cpanfile-faq - cpanfile FAQ
cpanfile is a simpler way to declare CPAN dependencies,
mainly to your application rather than CPAN distributions.
most CPAN distributions do not need to switch to
cpanfile unless they absolutely want to take advantage of some of the features (see below).
This is considered a new extension for applications and installers.
Here are some of the reasons that motivates the new cpanfile format.
First of all, it is annoying to write Makefile.PL when what you develop is not a CPAN distribution.
It gets more painful when you develop a web application that you want to deploy on a different environment using version control system (such as cloud infrastructure),
because it requires you to often commit the META file or
inc/ directory (or even worse,
botu) to a repository when your build script uses non-core modules such as Module::Install or File::Copy::Recursive.
Many web application frameworks generate a boiler-plate
Makefile.PL for dependency declaration and to let you install dependencies with
cpanm --installdeps .,
but that doesn't always mean they are meant to be installed.
Things can be often much simpler if you run the application from the checkout directory.
dependencies can be installed either globally or locally using supported tools such as cpanm or carton.
cpanfile lists all the dependencies of your entire application and will be updated over time,
it makes perfect sense to commit the file to a version control system,
and push the file for a deployment.
One of the limitation when I tried to implement a self-contained local::lib library path feature for cpanminus was that the configuration phase runs the build file as a separate perl process,
This makes it so hard for the script to not accidentally load any modules installed in the local
site_perl directory when determining the dynamic dependencies.
With the recent evolution of CPAN installer ecosystem such as local::lib support,
it makes things much easier if installers figure out whether dependencies are installed,
instead of by build tools such as Module::Install.
This is a new file type, but the format and syntax isn't entirely new. The metadata it can declare is exactly a subset of "Prereqs" in CPAN Meta Spec.
The syntax borrows a lot from Module::Install. Module::Install is a great way to easily declare module metadata such as name, author and dependencies. cpanfile format is simply to extract the dependencies into a separate file, which means most of the developers are familiar with the syntax.
cpanfile basically allows you to declare CPAN::Meta::Spec prerequisite specification using an easy Perl DSL syntax.
This makes it easy to declare per-phase dependencies and newer version 2 features such as conflicts and version ranges.
First of all, most distributions on CPAN are not required to update to this format.
If your application currently uses
for dependency declaration because of the current toolchain implementation (e.g.
cpanm --installdeps .),
you can upgrade to
cpanfile while keeping the build file based installation working for the backward compatibility.
TBD: Support in other tools such as MakeMaker