Potential opportunity for partial functionality without installer

[kentfredric]

In some discussion in #distzilla on irc.perl.org, we realised something:

That you could potentially support at very least doing

cpanm --installdeps .

With just a META.json, and no *.PL

Presently, if all you have is META.json, cpanm --installdeps . can only go as far as installing configure_requires, because it relies on an installer being present to generate MYMETA.json and resolve subsequent dependencies.

However, it seems possible to get useful behaviour, as long as:

1. There is no Build.PL / Makefile.PL
2. META.json says "dynamic_config": "0"

Then you can safely assume that the dependencies in META.json will not change in the production of MYMETA.json, and in the absence of an installer, simply assume META.json as a viable drop in.

And this would at least render a useful behaviour from --installdeps

You could possibly even get more useful behaviour, and potentially even install distributions that didn't explicitly ship with an installer script, assuming the above conditions are true, with

perl -MModule::Build::Tiny -e 'BuildPL(); Build(); Build("install")'

Though there's a degree of debate in my mind how "safe" that is to do, especially if for example, META.json has anything at all in configure.requires

If configure.requires however only contains Module::Build::Tiny, then it is indeed safe to do the above invocation in the absence of a Build.PL

And I guess by proxy you could attempt some sane behaviour by autovivifying a configure script as long as configure.requires contained only ExtUtils::MakeMaker or Module::Build, though I'm not 100% sure on the former.

Maybe an experimental option like --allow-no-installer would be required to trigger this behaviour.

[miyagawa]

With just a META.json, and no *.PL

Yes. This is something i always have had in mind.