git filter-branch and merging of signed tags

Hello,

Consider I want to rewrite a commit that is a merge of a signed tag. In my case that's 064ca93f7ab927c2752d86fc5727716e340d737c that currently sits in linux-next:

	~/gsrc/linux$ git version
	git version 2.6.1
	~/gsrc/linux$ git checkout 064ca93f7ab927c2752d86fc5727716e340d737c
	~/gsrc/linux$ git cat-file commit HEAD
	tree 7086bbd51d06ebd0e3fcca70380d0a066efce6ef
	parent e44a01fa0e0aec2f3a21dadb9c030d14831d4258
	parent f719a0d6a8541b383c506aaa4b4fa6b4109669f4
	author Arnd Bergmann <arnd@arndb.de> 1444139956 +0200
	committer Arnd Bergmann <arnd@arndb.de> 1444139956 +0200
	mergetag object f719a0d6a8541b383c506aaa4b4fa6b4109669f4
	 type commit
	 tag efm32-for-4.4-rc1
	 tagger Uwe Kleine-König <uwe@kleine-koenig.org> 1443549594 +0200
	 
	 efm32 cleanups for 4.4-rc1
	 
	 These are just two followup cleanups for commits that are in v3.17-rc1 and
	 waited in my private tree for application since that time.
	 -----BEGIN PGP SIGNATURE-----
	 
	 iQEcBAABCgAGBQJWCtIwAAoJEMH8FHityuwJFPYH/2LJpi0yUhI01s0D9U5rZgjl
	 8mLP70utAMaqXiGqP/O0ndH+za5TrrUTwDJE5jhAHru1Q6q62Ld2BfOR5+K8zlrP
	 4UDGBDj3ePJgEtbSsJYJIRT+AKque2GONbeGpJh2arPrNamWChKIz8HoGSgwdRlx
	 TvQuVFEa6C3ujP0ATM8x54f0vR4bYm9WmBS522DwZQY4JpGZC005A3Quw6fmFxPJ
	 vJRo1fE1d2OZ3Cuxb15m8PLtZw6sbMdMwgyirAFGrJsN9u/V6BzsSzH0s8suT7IP
	 WIohnmYtFSUfkQjaGrMl2wIpJSsIzettiXf9GrQDXSGZsQ4k7sW3U+qrcZ7ZUR4=
	 =ngv1
	 -----END PGP SIGNATURE-----

	Merge tag 'efm32-for-4.4-rc1' of git://git.pengutronix.de/git/ukl/linux into next/cleanup

	Merge "efm32 cleanups for 4.4-rc1" from Uwe Kleine-Koenig:

	These are just two followup cleanups for commits that are in v3.17-rc1 and
	waited in my private tree for application since that time.

	* tag 'efm32-for-4.4-rc1' of git://git.pengutronix.de/git/ukl/linux:
	  ARM: efm32: switch to vendor,device compatible strings
	  ARM: efm32: switch to properly namespaced location property

OK, to fix my name in the commit log I do:

	 git filter-branch -f --msg-filter "sed 's/Kleine-Koenig/$(echo Kleine-K+APY-nig | iconv -f utf-7 -t utf-8)/'" HEAD ^HEAD^ ^HEAD^2

This destroys the mergetag, as now I have:

	~/gsrc/linux$ git cat-file commit HEAD
	tree 7086bbd51d06ebd0e3fcca70380d0a066efce6ef
	parent e44a01fa0e0aec2f3a21dadb9c030d14831d4258
	parent f719a0d6a8541b383c506aaa4b4fa6b4109669f4
	author Arnd Bergmann <arnd@arndb.de> 1444139956 +0200
	committer Arnd Bergmann <arnd@arndb.de> 1444139956 +0200

	 efm32 cleanups for 4.4-rc1
	 
	 These are just two followup cleanups for commits that are in v3.17-rc1 and
	 waited in my private tree for application since that time.
	 -----BEGIN PGP SIGNATURE-----
	 
	 iQEcBAABCgAGBQJWCtIwAAoJEMH8FHityuwJFPYH/2LJpi0yUhI01s0D9U5rZgjl
	 8mLP70utAMaqXiGqP/O0ndH+za5TrrUTwDJE5jhAHru1Q6q62Ld2BfOR5+K8zlrP
	 4UDGBDj3ePJgEtbSsJYJIRT+AKque2GONbeGpJh2arPrNamWChKIz8HoGSgwdRlx
	 TvQuVFEa6C3ujP0ATM8x54f0vR4bYm9WmBS522DwZQY4JpGZC005A3Quw6fmFxPJ
	 vJRo1fE1d2OZ3Cuxb15m8PLtZw6sbMdMwgyirAFGrJsN9u/V6BzsSzH0s8suT7IP
	 WIohnmYtFSUfkQjaGrMl2wIpJSsIzettiXf9GrQDXSGZsQ4k7sW3U+qrcZ7ZUR4=
	 =ngv1
	 -----END PGP SIGNATURE-----

	Merge tag 'efm32-for-4.4-rc1' of git://git.pengutronix.de/git/ukl/linux into next/cleanup

	Merge "efm32 cleanups for 4.4-rc1" from Uwe Kleine-König:

	These are just two followup cleanups for commits that are in v3.17-rc1 and
	waited in my private tree for application since that time.

	* tag 'efm32-for-4.4-rc1' of git://git.pengutronix.de/git/ukl/linux:
	  ARM: efm32: switch to vendor,device compatible strings
	  ARM: efm32: switch to properly namespaced location property

	~/gsrc/linux$ diff -u <(git cat-file commit HEAD) <(git cat-file commit 064ca93f7ab927c2752d86fc5727716e340d737c)
	--- /dev/fd/63	2015-11-02 09:02:17.310373539 +0100
	+++ /dev/fd/62	2015-11-02 09:02:17.310373539 +0100
	@@ -3,7 +3,11 @@
	 parent f719a0d6a8541b383c506aaa4b4fa6b4109669f4
	 author Arnd Bergmann <arnd@arndb.de> 1444139956 +0200
	 committer Arnd Bergmann <arnd@arndb.de> 1444139956 +0200
	-
	+mergetag object f719a0d6a8541b383c506aaa4b4fa6b4109669f4
	+ type commit
	+ tag efm32-for-4.4-rc1
	+ tagger Uwe Kleine-König <uwe@kleine-koenig.org> 1443549594 +0200
	+ 
	  efm32 cleanups for 4.4-rc1
	  
	  These are just two followup cleanups for commits that are in v3.17-rc1 and
	@@ -21,7 +25,7 @@
	 
	 Merge tag 'efm32-for-4.4-rc1' of git://git.pengutronix.de/git/ukl/linux into next/cleanup
	 
	-Merge "efm32 cleanups for 4.4-rc1" from Uwe Kleine-König:
	+Merge "efm32 cleanups for 4.4-rc1" from Uwe Kleine-Koenig:
	 
	 These are just two followup cleanups for commits that are in v3.17-rc1 and
	 waited in my private tree for application since that time.

So now the PGP-Signature also appears in the regular commit log. So either remove the mergetag info completely or (preferably) keep it completely if the merged parent didn't change.

Best regards Uwe