Introduce Git.pm (v4)

This patch introduces a very basic and barebone Git.pm module
with a sketch of how the generic interface would look like;
most functions are missing, but this should give some good base.
I will continue expanding it.

Most desirable now is more careful error reporting, generic_in() for feeding
input to Git commands and the repository() constructor doing some poking
with git-rev-parse to get the git directory and subdirectory prefix.
Those three are basically the prerequisities for converting git-mv.
I will send them as follow-ups to this patch.

Currently Git.pm just wraps up exec()s of Git commands, but even that
is not trivial to get right and various Git perl scripts do it in
various inconsistent ways. In addition to Git.pm, there is now also
Git.xs which provides barebone Git.xs for directly interfacing with
libgit.a, and as an example providing the hash_object() function using
libgit.

This adds the Git module, integrates it to the build system and as
an example converts the git-fmt-merge-msg.perl script to it (the result
is not very impressive since its advantage is not quite apparent in this
one, but I just picked up the simplest Git user around).

Compared to v3, only very minor things were fixed in this patch (some
whitespaces, a missing export, tiny bug in git-fmt-merge-msg.perl);
at first I wanted to post them as a separate patch but since this
is still only in pu, I decided that it will be cleaner to just resend
the patch.

My current working state is available all the time at

	http://pasky.or.cz/~xpasky/git-perl/Git.pm

and an irregularily updated API documentation is at

	http://pasky.or.cz/~xpasky/git-perl/Git.html

Many thanks to Jakub Narebski, Junio and others for their feedback.

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

1 files changed, 408 insertions, 0 deletions

diff --git a/perl/Git.pm b/perl/Git.pm
new file mode 100644
index 000000000..8fff785e0
--- /dev/null
+++ b/perl/Git.pm
@@ -0,0 +1,408 @@
+=head1 NAME
+
+Git - Perl interface to the Git version control system
+
+=cut
+
+
+package Git;
+
+use strict;
+
+
+BEGIN {
+
+our ($VERSION, @ISA, @EXPORT, @EXPORT_OK);
+
+# Totally unstable API.
+$VERSION = '0.01';
+
+
+=head1 SYNOPSIS
+
+  use Git;
+
+  my $version = Git::command_oneline('version');
+
+  Git::command_noisy('update-server-info');
+
+  my $repo = Git->repository (Directory => '/srv/git/cogito.git');
+
+
+  my @revs = $repo->command('rev-list', '--since=last monday', '--all');
+
+  my $fh = $repo->command_pipe('rev-list', '--since=last monday', '--all');
+  my $lastrev = <$fh>; chomp $lastrev;
+  close $fh; # You may want to test rev-list exit status here
+
+  my $lastrev = $repo->command_oneline('rev-list', '--all');
+
+=cut
+
+
+require Exporter;
+
+@ISA = qw(Exporter);
+
+@EXPORT = qw();
+
+# Methods which can be called as standalone functions as well:
+@EXPORT_OK = qw(command command_oneline command_pipe command_noisy
+                hash_object);
+
+
+=head1 DESCRIPTION
+
+This module provides Perl scripts easy way to interface the Git version control
+system. The modules have an easy and well-tested way to call arbitrary Git
+commands; in the future, the interface will also provide specialized methods
+for doing easily operations which are not totally trivial to do over
+the generic command interface.
+
+While some commands can be executed outside of any context (e.g. 'version'
+or 'init-db'), most operations require a repository context, which in practice
+means getting an instance of the Git object using the repository() constructor.
+(In the future, we will also get a new_repository() constructor.) All commands
+called as methods of the object are then executed in the context of the
+repository.
+
+TODO: In the future, we might also do
+
+	my $subdir = $repo->subdir('Documentation');
+	# Gets called in the subdirectory context:
+	$subdir->command('status');
+
+	my $remoterepo = $repo->remote_repository (Name => 'cogito', Branch => 'master');
+	$remoterepo ||= Git->remote_repository ('http://git.or.cz/cogito.git/');
+	my @refs = $remoterepo->refs();
+
+So far, all functions just die if anything goes wrong. If you don't want that,
+make appropriate provisions to catch the possible deaths. Better error recovery
+mechanisms will be provided in the future.
+
+Currently, the module merely wraps calls to external Git tools. In the future,
+it will provide a much faster way to interact with Git by linking directly
+to libgit. This should be completely opaque to the user, though (performance
+increate nonwithstanding).
+
+=cut
+
+
+use Carp qw(carp croak);
+
+require XSLoader;
+XSLoader::load('Git', $VERSION);
+
+}
+
+
+=head1 CONSTRUCTORS
+
+=over 4
+
+=item repository ( OPTIONS )
+
+=item repository ( DIRECTORY )
+
+=item repository ()
+
+Construct a new repository object.
+C<OPTIONS> are passed in a hash like fashion, using key and value pairs.
+Possible options are:
+
+B<Repository> - Path to the Git repository.
+
+B<WorkingCopy> - Path to the associated working copy; not strictly required
+as many commands will happily crunch on a bare repository.
+
+B<Directory> - Path to the Git working directory in its usual setup. This
+is just for convenient setting of both C<Repository> and C<WorkingCopy>
+at once: If the directory as a C<.git> subdirectory, C<Repository> is pointed
+to the subdirectory and the directory is assumed to be the working copy.
+If the directory does not have the subdirectory, C<WorkingCopy> is left
+undefined and C<Repository> is pointed to the directory itself.
+
+B<GitPath> - Path to the C<git> binary executable. By default the C<$PATH>
+is searched for it.
+
+You should not use both C<Directory> and either of C<Repository> and
+C<WorkingCopy> - the results of that are undefined.
+
+Alternatively, a directory path may be passed as a single scalar argument
+to the constructor; it is equivalent to setting only the C<Directory> option
+field.
+
+Calling the constructor with no options whatsoever is equivalent to
+calling it with C<< Directory => '.' >>.
+
+=cut
+
+sub repository {
+	my $class = shift;
+	my @args = @_;
+	my %opts = ();
+	my $self;
+
+	if (defined $args[0]) {
+		if ($#args % 2 != 1) {
+			# Not a hash.
+			$#args == 0 or croak "bad usage";
+			%opts = (Directory => $args[0]);
+		} else {
+			%opts = @args;
+		}
+
+		if ($opts{Directory}) {
+			-d $opts{Directory} or croak "Directory not found: $!";
+			if (-d $opts{Directory}."/.git") {
+				# TODO: Might make this more clever
+				$opts{WorkingCopy} = $opts{Directory};
+				$opts{Repository} = $opts{Directory}."/.git";
+			} else {
+				$opts{Repository} = $opts{Directory};
+			}
+			delete $opts{Directory};
+		}
+	}
+
+	$self = { opts => \%opts };
+	bless $self, $class;
+}
+
+
+=back
+
+=head1 METHODS
+
+=over 4
+
+=item command ( COMMAND [, ARGUMENTS... ] )
+
+Execute the given Git C<COMMAND> (specify it without the 'git-'
+prefix), optionally with the specified extra C<ARGUMENTS>.
+
+The method can be called without any instance or on a specified Git repository
+(in that case the command will be run in the repository context).
+
+In scalar context, it returns all the command output in a single string
+(verbatim).
+
+In array context, it returns an array containing lines printed to the
+command's stdout (without trailing newlines).
+
+In both cases, the command's stdin and stderr are the same as the caller's.
+
+=cut
+
+sub command {
+	my $fh = command_pipe(@_);
+
+	if (not defined wantarray) {
+		_cmd_close($fh);
+
+	} elsif (not wantarray) {
+		local $/;
+		my $text = <$fh>;
+		_cmd_close($fh);
+		return $text;
+
+	} else {
+		my @lines = <$fh>;
+		_cmd_close($fh);
+		chomp @lines;
+		return @lines;
+	}
+}
+
+
+=item command_oneline ( COMMAND [, ARGUMENTS... ] )
+
+Execute the given C<COMMAND> in the same way as command()
+does but always return a scalar string containing the first line
+of the command's standard output.
+
+=cut
+
+sub command_oneline {
+	my $fh = command_pipe(@_);
+
+	my $line = <$fh>;
+	_cmd_close($fh);
+
+	chomp $line;
+	return $line;
+}
+
+
+=item command_pipe ( COMMAND [, ARGUMENTS... ] )
+
+Execute the given C<COMMAND> in the same way as command()
+does but return a pipe filehandle from which the command output can be
+read.
+
+=cut
+
+sub command_pipe {
+	my ($self, $cmd, @args) = _maybe_self(@_);
+
+	$cmd =~ /^[a-z0-9A-Z_-]+$/ or croak "bad command: $cmd";
+
+	my $pid = open(my $fh, "-|");
+	if (not defined $pid) {
+		croak "open failed: $!";
+	} elsif ($pid == 0) {
+		_cmd_exec($self, $cmd, @args);
+	}
+	return $fh;
+}
+
+
+=item command_noisy ( COMMAND [, ARGUMENTS... ] )
+
+Execute the given C<COMMAND> in the same way as command() does but do not
+capture the command output - the standard output is not redirected and goes
+to the standard output of the caller application.
+
+While the method is called command_noisy(), you might want to as well use
+it for the most silent Git commands which you know will never pollute your
+stdout but you want to avoid the overhead of the pipe setup when calling them.
+
+The function returns only after the command has finished running.
+
+=cut
+
+sub command_noisy {
+	my ($self, $cmd, @args) = _maybe_self(@_);
+
+	$cmd =~ /^[a-z0-9A-Z_-]+$/ or croak "bad command: $cmd";
+
+	my $pid = fork;
+	if (not defined $pid) {
+		croak "fork failed: $!";
+	} elsif ($pid == 0) {
+		_cmd_exec($self, $cmd, @args);
+	}
+	if (waitpid($pid, 0) > 0 and $? != 0) {
+		croak "exit status: $?";
+	}
+}
+
+
+=item hash_object ( FILENAME [, TYPE ] )
+
+=item hash_object ( FILEHANDLE [, TYPE ] )
+
+Compute the SHA1 object id of the given C<FILENAME> (or data waiting in
+C<FILEHANDLE>) considering it is of the C<TYPE> object type (C<blob>
+(default), C<commit>, C<tree>).
+
+In case of C<FILEHANDLE> passed instead of file name, all the data
+available are read and hashed, and the filehandle is automatically
+closed. The file handle should be freshly opened - if you have already
+read anything from the file handle, the results are undefined (since
+this function works directly with the file descriptor and internal
+PerlIO buffering might have messed things up).
+
+The method can be called without any instance or on a specified Git repository,
+it makes zero difference.
+
+The function returns the SHA1 hash.
+
+Implementation of this function is very fast; no external command calls
+are involved.
+
+=cut
+
+# Implemented in Git.xs.
+
+
+=back
+
+=head1 TODO
+
+This is still fairly crude.
+We need some good way to report errors back except just dying.
+
+=head1 COPYRIGHT
+
+Copyright 2006 by Petr Baudis E<lt>pasky@suse.czE<gt>.
+
+This module is free software; it may be used, copied, modified
+and distributed under the terms of the GNU General Public Licence,
+either version 2, or (at your option) any later version.
+
+=cut
+
+
+# Take raw method argument list and return ($obj, @args) in case
+# the method was called upon an instance and (undef, @args) if
+# it was called directly.
+sub _maybe_self {
+	# This breaks inheritance. Oh well.
+	ref $_[0] eq 'Git' ? @_ : (undef, @_);
+}
+
+# When already in the subprocess, set up the appropriate state
+# for the given repository and execute the git command.
+sub _cmd_exec {
+	my ($self, @args) = @_;
+	if ($self) {
+		$self->{opts}->{Repository} and $ENV{'GIT_DIR'} = $self->{opts}->{Repository};
+		$self->{opts}->{WorkingCopy} and chdir($self->{opts}->{WorkingCopy});
+	}
+	my $git = $self->{opts}->{GitPath};
+	$git ||= 'git';
+	exec ($git, @args) or croak "exec failed: $!";
+}
+
+# Close pipe to a subprocess.
+sub _cmd_close {
+	my ($fh) = @_;
+	if (not close $fh) {
+		if ($!) {
+			# It's just close, no point in fatalities
+			carp "error closing pipe: $!";
+		} elsif ($? >> 8) {
+			croak "exit status: ".($? >> 8);
+		}
+		# else we might e.g. closed a live stream; the command
+		# dying of SIGPIPE would drive us here.
+	}
+}
+
+
+# Trickery for .xs routines: In order to avoid having some horrid
+# C code trying to do stuff with undefs and hashes, we gate all
+# xs calls through the following and in case we are being ran upon
+# an instance call a C part of the gate which will set up the
+# environment properly.
+sub _call_gate {
+	my $xsfunc = shift;
+	my ($self, @args) = _maybe_self(@_);
+
+	if (defined $self) {
+		# XXX: We ignore the WorkingCopy! To properly support
+		# that will require heavy changes in libgit.
+
+		# XXX: And we ignore everything else as well. libgit
+		# at least needs to be extended to let us specify
+		# the $GIT_DIR instead of looking it up in environment.
+		#xs_call_gate($self->{opts}->{Repository});
+	}
+
+	&$xsfunc(@args);
+}
+
+sub AUTOLOAD {
+	my $xsname;
+	our $AUTOLOAD;
+	($xsname = $AUTOLOAD) =~ s/.*:://;
+	croak "&Git::$xsname not defined" if $xsname =~ /^xs_/;
+	$xsname = 'xs_'.$xsname;
+	_call_gate(\&$xsname, @_);
+}
+
+sub DESTROY { }
+
+
+1; # Famous last words