wip: Fall back to CPAN by default. #55

[miyagawa]

Change the default behavior (configuration option to be added later) to fallback to CPAN if the module doesn't exist in the custom mirror.

TODO:

• this breaks mirror.t where you run carmel install for the first time (without snapshot) with a custom mirror, you expect to pull the version if it exists in the mirror, but the current implementation pulls the latest from CPAN.

[miyagawa]

When you have HTTP-Tiny-0.078.tar.gz in your mirror index:

➜  cpanm --mirror file://$PWD/vendor/cache --info HTTP::Tiny -v 
cpanm (App::cpanminus) 1.7046 on perl 5.034001 built for darwin-2level
Work directory is /Users/miyagawa/.cpanm/work/1654067874.5707
You have make /usr/bin/make
You have LWP 6.66
You have /usr/bin/tar: bsdtar 3.5.1 - libarchive 3.5.1 zlib/1.2.11 liblzma/5.0.5 bz2lib/1.0.8 
You have /usr/bin/unzip
Searching HTTP::Tiny () on cpanmetadb ...
DAGOLDEN/HTTP-Tiny-0.080.tar.gz

➜  cpanm -M file://$PWD/vendor/cache --info HTTP::Tiny -v       
cpanm (App::cpanminus) 1.7046 on perl 5.034001 built for darwin-2level
Work directory is /Users/miyagawa/.cpanm/work/1654067884.5742
You have make /usr/bin/make
You have LWP 6.66
You have /usr/bin/tar: bsdtar 3.5.1 - libarchive 3.5.1 zlib/1.2.11 liblzma/5.0.5 bz2lib/1.0.8 
You have /usr/bin/unzip
Searching HTTP::Tiny on mirror file:///tmp/scratch/vendor/cache ...
Downloading index file file:///tmp/scratch/vendor/cache/modules/02packages.details.txt.gz ...
DAGOLDEN/HTTP-Tiny-0.078.tar.gz

We need --mirror-only (-M) to stop searching for CPAN but that's exactly what this PR disables.