#  from [dfe115d89079ca859e1af838ffd51d6762b6cc76]
#    to [3d6d05502a4790b6651660c84bbba4bac1391ab8]
--- 
+++ 
@@ -0,0 +1,2470 @@
+##############################################################################
+#
+#   File Name    - History.pm
+#
+#   Description  - The history module for the mtn-browse application. This
+#                  module contains all the routines for implementing the
+#                  revision and file history windows.
+#
+#   Author       - A.E.Cooper.
+#
+#   Legal Stuff  - Copyright (c) 2007 Anthony Edward Cooper
+#                  <address@hidden>.
+#
+#                  This program is free software; you can redistribute it
+#                  and/or modify it under the terms of the GNU General Public
+#                  License as published by the Free Software Foundation;
+#                  either version 3 of the License, or (at your option) any
+#                  later version.
+#
+#                  This program is distributed in the hope that it will be
+#                  useful, but WITHOUT ANY WARRANTY; without even the implied
+#                  warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
+#                  PURPOSE. See the GNU General Public License for more
+#                  details.
+#
+#                  You should have received a copy of the GNU General Public
+#                  License along with this software; if not, write to the Free
+#                  Software Foundation, Inc., 59 Temple Place - Suite 330,
+#                  Boston, MA 02111-1307 USA.
+#
+##############################################################################
+#
+##############################################################################
+#
+#   Global Data For This Module
+#
+##############################################################################
+
+
+
+# ***** DIRECTIVES *****
+
+require 5.008005;
+
+use locale;
+use strict;
+use warnings;
+no warnings qw(recursion);
+
+# ***** GLOBAL DATA DECLARATIONS *****
+
+# Constants for the columns within the comparison files ListStore widget.
+
+use constant CLS_FILE_NAME_COLUMN => 0;
+use constant CLS_LINE_NR_COLUMN   => 1;
+use constant CLS_FILE_ID_1_COLUMN => 2;
+use constant CLS_FILE_ID_2_COLUMN => 3;
+
+# The translated history strings.
+
+my $__browse_file           = __("Browse File");
+my $__browse_file_ttip      = __("Browse the file in\na new browser window");
+my $__browse_rev            = __("Browse Revision");
+my $__browse_rev_ttip       = __("Browse the revision in\n"
+				 . "a new browser window");
+my $__full_changelog        = __("Full Change Log");
+my $__full_changelog_ttip   = __("View the revision's full change log");
+my $__select_id_1           = __("Select As Id 1");
+my $__select_id_2           = __("Select As Id 2");
+my $__select_id_file_1_ttip = __("Select this file revision for\n"
+				 . "comparison as the first file");
+my $__select_id_file_2_ttip = __("Select this file revision for\n"
+				 . "comparison as the second file");
+my $__select_id_rev_1_ttip  = __("Select this revision for comparison\n"
+				 . "as the second revision");
+my $__select_id_rev_2_ttip  = __("Select this revision for comparison\n"
+				 . "as the first revision");
+
+# ***** FUNCTIONAL PROTOTYPES *****
+
+# Public routines.
+
+sub display_arbitrary_revision_comparison($);
+sub display_file_change_history($$$);
+sub display_renamed_file_comparison($$$$$$);
+sub display_revision_change_history($$$);
+sub display_revision_comparison($$$;$);
+
+# Private routines.
+
+sub compare_arbitrary_revision_advanced_find_button_clicked_cb($$);
+sub compare_button_clicked_cb($$);
+sub comparison_revision_change_log_button_clicked_cb($$);
+sub external_diffs($$$$$$);
+sub external_diffs_button_clicked_cb($$);
+sub file_comparison_combobox_changed_cb($$);
+sub get_compare_arbitrary_revisions_window();
+sub get_file_history_helper($$$);
+sub get_history_window();
+sub get_revision_comparison_window($);
+sub get_revision_history_helper($$);
+sub history_list_button_clicked_cb($$);
+sub mtn_diff($$$$$;$);
+sub save_differences_button_clicked_cb($$);
+#
+##############################################################################
+#
+#   Routine      - display_revision_change_history
+#
+#   Description  - Display a revision's change history, complete with
+#                  selection and comparison buttons.
+#
+#   Data         - $mtn         : The Monotone::AutomateStdio object that is
+#                                 to be used to get the change history.
+#                  $tag         : Either a tag name for the specified revision
+#                                 that is to be used in the window title
+#                                 instead of the revision id or undef if the
+#                                 revision id should be used.
+#                  $revision_id : The id of the revision that is to have its
+#                                 change log displayed.
+#
+##############################################################################
+
+
+
+sub display_revision_change_history($$$)
+{
+
+    my($mtn, $tag, $revision_id) = @_;
+
+    my($button,
+       @certs_list,
+       $counter,
+       $instance);
+    my $wm = WindowManager->instance();
+
+    $instance = get_history_window();
+    local $instance->{in_cb} = 1;
+
+    $instance->{mtn} = $mtn;
+    $instance->{file_name} = undef;
+    $instance->{first_revision_id} = "";
+    $instance->{second_revision_id} = "";
+    $instance->{window}->set_title(__x("Revision History For {rev}",
+				       rev => defined($tag) ?
+				           $tag : $revision_id));
+    $instance->{history_label}->set_markup(__("<b>Revision History</b>"));
+    $instance->{window}->show_all();
+    $instance->{window}->present();
+
+    $wm->make_busy($instance, 1);
+    $instance->{appbar}->push($instance->{appbar}->get_status()->get_text());
+    $wm->update_gui();
+
+    $instance->{stop_button}->set_sensitive(TRUE);
+
+    # Get the list of file change revisions. Remember to include the current
+    # revision in the history.
+
+    $instance->{appbar}->set_status(__("Fetching revision list"));
+    $wm->update_gui();
+    $instance->{revision_hits} = {};
+    get_revision_history_helper($instance, $revision_id);
+
+    # Sort the list.
+
+    $instance->{appbar}->set_progress_percentage(0.5);
+    $instance->{appbar}->set_status(__("Sorting revision list"));
+    $wm->update_gui();
+    $instance->{history} = [];
+    $instance->{mtn}->toposort($instance->{history},
+			       keys(%{$instance->{revision_hits}}));
+    $instance->{revision_hits} = undef;
+    @{$instance->{history}} = reverse(@{$instance->{history}});
+    $instance->{appbar}->set_progress_percentage(1);
+    $wm->update_gui();
+
+    # Display the file's history.
+
+    $instance->{appbar}->set_progress_percentage(0);
+    $instance->{appbar}->set_status(__("Displaying revision history"));
+    $wm->update_gui();
+    $counter = 0;
+    $instance->{stop} = 0;
+    $instance->{history_buffer}->set_text("");
+    for my $revision_id (@{$instance->{history}})
+    {
+
+	++ $counter;
+
+	# Print out the revision summary.
+
+	$instance->{mtn}->certs(address@hidden, $revision_id);
+	generate_revision_report($instance->{history_buffer},
+				 $revision_id,
+				 address@hidden,
+				 "");
+	$instance->{history_buffer}->
+	    insert($instance->{history_buffer}->get_end_iter(), "\n\n ");
+
+	# Add the buttons.
+
+	$button = Gtk2::Button->new($__select_id_1);
+	$button->signal_connect("clicked",
+				\&history_list_button_clicked_cb,
+				{instance    => $instance,
+				 revision_id => $revision_id,
+				 button_type => "1"});
+	$tooltips->set_tip($button, $__select_id_rev_1_ttip);
+	$instance->{history_textview}->add_child_at_anchor
+	    ($button,
+	     $instance->{history_buffer}->
+	         create_child_anchor($instance->{history_buffer}->
+				     get_end_iter()));
+	$button->show_all();
+	$instance->{history_buffer}->
+	    insert($instance->{history_buffer}->get_end_iter(), " ");
+
+	$button = Gtk2::Button->new($__select_id_2);
+	$button->signal_connect("clicked",
+				\&history_list_button_clicked_cb,
+				{instance    => $instance,
+				 revision_id => $revision_id,
+				 button_type => "2"});
+	$tooltips->set_tip($button, $__select_id_rev_2_ttip);
+	$instance->{history_textview}->add_child_at_anchor
+	    ($button,
+	     $instance->{history_buffer}->
+	         create_child_anchor($instance->{history_buffer}->
+				     get_end_iter()));
+	$button->show_all();
+	$instance->{history_buffer}->
+	    insert($instance->{history_buffer}->get_end_iter(), " ");
+
+	$button = Gtk2::Button->new($__browse_rev);
+	$button->signal_connect("clicked",
+				\&history_list_button_clicked_cb,
+				{instance    => $instance,
+				 revision_id => $revision_id,
+				 button_type => "browse-revision"});
+	$tooltips->set_tip($button, $__browse_rev_ttip);
+	$instance->{history_textview}->add_child_at_anchor
+	    ($button,
+	     $instance->{history_buffer}->
+	         create_child_anchor($instance->{history_buffer}->
+				     get_end_iter()));
+	$button->show_all();
+	$instance->{history_buffer}->
+	    insert($instance->{history_buffer}->get_end_iter(), " ");
+
+	$button = Gtk2::Button->new($__full_changelog);
+	$button->signal_connect("clicked",
+				\&history_list_button_clicked_cb,
+				{instance    => $instance,
+				 revision_id => $revision_id,
+				 button_type => "revision-changelog"});
+	$tooltips->set_tip($button, $__full_changelog_ttip);
+	$instance->{history_textview}->add_child_at_anchor
+	    ($button,
+	     $instance->{history_buffer}->
+	         create_child_anchor($instance->{history_buffer}->
+				     get_end_iter()));
+	$button->show_all();
+
+	if ($counter % 100 == 0)
+	{
+	    $instance->{appbar}->set_progress_percentage
+		($counter / scalar(@{$instance->{history}}));
+	    $wm->update_gui();
+	}
+
+	# Stop if the user wants to.
+
+	last if ($instance->{stop});
+
+	# If we aren't at the end, print out the revision separator.
+
+	if ($counter < scalar(@{$instance->{history}}))
+	{
+	    $instance->{history_buffer}->
+		insert($instance->{history_buffer}->get_end_iter(), "\n");
+	    $instance->{history_buffer}->
+		insert_pixbuf($instance->{history_buffer}->get_end_iter(),
+			      $line_image);
+	    $instance->{history_buffer}->
+		insert($instance->{history_buffer}->get_end_iter(), "\n");
+	}
+
+    }
+    $instance->{appbar}->set_progress_percentage(1);
+    $wm->update_gui();
+
+    $instance->{stop_button}->set_sensitive(FALSE);
+    set_label_value($instance->{numbers_value_label}, $counter)
+	if ($instance->{stop});
+
+    # Make sure we are at the top.
+
+    $instance->{history_buffer}->
+	place_cursor($instance->{history_buffer}->get_start_iter());
+    $instance->{history_scrolledwindow}->get_vadjustment()->set_value(0);
+    $instance->{history_scrolledwindow}->get_hadjustment()->set_value(0);
+    $instance->{appbar}->set_progress_percentage(0);
+    $instance->{appbar}->set_status("");
+    $wm->update_gui();
+
+    $instance->{appbar}->pop();
+    $wm->make_busy($instance, 0);
+
+}
+#
+##############################################################################
+#
+#   Routine      - display_file_change_history
+#
+#   Description  - Display a file's change history, complete with selection
+#                  and comparison buttons.
+#
+#   Data         - $mtn         : The Monotone::AutomateStdio object that is
+#                                 to be used to get the change history.
+#                  $revision_id : The revision id in which the desired version
+#                                 of the file resides.
+#                  $file_name   : The name of the file that is to have its
+#                                 change log displayed.
+#
+##############################################################################
+
+
+
+sub display_file_change_history($$$)
+{
+
+    my($mtn, $revision_id, $file_name) = @_;
+
+    my($button,
+       @certs_list,
+       $counter,
+       $instance);
+    my $wm = WindowManager->instance();
+
+    $instance = get_history_window();
+    local $instance->{in_cb} = 1;
+
+    $instance->{mtn} = $mtn;
+    $instance->{file_name} = $file_name;
+    $instance->{first_revision_id} = "";
+    $instance->{second_revision_id} = "";
+    $instance->{window}->set_title(__x("File History For {file}",
+				       file => $instance->{file_name}));
+    $instance->{history_label}->set_markup(__("<b>File History</b>"));
+    $instance->{window}->show_all();
+    $instance->{window}->present();
+
+    $wm->make_busy($instance, 1);
+    $instance->{appbar}->push($instance->{appbar}->get_status()->get_text());
+    $wm->update_gui();
+
+    # Get the list of file change revisions. Remember that a warning is
+    # generated when one goes back beyond a file's addition revision, so
+    # temporarily disable the warning handler.
+
+    $instance->{appbar}->set_status(__("Fetching revision list"));
+    $instance->{stop_button}->set_sensitive(TRUE);
+    $wm->update_gui();
+    $instance->{revision_hits} = {};
+    {
+	local $suppress_mtn_warnings = 1;
+	get_file_history_helper($instance,
+				$revision_id,
+				\$instance->{file_name});
+    }
+    $instance->{stop_button}->set_sensitive(FALSE);
+
+    # Sort the list.
+
+    $instance->{appbar}->set_progress_percentage(0.5);
+    $instance->{appbar}->set_status(__("Sorting revision list"));
+    $wm->update_gui();
+    $instance->{history} = [];
+    $instance->{mtn}->toposort($instance->{history},
+			       keys(%{$instance->{revision_hits}}));
+    @{$instance->{history}} = reverse(@{$instance->{history}});
+    $instance->{appbar}->set_progress_percentage(1);
+    $wm->update_gui();
+
+    # Display the file's history.
+
+    $instance->{appbar}->set_progress_percentage(0);
+    $instance->{appbar}->set_status(__("Displaying file history"));
+    $wm->update_gui();
+    $counter = 1;
+    $instance->{history_buffer}->set_text("");
+    for my $revision_id (@{$instance->{history}})
+    {
+
+	# Print out the revision summary.
+
+	$instance->{mtn}->certs(address@hidden, $revision_id);
+	generate_revision_report($instance->{history_buffer},
+				 $revision_id,
+				 address@hidden,
+				 "");
+	$instance->{history_buffer}->
+	    insert($instance->{history_buffer}->get_end_iter(), "\n\n ");
+
+	# Add the buttons.
+
+	$button = Gtk2::Button->new($__select_id_1);
+	$button->signal_connect("clicked",
+				\&history_list_button_clicked_cb,
+				{instance    => $instance,
+				 revision_id => $revision_id,
+				 button_type => "1"});
+	$tooltips->set_tip($button, $__select_id_file_1_ttip);
+	$instance->{history_textview}->add_child_at_anchor
+	    ($button,
+	     $instance->{history_buffer}->
+	         create_child_anchor($instance->{history_buffer}->
+				     get_end_iter()));
+	$button->show_all();
+	$instance->{history_buffer}->
+	    insert($instance->{history_buffer}->get_end_iter(), " ");
+
+	$button = Gtk2::Button->new($__select_id_2);
+	$button->signal_connect("clicked",
+				\&history_list_button_clicked_cb,
+				{instance    => $instance,
+				 revision_id => $revision_id,
+				 button_type => "2"});
+	$tooltips->set_tip($button, $__select_id_file_2_ttip);
+	$instance->{history_textview}->add_child_at_anchor
+	    ($button,
+	     $instance->{history_buffer}->
+	         create_child_anchor($instance->{history_buffer}->
+				     get_end_iter()));
+	$button->show_all();
+	$instance->{history_buffer}->
+	    insert($instance->{history_buffer}->get_end_iter(), " ");
+
+	$button = Gtk2::Button->new($__browse_file);
+	$button->signal_connect("clicked",
+				\&history_list_button_clicked_cb,
+				{instance    => $instance,
+				 revision_id => $revision_id,
+				 button_type => "browse-file"});
+	$tooltips->set_tip($button, $__browse_file_ttip);
+	$instance->{history_textview}->add_child_at_anchor
+	    ($button,
+	     $instance->{history_buffer}->
+	         create_child_anchor($instance->{history_buffer}->
+				     get_end_iter()));
+	$button->show_all();
+	$instance->{history_buffer}->
+	    insert($instance->{history_buffer}->get_end_iter(), " ");
+
+	$button = Gtk2::Button->new($__full_changelog);
+	$button->signal_connect("clicked",
+				\&history_list_button_clicked_cb,
+				{instance    => $instance,
+				 revision_id => $revision_id,
+				 button_type => "revision-changelog"});
+	$tooltips->set_tip($button, $__full_changelog_ttip);
+	$instance->{history_textview}->add_child_at_anchor
+	    ($button,
+	     $instance->{history_buffer}->
+	         create_child_anchor($instance->{history_buffer}->
+				     get_end_iter()));
+	$button->show_all();
+
+	# If we aren't at the end, print out the revision separator.
+
+	if ($counter < scalar(@{$instance->{history}}))
+	{
+	    $instance->{history_buffer}->
+		insert($instance->{history_buffer}->get_end_iter(), "\n");
+	    $instance->{history_buffer}->
+		insert_pixbuf($instance->{history_buffer}->get_end_iter(),
+			      $line_image);
+	    $instance->{history_buffer}->
+		insert($instance->{history_buffer}->get_end_iter(), "\n");
+	}
+
+	if (($counter % 10) == 0)
+	{
+	    $instance->{appbar}->set_progress_percentage
+		($counter / scalar(@{$instance->{history}}));
+	    $wm->update_gui();
+	}
+	++ $counter;
+
+    }
+    $instance->{appbar}->set_progress_percentage(1);
+    $wm->update_gui();
+
+    # Make sure we are at the top.
+
+    $instance->{history_buffer}->
+	place_cursor($instance->{history_buffer}->get_start_iter());
+    $instance->{history_scrolledwindow}->get_vadjustment()->set_value(0);
+    $instance->{history_scrolledwindow}->get_hadjustment()->set_value(0);
+    $instance->{appbar}->set_progress_percentage(0);
+    $instance->{appbar}->set_status("");
+    $wm->update_gui();
+
+    $instance->{appbar}->pop();
+    $wm->make_busy($instance, 0);
+
+}
+#
+##############################################################################
+#
+#   Routine      - display_revision_comparison
+#
+#   Description  - Compares and then displays the differences between the two
+#                  specified revisions, optionally restricting it to the
+#                  specified file.
+#
+#   Data         - $mtn           : The Monotone::AutomateStdio object that is
+#                                   to be used to do the comparison.
+#                  $revision_id_1 : The first revision id that is to be
+#                                   compared.
+#                  $revision_id_2 : The second revision id that is to be
+#                                   compared.
+#                  $file_name     : Either the name of the file that the
+#                                   revision comparison should be restricted
+#                                   to or undef for a full revision
+#                                   comparison.
+#
+##############################################################################
+
+
+
+sub display_revision_comparison($$$;$)
+{
+
+    my($mtn, $revision_id_1, $revision_id_2, $file_name) = @_;
+
+    my(@files,
+       $i,
+       $instance,
+       $iter);
+    my $wm = WindowManager->instance();
+
+    $instance = get_revision_comparison_window($mtn);
+    local $instance->{in_cb} = 1;
+
+    $instance->{window}->
+	set_title(__x("Differences Between Revisions {rev_1} and {rev_2}",
+		      rev_1 => $revision_id_1,
+		      rev_2 => $revision_id_2));
+    if (defined($file_name))
+    {
+	$instance->{comparison_label}->
+	    set_markup(__("<b>File Comparison</b>"));
+    }
+    else
+    {
+	$instance->{comparison_label}->
+	    set_markup(__("<b>Revision Comparison</b>"));
+    }
+    $instance->{window}->show_all();
+    $instance->{window}->present();
+
+    $wm->make_busy($instance, 1);
+    $instance->{appbar}->push($instance->{appbar}->get_status()->get_text());
+    $instance->{stop_button}->set_sensitive(TRUE);
+    $wm->update_gui();
+
+    $instance->{mtn} = $mtn;
+    $instance->{revision_id_1} = $revision_id_1;
+    $instance->{revision_id_2} = $revision_id_2;
+
+    # Get Monotone to do the comparison, later versions can do this via
+    # automate stdio.
+
+    $instance->{appbar}->set_status(__("Calculating differences"));
+    $wm->update_gui();
+    if ($mtn->supports(MTN_CONTENT_DIFF_EXTRA_OPTIONS))
+    {
+
+	my $exception;
+
+	local $instance->{kill_mtn_subprocess} = 1;
+
+	# The stop button callback will kill off the mtn subprocess so suppress
+	# any resultant errors.
+
+	$mtn->suppress_utf8_conversion(1);
+	CachingAutomateStdio->register_error_handler
+	    (MTN_SEVERITY_ALL,
+	     sub {
+		 my($severity, $message, $instance) = @_;
+		 mtn_error_handler($severity, $message)
+		     if ($severity == MTN_SEVERITY_WARNING
+			 || ! $instance->{stop});
+	     },
+	     $instance);
+	eval
+	{
+	    $mtn->content_diff($instance->{diff_output},
+			       ["with-header"],
+			       $revision_id_1,
+			       $revision_id_2,
+			       $file_name);
+	};
+	$exception = $@;
+	CachingAutomateStdio->register_error_handler(MTN_SEVERITY_ALL,
+						     \&mtn_error_handler);
+	$mtn->suppress_utf8_conversion(0);
+
+	# If we have aborted the comparison by killing off the mtn subprocess
+	# then cleanly closedown and restart it, otherwise rethrow any raised
+	# exceptions.
+
+	if ($instance->{stop})
+	{
+	    my $dummy;
+	    $mtn->closedown();
+	    $mtn->interface_version(\$dummy);
+	}
+	elsif ($exception)
+	{
+	    die($exception);
+	}
+
+    }
+    else
+    {
+	mtn_diff($instance->{diff_output},
+		 \$instance->{stop},
+		 $mtn->get_db_name(),
+		 $revision_id_1,
+		 $revision_id_2,
+		 $file_name);
+    }
+
+    # Does the user want pretty printed differences output?
+
+    if ($user_preferences->{coloured_diffs})
+    {
+
+	my($char,
+	   $file_id_1,
+	   $file_id_2,
+	   $is_binary,
+	   $len,
+	   $line,
+	   @lines,
+	   $max_len,
+	   $name,
+	   $padding,
+	   $rest,
+	   $separator);
+
+	# Yes the user wants pretty printed differences output.
+
+	@lines = @{$instance->{diff_output}};
+
+	# Find the longest line for future padding, having expanded tabs
+	# (except for file details lines as tab is used as a separator (these
+	# are expanded later)). Please note that the use of unpack un-utf8s the
+	# returned strings.
+
+	$max_len = $separator = 0;
+	foreach my $line (@lines)
+	{
+	    if ($line =~ m/^==/)
+	    {
+		$separator = 1;
+	    }
+	    elsif ($separator)
+	    {
+		$rest = expand(substr($line, 3)) . " ";
+		$max_len = $len if (($len = length($rest)) > $max_len);
+		$separator = 0 if ($line =~ m/^\+\+\+ .+$/);
+	    }
+	    else
+	    {
+		($char, $rest) = unpack("a1a*", $line);
+		eval
+		{
+		    $rest = decode($file_encoding, $rest, Encode::FB_CROAK);
+		};
+		$rest =~ s/\s+$//;
+		$rest = expand($rest);
+		$max_len = $len if (($len = length($rest)) > $max_len);
+		$line = $char . $rest;
+	    }
+	}
+
+	# Display the result, highlighting according to the diff output.
+	# Remember the first two lines are just empty comment lines.
+
+	$instance->{appbar}->
+	    set_status(__("Formatting and displaying differences"));
+	$wm->update_gui();
+	$padding = " " x $max_len;
+	$line = substr(" Summary" . $padding, 0, $max_len);
+	$instance->{comparison_buffer}->insert_with_tags_by_name
+	    ($instance->{comparison_buffer}->get_end_iter(),
+	     $line . "\n",
+	     "compare-info");
+	for ($i = 1; $i < scalar(@lines); ++ $i)
+	{
+
+	    # Deal with the initial comment lines that summarise the entire set
+	    # of differences between the revisions.
+
+	    if ($lines[$i] =~ m/^\#/)
+	    {
+		$line = substr($lines[$i], 1);
+		$instance->{comparison_buffer}->insert
+		    ($instance->{comparison_buffer}->get_end_iter(),
+		     $line . "\n");
+	    }
+
+	    # Deal with lines that introduce a new file comparison.
+
+	    elsif ($lines[$i] =~ m/^==/)
+	    {
+
+		# Check for aborts.
+
+		last if ($instance->{stop});
+
+		# Print separator.
+
+		$instance->{comparison_buffer}->
+		    insert_pixbuf($instance->{comparison_buffer}->
+				      get_end_iter(),
+				  $line_image);
+		$instance->{comparison_buffer}->
+		    insert($instance->{comparison_buffer}->get_end_iter(),
+			   "\n");
+
+		# Attempt to extract the file name and its id, if this doesn't
+		# work then it is probably a comment stating that the file is
+		# binary.
+
+		++ $i;
+		if ($lines[$i] =~ m/^--- (.+)\t[0-9a-f]{40}$/)
+		{
+		    $name = $1;
+		}
+		elsif ($lines[$i + 1] =~ m/^\+\+\+ (.+)\t[0-9a-f]{40}$/)
+		{
+		    $name = $1;
+		}
+		else
+		{
+		    $name = undef;
+		}
+		if (defined($name))
+		{
+		    $is_binary = 0;
+		    if ($lines[$i] =~ m/^--- .+\t([0-9a-f]{40})$/)
+		    {
+			$file_id_1 = $1;
+		    }
+		    else
+		    {
+			$file_id_1 = "";
+		    }
+		    if ($lines[$i + 1] =~ m/^\+\+\+ .+\t([0-9a-f]{40})$/)
+		    {
+			$file_id_2 = $1;
+		    }
+		    else
+		    {
+			$file_id_2 = "";
+		    }
+		}
+		else
+		{
+		    $is_binary = 1;
+		    ($name) = ($lines[$i] =~ m/^\# (.+) is binary$/);
+		    $file_id_1 = $file_id_2 = "";
+		}
+
+		# Print out the details for the first file.
+
+		$line = substr(expand(substr($lines[$i], $is_binary ? 1 : 3))
+			           . $padding,
+			       0,
+			       $max_len);
+		$instance->{comparison_buffer}->insert_with_tags_by_name
+		    ($instance->{comparison_buffer}->get_end_iter(),
+		     $line . "\n",
+		     "compare-file-info-1");
+
+		# Store the file name and the starting line number so that the
+		# user can later jump straight to it using the file combobox.
+
+		$iter = $instance->{comparison_buffer}->get_end_iter();
+		$iter->backward_line();
+		push(@files, {file_name => $name,
+			      line_nr   => $iter->get_line(),
+			      file_id_1 => $file_id_1,
+			      file_id_2 => $file_id_2});
+
+		# Print out the details for the second file if there is one.
+
+		if (! $is_binary)
+		{
+		    ++ $i;
+		    $line = substr(expand(substr($lines[$i], 3)) . $padding,
+				   0,
+				   $max_len);
+		    $instance->{comparison_buffer}->insert_with_tags_by_name
+			($instance->{comparison_buffer}->get_end_iter(),
+			 $line . "\n",
+			 "compare-file-info-2");
+		}
+
+	    }
+
+	    # Deal with difference context lines.
+
+	    elsif ($lines[$i] =~ m/^@@/)
+	    {
+		$line = substr(substr($lines[$i], 2) . $padding, 0, $max_len);
+		$instance->{comparison_buffer}->insert_with_tags_by_name
+		    ($instance->{comparison_buffer}->get_end_iter(),
+		     $line . "\n",
+		     "compare-info");
+	    }
+
+	    # Deal with - change lines.
+
+	    elsif ($lines[$i] =~ m/^-/)
+	    {
+		$line = substr(substr($lines[$i], 1) . $padding, 0, $max_len);
+		$instance->{comparison_buffer}->insert_with_tags_by_name
+		    ($instance->{comparison_buffer}->get_end_iter(),
+		     $line . "\n",
+		     "compare-file-1");
+	    }
+
+	    # Deal with + change lines.
+
+	    elsif ($lines[$i] =~ m/^\+/)
+	    {
+		$line = substr(substr($lines[$i], 1) . $padding, 0, $max_len);
+		$instance->{comparison_buffer}->insert_with_tags_by_name
+		    ($instance->{comparison_buffer}->get_end_iter(),
+		     $line . "\n",
+		     "compare-file-2");
+	    }
+
+	    # Print out the rest.
+
+	    else
+	    {
+		$line = substr($lines[$i], 1);
+		$instance->{comparison_buffer}->insert
+		    ($instance->{comparison_buffer}->get_end_iter(),
+		     $line . "\n");
+	    }
+
+	    if (($i % 100) == 0)
+	    {
+		$instance->{appbar}->set_progress_percentage
+		    (($i + 1) / scalar(@lines));
+		$wm->update_gui();
+	    }
+
+	}
+
+    }
+    else
+    {
+
+	my($file_id_1,
+	   $file_id_2,
+	   $is_binary,
+	   $name);
+
+	# No the user wants the raw differences output.
+
+	# Display the result, storing the locations of the files.
+
+	$instance->{appbar}->set_status(__("Displaying differences"));
+	$wm->update_gui();
+	for ($i = 0; $i < scalar(@{$instance->{diff_output}}); ++ $i)
+	{
+
+	    # Deal with lines that introduce a new file comparison.
+
+	    if ($instance->{diff_output}->[$i] =~ m/^==/)
+	    {
+
+		# Check for aborts.
+
+		last if ($instance->{stop});
+
+		# Extract the file name, if this doesn't work then it is
+		# probably a comment stating that the file is binary.
+
+		++ $i;
+		if ($instance->{diff_output}->[$i] =~
+		    m/^--- (.+)\t[0-9a-f]{40}$/)
+		{
+		    $name = $1;
+		}
+		elsif ($instance->{diff_output}->[$i + 1] =~
+		       m/^\+\+\+ (.+)\t[0-9a-f]{40}$/)
+		{
+		    $name = $1;
+		}
+		else
+		{
+		    $name = undef;
+		}
+		if (defined($name))
+		{
+		    $is_binary = 0;
+		    if ($instance->{diff_output}->[$i] =~
+			m/^--- .+\t([0-9a-f]{40})$/)
+		    {
+			$file_id_1 = $1;
+		    }
+		    else
+		    {
+			$file_id_1 = "";
+		    }
+		    if ($instance->{diff_output}->[$i + 1]
+			=~ m/^\+\+\+ .+\t([0-9a-f]{40})$/)
+		    {
+			$file_id_2 = $1;
+		    }
+		    else
+		    {
+			$file_id_2 = "";
+		    }
+		}
+		else
+		{
+		    ($name) = ($instance->{diff_output}->[$i] =~
+			       m/^\# (.+) is binary$/);
+		    $is_binary = 1;
+		    $file_id_1 = $file_id_2 = "";
+		}
+
+		# Print out the details for the first file.
+
+		$instance->{comparison_buffer}->insert
+		    ($instance->{comparison_buffer}->get_end_iter(),
+		     $instance->{diff_output}->[$i] . "\n");
+
+		# Store the file name and the starting line number so that the
+		# user can later jump straight to it using the file combobox.
+
+		$iter = $instance->{comparison_buffer}->get_end_iter();
+		$iter->backward_line();
+		push(@files, {file_name => $name,
+			      line_nr   => $iter->get_line(),
+			      file_id_1 => $file_id_1,
+			      file_id_2 => $file_id_2});
+
+		# Print out the details for the second file if there is one.
+
+		if (! $is_binary)
+		{
+		    ++ $i;
+		    $instance->{comparison_buffer}->insert
+			($instance->{comparison_buffer}->get_end_iter(),
+			 $instance->{diff_output}->[$i] . "\n");
+		}
+
+	    }
+
+	    # Print out the rest.
+
+	    else
+	    {
+		my $line = $instance->{diff_output}->[$i];
+		eval
+		{
+		    $line = decode($file_encoding, $line, Encode::FB_CROAK);
+		};
+		$instance->{comparison_buffer}->insert
+		    ($instance->{comparison_buffer}->get_end_iter(),
+		     $line . "\n");
+	    }
+
+	    if (($i % 100) == 0)
+	    {
+		$instance->{appbar}->set_progress_percentage
+		    (($i + 1) / scalar(@{$instance->{diff_output}}));
+		$wm->update_gui();
+	    }
+
+	}
+
+    }
+
+    $instance->{appbar}->set_progress_percentage(1);
+    $wm->update_gui();
+
+    $instance->{stop_button}->set_sensitive(FALSE);
+
+    # Delete the trailing newline.
+
+    $iter = $instance->{comparison_buffer}->get_end_iter();
+    $instance->{comparison_buffer}->delete
+	($iter, $instance->{comparison_buffer}->get_end_iter())
+	if ($iter->backward_char());
+
+    # Populate the file combobox.
+
+    $instance->{appbar}->set_progress_percentage(0);
+    $instance->{appbar}->set_status(__("Populating file list"));
+    $wm->update_gui();
+    @files = sort({ $a->{file_name} cmp $b->{file_name} } @files);
+    $i = 1;
+    $instance->{file_comparison_combobox}->get_model()->clear();
+    $instance->{file_comparison_combobox}->get_model()->set
+	($instance->{file_comparison_combobox}->get_model()->append(),
+	 CLS_FILE_NAME_COLUMN, __("Summary"),
+	 CLS_LINE_NR_COLUMN,
+	     $instance->{comparison_buffer}->get_start_iter()->get_line(),
+	 CLS_FILE_ID_1_COLUMN, "",
+	 CLS_FILE_ID_2_COLUMN, "");
+    foreach my $file (@files)
+    {
+	$instance->{file_comparison_combobox}->get_model()->set
+	    ($instance->{file_comparison_combobox}->get_model()->append(),
+	     CLS_FILE_NAME_COLUMN, $file->{file_name},
+	     CLS_LINE_NR_COLUMN, $file->{line_nr},
+	     CLS_FILE_ID_1_COLUMN, $file->{file_id_1},
+	     CLS_FILE_ID_2_COLUMN, $file->{file_id_2});
+	if (($i % 10) == 0)
+	{
+	    $instance->{appbar}->set_progress_percentage($i / scalar(@files));
+	    $wm->update_gui();
+	}
+	++ $i;
+    }
+    $instance->{file_comparison_combobox}->set_active(0);
+    $instance->{appbar}->set_progress_percentage(1);
+
+    # Make sure we are at the top.
+
+    $instance->{comparison_buffer}->
+	place_cursor($instance->{comparison_buffer}->get_start_iter());
+    $instance->{comparison_scrolledwindow}->get_vadjustment()->set_value(0);
+    $instance->{comparison_scrolledwindow}->get_hadjustment()->set_value(0);
+    $wm->update_gui();
+
+    # Move to the file if a file comparison is being done.
+
+    if (defined($file_name) && scalar(@files) > 0)
+    {
+
+	# Simply let the combobox's change callback fire after setting its
+	# value.
+
+	local $instance->{in_cb} = 0;
+	$instance->{file_comparison_combobox}->set_active(1);
+	$wm->update_gui();
+
+    }
+
+    $instance->{appbar}->set_progress_percentage(0);
+    $instance->{appbar}->set_status("");
+    $wm->update_gui();
+
+    $instance->{appbar}->pop();
+    $wm->make_busy($instance, 0);
+
+}
+#
+##############################################################################
+#
+#   Routine      - display_renamed_file_comparison
+#
+#   Description  - Compares and then displays the differences between two
+#                  versions of a file that has either been renamed or moved
+#                  somewhere between the specified revisions. The comparison
+#                  has to be done with the external helper application.
+#
+#   Data         - $parent          : The parent window widget for any dialogs
+#                                     that may appear.
+#                  $mtn             : The Monotone::AutomateStdio object that
+#                                     is to be used to get the files' details.
+#                  $old_revision_id : The revision id for the older revision.
+#                  $old_file_name   : The name of the file on the older
+#                  $new_revision_id : The revision id for the newer revision.
+#                  $new_file_name   : The name of the file on the newer
+#                                     revision.
+#
+##############################################################################
+
+
+
+sub display_renamed_file_comparison($$$$$$)
+{
+
+    my($parent,
+       $mtn,
+       $old_revision_id,
+       $old_file_name,
+       $new_revision_id,
+       $new_file_name) = @_;
+
+    my($answer,
+       $dialog,
+       @manifest,
+       $new_file_id,
+       $old_file_id);
+    my $wm = WindowManager->instance();
+
+    $dialog = Gtk2::MessageDialog->new
+	($parent,
+	 ["modal"],
+	 "question",
+	 "yes-no",
+	 __("The name of the selected file has changed\n"
+	    . "between the two selected revisions and cannot\n"
+	    . "be compared internally. Would you like to do\n"
+	    . "the comparison using the external helper application?"));
+    $dialog->set_title(__("External Comparison"));
+    $wm->allow_input(sub { $answer = $dialog->run(); });
+    $dialog->destroy();
+
+    # Only continue if asked to do so.
+
+    if ($answer eq "yes")
+    {
+
+	# Get the manifests of the two revisions and look for the files in
+	# order to get their file ids.
+
+	$mtn->get_manifest_of(address@hidden, $old_revision_id);
+	foreach my $entry (@manifest)
+	{
+	    if ($entry->{name} eq $old_file_name)
+	    {
+		$old_file_id = $entry->{file_id};
+		last;
+	    }
+	}
+	$mtn->get_manifest_of(address@hidden, $new_revision_id);
+	foreach my $entry (@manifest)
+	{
+	    if ($entry->{name} eq $new_file_name)
+	    {
+		$new_file_id = $entry->{file_id};
+		last;
+	    }
+	}
+
+	# Make sure we have the file ids.
+
+	if (! defined($old_file_id) || ! defined ($new_file_id))
+	{
+	    my $dialog;
+	    $dialog = Gtk2::MessageDialog->new
+		($parent,
+		 ["modal"],
+		 "warning",
+		 "close",
+		 __("The file contents cannot be\n"
+		    . "found in the selected revisions.\n"
+		    . "This should not be happening."));
+	    $wm->allow_input(sub { $dialog->run(); });
+	    $dialog->destroy();
+	    return;
+	}
+
+	# Use the external helper application to compare the files.
+
+	external_diffs($parent,
+		       $mtn,
+		       $old_file_name,
+		       $old_file_id,
+		       $new_file_name,
+		       $new_file_id);
+
+    }
+
+}
+#
+##############################################################################
+#
+#   Routine      - display_arbitrary_revision_comparison
+#
+#   Description  - Display a window that allows the user to select two
+#                  arbitrary revisions for comparison.
+#
+#   Data         - $mtn : The Monotone::AutomateStdio object that is to be
+#                         used to do the comparison.
+#
+##############################################################################
+
+
+
+sub display_arbitrary_revision_comparison($)
+{
+
+    my $mtn = $_[0];
+
+    my $instance;
+
+    $instance = get_compare_arbitrary_revisions_window();
+    local $instance->{in_cb} = 1;
+
+    $instance->{mtn} = $mtn;
+    $instance->{first_revision_id} = "";
+    $instance->{second_revision_id} = "";
+
+}
+#
+##############################################################################
+#
+#   Routine      - history_list_button_clicked_cb
+#
+#   Description  - Callback routine called when the user clicks on any of the
+#                  buttons displayed in the history list in a history window.
+#
+#   Data         - $widget  : The widget object that received the signal.
+#                  $details : A reference to an anonymous hash containing the
+#                             window instance, revision and action that is
+#                             associated with this widget.
+#
+##############################################################################
+
+
+
+sub history_list_button_clicked_cb($$)
+{
+
+    my($widget, $details) = @_;
+
+    my($instance,
+       $revision_id);
+
+    $instance = $details->{instance};
+    $revision_id = $details->{revision_id};
+
+    return if ($instance->{in_cb});
+    local $instance->{in_cb} = 1;
+
+    if ($details->{button_type} eq "1" || $details->{button_type} eq "2")
+    {
+	if ($details->{button_type} eq "1")
+	{
+	    $instance->{first_revision_id} = $revision_id;
+	    set_label_value($instance->{revision_id_1_value_label},
+			    $revision_id);
+	    if ($instance->{first_revision_id}
+		eq $instance->{second_revision_id})
+	    {
+		$instance->{second_revision_id} = "";
+		set_label_value($instance->{revision_id_2_value_label}, "");
+	    }
+	}
+	else
+	{
+	    $instance->{second_revision_id} = $revision_id;
+	    set_label_value($instance->{revision_id_2_value_label},
+			    $revision_id);
+	    if ($instance->{second_revision_id}
+		eq $instance->{first_revision_id})
+	    {
+		$instance->{first_revision_id} = "";
+		set_label_value($instance->{revision_id_1_value_label}, "");
+	    }
+	}
+	if ($instance->{first_revision_id} ne ""
+	    && $instance->{second_revision_id} ne "")
+	{
+	    $instance->{compare_button}->set_sensitive(TRUE);
+	}
+	else
+	{
+	    $instance->{compare_button}->set_sensitive(FALSE);
+	}
+    }
+    elsif ($details->{button_type} eq "browse-revision")
+    {
+
+	my($branch,
+	   @certs_list);
+
+	# First find out what branch the revision is on (take the first one).
+
+	$instance->{mtn}->certs(address@hidden, $revision_id);
+	$branch = "";
+	foreach my $cert (@certs_list)
+	{
+	    if ($cert->{name} eq "branch")
+	    {
+		$branch = $cert->{value};
+		last;
+	    }
+	}
+
+	# Get a new browser window preloaded with the desired file.
+
+	get_browser_window($instance->{mtn}, $branch, $revision_id);
+
+    }
+    elsif ($details->{button_type} eq "browse-file")
+    {
+
+	my($branch,
+	   @certs_list,
+	   $dir,
+	   $file,
+	   $path_ref);
+
+	# First find out what branch the revision is on (take the first one).
+
+	$instance->{mtn}->certs(address@hidden, $revision_id);
+	$branch = "";
+	foreach my $cert (@certs_list)
+	{
+	    if ($cert->{name} eq "branch")
+	    {
+		$branch = $cert->{value};
+		last;
+	    }
+	}
+
+	# Split the file name into directory and file components.
+
+	$path_ref = $instance->{revision_hits}->{$revision_id};
+	$dir = dirname($$path_ref);
+	$dir = "" if ($dir eq ".");
+	$file = basename($$path_ref);
+
+	# Get a new browser window preloaded with the desired file.
+
+	get_browser_window($instance->{mtn},
+			   $branch,
+			   $revision_id,
+			   $dir,
+			   $file);
+
+    }
+    else
+    {
+
+	# Display the full revision change log.
+
+	display_change_log($instance->{mtn}, $revision_id);
+
+    }
+
+}
+#
+##############################################################################
+#
+#   Routine      - compare_arbitrary_revision_advanced_find_button_clicked_cb
+#
+#   Description  - Callback routine called when the user clicks on either of
+#                  the advanced find buttons displayed in the compare
+#                  arbitrary revisions window.
+#
+#   Data         - $widget  : The widget object that received the signal.
+#                  $details : A reference to an anonymous hash containing the
+#                             window instance and the number of the button
+#                             pressed.
+#
+##############################################################################
+
+
+
+sub compare_arbitrary_revision_advanced_find_button_clicked_cb($$)
+{
+
+    my($widget, $details) = @_;
+
+    my(@dummy,
+       $instance,
+       $revision_id);
+
+    $instance = $details->{instance};
+
+    return if ($instance->{in_cb});
+    local $instance->{in_cb} = 1;
+
+    # Let the user choose the revision (we aren't interested in the branch
+    # name(s)) and then store and display the result.
+
+    if (advanced_find($instance, \$revision_id, address@hidden))
+    {
+	if ($details->{button} == 1)
+	{
+	    $instance->{first_revision_id} = $revision_id;
+	    set_label_value($instance->{arbitrary_revision_id_1_value_label},
+			    $revision_id);
+	    if ($instance->{first_revision_id}
+		eq $instance->{second_revision_id})
+	    {
+		$instance->{second_revision_id} = "";
+		set_label_value
+		    ($instance->{arbitrary_revision_id_2_value_label}, "");
+	    }
+	}
+	else
+	{
+	    $instance->{second_revision_id} = $revision_id;
+	    set_label_value($instance->{arbitrary_revision_id_2_value_label},
+			    $revision_id);
+	    if ($instance->{second_revision_id}
+		eq $instance->{first_revision_id})
+	    {
+		$instance->{first_revision_id} = "";
+		set_label_value
+		    ($instance->{arbitrary_revision_id_1_value_label}, "");
+	    }
+	}
+	if ($instance->{first_revision_id} ne ""
+	    && $instance->{second_revision_id} ne "")
+	{
+	    $instance->{arbitrary_compare_button}->set_sensitive(TRUE);
+	}
+	else
+	{
+	    $instance->{arbitrary_compare_button}->set_sensitive(FALSE);
+	}
+    }
+
+}
+#
+##############################################################################
+#
+#   Routine      - compare_button_clicked_cb
+#
+#   Description  - Callback routine called when the user clicks on the
+#                  revision comparison button in a history window.
+#
+#   Data         - $widget   : The widget object that received the signal.
+#                  $instance : The window instance that is associated with
+#                              this widget.
+#
+##############################################################################
+
+
+
+sub compare_button_clicked_cb($$)
+{
+
+    my($widget, $instance) = @_;
+
+    return if ($instance->{in_cb});
+    local $instance->{in_cb} = 1;
+
+    my @revision_ids;
+
+    # Sort the revisions by date, oldest first.
+
+    @revision_ids = ($instance->{first_revision_id},
+		     $instance->{second_revision_id});
+    $instance->{mtn}->toposort(address@hidden, @revision_ids);
+
+    # If a file is being compared and it has been renamed between the two
+    # comparison revisions then we have to fall back on the external helper
+    # application, otherwise we can use Monotone's comparison feature.
+
+    if (defined($instance->{file_name})
+	&& $instance->{revision_hits}->{$revision_ids[0]}
+	!= $instance->{revision_hits}->{$revision_ids[1]})
+    {
+	display_renamed_file_comparison($instance->{window},
+					$instance->{mtn},
+					$revision_ids[0],
+					${$instance->{revision_hits}->
+					  {$revision_ids[0]}},
+					$revision_ids[1],
+					${$instance->{revision_hits}->
+					  {$revision_ids[1]}});
+    }
+    else
+    {
+
+	# Use Monotone's comparison feature.
+
+	display_revision_comparison($instance->{mtn},
+				    $revision_ids[0],
+				    $revision_ids[1],
+				    defined($instance->{file_name})
+				        ? ${$instance->{revision_hits}->
+					    {$revision_ids[0]}}
+				        : undef);
+
+    }
+
+}
+#
+##############################################################################
+#
+#   Routine      - file_comparison_combobox_changed_cb
+#
+#   Description  - Callback routine called when the user changes the value of
+#                  the file combobox by selecting an entry from its pulldown
+#                  list in a revision comparison window.
+#
+#   Data         - $widget   : The widget object that received the signal.
+#                  $instance : The window instance that is associated with
+#                              this widget.
+#
+##############################################################################
+
+
+
+sub file_comparison_combobox_changed_cb($$)
+{
+
+    my($widget, $instance) = @_;
+
+    return if ($instance->{in_cb});
+    local $instance->{in_cb} = 1;
+
+    my($iter,
+       $line_iter,
+       $line_nr);
+
+    # Get the line number related to the selected file and then jump to it.
+
+    $iter = $instance->{file_comparison_combobox}->get_active_iter();
+    $line_nr = $instance->{file_comparison_combobox}->get_model()->
+	get($iter, CLS_LINE_NR_COLUMN);
+    $line_iter = $instance->{comparison_buffer}->get_iter_at_line($line_nr);
+    $instance->{comparison_textview}->
+	scroll_to_iter($line_iter, 0, TRUE, 0, 0);
+
+    # Only enable the external differences button if an actual file is
+    # selected.
+
+    if ($line_nr > 0)
+    {
+	my $file_id_1 = $instance->{file_comparison_combobox}->get_model()->
+	    get($iter, CLS_FILE_ID_1_COLUMN);
+	my $file_id_2 = $instance->{file_comparison_combobox}->get_model()->
+	    get($iter, CLS_FILE_ID_2_COLUMN);
+	if ($file_id_1 ne "" && $file_id_2 ne "" && $file_id_1 ne $file_id_2)
+	{
+	    $instance->{external_diffs_button}->set_sensitive(TRUE);
+	}
+	else
+	{
+	    $instance->{external_diffs_button}->set_sensitive(FALSE);
+	}
+    }
+    else
+    {
+	$instance->{external_diffs_button}->set_sensitive(FALSE);
+    }
+
+}
+#
+##############################################################################
+#
+#   Routine      - external_diffs_button_clicked_cb
+#
+#   Description  - Callback routine called when the user clicks on the
+#                  external differences button in a revision comparison
+#                  window.
+#
+#   Data         - $widget   : The widget object that received the signal.
+#                  $instance : The window instance that is associated with
+#                              this widget.
+#
+##############################################################################
+
+
+
+sub external_diffs_button_clicked_cb($$)
+{
+
+    my($widget, $instance) = @_;
+
+    return if ($instance->{in_cb});
+    local $instance->{in_cb} = 1;
+
+    my($file_id_1,
+       $file_id_2,
+       $file_name,
+       $iter);
+
+    # Get the details associated with the currently selected file.
+
+    $iter = $instance->{file_comparison_combobox}->get_active_iter();
+    $file_name = $instance->{file_comparison_combobox}->get_model()->
+	get($iter, CLS_FILE_NAME_COLUMN);
+    $file_id_1 = $instance->{file_comparison_combobox}->get_model()->
+	get($iter, CLS_FILE_ID_1_COLUMN);
+    $file_id_2 = $instance->{file_comparison_combobox}->get_model()->
+	get($iter, CLS_FILE_ID_2_COLUMN);
+
+    # Use the external helper application to compare the files.
+
+    external_diffs($instance->{window},
+		   $instance->{mtn},
+		   $file_name,
+		   $file_id_1,
+		   $file_name,
+		   $file_id_2);
+
+}
+#
+##############################################################################
+#
+#   Routine      - save_differences_button_clicked_cb
+#
+#   Description  - Callback routine called when the user clicks on the save
+#                  differences button in a revision comparison window.
+#
+#   Data         - $widget   : The widget object that received the signal.
+#                  $instance : The window instance that is associated with
+#                              this widget.
+#
+##############################################################################
+
+
+
+sub save_differences_button_clicked_cb($$)
+{
+
+    my($widget, $instance) = @_;
+
+    return if ($instance->{in_cb});
+    local $instance->{in_cb} = 1;
+
+    my $data;
+
+    $data = join("\n", @{$instance->{diff_output}}) . "\n";
+    save_as_file($instance->{window}, __("unified_diff.patch"), \$data);
+
+}
+#
+##############################################################################
+#
+#   Routine      - comparison_revision_change_log_button_clicked_cb
+#
+#   Description  - Callback routine called when the user clicks on either of
+#                  the two revision change log buttons in a revision
+#                  comparison window.
+#
+#   Data         - $widget  : The widget object that received the signal.
+#                  $details : A reference to an anonymous hash containing the
+#                             window instance, revision and action that is
+#                             associated with this widget.
+#
+##############################################################################
+
+
+
+sub comparison_revision_change_log_button_clicked_cb($$)
+{
+
+    my($widget, $instance) = @_;
+
+    return if ($instance->{in_cb});
+    local $instance->{in_cb} = 1;
+
+    my($colour,
+       $revision_id,
+       $revision_name);
+
+    # Work out what to do.
+
+    if ($widget == $instance->{revision_change_log_1_button})
+    {
+	$revision_id = $instance->{revision_id_1};
+	if ($user_preferences->{coloured_diffs})
+	{
+	    $colour = "compare-1";
+	}
+	else
+	{
+	    $revision_name = "- " . $revision_id;
+	}
+    }
+    else
+    {
+	$revision_id = $instance->{revision_id_2};
+	if ($user_preferences->{coloured_diffs})
+	{
+	    $colour = "compare-2";
+	}
+	else
+	{
+	    $revision_name = "+ " . $revision_id;
+	}
+    }
+
+    # Display the full revision change log.
+
+    display_change_log($instance->{mtn},
+		       $revision_id,
+		       $colour,
+		       $revision_name);
+
+}
+#
+##############################################################################
+#
+#   Routine      - get_history_window
+#
+#   Description  - Creates or prepares an existing history window for use.
+#
+#   Data         - Return Value : A reference to the newly created or unused
+#                                 history instance record.
+#
+##############################################################################
+
+
+
+sub get_history_window()
+{
+
+    my $instance;
+    my $window_type = "history_window";
+    my $wm = WindowManager->instance();
+
+    # Create a new history window if an unused one wasn't found, otherwise
+    # reuse an existing unused one.
+
+    if (! defined($instance = $wm->find_unused($window_type)))
+    {
+	$instance = {};
+	$instance->{glade} = Gtk2::GladeXML->new($glade_file,
+						 $window_type,
+						 APPLICATION_NAME);
+
+	# Flag to stop recursive calling of callbacks.
+
+	$instance->{in_cb} = 0;
+	local $instance->{in_cb} = 1;
+
+	# Connect Glade registered signal handlers.
+
+	glade_signal_autoconnect($instance->{glade}, $instance);
+
+	# Get the widgets that we are interested in.
+
+	$instance->{window} = $instance->{glade}->get_widget($window_type);
+	foreach my $widget ("appbar",
+			    "history_label",
+			    "history_textview",
+			    "history_scrolledwindow",
+			    "stop_button",
+			    "compare_button",
+			    "numbers_value_label",
+			    "revision_id_1_value_label",
+			    "revision_id_2_value_label")
+	{
+	    $instance->{$widget} = $instance->{glade}->get_widget($widget);
+	}
+
+	# Setup the history callbacks.
+
+	$instance->{window}->signal_connect
+	    ("delete_event",
+	     sub {
+		 my($widget, $event, $instance) = @_;
+		 return TRUE if ($instance->{in_cb});
+		 local $instance->{in_cb} = 1;
+		 hide_find_text($instance->{history_textview});
+		 $widget->hide();
+		 $instance->{history_buffer}->set_text("");
+		 $instance->{history} = undef;
+		 $instance->{revision_hits} = undef;
+		 $instance->{mtn} = undef;
+		 return TRUE;
+	     },
+	     $instance);
+	$instance->{stop_button}->signal_connect
+	    ("clicked", sub { $_[1]->{stop} = 1; }, $instance);
+
+	# Setup the history viewer.
+
+	$instance->{history_buffer} =
+	    $instance->{history_textview}->get_buffer();
+	create_format_tags($instance->{history_buffer});
+	$instance->{history_textview}->modify_font($mono_font);
+
+	# Register the window for management and set up the help callbacks.
+
+	$wm->manage($instance,
+		    $window_type,
+		    $instance->{window},
+		    $instance->{stop_button});
+	register_help_callbacks
+	    ($instance,
+	     {widget   => "stop_button",
+	      help_ref => __("mtnb-lachc-history-buttons")},
+	     {widget   => "compare_button",
+	      help_ref => __("mtnb-lachc-history-buttons")},
+	     {widget   => undef,
+	      help_ref => __("mtnb-lachc-the-revision-and-file-history-"
+			     . "windows")});
+    }
+    else
+    {
+	my($height,
+	   $width);
+	$instance->{in_cb} = 0;
+	local $instance->{in_cb} = 1;
+	($width, $height) = $instance->{window}->get_default_size();
+	$instance->{window}->resize($width, $height);
+	$instance->{stop_button}->set_sensitive(FALSE);
+	$instance->{compare_button}->set_sensitive(FALSE);
+	set_label_value($instance->{numbers_value_label}, "");
+	set_label_value($instance->{revision_id_1_value_label}, "");
+	set_label_value($instance->{revision_id_2_value_label}, "");
+	$instance->{appbar}->set_progress_percentage(0);
+	$instance->{appbar}->clear_stack();
+    }
+
+    $instance->{stop} = 0;
+
+    # Empty out the contents.
+
+    $instance->{history_buffer}->set_text("");
+
+    return $instance;
+
+}
+#
+##############################################################################
+#
+#   Routine      - get_file_history_helper
+#
+#   Description  - Recursive routine for getting the revisions in a file's
+#                  change history.
+#
+#   Data         - $instance      : The file history window instance.
+#                  $revision_id   : The revision id from where the search is
+#                                   to commence.
+#                  $file_name_ref : A reference to the name of the file that
+#                                   is to have its history returned.
+#
+##############################################################################
+
+
+
+sub get_file_history_helper($$$)
+{
+
+    my($instance, $revision_id, $file_name_ref) = @_;
+
+    return if ($instance->{stop});
+
+    my @changed_ancestors;
+
+    $instance->{mtn}->get_content_changed(address@hidden,
+					  $revision_id,
+					  $$file_name_ref);
+    foreach my $chg_ancestor (@changed_ancestors)
+    {
+	if (! exists($instance->{revision_hits}->{$chg_ancestor}))
+	{
+
+	    my @parents;
+
+	    # Track file renames in the changed ancestor revisions (no need to
+	    # bother if the ancestor revision is the same as the current one as
+	    # we were passed the file name).
+
+	    if ($chg_ancestor ne $revision_id)
+	    {
+		my $file_name;
+		$instance->{mtn}->
+		    get_corresponding_path(\$file_name,
+					   $revision_id,
+					   $$file_name_ref,
+					   $chg_ancestor);
+		$file_name_ref = \$file_name
+		    if ($file_name ne $$file_name_ref);
+	    }
+
+	    # Store a reference to the current file name in the revision hit
+	    # hash, this can be used later to refer to the correct file name
+	    # for a given changed ancestor revision.
+
+	    $instance->{revision_hits}->{$chg_ancestor} = $file_name_ref;
+
+	    set_label_value($instance->{numbers_value_label},
+			    scalar(keys(%{$instance->{revision_hits}})));
+	    WindowManager->update_gui();
+
+	    # Now repeat for each parent, remembering to track file renames.
+
+	    $instance->{mtn}->parents(address@hidden, $chg_ancestor);
+	    foreach my $parent (@parents)
+	    {
+		my $file_name;
+		$instance->{mtn}->get_corresponding_path(\$file_name,
+							 $chg_ancestor,
+							 $$file_name_ref,
+							 $parent);
+		$file_name_ref = \$file_name
+		    if ($file_name ne $$file_name_ref);
+		get_file_history_helper($instance, $parent, $file_name_ref);
+	    }
+
+	}
+    }
+
+}
+#
+##############################################################################
+#
+#   Routine      - get_revision_history_helper
+#
+#   Description  - Recursive routine for getting the revisions in a revision's
+#                  change history.
+#
+#   Data         - $instance    : The revision history window instance.
+#                  $revision_id : The revision id from where the search is to
+#                                 commence.
+#
+##############################################################################
+
+
+
+sub get_revision_history_helper($$)
+{
+
+    my($instance, $revision_id) = @_;
+
+    return if ($instance->{stop});
+
+    my @parents;
+
+    $instance->{revision_hits}->{$revision_id} = 1;
+    set_label_value($instance->{numbers_value_label},
+		    scalar(keys(%{$instance->{revision_hits}})));
+    WindowManager->update_gui();
+    $instance->{mtn}->parents(address@hidden, $revision_id);
+    foreach my $parent (@parents)
+    {
+	get_revision_history_helper($instance, $parent)
+	    if (! exists($instance->{revision_hits}->{$parent}));
+    }
+
+}
+#
+##############################################################################
+#
+#   Routine      - get_compare_arbitrary_revisions_window
+#
+#   Description  - Creates or prepares an existing compare arbitrary revisions
+#                  window for use.
+#
+#   Data         - Return Value : A reference to the newly created or unused
+#                                 compare arbitrary revisions instance record.
+#
+##############################################################################
+
+
+
+sub get_compare_arbitrary_revisions_window()
+{
+
+    my $instance;
+    my $window_type = "compare_arbitrary_revisions_window";
+    my $wm = WindowManager->instance();
+
+    # Create a new file history window if an unused one wasn't found, otherwise
+    # reuse an existing unused one.
+
+    if (! defined($instance = $wm->find_unused($window_type)))
+    {
+	$instance = {};
+	$instance->{glade} = Gtk2::GladeXML->new($glade_file,
+						 $window_type,
+						 APPLICATION_NAME);
+
+	# Flag to stop recursive calling of callbacks.
+
+	$instance->{in_cb} = 0;
+	local $instance->{in_cb} = 1;
+
+	# Connect Glade registered signal handlers.
+
+	glade_signal_autoconnect($instance->{glade}, $instance);
+
+	# Get the widgets that we are interested in.
+
+	$instance->{window} = $instance->{glade}->get_widget($window_type);
+	foreach my $widget ("arbitrary_revision_id_1_value_label",
+			    "arbitrary_revision_id_2_value_label",
+			    "arbitrary_revision_1_advanced_find_button",
+			    "arbitrary_revision_2_advanced_find_button",
+			    "arbitrary_compare_button")
+	{
+	    $instance->{$widget} = $instance->{glade}->get_widget($widget);
+	}
+
+	# Setup the arbitrary compare callbacks.
+
+	$instance->{window}->signal_connect
+	    ("delete_event",
+	     sub {
+		 my($widget, $event, $instance) = @_;
+		 return TRUE if ($instance->{in_cb});
+		 local $instance->{in_cb} = 1;
+		 $widget->hide();
+		 $instance->{mtn} = undef;
+		 return TRUE;
+	     },
+	     $instance);
+	foreach my $button (1 .. 2)
+	{
+	    my $widget =
+		"arbitrary_revision_" . $button . "_advanced_find_button";
+	    $instance->{$widget}->signal_connect
+		("clicked",
+		 \&compare_arbitrary_revision_advanced_find_button_clicked_cb,
+		 {instance => $instance,
+		  button   => $button});
+	}
+
+	# Display the window.
+
+	$instance->{window}->show_all();
+	$instance->{window}->present();
+
+	# Register the window for management and set up the help callbacks.
+
+	$wm->manage($instance,
+		    $window_type,
+		    $instance->{window});
+	register_help_callbacks
+	    ($instance,
+	     {widget   => "arbitrary_revision_1_advanced_find_button",
+	      help_ref => __("mtnb-lachc-compare-arbitrary-revisions-"
+			     . "buttons")},
+	     {widget   => "arbitrary_revision_1_advanced_find_button",
+	      help_ref => __("mtnb-lachc-compare-arbitrary-revisions-"
+			     . "buttons")},
+	     {widget   => "arbitrary_compare_button",
+	      help_ref => __("mtnb-lachc-compare-arbitrary-revisions-"
+			     . "buttons")},
+	     {widget   => undef,
+	      help_ref => __("mtnb-lachc-the-compare-arbitrary-revisions-"
+			     . "window")});
+    }
+    else
+    {
+	$instance->{in_cb} = 0;
+	local $instance->{in_cb} = 1;
+	$instance->{arbitrary_compare_button}->set_sensitive(FALSE);
+	set_label_value($instance->{arbitrary_revision_id_1_value_label}, "");
+	set_label_value($instance->{arbitrary_revision_id_2_value_label}, "");
+	$instance->{window}->show_all();
+	$instance->{window}->present();
+    }
+
+    return $instance;
+
+}
+#
+##############################################################################
+#
+#   Routine      - get_revision_comparison_window
+#
+#   Description  - Creates or prepares an existing revision comparison window
+#                  for use.
+#
+#   Data         - $mtn         : The Monotone::AutomateStdio object that is
+#                                 to be used to do the comparison.
+#                  Return Value : A reference to the newly created or unused
+#                                 change log instance record.
+#
+##############################################################################
+
+
+
+sub get_revision_comparison_window($)
+{
+
+    my $mtn = $_[0];
+
+    my($height,
+       $instance,
+       $renderer,
+       $width);
+    my $window_type = "revision_comparison_window";
+    my $wm = WindowManager->instance();
+
+    # Create a new revision comparison window if an unused one wasn't found,
+    # otherwise reuse an existing unused one.
+
+    if (! defined($instance = $wm->find_unused($window_type)))
+    {
+	$instance = {};
+	$instance->{glade} = Gtk2::GladeXML->new($glade_file,
+						 $window_type,
+						 APPLICATION_NAME);
+
+	# Flag to stop recursive calling of callbacks.
+
+	$instance->{in_cb} = 0;
+	local $instance->{in_cb} = 1;
+
+	# Connect Glade registered signal handlers.
+
+	glade_signal_autoconnect($instance->{glade}, $instance);
+
+	# Get the widgets that we are interested in.
+
+	$instance->{window} = $instance->{glade}->get_widget($window_type);
+	foreach my $widget ("appbar",
+			    "comparison_label",
+			    "file_comparison_combobox",
+			    "external_diffs_button",
+			    "stop_button",
+			    "comparison_textview",
+			    "comparison_scrolledwindow",
+			    "revision_change_log_1_button",
+			    "revision_change_log_1_button_label",
+			    "revision_change_log_2_button_label")
+	{
+	    $instance->{$widget} = $instance->{glade}->get_widget($widget);
+	}
+
+	# Setup the file history callbacks.
+
+	$instance->{window}->signal_connect
+	    ("delete_event",
+	     sub {
+		 my($widget, $event, $instance) = @_;
+		 return TRUE if ($instance->{in_cb});
+		 local $instance->{in_cb} = 1;
+		 hide_find_text($instance->{comparison_textview});
+		 $widget->hide();
+		 $instance->{file_comparison_combobox}->get_model()->clear();
+		 $instance->{comparison_buffer}->set_text("");
+		 $instance->{diff_output} = [];
+		 $instance->{mtn} = undef;
+		 return TRUE;
+	     },
+	     $instance);
+	if ($mtn->supports(MTN_CONTENT_DIFF_EXTRA_OPTIONS))
+	{
+	    $instance->{kill_mtn_subprocess} = 0;
+	    $instance->{stop_button}->signal_connect
+		("clicked",
+		 sub {
+		     my($widget, $instance) = @_;
+		     $instance->{stop} = 1;
+		     kill("TERM", $instance->{mtn}->get_pid())
+			 if ($instance->{kill_mtn_subprocess});
+		 },
+		 $instance);
+	}
+	else
+	{
+	    $instance->{stop_button}->signal_connect
+		("clicked", sub { $_[1]->{stop} = 1; }, $instance);
+	}
+
+	# Setup the file combobox.
+
+	$instance->{file_comparison_combobox}->
+	    set_model(Gtk2::ListStore->new("Glib::String",
+					   "Glib::Int",
+					   "Glib::String",
+					   "Glib::String"));
+	$renderer = Gtk2::CellRendererText->new();
+	$instance->{file_comparison_combobox}->pack_start($renderer, TRUE);
+	$instance->{file_comparison_combobox}->add_attribute($renderer,
+							     "text" => 0);
+	$instance->{file_comparison_combobox}->get_model()->set
+	    ($instance->{file_comparison_combobox}->get_model()->append(),
+	     CLS_FILE_NAME_COLUMN, " ",
+	     CLS_LINE_NR_COLUMN, 0,
+	     CLS_FILE_ID_1_COLUMN, "",
+	     CLS_FILE_ID_2_COLUMN, "");
+
+	# Setup the revision comparison viewer.
+
+	$instance->{comparison_buffer} =
+	    $instance->{comparison_textview}->get_buffer();
+	create_format_tags($instance->{comparison_buffer});
+	$instance->{comparison_textview}->modify_font($mono_font);
+
+	# Setup the revision log button labels.
+
+	if ($user_preferences->{coloured_diffs})
+	{
+	    $instance->{revision_change_log_1_button_label}->
+		set_markup("<span foreground='"
+			   . $user_preferences->{colours}->{cmp_revision_1}->
+			       {fg}
+			   . "'>"
+			   . __("Revision Change Log")
+			   . "</span>");
+	    $instance->{revision_change_log_2_button_label}->
+		set_markup("<span foreground='"
+			   . $user_preferences->{colours}->{cmp_revision_2}->
+			       {fg}
+			   . "'>"
+			   . __("Revision Change Log")
+			   . "</span>");
+	}
+	else
+	{
+	    $instance->{revision_change_log_1_button_label}->
+		set_text(__("- Revision Change Log"));
+	    $instance->{revision_change_log_2_button_label}->
+		set_text(__("+ Revision Change Log"));
+	}
+
+	# Register the window for management and set up the help callbacks.
+
+	$wm->manage($instance,
+		    $window_type,
+		    $instance->{window},
+		    $instance->{stop_button});
+	register_help_callbacks
+	    ($instance,
+	     {widget   => "file_comparison_hbox",
+	      help_ref => __("mtnb-lachc-differences-buttons")},
+	     {widget   => "comparison_hbuttonbox",
+	      help_ref => __("mtnb-lachc-differences-buttons")},
+	     {widget   => undef,
+	      help_ref => __("mtnb-lachc-the-differences-window")});
+    }
+    else
+    {
+	$instance->{in_cb} = 0;
+	local $instance->{in_cb} = 1;
+	($width, $height) = $instance->{window}->get_default_size();
+	$instance->{window}->resize($width, $height);
+	$instance->{external_diffs_button}->set_sensitive(FALSE);
+	$instance->{stop_button}->set_sensitive(FALSE);
+	$instance->{file_comparison_combobox}->get_model()->clear();
+	$instance->{appbar}->set_progress_percentage(0);
+	$instance->{appbar}->clear_stack();
+    }
+
+    # Empty out the contents.
+
+    $instance->{diff_output} = [];
+    $instance->{comparison_buffer}->set_text("");
+    $instance->{stop} = 0;
+
+    return $instance;
+
+}
+#
+##############################################################################
+#
+#   Routine      - external_diffs
+#
+#   Description  - Launch the external differences helper program, loading in
+#                  the contents of the specified files.
+#
+#   Data         - $parent        : The parent window widget for any dialogs
+#                                   that may appear.
+#                  $mtn           : The Monotone::AutomateStdio object that is
+#                                   to be used to get the files' details.
+#                  $old_file_name : The file name of the older version of the
+#                                   file.
+#                  $old_file_id   : Monotone's file id for the older version
+#                                   of the file.
+#                  $new_file_name : The file name of the newer version of the
+#                                   file.
+#                  $new_file_id   : Monotone's file id for the newer version
+#                                   of the file.
+#
+##############################################################################
+
+
+
+sub external_diffs($$$$$$)
+{
+
+    my($parent,
+       $mtn,
+       $old_file_name,
+       $old_file_id,
+       $new_file_name,
+       $new_file_id) = @_;
+
+    my($cmd,
+       $data,
+       $new_fh,
+       $new_file,
+       $old_fh,
+       $old_file);
+    my $wm = WindowManager->instance();
+
+    # Just check that we do actually have an external helper application to
+    # call.
+
+    if (! defined($user_preferences->{diffs_application})
+	|| $user_preferences->{diffs_application} =~ m/^\s*$/)
+    {
+	my $dialog = Gtk2::MessageDialog->new
+	    ($parent,
+	     ["modal"],
+	     "warning",
+	     "close",
+	     __("Cannot call the external helper application\n"
+		. "to do the comparison as one has not been\n"
+		. "specified in the user's preferences."));
+	$wm->allow_input(sub { $dialog->run(); });
+	$dialog->destroy();
+	return;
+    }
+    return unless (program_valid((split(/[[:blank:]]/,
+					$user_preferences->{diffs_application})
+				  )[0],
+				 $parent));
+
+    # Generate temporary disk file names.
+
+    if (! defined($old_file = generate_tmp_path(__("OLDER_")
+						. basename($old_file_name)))
+	|| ! defined($new_file =
+		     generate_tmp_path(__("NEWER_")
+				       . basename($new_file_name))))
+    {
+	my $dialog = Gtk2::MessageDialog->new
+	    ($parent,
+	     ["modal"],
+	     "warning",
+	     __x("Cannot generate temporary file name:\n{error_message}.",
+		 error_message => $!));
+	$wm->allow_input(sub { $dialog->run(); });
+	$dialog->destroy();
+	return;
+    }
+
+    # Attempt to save the contents to the files.
+
+    if (! defined($old_fh = IO::File->new($old_file, "w"))
+	|| ! defined($new_fh = IO::File->new($new_file, "w")))
+    {
+	my $dialog = Gtk2::MessageDialog->new
+	    ($parent,
+	     ["modal"],
+	     "warning",
+	     "close",
+	     __x("{error_message}.", error_message => $!));
+	$wm->allow_input(sub { $dialog->run(); });
+	$dialog->destroy();
+	return;
+    }
+    binmode($old_fh);
+    binmode($new_fh);
+    $mtn->get_file(\$data, $old_file_id);
+    $old_fh->print($data);
+    $mtn->get_file(\$data, $new_file_id);
+    $new_fh->print($data);
+    $old_fh->close();
+    $new_fh->close();
+    $old_fh = $new_fh = undef;
+
+    # Use the specified differences application, replacing `{file1}' and
+    # `{file2}' with the real file names.
+
+    $cmd = $user_preferences->{diffs_application};
+    $cmd =~ s/\{file1\}/$old_file/g;
+    $cmd =~ s/\{file2\}/$new_file/g;
+
+    # Launch it.
+
+    system($cmd . " &");
+
+}
+#
+##############################################################################
+#
+#   Routine      - mtn_diff
+#
+#   Description  - Compare two the specified two revisions, optionally
+#                  restricting the comparison to the specified file.
+#
+#   Data         - $list          : A reference to the list that is to contain
+#                                   the output from the diff command.
+#                  $abort         : A reference to an abort flag that when
+#                                   true will cause the mtn diff process to
+#                                   stop.
+#                  $mtn_db        : The Monotone database that is to be used
+#                                   or undef if the database associated with
+#                                   the current workspace is to be used.
+#                  $revision_id_1 : The first revision id that is to be
+#                                   compared.
+#                  $revision_id_2 : The second revision id that is to be
+#                                   compared.
+#                  $file_name     : Either the name of the file that the
+#                                   revision comparison should be restricted
+#                                   to or undef for a full revision
+#                                   comparison.
+#                  Return Value   : True if the comparison worked, otherwise
+#                                   false if something went wrong.
+#
+##############################################################################
+
+
+
+sub mtn_diff($$$$$;$)
+{
+
+    my($list,
+       $abort,
+       $mtn_db,
+       $revision_id_1,
+       $revision_id_2,
+       $file_name) = @_;
+
+    my($buffer,
+       @cmd,
+       $cwd,
+       $exception,
+       $ret_val);
+
+    # Run mtn diff in the root directory so as to avoid any workspace
+    # conflicts.
+
+    @$list = ();
+    push(@cmd, "mtn");
+    push(@cmd, "--db=" . $mtn_db) if (defined($mtn_db));
+    push(@cmd, "diff");
+    push(@cmd, "-r");
+    push(@cmd, "i:" . $revision_id_1);
+    push(@cmd, "-r");
+    push(@cmd, "i:" . $revision_id_2);
+    push(@cmd, $file_name) if (defined($file_name));
+    $cwd = getcwd();
+    eval
+    {
+	die("chdir failed: " . $!) unless (chdir(File::Spec->rootdir()));
+	$ret_val = run_command(\$buffer, $abort, @cmd);
+    };
+    $exception = $@;
+    chdir($cwd);
+    if (! $$abort)
+    {
+	if ($exception)
+	{
+	    my $dialog = Gtk2::MessageDialog->new_with_markup
+		(undef,
+		 ["modal"],
+		 "warning",
+		 "close",
+		 __x("Problem running mtn diff, got:\n"
+		         . "<b><i>{error_message}</i></b>\n"
+		         . "This should not be happening!",
+		     error_message => Glib::Markup::escape_text($exception)));
+	    WindowManager->instance()->allow_input(sub { $dialog->run(); });
+	    $dialog->destroy();
+	    return;
+	}
+
+	# Break up the input into a list of lines.
+
+	@$list = split(/\n/, $buffer);
+
+    }
+    else
+    {
+	@$list = ();
+    }
+
+    return $ret_val;
+
+}
+
+1;