Re: [PATCH] experimental: default to fetch.writeCommitGraph=false

[Junio C Hamano <gitster@pobox.com>]

Jonathan Nieder <jrnieder@gmail.com> writes:

> The fetch.writeCommitGraph feature makes fetches write out a commit

> In other words:
>
> - this patch only affects behavior with feature.experimental=true
>
> - it makes feature.experimental match the configuration Google has
>   been using for the last few months, meaning it would leave users in
>   a better tested state than without it
>
> - this should improve testing for other features guarded by
>   feature.experimental, by making feature.experimental safer to use


In other words, fetch.writeCommitGraph in its current form is too
broken to be recommended even for brave souls with "experimental"
bit on.

I wonder if we perhaps wnat to add to the documentation for
writeCommitGraph configuration that its use is currently not
recommended in a shallow clone or something (I know it is not
a problem just to use it with shallow but the breakage needs
to involve unshallowing, but by definition those who do not
use shallow would not hit the unshallowing bug, so...).

> Reported-by: Jay Conrod <jayconrod@google.com>
> Helped-by: Taylor Blau <me@ttaylorr.com>
> Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
> ---
> I realize this is late to send.  That said, as described above, I
> think it's a good way to buy time by minimizing user exposure to
> fetch.writeCommitGraph=true until a fix for it is well cooked.
>
> In other words, I'd like to see this patch in Git 2.28-rc0.

Yes, I do, too.

Thanks.

> diff --git a/Documentation/config/fetch.txt b/Documentation/config/fetch.txt
> index b1a9b1461d3..b20394038d1 100644
> --- a/Documentation/config/fetch.txt
> +++ b/Documentation/config/fetch.txt
> @@ -90,5 +90,4 @@ fetch.writeCommitGraph::
>  	the existing commit-graph file(s). Occasionally, these files will
>  	merge and the write may take longer. Having an updated commit-graph
>  	file helps performance of many Git commands, including `git merge-base`,
> -	`git push -f`, and `git log --graph`. Defaults to false, unless
> -	`feature.experimental` is true.
> +	`git push -f`, and `git log --graph`. Defaults to false.
> diff --git a/repo-settings.c b/repo-settings.c
> index dc6817daa95..0918408b344 100644
> --- a/repo-settings.c
> +++ b/repo-settings.c
> @@ -51,14 +51,14 @@ void prepare_repo_settings(struct repository *r)
>  		UPDATE_DEFAULT_BOOL(r->settings.index_version, 4);
>  		UPDATE_DEFAULT_BOOL(r->settings.core_untracked_cache, UNTRACKED_CACHE_WRITE);
>  	}
> +
>  	if (!repo_config_get_bool(r, "fetch.writecommitgraph", &value))
>  		r->settings.fetch_write_commit_graph = value;
> -	if (!repo_config_get_bool(r, "feature.experimental", &value) && value) {
> -		UPDATE_DEFAULT_BOOL(r->settings.fetch_negotiation_algorithm, FETCH_NEGOTIATION_SKIPPING);
> -		UPDATE_DEFAULT_BOOL(r->settings.fetch_write_commit_graph, 1);
> -	}
>  	UPDATE_DEFAULT_BOOL(r->settings.fetch_write_commit_graph, 0);
>  
> +	if (!repo_config_get_bool(r, "feature.experimental", &value) && value)
> +		UPDATE_DEFAULT_BOOL(r->settings.fetch_negotiation_algorithm, FETCH_NEGOTIATION_SKIPPING);
> +
>  	/* Hack for test programs like test-dump-untracked-cache */
>  	if (ignore_untracked_cache_config)
>  		r->settings.core_untracked_cache = UNTRACKED_CACHE_KEEP;