Re: [PATCH v9 3/5] history: add squash subcommand to fold a range

> ++
> +The range is given in the usual `<base>..<tip>` form, where _<base>_ is
> +the commit just below the oldest commit to squash. For example, `git
> +history squash HEAD~3..HEAD` folds the three most recent commits into
> +one, and `git history squash HEAD~5..HEAD~2` squashes an interior range
> +while leaving the two newest commits in place. Several revisions may be
> +given, for example `HEAD~3..HEAD ^topic` to additionally exclude what is
> +already on `topic`. Rev-list options may also be given, but any that would
> +change how the range is walked are overridden with a warning.
> ++
> +The oldest commit's message is preserved by default, except that an `amend!`
> +commit targeting it replaces its message.

>                                            Specify `--reedit-message` to edit
> +the resulting message. A merge commit inside the range is folded like any
> +other, but the range must have a single base, so a range that reaches more
> +than one entry point (for example a side branch that forked before the range
> +and was later merged into it) is rejected.
> ++
> +A `fixup!`, `squash!`, or `amend!` commit is refused unless the commit it
> +targets is also in the range, so the fold does not silently absorb a
> +marker meant for a commit outside it. The body after an `amend!` subject
> +replaces the oldest commit's message when the marker targets that commit.

> +As an exception, a range made up entirely of markers for one target is combined
> +into a single commit, keeping the last `amend!` message if there is one.
> ++
> +A branch or tag that points at a commit inside the range would be left
> +dangling once those commits are folded away, so with the default
> +`--update-refs=branches` the command refuses. Rerun with
> +`--update-refs=head` to rewrite only the current branch and leave such
> +refs pointing at the old commits.
> +
>  OPTIONS
>  -------
>  
> @@ -107,7 +147,8 @@ OPTIONS
>  	ref updates is generally safe.
>  
>  `--reedit-message`::
> -	Open an editor to modify the target commit's message.
> +	Open an editor to modify the rewritten commit's message. For `squash`
> +	the editor is pre-filled with the messages of all the folded commits.

> diff --git a/builtin/history.c b/builtin/history.c
> index cbba25096f..edf98a21d3 100644
> --- a/builtin/history.c
> +++ b/builtin/history.c
> +
> +	repo_init_revisions(repo, &revs, NULL);
> +	revs.reverse = 1;
> +	revs.topo_order = 1;
> +	revs.sort_order = REV_SORT_IN_GRAPH_ORDER;
> +	revs.simplify_history = 0;
> +	revs.boundary = 1;
> +
> +	strvec_push(&args, "ignored");
> +	strvec_push(&args, "--ancestry-path");
> +	strvec_pushv(&args, argv);
> +	setup_revisions_from_strvec(&args, &revs, NULL);
> +	if (args.nr != 1) {
> +		ret = error(_("unrecognized argument: %s"), args.v[1]);
> +		goto out;
> +	}
> +
> +	if (revs.reverse != 1 || revs.topo_order != 1 ||
> +	    revs.sort_order != REV_SORT_IN_GRAPH_ORDER ||
> +	    revs.simplify_history != 0) {
> +		warning(_("ignoring rev-list options that would change how the "
> +			  "range is walked"));
> +		revs.reverse = 1;
> +		revs.topo_order = 1;
> +		revs.sort_order = REV_SORT_IN_GRAPH_ORDER;
> +		revs.simplify_history = 0;
> +	}

> +
> +	base_tree_oid = &repo_get_commit_tree(repo, base)->object.oid;
> +	tip_tree_oid = &repo_get_commit_tree(repo, tip)->object.oid;
> +	commit_list_append(base, &parents);
> +
> +	ret = commit_tree_ext(repo, "squash", msg_source, message_template,
> +			      parents,
> +			      base_tree_oid, tip_tree_oid, &rewritten, flags);
> +	if (ret < 0) {
> +		ret = error(_("failed writing squashed commit"));
> +		goto out;
> +	}
> +
> +	strbuf_addf(&reflog_msg, "squash: updating %s", argv[0]);