request-pull: warn if the remote object is not the same as the local one

In some cases, git request-pull might be invoked with remote and
local objects that differ even though they point to the same commit.
For example, the remote object might be a lightweight tag
vs. an annotated tag on the local side; or the user might have
reworded the tag locally and forgotten to push it.

When this happens git-request-pull will not warn, because it only
checks that "git ls-remote" returns an SHA1 that matches the local
commit (known as $headrev in the script).  This patch makes
git-request-pull retrieve the tag object SHA1 while processing
the "git ls-remote" output, so that it can be matched against the
local object.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-request-pull.sh

@@ -65,6 +65,8 @@ test -z "$head" && die "fatal: Not a valid revision: $local"
 headrev=$(git rev-parse --verify --quiet "$head"^0)
 test -z "$headrev" && die "fatal: Ambiguous revision: $local"
 
+local_sha1=$(git rev-parse --verify --quiet "$head")
+
 # Was it a branch with a description?
 branch_name=${head#refs/heads/}
 if test "z$branch_name" = "z$headref" ||
@@ -77,42 +79,53 @@ merge_base=$(git merge-base $baserev $headrev) ||
 die "fatal: No commits in common between $base and $head"
 
 # $head is the refname from the command line.
-# If a ref with the same name as $head exists at the remote
-# and their values match, use that.
-#
-# Otherwise find a random ref that matches $headrev.
+# Find a ref with the same name as $head that exists at the remote
+# and points to the same commit as the local object.
 find_matching_ref='
 	my ($head,$headrev) = (@ARGV);
 	my $pattern = qr{/\Q$head\E$};
-	my ($found);
+	my ($remote_sha1, $found);
 
 	while (<STDIN>) {
 		chomp;
 		my ($sha1, $ref, $deref) = /^(\S+)\s+([^^]+)(\S*)$/;
-		next unless ($sha1 eq $headrev);
 
-		if ($ref eq $head) {
-			$found = $ref;
-		}
-		if ($ref =~ $pattern) {
-			$found = $ref;
-		}
 		if ($sha1 eq $head) {
-			$found = $sha1;
+			$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) {
-		print "$found\n";
+		$remote_sha1 = $headrev if ! defined $remote_sha1;
+		print "$remote_sha1 $found\n";
 	}
 '
 
-ref=$(git ls-remote "$url" | @@PERL@@ -e "$find_matching_ref" "${remote:-HEAD}" "$headrev")
+set fnord $(git ls-remote "$url" | @@PERL@@ -e "$find_matching_ref" "${remote:-HEAD}" "$headrev")
+remote_sha1=$2
+ref=$3
 
 if test -z "$ref"
 then
 	echo "warn: No match for commit $headrev found at $url" >&2
 	echo "warn: Are you sure you pushed '${remote:-HEAD}' there?" >&2
 	status=1
+elif test "$local_sha1" != "$remote_sha1"
+then
+	echo "warn: $head found at $url but points to a different object" >&2
+	echo "warn: Are you sure you pushed '${remote:-HEAD}' there?" >&2
+	status=1
 fi
 
 # Special case: turn "for_linus" to "tags/for_linus" when it is correct

t/t5150-request-pull.sh

@@ -264,4 +264,39 @@ test_expect_success 'request-pull quotes regex metacharacters properly' '
 
 '
 
+test_expect_success 'pull request with mismatched object' '
+
+	rm -fr downstream.git &&
+	git init --bare downstream.git &&
+	(
+		cd local &&
+		git checkout initial &&
+		git merge --ff-only master &&
+		git push origin HEAD:refs/tags/full &&
+		test_must_fail git request-pull initial "$downstream_url" tags/full \
+			2>../err
+	) &&
+	grep "points to a different object" err &&
+	grep "Are you sure you pushed" err
+
+'
+
+test_expect_success 'pull request with stale object' '
+
+	rm -fr downstream.git &&
+	git init --bare downstream.git &&
+	(
+		cd local &&
+		git checkout initial &&
+		git merge --ff-only master &&
+		git push origin refs/tags/full &&
+		git tag -f -m"Thirty-one days" full &&
+		test_must_fail git request-pull initial "$downstream_url" tags/full \
+			2>../err
+	) &&
+	grep "points to a different object" err &&
+	grep "Are you sure you pushed" err
+
+'
+
 test_done