Re: [PATCH v3 6/8] rebase: add --update-refs option

> From: Derrick Stolee <derrickstolee@github.com>
> 
> When working on a large feature, it can be helpful to break that feature
> into multiple smaller parts that become reviewed in sequence. During
> development or during review, a change to one part of the feature could
> affect multiple of these parts. An interactive rebase can help adjust
> the multi-part "story" of the branch.
> 
> However, if there are branches tracking the different parts of the
> feature, then rebasing the entire list of commits can create commits not
> reachable from those "sub branches". It can take a manual step to update
> those branches.
> 
> Add a new --update-refs option to 'git rebase -i' that adds 'update-ref
> <ref>' steps to the todo file whenever a commit that is being rebased is
> decorated with that <ref>. At the very end, the rebase process updates
> all of the listed refs to the values stored during the rebase operation.
> 
> Be sure to iterate after any squashing or fixups are placed. Update the
> branch only after those squashes and fixups are complete. This allows a
> --fixup commit at the tip of the feature to apply correctly to the sub
> branch, even if it is fixing up the most-recent commit in that part.
> 
> One potential problem here is that refs decorating commits that are
> already marked as "fixup!" or "squash!" will not be included in this
> list. Generally, the reordering of the "fixup!" and "squash!" is likely
> to change the relative order of these refs, so it is not recommended.
> The workflow here is intended to allow these kinds of commits at the tip
> of the rebased branch while the other sub branches come along for the
> ride without intervention.
> 
> This change update the documentation and builtin to accept the
> --update-refs option as well as updating the todo file with the
> 'update-ref' commands. Tests are added to ensure that these todo
> commands are added in the correct locations.
> 
> A future change will update the behavior to actually update the refs
> at the end of the rebase sequence.

> +struct todo_add_branch_context {
> +	struct todo_item *items;
> +	size_t items_nr;
> +	size_t items_alloc;
> +	struct strbuf *buf;
> +	struct commit *commit;
> +	struct string_list refs_to_oids;
> +};
> +
> +static int add_decorations_to_list(const struct commit *commit,
> +				   struct todo_add_branch_context *ctx)
> +{
> +	const struct name_decoration *decoration = get_name_decoration(&commit->object);
> +
> +	while (decoration) {
> +		struct todo_item *item;
> +		const char *path;
> +		size_t base_offset = ctx->buf->len;
> +
> +		ALLOC_GROW(ctx->items,
> +			ctx->items_nr + 1,
> +			ctx->items_alloc);
> +		item = &ctx->items[ctx->items_nr];
> +		memset(item, 0, sizeof(*item));
> +
> +		/* If the branch is checked out, then leave a comment instead. */
> +		if ((path = branch_checked_out(decoration->name))) {
> +			item->command = TODO_COMMENT;
> +			strbuf_addf(ctx->buf, "# Ref %s checked out at '%s'\n",
> +				    decoration->name, path);
> +		} else {
> +			struct string_list_item *sti;
> +			item->command = TODO_UPDATE_REF;
> +			strbuf_addf(ctx->buf, "%s\n", decoration->name);
> +
> +			sti = string_list_append(&ctx->refs_to_oids,
> +						 decoration->name);
> +			sti->util = oiddup(the_hash_algo->null_oid);

> +		}
> +
> +		item->offset_in_buf = base_offset;
> +		item->arg_offset = base_offset;
> +		item->arg_len = ctx->buf->len - base_offset;
> +		ctx->items_nr++;
> +
> +		decoration = decoration->next;
> +	}
> +
> +	return 0;
> +}
> +
> +/*
> + * For each 'pick' command, find out if the commit has a decoration in
> + * refs/heads/. If so, then add a 'label for-update-refs/' command.
> + */
> +static int todo_list_add_update_ref_commands(struct todo_list *todo_list)
> +{
> +	int i;
> +	static struct string_list decorate_refs_exclude = STRING_LIST_INIT_NODUP;
> +	static struct string_list decorate_refs_exclude_config = STRING_LIST_INIT_NODUP;
> +	static struct string_list decorate_refs_include = STRING_LIST_INIT_NODUP;
> +	struct decoration_filter decoration_filter = {
> +		.include_ref_pattern = &decorate_refs_include,
> +		.exclude_ref_pattern = &decorate_refs_exclude,
> +		.exclude_ref_config_pattern = &decorate_refs_exclude_config,
> +	};
> +	struct todo_add_branch_context ctx = {
> +		.buf = &todo_list->buf,
> +		.refs_to_oids = STRING_LIST_INIT_DUP,
> +	};
> +
> +	ctx.items_alloc = 2 * todo_list->nr + 1;

> +	ALLOC_ARRAY(ctx.items, ctx.items_alloc);
> +
> +	string_list_append(&decorate_refs_include, "refs/heads/");
> +	load_ref_decorations(&decoration_filter, 0);
> +
> +	for (i = 0; i < todo_list->nr; ) {
> +		struct todo_item *item = &todo_list->items[i];
> +
> +		/* insert ith item into new list */
> +		ALLOC_GROW(ctx.items,
> +			   ctx.items_nr + 1,
> +			   ctx.items_alloc);

> +		ctx.items[ctx.items_nr++] = todo_list->items[i++];
> +
> +		if (item->commit) {
> +			ctx.commit = item->commit;
> +			add_decorations_to_list(item->commit, &ctx);
> +		}
> +	}
> +
> +	string_list_clear(&ctx.refs_to_oids, 1);
> +	free(todo_list->items);
> +	todo_list->items = ctx.items;
> +	todo_list->nr = ctx.items_nr;
> +	todo_list->alloc = ctx.items_alloc;
> +
> +	return 0;
> +}
> +
>   int complete_action(struct repository *r, struct replay_opts *opts, unsigned flags,
>   		    const char *shortrevisions, const char *onto_name,
>   		    struct commit *onto, const struct object_id *orig_head,
>   		    struct string_list *commands, unsigned autosquash,
> +		    unsigned update_refs,
>   		    struct todo_list *todo_list)
>   {
>   	char shortonto[GIT_MAX_HEXSZ + 1];
> @@ -5637,6 +5741,9 @@ int complete_action(struct repository *r, struct replay_opts *opts, unsigned fla
>   		item->arg_len = item->arg_offset = item->flags = item->offset_in_buf = 0;
>   	}
>   
> +	if (update_refs && todo_list_add_update_ref_commands(todo_list))
> +		return -1;
> +