Subject: Re: [PATCH 5/6] sequencer: duplicate the result of resolve_ref_unsafe()

From: Ævar Arnfjörð Bjarmason <[email-masked]>
Date: Fri, 30 Sep 2022 18:45:12 +0200

On Fri, Sep 30 2022, SZEDER Gábor wrote:

> When 'git rebase -i --update-refs' generates the todo list for the
> rebased commit range, an 'update-ref' instruction is inserted for each
> ref that points to one of those commits, except for the rebased branch
> (because at the end of the rebase it will be updated anyway) and any
> refs that are checked out in a worktree; for the latter a "Ref <ref>
> checked out at '<worktree>'" comment is added.  One of these comments
> can be missing under some circumstances: if the oldest commit with a
> ref pointing to it has multiple refs pointing to it, and at least one
> of those refs is checked out in a worktree, and one of them (but not
> the first) is checked out in the worktree associated with the last
> directory entry in '.git/worktrees'.
>
> The culprit is the add_decorations_to_list() function, which calls
> resolve_ref_unsafe() to figure out the refname of the rebased branch.
> However, resolve_ref_unsafe() can (and in this case does) return a
> pointer to a static buffer.  Alas, add_decorations_to_list() holds on
> that static buffer until the end of the function, using its contents
> to compare refnames with the rebased branch, while it also calls a
> function that invokes refs_resolve_ref_unsafe() internally [1], and
> which overwrites the content of that static buffer, and messes up
> subsequent refname comparisons.

Good catch...

> Use xstrdup_or_null() to keep a copy of resolve_ref_unsafe()'s return
> value for the duration of add_decorations_to_list().

...and this makes sense...

>  	const struct name_decoration *decoration = get_name_decoration(&commit->object);
> -	const char *head_ref = resolve_ref_unsafe("HEAD",
> +	const char *head_ref = xstrdup_or_null(resolve_ref_unsafe("HEAD",

...but let's change this to a "char *" then...

>  						  RESOLVE_REF_READING,
>  						  NULL,
> -						  NULL);
> +						  NULL));
>  
>  	while (decoration) {
>  		struct todo_item *item;
> @@ -5965,6 +5965,7 @@ static int add_decorations_to_list(const struct commit *commit,
>  		decoration = decoration->next;
>  	}
>  
> +	free((char *)head_ref);

...so we don't need this cast...?