[PATCH 2/3] gitweb: Cache $parent_commit info in git_blame()

[Jakub Narebski <jnareb@gmail.com>]

Luben Tuikov changed 'lineno' link from leading to commit which lead
to current version of given block of lines, to leading to parent of
this commit in 244a70e (Blame "linenr" link jumps to previous state at
"orig_lineno").  This supposedly made data mining possible (or just
better).

Unfortunately the implementation in 244a70e used one call for
git-rev-parse to find parent revision per line in file, instead of
using long lived "git cat-file --batch-check" (which might not existed
then), or changing validate_refname to validate_revision and made it
accept <rev>^, <rev>^^, <rev>^^^ etc. syntax.

This patch attempts to migitate issue a bit by caching $parent_commit
info in %metainfo, which makes gitweb to call git-rev-parse only once
per unique commit in blame output.

Signed-off-by: Jakub Narebski <jnareb@gmail.com>
---
That is what I have noticed during browsing git_blame() code.

We can change it to even more effective implementation (like the ones
proposed above in the commit message) later.

Indenting is cause for artifically large diff

 gitweb/gitweb.perl |   16 +++++++++++-----
 1 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/gitweb/gitweb.perl b/gitweb/gitweb.perl
index 1b800f4..916396a 100755
--- a/gitweb/gitweb.perl
+++ b/gitweb/gitweb.perl
@@ -4657,11 +4657,17 @@ HTML
 			              esc_html($rev));
 			print "</td>\n";
 		}
-		open (my $dd, "-|", git_cmd(), "rev-parse", "$full_rev^")
-			or die_error(500, "Open git-rev-parse failed");
-		my $parent_commit = <$dd>;
-		close $dd;
-		chomp($parent_commit);
+		my $parent_commit;
+		if (!exists $meta->{'parent'}) {
+			open (my $dd, "-|", git_cmd(), "rev-parse", "$full_rev^")
+				or die_error(500, "Open git-rev-parse failed");
+			$parent_commit = <$dd>;
+			close $dd;
+			chomp($parent_commit);
+			$meta->{'parent'} = $parent_commit;
+		} else {
+			$parent_commit = $meta->{'parent'};
+		}
 		my $blamed = href(action => 'blame',
 		                  file_name => $meta->{'filename'},
 		                  hash_base => $parent_commit);