Subject: Re: [PATCH v3] add status config and command line options for rename detection

From: "Eckhard Maaß" <[email-masked]>
Date: Sat, 12 May 2018 10:04:37 +0200

On Fri, May 11, 2018 at 12:56:39PM +0000, Ben Peart wrote:
> After performing a merge that has conflicts git status will, by default,
> attempt to detect renames which causes many objects to be examined.  In a
> virtualized repo, those objects do not exist locally so the rename logic
> triggers them to be fetched from the server. This results in the status call
> taking hours to complete on very large repos vs seconds with this patch.

I see where your need comes from, but as you based this on my little
patch one can achieve this already with tweaking diff.renames itself. I
do wonder why there is a special need for the status command here. And
if there is, I personally would like it more in a style that you could
take all the options provided by diff.*-configuration and prefix that
with status, eg status.diff.renames = true. What do you think? If you
really only need this for merges, maybe a more specialised option is
called for that only kicks in when there is a merge going on?

I would like that status behaves as similar as possible to
diff/show/log. Special options will pull away from that again - passing
-m to show or log will lead to the same performance issues, correct?
Could it be feasible to impose an overall time limit on the detection?

And after writing this I wonder what were your experience with just
tweaking renameLimit - setting it very low should have helped the
fetching from server part already, shouldn't it?

> Add --no-renames command line option to status that enables overriding the
> config setting from the command line. Add --find-renames[=<n>] command line
> option to status that enables detecting renames and optionally setting the
> similarity index.

Would it be reasonable to extend this so that we just use the same
machinery for parsing command line options for the diffcore options and
pass this along? It seems to me that git status wants the same init as
diff/show/log has anyway. But I like the direction towards passing more
command line options to the git status command. 

>  static void wt_longstatus_print_unmerged_header(struct wt_status *s)
> @@ -592,6 +595,9 @@ static void wt_status_collect_changes_worktree(struct wt_status *s)
>  	}
>  	rev.diffopt.format_callback = wt_status_collect_changed_cb;
>  	rev.diffopt.format_callback_data = s;
> +	rev.diffopt.detect_rename = s->detect_rename >= 0 ? s->detect_rename : rev.diffopt.detect_rename;
> +	rev.diffopt.rename_limit = s->rename_limit >= 0 ? s->rename_limit : rev.diffopt.rename_limit;
> +	rev.diffopt.rename_score = s->rename_score >= 0 ? s->rename_score : rev.diffopt.rename_score;
>  	copy_pathspec(&rev.prune_data, &s->pathspec);
>  	run_diff_files(&rev, 0);
>  }
> @@ -625,6 +631,9 @@ static void wt_status_collect_changes_index(struct wt_status *s)
>  	rev.diffopt.output_format |= DIFF_FORMAT_CALLBACK;
>  	rev.diffopt.format_callback = wt_status_collect_updated_cb;
>  	rev.diffopt.format_callback_data = s;
> +	rev.diffopt.detect_rename = s->detect_rename >= 0 ? s->detect_rename : rev.diffopt.detect_rename;
> +	rev.diffopt.rename_limit = s->rename_limit >= 0 ? s->rename_limit : rev.diffopt.rename_limit;
> +	rev.diffopt.rename_score = s->rename_score >= 0 ? s->rename_score : rev.diffopt.rename_score;
>  	copy_pathspec(&rev.prune_data, &s->pathspec);
>  	run_diff_index(&rev, 1);
>  }
> @@ -982,6 +991,9 @@ static void wt_longstatus_print_verbose(struct wt_status *s)
>  	setup_revisions(0, NULL, &rev, &opt);
>  
>  	rev.diffopt.output_format |= DIFF_FORMAT_PATCH;
> +	rev.diffopt.detect_rename = s->detect_rename >= 0 ? s->detect_rename : rev.diffopt.detect_rename;
> +	rev.diffopt.rename_limit = s->rename_limit >= 0 ? s->rename_limit : rev.diffopt.rename_limit;
> +	rev.diffopt.rename_score = s->rename_score >= 0 ? s->rename_score : rev.diffopt.rename_score;
>  	rev.diffopt.file = s->fp;
>  	rev.diffopt.close_file = 0;
>  	/*

Somehow I am inclined that those should be factored out to a common
method if the rest of the patch stays as it is.

Greetings,
Eckhard