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From: Jeff King <peff@peff.net>
To: Elijah Newren <newren@gmail.com>
Cc: git@vger.kernel.org, larsxschneider@gmail.com,
	sandals@crustytoothpaste.net, me@ttaylorr.com,
	jrnieder@gmail.com
Subject: Re: [PATCH 08/10] fast-export: add --reference-excluded-parents option
Date: Sun, 11 Nov 2018 02:11:03 -0500
Message-ID: <20181111071102.GH30850@sigill.intra.peff.net> (raw)
In-Reply-To: <20181111062312.16342-9-newren@gmail.com>

On Sat, Nov 10, 2018 at 10:23:10PM -0800, Elijah Newren wrote:

> git filter-branch has a nifty feature allowing you to rewrite, e.g. just
> the last 8 commits of a linear history
>   git filter-branch $OPTIONS HEAD~8..HEAD
> 
> If you try the same with git fast-export, you instead get a history of
> only 8 commits, with HEAD~7 being rewritten into a root commit.  There
> are two alternatives:

Ah, I think this maybe answers some of my earlier questions, too. You
cannot use fast-import as it stands to do a partial rewrite.

>   1) Don't use the negative revision specification, and when you're
>      filtering the output to make modifications to the last 8 commits,
>      just be careful to not modify any earlier commits somehow.
> 
>   2) First run 'git fast-export --export-marks=somefile HEAD~8', then
>      run 'git fast-export --import-marks=somefile HEAD~8..HEAD'.
> 
> Both are more error prone than I'd like (the first for obvious reasons;
> with the second option I have sometimes accidentally included too many
> revisions in the first command and then found that the corresponding
> extra revisions were not exported by the second command and thus were
> not modified as I expected).  Also, both are poor from a performance
> perspective.

Yeah, this should be O(commits you're touching), and it the current code
does not allow that at all. So I think this feature makes a lot of sense
(it probably _should_ have been the default, but it's a bit late for
that now).

> @@ -638,13 +640,21 @@ static void handle_commit(struct commit *commit, struct rev_info *rev,
>  	unuse_commit_buffer(commit, commit_buffer);
>  
>  	for (i = 0, p = commit->parents; p; p = p->next) {
> -		int mark = get_object_mark(&p->item->object);
> -		if (!mark)
> +		struct object *obj = &p->item->object;
> +		int mark = get_object_mark(obj);
> +
> +		if (!mark && !reference_excluded_commits)
>  			continue;
>  		if (i == 0)
> -			printf("from :%d\n", mark);
> +			printf("from ");
> +		else
> +			printf("merge ");
> +		if (mark)
> +			printf(":%d\n", mark);
>  		else
> -			printf("merge :%d\n", mark);
> +			printf("%s\n", sha1_to_hex(anonymize ?
> +						   anonymize_sha1(&obj->oid) :
> +						   obj->oid.hash));
>  		i++;
>  	}

OK, so this just teaches us to start with the sensible "from" directive.
I think we might be able to do a little more optimization here. If we're
exporting HEAD^..HEAD and there's an object in HEAD^ which is unchanged
in HEAD, I think we'd still print it (because it would not be marked
SHOWN), but we could omit it (by walking the tree of the boundary
commits and marking them shown).

I don't think it's a blocker for what you're doing here, but just a
possible future optimization.

> @@ -925,13 +935,22 @@ static void handle_tags_and_duplicates(struct string_list *extras)
>  				/*
>  				 * Getting here means we have a commit which
>  				 * was excluded by a negative refspec (e.g.
> -				 * fast-export ^master master).  If the user
> +				 * fast-export ^master master).  If we are
> +				 * referencing excluded commits, set the ref
> +				 * to the exact commit.  Otherwise, the user
>  				 * wants the branch exported but every commit
> -				 * in its history to be deleted, that sounds
> -				 * like a ref deletion to me.
> +				 * in its history to be deleted, which basically
> +				 * just means deletion of the ref.
>  				 */
> -				printf("reset %s\nfrom %s\n\n",
> -				       name, sha1_to_hex(null_sha1));
> +				if (!reference_excluded_commits) {
> +					/* delete the ref */
> +					printf("reset %s\nfrom %s\n\n",
> +					       name, sha1_to_hex(null_sha1));
> +					continue;
> +				}
> +				/* set ref to commit using oid, not mark */
> +				printf("reset %s\nfrom %s\n\n", name,
> +				       sha1_to_hex(commit->object.oid.hash));

OK, and this is basically answering my earlier questions again: yes, you
_would_ want to keep old tags pointing at their commits. But only in
this much more sensible mode.

-Peff

  reply index

Thread overview: 90+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-09-23 13:04 Import/Export as a fast way to purge files from Git? Lars Schneider
2018-09-23 14:55 ` Eric Sunshine
2018-09-23 15:58   ` Lars Schneider
2018-09-23 15:53 ` brian m. carlson
2018-09-23 17:04   ` Jeff King
2018-09-24 17:24 ` Elijah Newren
2018-10-31 19:15   ` Lars Schneider
2018-11-01  7:12     ` Elijah Newren
2018-11-11  6:23       ` [PATCH 00/10] fast export and import fixes and features Elijah Newren
2018-11-11  6:23         ` [PATCH 01/10] git-fast-import.txt: fix documentation for --quiet option Elijah Newren
2018-11-11  6:33           ` Jeff King
2018-11-11  6:23         ` [PATCH 02/10] git-fast-export.txt: clarify misleading documentation about rev-list args Elijah Newren
2018-11-11  6:36           ` Jeff King
2018-11-11  7:17             ` Elijah Newren
2018-11-13 23:25               ` Elijah Newren
2018-11-13 23:39                 ` Jonathan Nieder
2018-11-14  0:02                   ` Elijah Newren
2018-11-11  6:23         ` [PATCH 03/10] fast-export: use value from correct enum Elijah Newren
2018-11-11  6:36           ` Jeff King
2018-11-11 20:10             ` Ævar Arnfjörð Bjarmason
2018-11-12  9:12               ` Ævar Arnfjörð Bjarmason
2018-11-12 11:31               ` Jeff King
2018-11-11  6:23         ` [PATCH 04/10] fast-export: avoid dying when filtering by paths and old tags exist Elijah Newren
2018-11-11  6:44           ` Jeff King
2018-11-11  7:38             ` Elijah Newren
2018-11-12 12:32               ` Jeff King
2018-11-12 22:50             ` brian m. carlson
2018-11-13 14:38               ` Jeff King
2018-11-11  6:23         ` [PATCH 05/10] fast-export: move commit rewriting logic into a function for reuse Elijah Newren
2018-11-11  6:47           ` Jeff King
2018-11-11  6:23         ` [PATCH 06/10] fast-export: when using paths, avoid corrupt stream with non-existent mark Elijah Newren
2018-11-11  6:53           ` Jeff King
2018-11-11  8:01             ` Elijah Newren
2018-11-12 12:45               ` Jeff King
2018-11-12 15:36                 ` Elijah Newren
2018-11-11  6:23         ` [PATCH 07/10] fast-export: ensure we export requested refs Elijah Newren
2018-11-11  7:02           ` Jeff King
2018-11-11  8:20             ` Elijah Newren
2018-11-11  6:23         ` [PATCH 08/10] fast-export: add --reference-excluded-parents option Elijah Newren
2018-11-11  7:11           ` Jeff King [this message]
2018-11-11  6:23         ` [PATCH 09/10] fast-export: add a --show-original-ids option to show original names Elijah Newren
2018-11-11  7:20           ` Jeff King
2018-11-11  8:32             ` Elijah Newren
2018-11-12 12:53               ` Jeff King
2018-11-12 15:46                 ` Elijah Newren
2018-11-12 16:31                   ` Jeff King
2018-11-11  6:23         ` [PATCH 10/10] fast-export: add --always-show-modify-after-rename Elijah Newren
2018-11-11  7:23           ` Jeff King
2018-11-11  8:42             ` Elijah Newren
2018-11-12 12:58               ` Jeff King
2018-11-12 18:08                 ` Elijah Newren
2018-11-13 14:45                   ` Jeff King
2018-11-13 17:10                     ` Elijah Newren
2018-11-14  7:14                       ` Jeff King
2018-11-11  7:27         ` [PATCH 00/10] fast export and import fixes and features Jeff King
2018-11-11  8:44           ` Elijah Newren
2018-11-12 13:00             ` Jeff King
2018-11-14  0:25         ` [PATCH v2 00/11] " Elijah Newren
2018-11-14  0:25           ` [PATCH v2 01/11] git-fast-import.txt: fix documentation for --quiet option Elijah Newren
2018-11-14  0:25           ` [PATCH v2 02/11] git-fast-export.txt: clarify misleading documentation about rev-list args Elijah Newren
2018-11-14  0:25           ` [PATCH v2 03/11] fast-export: use value from correct enum Elijah Newren
2018-11-14  0:25           ` [PATCH v2 04/11] fast-export: avoid dying when filtering by paths and old tags exist Elijah Newren
2018-11-14 19:17             ` SZEDER Gábor
2018-11-14 23:13               ` Elijah Newren
2018-11-14  0:25           ` [PATCH v2 05/11] fast-export: move commit rewriting logic into a function for reuse Elijah Newren
2018-11-14  0:25           ` [PATCH v2 06/11] fast-export: when using paths, avoid corrupt stream with non-existent mark Elijah Newren
2018-11-14  0:25           ` [PATCH v2 07/11] fast-export: ensure we export requested refs Elijah Newren
2018-11-14  0:25           ` [PATCH v2 08/11] fast-export: add --reference-excluded-parents option Elijah Newren
2018-11-14 19:27             ` SZEDER Gábor
2018-11-14 23:16               ` Elijah Newren
2018-11-14  0:25           ` [PATCH v2 09/11] fast-import: remove unmaintained duplicate documentation Elijah Newren
2018-11-14  0:25           ` [PATCH v2 10/11] fast-export: add a --show-original-ids option to show original names Elijah Newren
2018-11-14  0:26           ` [PATCH v2 11/11] fast-export: add --always-show-modify-after-rename Elijah Newren
2018-11-14  7:25           ` [PATCH v2 00/11] fast export and import fixes and features Jeff King
2018-11-16  7:59           ` [PATCH v3 " Elijah Newren
2018-11-16  7:59             ` [PATCH v3 01/11] fast-export: convert sha1 to oid Elijah Newren
2018-11-16  7:59             ` [PATCH v3 02/11] git-fast-import.txt: fix documentation for --quiet option Elijah Newren
2018-11-16  7:59             ` [PATCH v3 03/11] git-fast-export.txt: clarify misleading documentation about rev-list args Elijah Newren
2018-11-16  7:59             ` [PATCH v3 04/11] fast-export: use value from correct enum Elijah Newren
2018-11-16  7:59             ` [PATCH v3 05/11] fast-export: avoid dying when filtering by paths and old tags exist Elijah Newren
2018-11-16  7:59             ` [PATCH v3 06/11] fast-export: move commit rewriting logic into a function for reuse Elijah Newren
2018-11-16  7:59             ` [PATCH v3 07/11] fast-export: when using paths, avoid corrupt stream with non-existent mark Elijah Newren
2018-11-16  7:59             ` [PATCH v3 08/11] fast-export: ensure we export requested refs Elijah Newren
2018-11-16  7:59             ` [PATCH v3 09/11] fast-export: add --reference-excluded-parents option Elijah Newren
2018-11-16  7:59             ` [PATCH v3 10/11] fast-import: remove unmaintained duplicate documentation Elijah Newren
2018-11-16  7:59             ` [PATCH v3 11/11] fast-export: add a --show-original-ids option to show original names Elijah Newren
2018-11-16 12:29               ` SZEDER Gábor
2018-11-16  8:50             ` [PATCH v3 00/11] fast export and import fixes and features Jeff King
2018-11-12  9:17       ` Import/Export as a fast way to purge files from Git? Ævar Arnfjörð Bjarmason
2018-11-12 15:34         ` Elijah Newren

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