them off and on respectively.

The B<-verbose> flag first prints out the L<perldiag> introduction before
any other diagnostics.  The $diagnostics::PRETTY variable can generate nicer
escape sequences for pagers.

Warnings dispatched from perl itself (or more accurately, those that match
descriptions found in L<perldiag>) are only displayed once (no duplicate
descriptions).  User code generated warnings a la warn() are unaffected,
allowing duplicate user messages to be displayed.

This module also adds a stack trace to the error message when perl dies.
This is useful for pinpointing what caused the death. The B<-traceonly> (or
just B<-t>) flag turns off the explanations of warning messages leaving just
the stack traces. So if your script is dieing, run it again with

  perl -Mdiagnostics=-traceonly my_bad_script

to see the call stack at the time of death. By supplying the B<-warntrace>
(or just B<-w>) flag, any warnings emitted will also come with a stack
trace.

=head2 The I<splain> Program

While apparently a whole nuther program, I<splain> is actually nothing
more than a link to the (executable) F<diagnostics.pm> module, as well as
a link to the F<diagnostics.pod> documentation.  The B<-v> flag is like
the C<use diagnostics -verbose> directive.
The B<-p> flag is like the
$diagnostics::PRETTY variable.  Since you're post-processing with 
I<splain>, there's no sense in being able to enable() or disable() processing.

Output from I<splain> is directed to B<STDOUT>, unlike the pragma.

=head1 EXAMPLES

The following file is certain to trigger a few errors at both
runtime and compiletime:

    use diagnostics;
    print NOWHERE "nothing\n";
    print STDERR "\n\tThis message should be unadorned.\n";
    warn "\tThis is a user warning";
    print "\nDIAGNOSTIC TESTER: Please enter a <CR> here: ";
    my $a, $b = scalar <STDIN>;
    print "\n";
    print $x/$y;

If you prefer to run your program first and look at its problem
afterwards, do this:

    perl -w test.pl 2>test.out
    ./splain < test.out

Note that this is not in general possible in shells of more dubious heritage, 
as the theoretical 

    (perl -w test.pl >/dev/tty) >& test.out
    ./splain < test.out

Because you just moved the existing B<stdout> to somewhere else.

If you don't want to modify your source code, but still have on-the-fly
warnings, do this:

    exec 3>&1; perl -w test.pl 2>&1 1>&3 3>&- | splain 1>&2 3>&- 

Nifty, eh?

If you want to control warnings on the fly, do something like this.
Make sure you do the C<use> first, or you won't be able to get
at the enable() or disable() methods.

    use diagnostics; # checks entire compilation phase 
	print "\ntime for 1st bogus diags: SQUAWKINGS\n";
	print BOGUS1 'nada';
	print "done with 1st bogus\n";

    disable diagnostics; # only turns off runtime warnings
	print "\ntime for 2nd bogus: (squelched)\n";
	print BOGUS2 'nada';
	print "done with 2nd bogus\n";

    enable diagnostics; # turns back on runtime warnings
	print "\ntime for 3rd bogus: SQUAWKINGS\n";
	print BOGUS3 'nada';
	print "done with 3rd bogus\n";

    disable diagnostics;
	print "\ntime for 4th bogus: (squelched)\n";
	print BOGUS4 'nada';
	print "done with 4th bogus\n";

=head1 INTERNALS

Diagnostic messages derive from the F<perldiag.pod> file when available at
runtime.  Otherwise, they may be embedded in the file itself when the
splain package is built.   See the F<Makefile> for details.

If an extant $SIG{__WARN__} handler is discovered, it will continue
to be honored, but only after the diagnostics::splainthis() function 
(the module's $SIG{__WARN__} interceptor) has had its way with your
warnings.

There is a $diagnostics::DEBUG variable you may set if you're desperately
curious what sorts of things are being intercepted.

    BEGIN { $diagnostics::DEBUG = 1 } 


=head1 BUGS

Not being able to say "no diagnostics" is annoying, but may not be
insurmountable.

The C<-pretty> directive is called too late to affect matters.
You have to do this instead, and I<before> you load the module.

    BEGIN { $diagnostics::PRETTY = 1 } 

I could start up faster by delaying compilation until it should be
needed, but this gets a "panic: top_level" when using the pragma form
in Perl 5.001e.

While it's true that this documentation is somewhat subserious, if you use
a program named I<splain>, you should expect a bit of whimsy.

=head1 AUTHOR

Tom Christiansen <F<[e-mail]>>, 25 June 1995.

=cut

use strict;
use 5.009001;
use Carp;
$Carp::Internal{__PACKAGE__.""}++;

our $VERSION = 1.17;
our $DEBUG;
our $VERBOSE;
our $PRETTY;
our $TRACEONLY = 0;
our $WARNTRACE = 0;

use Config;
my($privlib, $archlib) = @Config{qw(privlibexp archlibexp)};
if ($^O eq 'VMS') {
    require VMS::Filespec;
    $privlib = VMS::Filespec::unixify($privlib);
    $archlib = VMS::Filespec::unixify($archlib);
}
my @trypod = (
	   "$archlib/pod/perldiag.pod",
	   "$privlib/pod/perldiag-$Config{version}.pod",
	   "$privlib/pod/perldiag.pod",
	   "$archlib/pods/perldiag.pod",
	   "$privlib/pods/perldiag-$Config{version}.pod",
	   "$privlib/pods/perldiag.pod",
	  );
# handy for development testing of new warnings etc
unshift @trypod, "./pod/perldiag.pod" if -e "pod/perldiag.pod";
(my $PODFILE) = ((grep { -e } @trypod), $trypod[$#trypod])[0];

if ($^O eq 'MacOS') {
    # just updir one from each lib dir, we'll find it ...
    ($PODFILE) = grep { -e } map { "$_:pod:perldiag.pod" } @INC;
}


$DEBUG ||= 0;
my $WHOAMI = ref bless [];  # nobody's business, prolly not even mine

local $| = 1;
my $_;

my $standalone;
my(%HTML_2_Troff, %HTML_2_Latin_1, %HTML_2_ASCII_7);

CONFIG: {
    our $opt_p = our $opt_d = our $opt_v = our $opt_f = '';

    unless (caller) {
	$standalone++;
	require Getopt::Std;
	Getopt::Std::getopts('pdvf:')
	    or die "Usage: $0 [-v] [-p] [-f splainpod]";
	$PODFILE = $opt_f if $opt_f;
	$DEBUG = 2 if $opt_d;
	$VERBOSE = $opt_v;
	$PRETTY = $opt_p;
    }

    if (open(POD_DIAG, $PODFILE)) {
	warn "Happy happy podfile from real $PODFILE\n" if $DEBUG;
	last CONFIG;
    } 

    if (caller) {
	INCPATH: {
	    for my $file ( (map { "$_/$WHOAMI.pm" } @INC), $0) {
		warn "Checking $file\n" if $DEBUG;
		if (open(POD_DIAG, $file)) {
		    while (<POD_DIAG>) {
			next unless
			    /^__END__\s*# wish diag dbase were more accessible/;
			print STDERR "podfile is $file\n" if $DEBUG;
			last INCPATH;
		    }
		}
	    } 
	}
    } else { 
	print STDERR "podfile is <DATA>\n" if $DEBUG;
	*POD_DIAG = *main::DATA;
    }
}
if (eof(POD_DIAG)) { 
    die "couldn't find diagnostic data in $PODFILE @INC $0";
}


%HTML_2_Troff = (
    'amp'	=>	'&',	#   ampersand
    'lt'	=>	'<',	#   left chevron, less-than
    'gt'	=>	'>',	#   right chevron, greater-than
    'quot'	=>	'"',	#   double quote

    "Aacute"	=>	"A\\*'",	#   capital A, acute accent
    # etc

);

%HTML_2_Latin_1 = (
    'amp'	=>	'&',	#   ampersand
    'lt'	=>	'<',	#   left chevron, less-than
    'gt'	=>	'>',	#   right chevron, greater-than
    'quot'	=>	'"',	#   double quote

    "Aacute"	=>	"\xC1"	#   capital A, acute accent

    # etc
);

%HTML_2_ASCII_7 = (
    'amp'	=>	'&',	#   ampersand
    'lt'	=>	'<',	#   left chevron, less-than
    'gt'	=>	'>',	#   right chevron, greater-than
    'quot'	=>	'"',	#   double quote

    "Aacute"	=>	"A"	#   capital A, acute accent
    # etc
);

our %HTML_Escapes;
*HTML_Escapes = do {
    if ($standalone) {
	$PRETTY ? \%HTML_2_Latin_1 : \%HTML_2_ASCII_7; 
    } else {
	\%HTML_2_Latin_1; 
    }
}; 

*THITHER = $standalone ? *STDOUT : *STDERR;

my %transfmt = (); 
my $transmo = <<EOFUNC;
sub transmo {
    #local \$^W = 0;  # recursive warnings we do NOT need!
    study;
EOFUNC

my %msg;
{
    print STDERR "FINISHING COMPILATION for $_\n" if $DEBUG;