package diagnostics;

=head1 NAME

diagnostics, splain - produce verbose warning diagnostics

=head1 SYNOPSIS

Using the C pragma:

    use diagnostics;
    use diagnostics -verbose;

    enable  diagnostics;
    disable diagnostics;

Using the C standalone filter program:

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

=head1 DESCRIPTION

=head2 The C Pragma

This module extends the terse diagnostics normally emitted by both the
perl compiler and the perl interpreter, augmenting them with the more
explicative and endearing descriptions found in L.  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 enable perl's B<-w> flag.)  Your whole
compilation will then be subject(ed :-) to the enhanced diagnostics.
These still go out B.

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 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 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) are only displayed once (no duplicate
descriptions).  User code generated warnings a la warn() are unaffected,
allowing duplicate user messages to be displayed.

=head2 The I Program

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

Output from I is directed to B, 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  here: ";
    my $a, $b = scalar ;
    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 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 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 file when available at
runtime.  Otherwise, they may be embedded in the file itself when the
splain package is built.   See the F 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 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, you should expect a bit of whimsy.

=head1 AUTHOR

Tom Christiansen >, 25 June 1995.

=cut

use strict;
use 5.006;
use Carp;

our $VERSION = 1.13;
our $DEBUG;
our $VERBOSE;
our $PRETTY;

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;
local $_;

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 () {
			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 \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 = <) {

	unescape();
	if ($PRETTY) {
	    sub noop   { return $_[0] }  # spensive for a noop
	    sub bold   { my $str =$_[0];  $str =~ s/(.)/$1\b$1/g; return $str; } 
	    sub italic { my $str = $_[0]; $str =~ s/(.)/_\b$1/g;  return $str; } 
	    s/C<<< (.*?) >>>|C<< (.*?) >>|[BC]<(.*?)>/bold($+)/ges;
	    s/[LIF]<(.*?)>/italic($1)/ges;
	} else {
	    s/C<<< (.*?) >>>|C<< (.*?) >>|[BC]<(.*?)>/$+/gs;
	    s/[LIF]<(.*?)>/$1/gs;
	} 
	unless (/^=/) {
	    if (defined $header) { 
		if ( $header eq 'DESCRIPTION' && 
		    (   /Optional warnings are enabled/ 
		     || /Some of these messages are generic./
		    ) )
		{
		    next;
		}
		s/^/    /gm;
		$msg{$header} .= $_;
	 	undef $for_item;	
	    }
	    next;
	} 
	unless ( s/=item (.*?)\s*\z//) {

	    if ( s/=head1\sDESCRIPTION//) {
		$msg{$header = 'DESCRIPTION'} = '';
		undef $for_item;
	    }
	    elsif( s/^=for\s+diagnostics\s*\n(.*?)\s*\z// ) {
		$for_item = $1;
	    } 
	    next;
	}

	if( $for_item ) { $header = $for_item; undef $for_item } 
	else {
	    $header = $1;
	    while( $header =~ /[;,]\z/ ) {
		 =~ /^\s*(.*?)\s*\z/;
		$header .= ' '.$1;
	    }
	}

	# strip formatting directives from =item line
	$header =~ s/[A-Z]<(.*?)>/$1/g;

        my @toks = split( /(%l?[dx]|%c|%(?:\.\d+)?s)/, $header );
	if (@toks > 1) {
            my $conlen = 0;
            for my $i (0..$#toks){
                if( $i % 2 ){
                    if(      $toks[$i] eq '%c' ){
                        $toks[$i] = '.';
                    } elsif( $toks[$i] eq '%d' ){
                        $toks[$i] = '\d+';
                    } elsif( $toks[$i] eq '%s' ){
                        $toks[$i] = $i == $#toks ? '.*' : '.*?';
                    } elsif( $toks[$i] =~ '%.(\d+)s' ){
                        $toks[$i] = ".{$1}";
                     } elsif( $toks[$i] =~ '^%l*x$' ){
                        $toks[$i] = '[\da-f]+';
                   }
                } elsif( length( $toks[$i] ) ){
                    $toks[$i] =~ s/^.*$/\Q$&\E/;
                    $conlen += length( $toks[$i] );
                }
            }  
            my $lhs = join( '', @toks );
	    $transfmt{$header}{pat} =
              "    s{^$lhs}\n     {\Q$header\E}s\n\t&& return 1;\n";
            $transfmt{$header}{len} = $conlen;
	} else {
            $transfmt{$header}{pat} =
	      "    m{^\Q$header\E} && return 1;\n";
            $transfmt{$header}{len} = length( $header );
	} 

	print STDERR "$WHOAMI: Duplicate entry: \"$header\"\n"
	    if $msg{$header};

	$msg{$header} = '';
    } 


    close POD_DIAG unless *main::DATA eq *POD_DIAG;

    die "No diagnostics?" unless %msg;

    # Apply patterns in order of decreasing sum of lengths of fixed parts
    # Seems the best way of hitting the right one.
    for my $hdr ( sort { $transfmt{$b}{len} <=> $transfmt{$a}{len} }
                  keys %transfmt ){
        $transmo .= $transfmt{$hdr}{pat};
    }
    $transmo .= "    return 0;\n}\n";
    print STDERR $transmo if $DEBUG;
    eval $transmo;
    die $@ if $@;
}

if ($standalone) {
    if (!@ARGV and -t STDIN) { print STDERR "$0: Reading from STDIN\n" } 
    while (defined (my $error = <>)) {
	splainthis($error) || print THITHER $error;
    } 
    exit;
} 

my $olddie;
my $oldwarn;

sub import {
    shift;
    $^W = 1; # yup, clobbered the global variable; 
	     # tough, if you want diags, you want diags.
    return if defined $SIG{__WARN__} && ($SIG{__WARN__} eq \&warn_trap);

    for (@_) {

	/^-d(ebug)?$/ 	   	&& do {
				    $DEBUG++;
				    next;
				   };

	/^-v(erbose)?$/ 	&& do {
				    $VERBOSE++;
				    next;
				   };

	/^-p(retty)?$/ 		&& do {
				    print STDERR "$0: I'm afraid it's too late for prettiness.\n";
				    $PRETTY++;
				    next;
			       };

	warn "Unknown flag: $_";
    } 

    $oldwarn = $SIG{__WARN__};
    $olddie = $SIG{__DIE__};
    $SIG{__WARN__} = \&warn_trap;
    $SIG{__DIE__} = \&death_trap;
} 

sub enable { &import }

sub disable {
    shift;
    return unless $SIG{__WARN__} eq \&warn_trap;
    $SIG{__WARN__} = $oldwarn || '';
    $SIG{__DIE__} = $olddie || '';
} 

sub warn_trap {
    my $warning = $_[0];
    if (caller eq $WHOAMI or !splainthis($warning)) {
	print STDERR $warning;
    } 
    &$oldwarn if defined $oldwarn and $oldwarn and $oldwarn ne \&warn_trap;
};

sub death_trap {
    my $exception = $_[0];

    # See if we are coming from anywhere within an eval. If so we don't
    # want to explain the exception because it's going to get caught.
    my $in_eval = 0;
    my $i = 0;
    while (1) {
      my $caller = (caller($i++))[3] or last;
      if ($caller eq '(eval)') {
	$in_eval = 1;
	last;
      }
    }

    splainthis($exception) unless $in_eval;
    if (caller eq $WHOAMI) { print STDERR "INTERNAL EXCEPTION: $exception"; } 
    &$olddie if defined $olddie and $olddie and $olddie ne \&death_trap;

    return if $in_eval;

    # We don't want to unset these if we're coming from an eval because
    # then we've turned off diagnostics.

    # Switch off our die/warn handlers so we don't wind up in our own
    # traps.
    $SIG{__DIE__} = $SIG{__WARN__} = '';

    # Have carp skip over death_trap() when showing the stack trace.
    local($Carp::CarpLevel) = 1;

    confess "Uncaught exception from user code:\n\t$exception";
	# up we go; where we stop, nobody knows, but i think we die now
	# but i'm deeply afraid of the &$olddie guy reraising and us getting
	# into an indirect recursion loop
};

my %exact_duplicate;
my %old_diag;
my $count;
my $wantspace;
sub splainthis {
    local $_ = shift;
    local $\;
    ### &finish_compilation unless %msg;
    s/\.?\n+$//;
    my $orig = $_;
    # return unless defined;

    # get rid of the where-are-we-in-input part
    s/, <.*?> (?:line|chunk).*$//;

    # Discard 1st " at  line " and all text beyond
    # but be aware of messsages containing " at this-or-that"
    my $real = 0;
    my @secs = split( / at / );
    $_ = $secs[0];
    for my $i ( 1..$#secs ){
        if( $secs[$i] =~ /.+? (?:line|chunk) \d+/ ){
            $real = 1;
            last;
        } else {
            $_ .= ' at ' . $secs[$i];
	}
    }
    
    # remove parenthesis occurring at the end of some messages 
    s/^\((.*)\)$/$1/;

    if ($exact_duplicate{$orig}++) {
	return &transmo;
    } else {
	return 0 unless &transmo;
    }

    $orig = shorten($orig);
    if ($old_diag{$_}) {
	autodescribe();
	print THITHER "$orig (#$old_diag{$_})\n";
	$wantspace = 1;
    } else {
	autodescribe();
	$old_diag{$_} = ++$count;
	print THITHER "\n" if $wantspace;
	$wantspace = 0;
	print THITHER "$orig (#$old_diag{$_})\n";
	if ($msg{$_}) {
	    print THITHER $msg{$_};
	} else {
	    if (0 and $standalone) { 
		print THITHER "    **** Error #$old_diag{$_} ",
			($real ? "is" : "appears to be"),
			" an unknown diagnostic message.\n\n";
	    }
	    return 0;
	} 
    }
    return 1;
} 

sub autodescribe {
    if ($VERBOSE and not $count) {
	print THITHER &{$PRETTY ? \&bold : \&noop}("DESCRIPTION OF DIAGNOSTICS"),
		"\n$msg{DESCRIPTION}\n";
    } 
} 

sub unescape { 
    s {
            E<  
            ( [A-Za-z]+ )       
            >   
    } { 
         do {   
             exists $HTML_Escapes{$1}
                ? do { $HTML_Escapes{$1} }
                : do {
                    warn "Unknown escape: E<$1> in $_";
                    "E<$1>";
                } 
         } 
    }egx;
}

sub shorten {
    my $line = $_[0];
    if (length($line) > 79 and index($line, "\n") == -1) {
	my $space_place = rindex($line, ' ', 79);
	if ($space_place != -1) {
	    substr($line, $space_place, 1) = "\n\t";
	} 
    } 
    return $line;
} 


1 unless $standalone;  # or it'll complain about itself
__END__ # wish diag dbase were more accessible