Merge branch 'bc/filter-branch'

* bc/filter-branch:
  filter-branch.sh: support nearly proper tag name filtering

Documentation/git-filter-branch.txt

@@ -133,10 +133,16 @@ use "--tag-name-filter cat" to simply update the tags.  In this
 case, be very careful and make sure you have the old tags
 backed up in case the conversion has run afoul.
 +
-Note that there is currently no support for proper rewriting of
-tag objects; in layman terms, if the tag has a message or signature
-attached, the rewritten tag won't have it.  Sorry.  (It is by
-definition impossible to preserve signatures at any rate.)
+Nearly proper rewriting of tag objects is supported. If the tag has
+a message attached, a new tag object will be created with the same message,
+author, and timestamp. If the tag has a signature attached, the
+signature will be stripped. It is by definition impossible to preserve
+signatures. The reason this is "nearly" proper, is because ideally if
+the tag did not change (points to the same object, has the same name, etc.)
+it should retain any signature. That is not the case, signatures will always
+be removed, buyer beware. There is also no support for changing the
+author or timestamp (or the tag message for that matter). Tags which point
+to other tags will be rewritten to point to the underlying commit.
 
 --subdirectory-filter <directory>::
 	Only look at the history which touches the given subdirectory.

git-filter-branch.sh

@@ -406,8 +406,22 @@ if [ "$filter_tag_name" ]; then
 		echo "$ref -> $new_ref ($sha1 -> $new_sha1)"
 
 		if [ "$type" = "tag" ]; then
-			# Warn that we are not rewriting the tag object itself.
-			warn "unreferencing tag object $sha1t"
+			new_sha1=$(git cat-file tag "$ref" |
+				sed -n \
+				    -e "1,/^$/{
+					  s/^object .*/object $new_sha1/
+					  s/^type .*/type commit/
+					  s/^tag .*/tag $new_ref/
+					}" \
+				    -e '/^-----BEGIN PGP SIGNATURE-----/q' \
+				    -e 'p' |
+				git mktag) ||
+				die "Could not create new tag object for $ref"
+			if git cat-file tag "$ref" | \
+			   grep '^-----BEGIN PGP SIGNATURE-----' >/dev/null 2>&1
+			then
+				warn "gpg signature stripped from tag object $sha1t"
+			fi
 		fi
 
 		git update-ref "refs/tags/$new_ref" "$new_sha1" ||

t/t7003-filter-branch.sh

@@ -219,4 +219,36 @@ test_expect_success 'Subdirectory filter with disappearing trees' '
 	test $(git rev-list master | wc -l) = 3
 '
 
+test_expect_success 'Tag name filtering retains tag message' '
+	git tag -m atag T &&
+	git cat-file tag T > expect &&
+	git filter-branch -f --tag-name-filter cat &&
+	git cat-file tag T > actual &&
+	git diff expect actual
+'
+
+faux_gpg_tag='object XXXXXX
+type commit
+tag S
+tagger T A Gger <tagger@example.com> 1206026339 -0500
+
+This is a faux gpg signed tag.
+-----BEGIN PGP SIGNATURE-----
+Version: FauxGPG v0.0.0 (FAUX/Linux)
+
+gdsfoewhxu/6l06f1kxyxhKdZkrcbaiOMtkJUA9ITAc1mlamh0ooasxkH1XwMbYQ
+acmwXaWET20H0GeAGP+7vow=
+=agpO
+-----END PGP SIGNATURE-----
+'
+test_expect_success 'Tag name filtering strips gpg signature' '
+	sha1=$(git rev-parse HEAD) &&
+	sha1t=$(echo "$faux_gpg_tag" | sed -e s/XXXXXX/$sha1/ | git mktag) &&
+	git update-ref "refs/tags/S" "$sha1t" &&
+	echo "$faux_gpg_tag" | sed -e s/XXXXXX/$sha1/ | head -n 6 > expect &&
+	git filter-branch -f --tag-name-filter cat &&
+	git cat-file tag S > actual &&
+	git diff expect actual
+'
+
 test_done