Re: [PATCH] Teach checkout the -n|--dry-run option

From: Junio C Hamano <gitster@pobox.com>
Date: May 7, 2011, 19:24 UTC
Message-ID: <7vfwoqwby5.fsf@alter.siamese.dyndns.org>
In-Reply-To: <7vhb97xx5g.fsf@alter.siamese.dyndns.org>

Junio C Hamano <gitster@pobox.com> writes:

Show 17 quoted lines

> In other words, can't the check you need in submodule be scripted around
> the specific plumbing responsible for the branch switching, which is:
>
>     $ git read-tree -m HEAD $other_branch
>
>> @@ -397,7 +400,7 @@ static int merge_working_tree(struct checkout_opts *opts,
>>
>>  		/* 2-way merge to the new branch */
>>  		topts.initial_checkout = is_cache_unborn();
>> -		topts.update = 1;
>> +		topts.update = !opts->dry_run;
>>  		topts.merge = 1;
>>  		topts.gently = opts->merge && old->commit;
>>  		topts.verbose_update = !opts->quiet;
>
> What you are doing in this part of your patch is exactly that two-tree
> form of the "read-tree -m", no?

That is, this would succeed:

	$ git reset --hard master
        $ git read-tree --index-output=rubbish -m master next
        
and these would fail:

	$ git reset --hard master
	$ echo >>Makefile
        $ git read-tree --index-output=rubbish -m master next
        error: Entry 'Makefile' not uptodate. Cannot merge.

	$ git reset --hard master
	$ echo >>Makefile
	$ git add Makefile
        $ git read-tree --index-output=rubbish -m master next
        error: Entry 'Makefile' would be overwritten by merge. Cannot merge.

Having said that, please do not discard your patch. After sleeping on this, I started to think that "checkout -n" might be a better interface than using the plumbing read-tree in the longer term, especially if you can enhance it to handle "checkout -m -n" to check if the local change can be merged without conflicts.

But if the only question you are interested in is "can I switch to that branch from the current state of the index and the working tree?", I would prefer to see if the script can use "read-tree -m" approach first.

We may also want to add "read-tree -n" so that you do not have to specify a dummy index output only to prevent from writing the real index over, though.