git-svn: persistent memoization

Make memoization of the svn:mergeinfo processing functions persistent with
Memoize::Storable so that the memoization tables don't need to be regenerated
every time the user runs git-svn fetch.

The Memoize::Storable hashes are stored in ENV{GIT_DIR}/svn/.caches.

[ew: changed caches path to avoid conflicts with old repos]
[ew: File::Path::{make_path => mkpath} for compatibility]
[ew: line-wrapped at 80 chars]

Acked-by: Eric Wong <normalperson@yhbt.net>
Signed-off-by: Andrew Myrick <amyrick@apple.com>

git-svn.perl

@@ -1656,6 +1656,7 @@ package Git::SVN;
 use File::Copy qw/copy/;
 use IPC::Open3;
 use Memoize;  # core since 5.8.0, Jul 2002
+use Memoize::Storable;
 
 my ($_gc_nr, $_gc_period);
 
@@ -3116,10 +3117,39 @@ sub has_no_changes {
 		command_oneline("rev-parse", "$commit~1^{tree}"));
 }
 
-BEGIN {
-	memoize 'lookup_svn_merge';
-	memoize 'check_cherry_pick';
-	memoize 'has_no_changes';
+# The GIT_DIR environment variable is not always set until after the command
+# line arguments are processed, so we can't memoize in a BEGIN block.
+{
+	my $memoized = 0;
+
+	sub memoize_svn_mergeinfo_functions {
+		return if $memoized;
+		$memoized = 1;
+
+		my $cache_path = "$ENV{GIT_DIR}/svn/.caches/";
+		mkpath([$cache_path]) unless -d $cache_path;
+
+		tie my %lookup_svn_merge_cache => 'Memoize::Storable',
+		    "$cache_path/lookup_svn_merge.db", 'nstore';
+		memoize 'lookup_svn_merge',
+			SCALAR_CACHE => 'FAULT',
+			LIST_CACHE => ['HASH' => \%lookup_svn_merge_cache],
+		;
+
+		tie my %check_cherry_pick_cache => 'Memoize::Storable',
+		    "$cache_path/check_cherry_pick.db", 'nstore';
+		memoize 'check_cherry_pick',
+			SCALAR_CACHE => 'FAULT',
+			LIST_CACHE => ['HASH' => \%check_cherry_pick_cache],
+		;
+
+		tie my %has_no_changes_cache => 'Memoize::Storable',
+		    "$cache_path/has_no_changes.db", 'nstore';
+		memoize 'has_no_changes',
+			SCALAR_CACHE => ['HASH' => \%has_no_changes_cache],
+			LIST_CACHE => 'FAULT',
+		;
+	}
 }
 
 sub parents_exclude {
@@ -3163,6 +3193,8 @@ sub find_extra_svn_parents {
 	my ($self, $ed, $mergeinfo, $parents) = @_;
 	# aha!  svk:merge property changed...
 
+	memoize_svn_mergeinfo_functions();
+
 	# We first search for merged tips which are not in our
 	# history.  Then, we figure out which git revisions are in
 	# that tip, but not this revision.  If all of those revisions