request-pull: stop depending on Perl

While git-request-pull(1) is written as a shell script, for it to
function we depend on Perl being available. The script gets installed
unconditionally though, regardless of whether or not Perl is even
available on the system. When it's not available, the `@PERL_PATH@`
variable may be substituted with a nonexistent executable path and thus
cause the script to fail.

Refactor the script so that it does not depend on Perl at all anymore.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: pks-t

git-request-pull.sh

@@ -78,41 +78,47 @@ fi
 merge_base=$(git merge-base $baserev $headrev) ||
 die "fatal: No commits in common between $base and $head"
 
-# $head is the refname from the command line.
-# Find a ref with the same name as $head that exists at the remote
+find_matching_ref () {
+	while read sha1 ref
+	do
+		case "$ref" in
+		*"^"?*)
+			ref="${ref%"^"*}"
+			deref=true
+			;;
+		*)
+			deref=
+			;;
+		esac
+
+		if test "$sha1" = "${remote:-HEAD}"
+		then
+			echo "$sha1 $sha1"
+			break
+		fi
+
+		case "$ref" in
+		"${remote:-HEAD}"|*"/${remote:-HEAD}")
+			if test -z "$deref"
+			then
+				# Remember the matching unpeeled object on the
+				# remote side.
+				remote_sha1="$sha1"
+			fi
+
+			if test "$sha1" = "$headrev"
+			then
+				echo "${remote_sha1:-$headrev} $ref"
+				break
+			fi
+			;;
+		esac
+	done
+}
+
+# Find a ref with the same name as $remote that exists at the remote
 # and points to the same commit as the local object.
-find_matching_ref='
-	my ($head,$headrev) = (@ARGV);
-	my $pattern = qr{/\Q$head\E$};
-	my ($remote_sha1, $found);
-
-	while (<STDIN>) {
-		chomp;
-		my ($sha1, $ref, $deref) = /^(\S+)\s+([^^]+)(\S*)$/;
-
-		if ($sha1 eq $head) {
-			$found = $remote_sha1 = $sha1;
-			break;
-		}
-
-		if ($ref eq $head || $ref =~ $pattern) {
-			if ($deref eq "") {
-				# Remember the matching object on the remote side
-				$remote_sha1 = $sha1;
-			}
-			if ($sha1 eq $headrev) {
-				$found = $ref;
-				break;
-			}
-		}
-	}
-	if ($found) {
-		$remote_sha1 = $headrev if ! defined $remote_sha1;
-		print "$remote_sha1 $found\n";
-	}
-'
-
-set fnord $(git ls-remote "$url" | @PERL_PATH@ -e "$find_matching_ref" "${remote:-HEAD}" "$headrev")
+set fnord $(git ls-remote "$url" | find_matching_ref)
 remote_sha1=$2
 ref=$3
 

t/t5150-request-pull.sh

@@ -7,12 +7,6 @@ export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 
 . ./test-lib.sh
 
-if ! test_have_prereq PERL
-then
-	skip_all='skipping request-pull tests, perl not available'
-	test_done
-fi
-
 test_expect_success 'setup' '
 
 	git init --bare upstream.git &&