Re: [PATCH] t3910: show failure of core.precomposeunicode with decomposed filenames

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

Jeff King <peff@peff.net> writes:

> This patch just adds a test to demonstrate the breakage.
> Some possible fixes are:
> ...
>   2. Do all index filename comparisons using a UTF-8 aware
>      comparison function when core.precomposeunicode is set.
>      This would probably have bad performance, and somewhat
>      defeats the point of converting the filenames at the
>      readdir level in the first place.

As we do this only when core.precomposeunicode is set, projects that
use pathnames encoded not in UTF-8 (e.g. 8859-1, EUC, etc.) will not
be affected by getting their path mangled, as long as we won't flip
the default to true (which I am not suggesting to do, by the way).

>   3. Convert index filenames to their precomposed form when
>      we read the index from disk. This would be efficient,
>      but we would have to be careful not to write the
>      precomposed forms back out to disk.

I think this may be the right approach, especially if you are going
to do this only when core.precomposeunicode is set.

the reasoning behind "we would have to be careful not to write"
part, is unclear to me, though.  Don't decomposing filesystems
perform the manglig from the precomposed form without even being
asked to do so, just like a case insensitive filesystem will
overwrite an existing "makefile" on a request to write to
"Makefile"?

>   4. Introduce some infrastructure to efficiently match up
>      the precomposed/decomposed forms. We already do
>      something similar for case-insensitive files using
>      name-hash.c. We might be able to adapt that strategy
>      here.
>
> Signed-off-by: Jeff King <peff@peff.net>
> ---
>  t/t3910-mac-os-precompose.sh | 10 ++++++++++
>  1 file changed, 10 insertions(+)
>
> diff --git a/t/t3910-mac-os-precompose.sh b/t/t3910-mac-os-precompose.sh
> index e4ba601..23aa61e 100755
> --- a/t/t3910-mac-os-precompose.sh
> +++ b/t/t3910-mac-os-precompose.sh
> @@ -140,6 +140,16 @@ test_expect_success "Add long precomposed filename" '
>  	git add * &&
>  	git commit -m "Long filename"
>  '
> +
> +test_expect_failure 'handle existing decomposed filenames' '
> +	echo content >"verbatim.$Adiarnfd" &&
> +	git -c core.precomposeunicode=false add "verbatim.$Adiarnfd" &&
> +	git commit -m "existing decomposed file" &&
> +	>expect &&
> +	git ls-files --exclude-standard -o "verbatim*" >untracked &&
> +	test_cmp expect untracked
> +'
> +
>  # Test if the global core.precomposeunicode stops autosensing
>  # Must be the last test case
>  test_expect_success "respect git config --global core.precomposeunicode" '