Add Error.pm to the distribution

I have been thinking about how to do the error reporting the best
way and after scraping various overcomplicated concepts, I have
decided that by far the most elegant way is to throw Error exceptions;
the closest sane alternative is to catch the dies in Git.pm by
enclosing the calls in eval{}s and that's really _quite_ ugly.

The only "small" trouble is that Error.pm turns out sadly not to be
part of the standard distribution, and installation from CPAN is
a bother, especially if you can't install it system-wide. But since
it is very small, I've decided to just bundle it.

Signed-off-by: Petr Baudis <pasky@suse.cz>
Signed-off-by: Junio C Hamano <junkio@cox.net>

2 files changed, 831 insertions, 0 deletions

diff --git a/perl/Error.pm b/perl/Error.pm
new file mode 100644
index 000000000..ebd07498a
--- /dev/null
+++ b/perl/Error.pm
@@ -0,0 +1,821 @@
+# 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
+
+use Scalar::Util ();
+
+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 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]->());
+		    $i -= 2;
+		    next CATCHLOOP;
+		}
+		elsif(Scalar::Util::blessed($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($err))
+    {
+        if (Scalar::Util::blessed($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 it's 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. It's
+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 $@ strings do, then
+this infomation will be used to set the C<-file> and C<-line> arguments
+of the error object.
+
+This class is used internally if an eval'd block die's with an error
+that is a plain string. (Unless C<$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 overrided 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
diff --git a/perl/Makefile.PL b/perl/Makefile.PL
index dd6105677..54e8b20ed 100644
--- a/perl/Makefile.PL
+++ b/perl/Makefile.PL
@@ -8,9 +8,19 @@ instlibdir:
 MAKE_FRAG
 }
 
+my %pm = ('Git.pm' => '$(INST_LIBDIR)/Git.pm');
+
+# We come with our own bundled Error.pm. It's not in the set of default
+# Perl modules so install it if it's not available on the system yet.
+eval { require 'Error' };
+if ($@) {
+	$pm{'Error.pm'} = '$(INST_LIBDIR)/Error.pm';
+}
+
 WriteMakefile(
 	NAME            => 'Git',
 	VERSION_FROM    => 'Git.pm',
+	PM		=> \%pm,
 	MYEXTLIB        => '../libgit.a',
 	INC             => '-I. -I..',
 );