Re: [PATCH 3/3] index: do not warn about unrecognized extensions

[Ben Peart <peartben@gmail.com>]

On 11/12/2018 7:40 PM, Jonathan Nieder wrote:
> Documentation/technical/index-format explains:
> 
>       4-byte extension signature. If the first byte is 'A'..'Z' the
>       extension is optional and can be ignored.
> 
> This allows gracefully introducing a new index extension without
> having to rely on all readers having support for it.  Mandatory
> extensions start with a lowercase letter and optional ones start with
> a capital.  Thus the versions of Git acting on a shared local
> repository do not have to upgrade in lockstep.
> 
> We almost obey that convention, but there is a problem: when
> encountering an unrecognized optional extension, we write
> 
> 	ignoring FNCY extension
> 
> to stderr, which alarms users.  This means that in practice we have
> had to introduce index extensions in two steps: first add read
> support, and then a while later, start writing by default.  This
> delays when users can benefit from improvements to the index format.
> 
> We cannot change the past, but for index extensions of the future,
> there is a straightforward improvement: silence that message except
> when tracing.  This way, the message is still available when
> debugging, but in everyday use it does not show up so (once most Git
> users have this patch) we can turn on new optional extensions right
> away without alarming people.
> 

The best patch of the bunch. Glad to see it.

I'm fine with doing this via advise.unknownIndexExtension as well.  Who 
knows, someone may actually want to see this and not have tracing turned 
on.  I don't know who but it is possible :-)

> Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
> ---
> Thanks for reading.  Thoughts?
> 
> Sincerely,
> Jonathan
> 
>   read-cache.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/read-cache.c b/read-cache.c
> index 290bd54708..65530a68c2 100644
> --- a/read-cache.c
> +++ b/read-cache.c
> @@ -1720,7 +1720,7 @@ static int read_index_extension(struct index_state *istate,
>   		if (*ext < 'A' || 'Z' < *ext)
>   			return error("index uses %.4s extension, which we do not understand",
>   				     ext);
> -		fprintf(stderr, "ignoring %.4s extension\n", ext);
> +		trace_printf("ignoring %.4s extension\n", ext);
>   		break;
>   	}
>   	return 0;
>