git-svn: lazy load some modules

We can delay loading some modules until we need them for uncommon
code paths.  For example, persistent memoization is not often
needed, so we can avoid loading the modules for it until we
encounter svn::mergeinfo during fetch.

This gives a tiny reduction in syscalls (from 15641 to 15305) when
running "git svn info" and counting via "strace -fc".  Further,
more invasive work will be needed to noticeably improve performance.

Signed-off-by: Eric Wong <normalperson@yhbt.net>

4 files changed, 19 insertions, 14 deletions

diff --git a/perl/Git/SVN.pm b/perl/Git/SVN.pm
index 8e4af7153..afa562c8b 100644
--- a/perl/Git/SVN.pm
+++ b/perl/Git/SVN.pm
@@ -9,10 +9,8 @@ use vars qw/$_no_metadata
 	    $_use_log_author $_add_author_from $_localtime/;
 use Carp qw/croak/;
 use File::Path qw/mkpath/;
-use File::Copy qw/copy/;
 use IPC::Open3;
 use Memoize;  # core since 5.8.0, Jul 2002
-use Memoize::Storable;
 use POSIX qw(:signal_h);
 
 use Git qw(
@@ -32,11 +30,7 @@ use Git::SVN::Utils qw(
 	add_path_to_url
 );
 
-my $can_use_yaml;
-BEGIN {
-	$can_use_yaml = eval { require Git::SVN::Memoize::YAML; 1};
-}
-
+my $memo_backend;
 our $_follow_parent  = 1;
 our $_minimize_url   = 'unset';
 our $default_repo_id = 'svn';
@@ -1578,7 +1572,16 @@ sub tie_for_persistent_memoization {
 	my $hash = shift;
 	my $path = shift;
 
-	if ($can_use_yaml) {
+	unless ($memo_backend) {
+		if (eval { require Git::SVN::Memoize::YAML; 1}) {
+			$memo_backend = 1;
+		} else {
+			require Memoize::Storable;
+			$memo_backend = -1;
+		}
+	}
+
+	if ($memo_backend > 0) {
 		tie %$hash => 'Git::SVN::Memoize::YAML', "$path.yaml";
 	} else {
 		tie %$hash => 'Memoize::Storable', "$path.db", 'nstore';
@@ -2188,8 +2191,9 @@ sub rev_map_set {
 	# both of these options make our .rev_db file very, very important
 	# and we can't afford to lose it because rebuild() won't work
 	if ($self->use_svm_props || $self->no_metadata) {
+		require File::Copy;
 		$sync = 1;
-		copy($db, $db_lock) or die "rev_map_set(@_): ",
+		File::Copy::copy($db, $db_lock) or die "rev_map_set(@_): ",
 					   "Failed to copy: ",
 					   "$db => $db_lock ($!)\n";
 	} else {
diff --git a/perl/Git/SVN/Editor.pm b/perl/Git/SVN/Editor.pm
index 4088f13e7..c50176eec 100644
--- a/perl/Git/SVN/Editor.pm
+++ b/perl/Git/SVN/Editor.pm
@@ -5,7 +5,6 @@ use warnings;
 use SVN::Core;
 use SVN::Delta;
 use Carp qw/croak/;
-use IO::File;
 use Git qw/command command_oneline command_noisy command_output_pipe
            command_input_pipe command_close_pipe
            command_bidi_pipe command_close_bidi_pipe/;
@@ -586,7 +585,7 @@ The interface will change as git-svn evolves.
 =head1 DEPENDENCIES
 
 Subversion perl bindings,
-the core L<Carp> and L<IO::File> modules,
+the core L<Carp> module,
 and git's L<Git> helper module.
 
 C<Git::SVN::Editor> has not been tested using callers other than
diff --git a/perl/Git/SVN/Fetcher.pm b/perl/Git/SVN/Fetcher.pm
index 10edb2773..6b9c6e013 100644
--- a/perl/Git/SVN/Fetcher.pm
+++ b/perl/Git/SVN/Fetcher.pm
@@ -7,7 +7,6 @@ use warnings;
 use SVN::Delta;
 use Carp qw/croak/;
 use File::Basename qw/dirname/;
-use IO::File qw//;
 use Git qw/command command_oneline command_noisy command_output_pipe
            command_input_pipe command_close_pipe
            command_bidi_pipe command_close_bidi_pipe/;
@@ -600,7 +599,7 @@ developing git-svn.
 =head1 DEPENDENCIES
 
 L<SVN::Delta> from the Subversion perl bindings,
-the core L<Carp>, L<File::Basename>, and L<IO::File> modules,
+the core L<Carp> and L<File::Basename> modules,
 and git's L<Git> helper module.
 
 C<Git::SVN::Fetcher> has not been tested using callers other than
diff --git a/perl/Git/SVN/Ra.pm b/perl/Git/SVN/Ra.pm
index 622535e21..cf36b9d3c 100644
--- a/perl/Git/SVN/Ra.pm
+++ b/perl/Git/SVN/Ra.pm
@@ -3,7 +3,6 @@ use vars qw/@ISA $config_dir $_ignore_refs_regex $_log_window_size/;
 use strict;
 use warnings;
 use Memoize;
-use SVN::Client;
 use Git::SVN::Utils qw(
 	canonicalize_url
 	canonicalize_path
@@ -42,6 +41,7 @@ END {
 }
 
 sub _auth_providers () {
+	require SVN::Client;
 	my @rv = (
 	  SVN::Client::get_simple_provider(),
 	  SVN::Client::get_ssl_server_trust_file_provider(),
@@ -247,7 +247,10 @@ sub get_log {
 	$ret;
 }
 
+# uncommon, only for ancient SVN (<= 1.4.2)
 sub trees_match {
+	require IO::File;
+	require SVN::Client;
 	my ($self, $url1, $rev1, $url2, $rev2) = @_;
 	my $ctx = SVN::Client->new(auth => _auth_providers);
 	my $out = IO::File->new_tmpfile;