Makefile: replace perl/Makefile.PL with simple make rules

Replace the perl/Makefile.PL and the fallback perl/Makefile used under
NO_PERL_MAKEMAKER=NoThanks with a much simpler implementation heavily
inspired by how the i18n infrastructure's build process works[1].

The reason for having the Makefile.PL in the first place is that it
was initially[2] building a perl C binding to interface with libgit,
this functionality, that was removed[3] before Git.pm ever made it to
the master branch.

We've since since started maintaining a fallback perl/Makefile, as
MakeMaker wouldn't work on some platforms[4]. That's just the tip of
the iceberg. We have the PM.stamp hack in the top-level Makefile[5] to
detect whether we need to regenerate the perl/perl.mak, which I fixed
just recently to deal with issues like the perl version changing from
under us[6].

There is absolutely no reason for why this needs to be so complex
anymore. All we're getting out of this elaborate Rube Goldberg machine
was copying perl/* to perl/blib/* as we do a string-replacement on
the *.pm files to hardcode @@LOCALEDIR@@ in the source, as well as
pod2man-ing Git.pm & friends.

So replace the whole thing with something that's pretty much a copy of
how we generate po/build/**.mo from po/*.po, just with a small sed(1)
command instead of msgfmt. As that's being done rename the files
from *.pm to *.pmc just to indicate that they're generated (see
"perldoc -f require").

While I'm at it, change the fallback for Error.pm from being something
where we'll ship our own Error.pm if one doesn't exist at build time
to one where we just use a Git::Error wrapper that'll always prefer
the system-wide Error.pm, only falling back to our own copy if it
really doesn't exist at runtime. It's now shipped as
Git::FromCPAN::Error, making it easy to add other modules to
Git::FromCPAN::* in the future if that's needed.

Functional changes:

 * This will not always install into perl's idea of its global
   "installsitelib". This only potentially matters for packagers that
   need to expose Git.pm for non-git use, and as explained in the
   INSTALL file there's a trivial workaround.

 * The scripts themselves will 'use lib' the target directory, but if
   INSTLIBDIR is set it overrides it. It doesn't have to be this way,
   it could be set in addition to INSTLIBDIR, but my reading of [7] is
   that this is the desired behavior.

 * We don't build man pages for all of the perl modules as we used to,
   only Git(3pm). As discussed on-list[8] that we were building
   installed manpages for purely internal APIs like Git::I18N or
   private-Error.pm was always a bug anyway, and all the Git::SVN::*
   ones say they're internal APIs.

   There are apparently external users of Git.pm, but I don't expect
   there to be any of the others.

   As a side-effect of these general changes the perl documentation
   now only installed by install-{doc,man}, not a mere "install" as
   before.

1. 5e9637c629 ("i18n: add infrastructure for translating Git with
   gettext", 2011-11-18)

2. b1edc53d06 ("Introduce Git.pm (v4)", 2006-06-24)

3. 18b0fc1ce1 ("Git.pm: Kill Git.xs for now", 2006-09-23)

4. f848718a69 ("Make perl/ build procedure ActiveState friendly.",
   2006-12-04)

5. ee9be06770 ("perl: detect new files in MakeMaker builds",
   2012-07-27)

6. c59c4939c2 ("perl: regenerate perl.mak if perl -V changes",
   2017-03-29)

7. 0386dd37b1 ("Makefile: add PERLLIB_EXTRA variable that adds to
   default perl path", 2013-11-15)

8. 87bmjjv1pu.fsf@evledraar.booking.com ("Re: [PATCH] Makefile:
   replace perl/Makefile.PL with simple make rules"

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 827 insertions, 0 deletions

diff --git a/perl/Git/FromCPAN/Error.pm b/perl/Git/FromCPAN/Error.pm
new file mode 100644
index 0000000000..6098135ae2
--- /dev/null
+++ b/perl/Git/FromCPAN/Error.pm
@@ -0,0 +1,827 @@
+# Error.pm
+#
+# Copyright (c) 1997-8 Graham Barr <gbarr@ti.com>. All rights reserved.
+# This program is free software; you can redistribute it and/or
+# modify it under the same terms as Perl itself.
+#
+# Based on my original Error.pm, and Exceptions.pm by Peter Seibel
+# <peter@weblogic.com> and adapted by Jesse Glick <jglick@sig.bsh.com>.
+#
+# but modified ***significantly***
+
+package Error;
+
+use strict;
+use vars qw($VERSION);
+use 5.004;
+
+$VERSION = "0.15009";
+
+use overload (
+	'""'	   =>	'stringify',
+	'0+'	   =>	'value',
+	'bool'     =>	sub { return 1; },
+	'fallback' =>	1
+);
+
+$Error::Depth = 0;	# Depth to pass to caller()
+$Error::Debug = 0;	# Generate verbose stack traces
+@Error::STACK = ();	# Clause stack for try
+$Error::THROWN = undef;	# last error thrown, a workaround until die $ref works
+
+my $LAST;		# Last error created
+my %ERROR;		# Last error associated with package
+
+sub throw_Error_Simple
+{
+    my $args = shift;
+    return Error::Simple->new($args->{'text'});
+}
+
+$Error::ObjectifyCallback = \&throw_Error_Simple;
+
+
+# Exported subs are defined in Error::subs
+
+sub import {
+    shift;
+    local $Exporter::ExportLevel = $Exporter::ExportLevel + 1;
+    Error::subs->import(@_);
+}
+
+# I really want to use last for the name of this method, but it is a keyword
+# which prevent the syntax  last Error
+
+sub prior {
+    shift; # ignore
+
+    return $LAST unless @_;
+
+    my $pkg = shift;
+    return exists $ERROR{$pkg} ? $ERROR{$pkg} : undef
+	unless ref($pkg);
+
+    my $obj = $pkg;
+    my $err = undef;
+    if($obj->isa('HASH')) {
+	$err = $obj->{'__Error__'}
+	    if exists $obj->{'__Error__'};
+    }
+    elsif($obj->isa('GLOB')) {
+	$err = ${*$obj}{'__Error__'}
+	    if exists ${*$obj}{'__Error__'};
+    }
+
+    $err;
+}
+
+sub flush {
+    shift; #ignore
+
+    unless (@_) {
+       $LAST = undef;
+       return;
+    }
+
+    my $pkg = shift;
+    return unless ref($pkg);
+
+    undef $ERROR{$pkg} if defined $ERROR{$pkg};
+}
+
+# Return as much information as possible about where the error
+# happened. The -stacktrace element only exists if $Error::DEBUG
+# was set when the error was created
+
+sub stacktrace {
+    my $self = shift;
+
+    return $self->{'-stacktrace'}
+	if exists $self->{'-stacktrace'};
+
+    my $text = exists $self->{'-text'} ? $self->{'-text'} : "Died";
+
+    $text .= sprintf(" at %s line %d.\n", $self->file, $self->line)
+	unless($text =~ /\n$/s);
+
+    $text;
+}
+
+# Allow error propagation, ie
+#
+# $ber->encode(...) or
+#    return Error->prior($ber)->associate($ldap);
+
+sub associate {
+    my $err = shift;
+    my $obj = shift;
+
+    return unless ref($obj);
+
+    if($obj->isa('HASH')) {
+	$obj->{'__Error__'} = $err;
+    }
+    elsif($obj->isa('GLOB')) {
+	${*$obj}{'__Error__'} = $err;
+    }
+    $obj = ref($obj);
+    $ERROR{ ref($obj) } = $err;
+
+    return;
+}
+
+sub new {
+    my $self = shift;
+    my($pkg,$file,$line) = caller($Error::Depth);
+
+    my $err = bless {
+	'-package' => $pkg,
+	'-file'    => $file,
+	'-line'    => $line,
+	@_
+    }, $self;
+
+    $err->associate($err->{'-object'})
+	if(exists $err->{'-object'});
+
+    # To always create a stacktrace would be very inefficient, so
+    # we only do it if $Error::Debug is set
+
+    if($Error::Debug) {
+	require Carp;
+	local $Carp::CarpLevel = $Error::Depth;
+	my $text = defined($err->{'-text'}) ? $err->{'-text'} : "Error";
+	my $trace = Carp::longmess($text);
+	# Remove try calls from the trace
+	$trace =~ s/(\n\s+\S+__ANON__[^\n]+)?\n\s+eval[^\n]+\n\s+Error::subs::try[^\n]+(?=\n)//sog;
+	$trace =~ s/(\n\s+\S+__ANON__[^\n]+)?\n\s+eval[^\n]+\n\s+Error::subs::run_clauses[^\n]+\n\s+Error::subs::try[^\n]+(?=\n)//sog;
+	$err->{'-stacktrace'} = $trace
+    }
+
+    $@ = $LAST = $ERROR{$pkg} = $err;
+}
+
+# Throw an error. this contains some very gory code.
+
+sub throw {
+    my $self = shift;
+    local $Error::Depth = $Error::Depth + 1;
+
+    # if we are not rethrow-ing then create the object to throw
+    $self = $self->new(@_) unless ref($self);
+
+    die $Error::THROWN = $self;
+}
+
+# syntactic sugar for
+#
+#    die with Error( ... );
+
+sub with {
+    my $self = shift;
+    local $Error::Depth = $Error::Depth + 1;
+
+    $self->new(@_);
+}
+
+# syntactic sugar for
+#
+#    record Error( ... ) and return;
+
+sub record {
+    my $self = shift;
+    local $Error::Depth = $Error::Depth + 1;
+
+    $self->new(@_);
+}
+
+# catch clause for
+#
+# try { ... } catch CLASS with { ... }
+
+sub catch {
+    my $pkg = shift;
+    my $code = shift;
+    my $clauses = shift || {};
+    my $catch = $clauses->{'catch'} ||= [];
+
+    unshift @$catch,  $pkg, $code;
+
+    $clauses;
+}
+
+# Object query methods
+
+sub object {
+    my $self = shift;
+    exists $self->{'-object'} ? $self->{'-object'} : undef;
+}
+
+sub file {
+    my $self = shift;
+    exists $self->{'-file'} ? $self->{'-file'} : undef;
+}
+
+sub line {
+    my $self = shift;
+    exists $self->{'-line'} ? $self->{'-line'} : undef;
+}
+
+sub text {
+    my $self = shift;
+    exists $self->{'-text'} ? $self->{'-text'} : undef;
+}
+
+# overload methods
+
+sub stringify {
+    my $self = shift;
+    defined $self->{'-text'} ? $self->{'-text'} : "Died";
+}
+
+sub value {
+    my $self = shift;
+    exists $self->{'-value'} ? $self->{'-value'} : undef;
+}
+
+package Error::Simple;
+
+@Error::Simple::ISA = qw(Error);
+
+sub new {
+    my $self  = shift;
+    my $text  = "" . shift;
+    my $value = shift;
+    my(@args) = ();
+
+    local $Error::Depth = $Error::Depth + 1;
+
+    @args = ( -file => $1, -line => $2)
+	if($text =~ s/\s+at\s+(\S+)\s+line\s+(\d+)(?:,\s*<[^>]*>\s+line\s+\d+)?\.?\n?$//s);
+    push(@args, '-value', 0 + $value)
+	if defined($value);
+
+    $self->SUPER::new(-text => $text, @args);
+}
+
+sub stringify {
+    my $self = shift;
+    my $text = $self->SUPER::stringify;
+    $text .= sprintf(" at %s line %d.\n", $self->file, $self->line)
+	unless($text =~ /\n$/s);
+    $text;
+}
+
+##########################################################################
+##########################################################################
+
+# Inspired by code from Jesse Glick <jglick@sig.bsh.com> and
+# Peter Seibel <peter@weblogic.com>
+
+package Error::subs;
+
+use Exporter ();
+use vars qw(@EXPORT_OK @ISA %EXPORT_TAGS);
+
+@EXPORT_OK   = qw(try with finally except otherwise);
+%EXPORT_TAGS = (try => \@EXPORT_OK);
+
+@ISA = qw(Exporter);
+
+
+sub blessed {
+	my $item = shift;
+	local $@; # don't kill an outer $@
+	ref $item and eval { $item->can('can') };
+}
+
+
+sub run_clauses ($$$\@) {
+    my($clauses,$err,$wantarray,$result) = @_;
+    my $code = undef;
+
+    $err = $Error::ObjectifyCallback->({'text' =>$err}) unless ref($err);
+
+    CATCH: {
+
+	# catch
+	my $catch;
+	if(defined($catch = $clauses->{'catch'})) {
+	    my $i = 0;
+
+	    CATCHLOOP:
+	    for( ; $i < @$catch ; $i += 2) {
+		my $pkg = $catch->[$i];
+		unless(defined $pkg) {
+		    #except
+		    splice(@$catch,$i,2,$catch->[$i+1]->());
+		    $i -= 2;
+		    next CATCHLOOP;
+		}
+		elsif(blessed($err) && $err->isa($pkg)) {
+		    $code = $catch->[$i+1];
+		    while(1) {
+			my $more = 0;
+			local($Error::THROWN);
+			my $ok = eval {
+			    if($wantarray) {
+				@{$result} = $code->($err,\$more);
+			    }
+			    elsif(defined($wantarray)) {
+			        @{$result} = ();
+				$result->[0] = $code->($err,\$more);
+			    }
+			    else {
+				$code->($err,\$more);
+			    }
+			    1;
+			};
+			if( $ok ) {
+			    next CATCHLOOP if $more;
+			    undef $err;
+			}
+			else {
+			    $err = defined($Error::THROWN)
+				    ? $Error::THROWN : $@;
+                $err = $Error::ObjectifyCallback->({'text' =>$err})
+                    unless ref($err);
+			}
+			last CATCH;
+		    };
+		}
+	    }
+	}
+
+	# otherwise
+	my $owise;
+	if(defined($owise = $clauses->{'otherwise'})) {
+	    my $code = $clauses->{'otherwise'};
+	    my $more = 0;
+	    my $ok = eval {
+		if($wantarray) {
+		    @{$result} = $code->($err,\$more);
+		}
+		elsif(defined($wantarray)) {
+		    @{$result} = ();
+		    $result->[0] = $code->($err,\$more);
+		}
+		else {
+		    $code->($err,\$more);
+		}
+		1;
+	    };
+	    if( $ok ) {
+		undef $err;
+	    }
+	    else {
+		$err = defined($Error::THROWN)
+			? $Error::THROWN : $@;
+
+        $err = $Error::ObjectifyCallback->({'text' =>$err})
+            unless ref($err);
+	    }
+	}
+    }
+    $err;
+}
+
+sub try (&;$) {
+    my $try = shift;
+    my $clauses = @_ ? shift : {};
+    my $ok = 0;
+    my $err = undef;
+    my @result = ();
+
+    unshift @Error::STACK, $clauses;
+
+    my $wantarray = wantarray();
+
+    do {
+	local $Error::THROWN = undef;
+    local $@ = undef;
+
+	$ok = eval {
+	    if($wantarray) {
+		@result = $try->();
+	    }
+	    elsif(defined $wantarray) {
+		$result[0] = $try->();
+	    }
+	    else {
+		$try->();
+	    }
+	    1;
+	};
+
+	$err = defined($Error::THROWN) ? $Error::THROWN : $@
+	    unless $ok;
+    };
+
+    shift @Error::STACK;
+
+    $err = run_clauses($clauses,$err,wantarray,@result)
+	unless($ok);
+
+    $clauses->{'finally'}->()
+	if(defined($clauses->{'finally'}));
+
+    if (defined($err))
+    {
+        if (blessed($err) && $err->can('throw'))
+        {
+            throw $err;
+        }
+        else
+        {
+            die $err;
+        }
+    }
+
+    wantarray ? @result : $result[0];
+}
+
+# Each clause adds a sub to the list of clauses. The finally clause is
+# always the last, and the otherwise clause is always added just before
+# the finally clause.
+#
+# All clauses, except the finally clause, add a sub which takes one argument
+# this argument will be the error being thrown. The sub will return a code ref
+# if that clause can handle that error, otherwise undef is returned.
+#
+# The otherwise clause adds a sub which unconditionally returns the users
+# code reference, this is why it is forced to be last.
+#
+# The catch clause is defined in Error.pm, as the syntax causes it to
+# be called as a method
+
+sub with (&;$) {
+    @_
+}
+
+sub finally (&) {
+    my $code = shift;
+    my $clauses = { 'finally' => $code };
+    $clauses;
+}
+
+# The except clause is a block which returns a hashref or a list of
+# key-value pairs, where the keys are the classes and the values are subs.
+
+sub except (&;$) {
+    my $code = shift;
+    my $clauses = shift || {};
+    my $catch = $clauses->{'catch'} ||= [];
+
+    my $sub = sub {
+	my $ref;
+	my(@array) = $code->($_[0]);
+	if(@array == 1 && ref($array[0])) {
+	    $ref = $array[0];
+	    $ref = [ %$ref ]
+		if(UNIVERSAL::isa($ref,'HASH'));
+	}
+	else {
+	    $ref = \@array;
+	}
+	@$ref
+    };
+
+    unshift @{$catch}, undef, $sub;
+
+    $clauses;
+}
+
+sub otherwise (&;$) {
+    my $code = shift;
+    my $clauses = shift || {};
+
+    if(exists $clauses->{'otherwise'}) {
+	require Carp;
+	Carp::croak("Multiple otherwise clauses");
+    }
+
+    $clauses->{'otherwise'} = $code;
+
+    $clauses;
+}
+
+1;
+__END__
+
+=head1 NAME
+
+Error - Error/exception handling in an OO-ish way
+
+=head1 SYNOPSIS
+
+    use Error qw(:try);
+
+    throw Error::Simple( "A simple error");
+
+    sub xyz {
+        ...
+	record Error::Simple("A simple error")
+	    and return;
+    }
+
+    unlink($file) or throw Error::Simple("$file: $!",$!);
+
+    try {
+	do_some_stuff();
+	die "error!" if $condition;
+	throw Error::Simple -text => "Oops!" if $other_condition;
+    }
+    catch Error::IO with {
+	my $E = shift;
+	print STDERR "File ", $E->{'-file'}, " had a problem\n";
+    }
+    except {
+	my $E = shift;
+	my $general_handler=sub {send_message $E->{-description}};
+	return {
+	    UserException1 => $general_handler,
+	    UserException2 => $general_handler
+	};
+    }
+    otherwise {
+	print STDERR "Well I don't know what to say\n";
+    }
+    finally {
+	close_the_garage_door_already(); # Should be reliable
+    }; # Don't forget the trailing ; or you might be surprised
+
+=head1 DESCRIPTION
+
+The C<Error> package provides two interfaces. Firstly C<Error> provides
+a procedural interface to exception handling. Secondly C<Error> is a
+base class for errors/exceptions that can either be thrown, for
+subsequent catch, or can simply be recorded.
+
+Errors in the class C<Error> should not be thrown directly, but the
+user should throw errors from a sub-class of C<Error>.
+
+=head1 PROCEDURAL INTERFACE
+
+C<Error> exports subroutines to perform exception handling. These will
+be exported if the C<:try> tag is used in the C<use> line.
+
+=over 4
+
+=item try BLOCK CLAUSES
+
+C<try> is the main subroutine called by the user. All other subroutines
+exported are clauses to the try subroutine.
+
+The BLOCK will be evaluated and, if no error is throw, try will return
+the result of the block.
+
+C<CLAUSES> are the subroutines below, which describe what to do in the
+event of an error being thrown within BLOCK.
+
+=item catch CLASS with BLOCK
+
+This clauses will cause all errors that satisfy C<$err-E<gt>isa(CLASS)>
+to be caught and handled by evaluating C<BLOCK>.
+
+C<BLOCK> will be passed two arguments. The first will be the error
+being thrown. The second is a reference to a scalar variable. If this
+variable is set by the catch block then, on return from the catch
+block, try will continue processing as if the catch block was never
+found.
+
+To propagate the error the catch block may call C<$err-E<gt>throw>
+
+If the scalar reference by the second argument is not set, and the
+error is not thrown. Then the current try block will return with the
+result from the catch block.
+
+=item except BLOCK
+
+When C<try> is looking for a handler, if an except clause is found
+C<BLOCK> is evaluated. The return value from this block should be a
+HASHREF or a list of key-value pairs, where the keys are class names
+and the values are CODE references for the handler of errors of that
+type.
+
+=item otherwise BLOCK
+
+Catch any error by executing the code in C<BLOCK>
+
+When evaluated C<BLOCK> will be passed one argument, which will be the
+error being processed.
+
+Only one otherwise block may be specified per try block
+
+=item finally BLOCK
+
+Execute the code in C<BLOCK> either after the code in the try block has
+successfully completed, or if the try block throws an error then
+C<BLOCK> will be executed after the handler has completed.
+
+If the handler throws an error then the error will be caught, the
+finally block will be executed and the error will be re-thrown.
+
+Only one finally block may be specified per try block
+
+=back
+
+=head1 CLASS INTERFACE
+
+=head2 CONSTRUCTORS
+
+The C<Error> object is implemented as a HASH. This HASH is initialized
+with the arguments that are passed to its constructor. The elements
+that are used by, or are retrievable by the C<Error> class are listed
+below, other classes may add to these.
+
+	-file
+	-line
+	-text
+	-value
+	-object
+
+If C<-file> or C<-line> are not specified in the constructor arguments
+then these will be initialized with the file name and line number where
+the constructor was called from.
+
+If the error is associated with an object then the object should be
+passed as the C<-object> argument. This will allow the C<Error> package
+to associate the error with the object.
+
+The C<Error> package remembers the last error created, and also the
+last error associated with a package. This could either be the last
+error created by a sub in that package, or the last error which passed
+an object blessed into that package as the C<-object> argument.
+
+=over 4
+
+=item throw ( [ ARGS ] )
+
+Create a new C<Error> object and throw an error, which will be caught
+by a surrounding C<try> block, if there is one. Otherwise it will cause
+the program to exit.
+
+C<throw> may also be called on an existing error to re-throw it.
+
+=item with ( [ ARGS ] )
+
+Create a new C<Error> object and returns it. This is defined for
+syntactic sugar, eg
+
+    die with Some::Error ( ... );
+
+=item record ( [ ARGS ] )
+
+Create a new C<Error> object and returns it. This is defined for
+syntactic sugar, eg
+
+    record Some::Error ( ... )
+	and return;
+
+=back
+
+=head2 STATIC METHODS
+
+=over 4
+
+=item prior ( [ PACKAGE ] )
+
+Return the last error created, or the last error associated with
+C<PACKAGE>
+
+=item flush ( [ PACKAGE ] )
+
+Flush the last error created, or the last error associated with
+C<PACKAGE>.It is necessary to clear the error stack before exiting the
+package or uncaught errors generated using C<record> will be reported.
+
+     $Error->flush;
+
+=cut
+
+=back
+
+=head2 OBJECT METHODS
+
+=over 4
+
+=item stacktrace
+
+If the variable C<$Error::Debug> was non-zero when the error was
+created, then C<stacktrace> returns a string created by calling
+C<Carp::longmess>. If the variable was zero the C<stacktrace> returns
+the text of the error appended with the filename and line number of
+where the error was created, providing the text does not end with a
+newline.
+
+=item object
+
+The object this error was associated with
+
+=item file
+
+The file where the constructor of this error was called from
+
+=item line
+
+The line where the constructor of this error was called from
+
+=item text
+
+The text of the error
+
+=back
+
+=head2 OVERLOAD METHODS
+
+=over 4
+
+=item stringify
+
+A method that converts the object into a string. This method may simply
+return the same as the C<text> method, or it may append more
+information. For example the file name and line number.
+
+By default this method returns the C<-text> argument that was passed to
+the constructor, or the string C<"Died"> if none was given.
+
+=item value
+
+A method that will return a value that can be associated with the
+error. For example if an error was created due to the failure of a
+system call, then this may return the numeric value of C<$!> at the
+time.
+
+By default this method returns the C<-value> argument that was passed
+to the constructor.
+
+=back
+
+=head1 PRE-DEFINED ERROR CLASSES
+
+=over 4
+
+=item Error::Simple
+
+This class can be used to hold simple error strings and values. Its
+constructor takes two arguments. The first is a text value, the second
+is a numeric value. These values are what will be returned by the
+overload methods.
+
+If the text value ends with C<at file line 1> as $@ strings do, then
+this information will be used to set the C<-file> and C<-line> arguments
+of the error object.
+
+This class is used internally if an eval'd block die's with an error
+that is a plain string. (Unless C<$Error::ObjectifyCallback> is modified)
+
+=back
+
+=head1 $Error::ObjectifyCallback
+
+This variable holds a reference to a subroutine that converts errors that
+are plain strings to objects. It is used by Error.pm to convert textual
+errors to objects, and can be overridden by the user.
+
+It accepts a single argument which is a hash reference to named parameters.
+Currently the only named parameter passed is C<'text'> which is the text
+of the error, but others may be available in the future.
+
+For example the following code will cause Error.pm to throw objects of the
+class MyError::Bar by default:
+
+    sub throw_MyError_Bar
+    {
+        my $args = shift;
+        my $err = MyError::Bar->new();
+        $err->{'MyBarText'} = $args->{'text'};
+        return $err;
+    }
+
+    {
+        local $Error::ObjectifyCallback = \&throw_MyError_Bar;
+
+        # Error handling here.
+    }
+
+=head1 KNOWN BUGS
+
+None, but that does not mean there are not any.
+
+=head1 AUTHORS
+
+Graham Barr <gbarr@pobox.com>
+
+The code that inspired me to write this was originally written by
+Peter Seibel <peter@weblogic.com> and adapted by Jesse Glick
+<jglick@sig.bsh.com>.
+
+=head1 MAINTAINER
+
+Shlomi Fish <shlomif@iglu.org.il>
+
+=head1 PAST MAINTAINERS
+
+Arun Kumar U <u_arunkumar@yahoo.com>
+
+=cut