Subject: Re: [PATCH 11/11] rebase: dereference tags

From: Ævar Arnfjörð Bjarmason <[email-masked]>
Date: Wed, 08 Sep 2021 12:45:20 +0200

On Wed, Sep 08 2021, Phillip Wood via GitGitGadget wrote:

> From: Phillip Wood <[email-masked]>
>
> Aborting a rebase stated with 'git rebase <upstream> <tag-object>'
> should checkout the commit pointed to by <tag-object>. Instead it gives
>
>     error: update_ref failed for ref 'HEAD': cannot update ref 'HEAD':
>     trying to write non-commit object
>     710d743b2b9892457fdcc3970f397e6ec07447e0 to branch 'HEAD'
>
> This is because when we parse the command line arguments although we
> check that the tag points to a commit we remember the oid of the tag
> and try and checkout that object rather than the commit it points
> to. Fix this by using lookup_commit_reference_by_name() when parsing
> the command line.
>
> Signed-off-by: Phillip Wood <[email-masked]>
> ---
> ---
>  builtin/rebase.c        | 18 +++++++++++-------
>  t/t3407-rebase-abort.sh | 18 ++++++++++++++----
>  2 files changed, 25 insertions(+), 11 deletions(-)
>
> diff --git a/builtin/rebase.c b/builtin/rebase.c
> index 93fcc0df2ad..8bf7660a24b 100644
> --- a/builtin/rebase.c
> +++ b/builtin/rebase.c
> @@ -1903,13 +1903,17 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
>  			die_if_checked_out(buf.buf, 1);
>  			options.head_name = xstrdup(buf.buf);
>  		/* If not is it a valid ref (branch or commit)? */
> -		} else if (!get_oid(branch_name, &options.orig_head) &&
> -			   lookup_commit_reference(the_repository,
> -						   &options.orig_head))
> -			options.head_name = NULL;
> -		else
> -			die(_("fatal: no such branch/commit '%s'"),
> -			    branch_name);
> +		} else {
> +			struct commit *commit =
> +				lookup_commit_reference_by_name(branch_name);
> +			if (commit) {
> +				oidcpy(&options.orig_head, &commit->object.oid);
> +				options.head_name = NULL;
> +			} else {
> +				die(_("fatal: no such branch/commit '%s'"),
> +				    branch_name);
> +			}
> +		}

Suggested style nit:

diff --git a/builtin/rebase.c b/builtin/rebase.c
index 8bf7660a24b..c751ef866fd 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -1906,13 +1906,12 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		} else {
 			struct commit *commit =
 				lookup_commit_reference_by_name(branch_name);
-			if (commit) {
-				oidcpy(&options.orig_head, &commit->object.oid);
-				options.head_name = NULL;
-			} else {
+			if (!commit)
 				die(_("fatal: no such branch/commit '%s'"),
 				    branch_name);
-			}
+
+			oidcpy(&options.orig_head, &commit->object.oid);
+			options.head_name = NULL;
 		}
 	} else if (argc == 0) {
 		/* Do not need to switch branches, we are already on it. */

I.e. handle the "die" case right away & skip the indenting of the
non-assert code.

(Also grepping around we could really use a fatal non-gentle version of
lookup_commit_reference_by_name(), but that's another more general
cleanup...)

>  	} else if (argc == 0) {
>  		/* Do not need to switch branches, we are already on it. */
>  		options.head_name =
> diff --git a/t/t3407-rebase-abort.sh b/t/t3407-rebase-abort.sh
> index 2f41b06e028..310cd0c736c 100755
> --- a/t/t3407-rebase-abort.sh
> +++ b/t/t3407-rebase-abort.sh
> @@ -11,18 +11,18 @@ test_expect_success setup '
>  	test_commit a a a &&
>  	git branch to-rebase &&
>  
> -	test_commit b a b &&
> -	test_commit c a c &&
> +	test_commit --annotate b a b &&
> +	test_commit --annotate c a c &&
>  
>  	git checkout to-rebase &&
>  	test_commit "merge should fail on this" a d d &&
> -	test_commit "merge should fail on this, too" a e pre-rebase
> +	test_commit --annotate "merge should fail on this, too" a e pre-rebase
>  '
>  
>  # Check that HEAD is equal to "pre-rebase" and the current branch is
>  # "to-rebase"
>  check_head() {
> -	test_cmp_rev HEAD pre-rebase &&
> +	test_cmp_rev HEAD pre-rebase^{commit} &&
>  	test "$(git symbolic-ref HEAD)" = refs/heads/to-rebase
>  }
>  
> @@ -67,6 +67,16 @@ testrebase() {
>  		test_path_is_missing "$state_dir"
>  	'
>  
> +	test_expect_success "rebase$type --abort when checking out a tag" '
> +		test_when_finished "git symbolic-ref HEAD refs/heads/to-rebase" &&
> +		git reset --hard a -- &&
> +		test_must_fail git rebase$type --onto b c pre-rebase &&
> +		test_cmp_rev HEAD b^{commit} &&
> +		git rebase --abort &&
> +		test_cmp_rev HEAD pre-rebase^{commit} &&
> +		! git symbolic-ref HEAD
> +	'
> +
>  	test_expect_success "rebase$type --abort does not update reflog" '
>  		# Clean up the state from the previous one
>  		git reset --hard pre-rebase &&

This whole series looks good to me, left some comments on other
patches. Consider the above suggested squash highly optional :)