From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on dcvr.yhbt.net X-Spam-Level: X-Spam-ASN: AS3215 2.6.0.0/16 X-Spam-Status: No, score=-0.2 required=3.0 tests=AWL,BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,T_SCC_BODY_TEXT_LINE, URIBL_CSS,URIBL_CSS_A shortcircuit=no autolearn=ham autolearn_force=no version=3.4.2 Received: from out1.vger.email (out1.vger.email [IPv6:2620:137:e000::1:20]) by dcvr.yhbt.net (Postfix) with ESMTP id 0EDED1F8C5 for ; Thu, 17 Mar 2022 21:39:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230322AbiCQVhj (ORCPT ); Thu, 17 Mar 2022 17:37:39 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59974 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230312AbiCQVhi (ORCPT ); Thu, 17 Mar 2022 17:37:38 -0400 Received: from pb-smtp20.pobox.com (pb-smtp20.pobox.com [173.228.157.52]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 713D615468D for ; Thu, 17 Mar 2022 14:36:21 -0700 (PDT) Received: from pb-smtp20.pobox.com (unknown [127.0.0.1]) by pb-smtp20.pobox.com (Postfix) with ESMTP id 214D318415D; Thu, 17 Mar 2022 17:36:21 -0400 (EDT) (envelope-from junio@pobox.com) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed; d=pobox.com; h=from:to:cc :subject:references:date:in-reply-to:message-id:mime-version :content-type; s=sasl; bh=GeAot5Okr56D7rW4ucgegvFNXHqwXN3NnqLwiF 5/aak=; b=J9v3mOLQekYaK+K5HklOsZ49lwa+W4NDtNwW0U64LvPC/ZTpfFZg1a WKm5pJa9+oNCMahzVjyJIChkwCAl/MgXbQS+AxtlgUai9gmtLMoLhOgi3KE7QGlv jGgMd3TuToFCfP/QeFhE1m8bQD79zgVQVniGh5D2rD4aPoCJiXgfE= Received: from pb-smtp20.sea.icgroup.com (unknown [127.0.0.1]) by pb-smtp20.pobox.com (Postfix) with ESMTP id 1973218415C; Thu, 17 Mar 2022 17:36:21 -0400 (EDT) (envelope-from junio@pobox.com) Received: from pobox.com (unknown [34.82.80.254]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by pb-smtp20.pobox.com (Postfix) with ESMTPSA id 3925918415A; Thu, 17 Mar 2022 17:36:17 -0400 (EDT) (envelope-from junio@pobox.com) From: Junio C Hamano To: "John Cai via GitGitGadget" Cc: git@vger.kernel.org, Phillip Wood , =?utf-8?B?w4Z2YXIgQXJuZmrDtnLDsA==?= Bjarmason , John Cai Subject: Re: [PATCH v4 3/3] rebase: set REF_HEAD_DETACH in checkout_up_to_date() References: <13c5955c317713bbc6a91b9f44081395880abb67.1647546828.git.gitgitgadget@gmail.com> Date: Thu, 17 Mar 2022 14:36:16 -0700 In-Reply-To: <13c5955c317713bbc6a91b9f44081395880abb67.1647546828.git.gitgitgadget@gmail.com> (John Cai via GitGitGadget's message of "Thu, 17 Mar 2022 19:53:48 +0000") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Pobox-Relay-ID: 47149A36-A63A-11EC-AA90-C85A9F429DF0-77302942!pb-smtp20.pobox.com Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org "John Cai via GitGitGadget" writes: > From: John Cai > > Fixes a bug whereby rebase updates the deferenced reference HEAD points > to instead of HEAD directly. Perhaps "git rebase A B", where B is not a commit, should behave as if the HEAD got detached at B and then the detached HEAD got rebased on top of A. A bug however overwrites the current branch to point at B, when B is a descendant of A (i.e. the rebase ends up being a fast-forward). > ... See [1] for > the original bug report. OK (URL is wrong; see below). The explanation of how the bug occurs (elided) in the patch looked all reasonable. It read well. > ... > Also add a test to ensure the correct behavior. Yup. _Add_ a test to ensure that. Not replace a misleading test that expected to see a wrong behaviour. > 1. https://lore.kernel.org/git/xmqqsfrpbepd.fsf@gitster.g/ This is not the original bug report. It was an early hint for diagnosis. [1] https://lore.kernel.org/git/YiokTm3GxIZQQUow@newk/ would be a more appropriate pointer. > ropts.oid = &options->orig_head; > ropts.branch = options->head_name; > ropts.flags = RESET_HEAD_RUN_POST_CHECKOUT_HOOK; > + if (!ropts.branch) > + ropts.flags |= RESET_HEAD_DETACH; > ropts.head_msg = buf.buf; OK. If head_name is not set, we do not want to touch the branch the HEAD happens to be pointing at, so we want to detach. > +test_expect_success 'switch to non-branch detaches HEAD' ' > git checkout main && > old_main=$(git rev-parse HEAD) && > git rebase First Second^0 && > - test_cmp_rev HEAD main && > - test_cmp_rev main $(git rev-parse Second) && > - git symbolic-ref HEAD > + test_cmp_rev HEAD Second && > + test_cmp_rev main $old_main && > + test_must_fail git symbolic-ref HEAD As we want (1) HEAD (detached) is pointing at Second, (2) 'main' stayed at $old_main, and (3) HEAD is detched, these three conditions look sane. Thanks. For reference, I discarded [1/3], queued [2/3] and replaced this [3/3] with the following for now. ---- >8 ---- ---- >8 ---- ---- >8 ---- ---- >8 ---- ---- >8 ---- From: John Cai Subject: [PATCH] rebase: set REF_HEAD_DETACH in checkout_up_to_date() "git rebase A B" where B is not a commit should behave as if the HEAD got detached at B and then the detached HEAD got rebased on top of A. A bug however overwrites the current branch to point at B, when B is a descendant of A (i.e. the rebase ends up being a fast-forward). See [1] for the original bug report. The callstack from checkout_up_to_date() is the following: cmd_rebase() -> checkout_up_to_date() -> reset_head() -> update_refs() -> update_ref() When B is not a valid branch but an oid, rebase sets the head_name of rebase_options to NULL. This value gets passed down this call chain through the branch member of reset_head_opts also getting set to NULL all the way to update_refs(). Then update_refs() checks ropts.branch to decide whether or not to switch branches. If ropts.branch is NULL, it calls update_ref() to update HEAD. At this point however, from rebase's point of view, we want a detached HEAD. But, since checkout_up_to_date() does not set the RESET_HEAD_DETACH flag, the update_ref() call will deference HEAD and update the branch its pointing to. We want the HEAD detached at B instead. Fix this bug by adding the RESET_HEAD_DETACH flag in checkout_up_to_date if B is not a valid branch, so that once reset_head() calls update_refs(), it calls update_ref() with REF_NO_DEREF which updates HEAD directly intead of deferencing it and updating the branch that HEAD points to. Also add a test to ensure the correct behavior. [1] https://lore.kernel.org/git/YiokTm3GxIZQQUow@newk/ Reported-by: Michael McClimon Signed-off-by: John Cai Signed-off-by: Junio C Hamano --- builtin/rebase.c | 2 ++ t/t3400-rebase.sh | 9 +++++++++ 2 files changed, 11 insertions(+) diff --git a/builtin/rebase.c b/builtin/rebase.c index b29ad2b65e..27fde7bf28 100644 --- a/builtin/rebase.c +++ b/builtin/rebase.c @@ -829,6 +829,8 @@ static int checkout_up_to_date(struct rebase_options *options) ropts.oid = &options->orig_head; ropts.branch = options->head_name; ropts.flags = RESET_HEAD_RUN_POST_CHECKOUT_HOOK; + if (!ropts.branch) + ropts.flags |= RESET_HEAD_DETACH; ropts.head_msg = buf.buf; if (reset_head(the_repository, &ropts) < 0) ret = error(_("could not switch to %s"), options->switch_to); diff --git a/t/t3400-rebase.sh b/t/t3400-rebase.sh index 6dc8df8be7..cf55b017ff 100755 --- a/t/t3400-rebase.sh +++ b/t/t3400-rebase.sh @@ -389,6 +389,15 @@ test_expect_success 'switch to branch not checked out' ' git rebase main other ' +test_expect_success 'switch to non-branch detaches HEAD' ' + git checkout main && + old_main=$(git rev-parse HEAD) && + git rebase First Second^0 && + test_cmp_rev HEAD Second && + test_cmp_rev main $old_main && + test_must_fail git symbolic-ref HEAD +' + test_expect_success 'refuse to switch to branch checked out elsewhere' ' git checkout main && git worktree add wt && -- 2.35.1-757-g4266a5c05c