CYGPORT: add configurable compressor for GIT class.

[Jon Turney]

On 10/06/2025 11:46, Carlo B. via Cygwin-apps wrote:
> Hello,
> I created a patch for implementing this feature inside cygport.
> I did several tests and it worked fine in my opinion.
> I hope that you will find this useful.

Thanks very much. This is great!

In future, if possible, please use patches generated by 'git 
format-patch', since it means there's less work for me to apply them 
with proper commentary and attribution.

> +       local _COMPRESSION_OPT COMPRESSION_EXT;

Seems like _COMPRESSION_EXT is meant here?

> -           TAR_COMPRESSION_OPT="-j"
> +           _COMPRESSION_OPT="${_tar_bz2_flag}"
>             ;;

Since _tar_bz2_flag might evaluate to "-I pbzip -", the comments below 
also apply here.

(And the use of '-j' might actually be deliberate here: long-ago, before 
we switched to xz compression for packages, there were some problems 
where setup would choke on pbzip-compressed packages, but I think that 
was all fixed)

(Indeed, digging into the history of the before-times finds 
56bfaecf0f91fad9174b15e07bf73e65699d3543 :))

> +       zst)
> +               _COMPRESSION_OPT="--zstd -"

Hmmm... embedding the implicit understanding of the option syntax here 
seems like a bad idea. (i.e. where this result is used it will be 
followed by more option letters, so we need a trailing '-')

It seems like a better idea to explicitly have a separate group of 
options after where this is used, with their own '-'?

And indeed, a few lines down, this is used like

> 	TAR_COMPRESSION_OPT=$(__tar_compress_opt ${TAR_COMPRESSION_EXT})
[...]
> 
> 	tar ${TAR_COMPRESSION_OPT} ${TAR_SOURCE_DATE_OPTS} --owner=Guest:501 --group=None:513 -cvf "$@"

which seems like is going to end up with a bare '-' passed to tar when 
zstd is selected...

The new function introduced (__tar_compress_opt) needs adding to the 
list of functions marked readonly at the end of the file (as this is 
seems to be good style for shell scripts)

I tweaked the patch to address those issues and applied it.


Then I generalized this so it applies to the source archives generated 
from bzr/cvs/fossil/hg/mtn/svn as well, so the variable which controls 
this is called 'VCS_COMPRESSION_EXT' now.

However, I left the default as 'bz2', as I have some concerns about 
changing it: If you try to unpack and build an old source package built 
using the old default with a cygport with a new default, it won't work 
unless you explicitly set VCS_COMPRESSION_EXT.

Not sure how that should be designed.

So for the moment, you'll probably want to add VCS_COMPRESSION_EXT=xz to 
your local ~/.cygport.conf file.


Thanks again!