[POC][WIP] Pack recipes

[kbond]

Proposal for "scaffolds" as recipes as discussed with @nicolas-grekas and @weaverryan as a possible alternative to symfony/maker-bundle#1085.

• Scaffolds make sense to be packs as we want their dependencies installed but not the "empty package".
• Since scaffolds contain both require/require-dev dependencies, I had to modify the unpacker to allow for this.
• We want pack recipes installed but not unconfigured when the pack is uninstalled.
• Pack/Scaffold recipes cannot be updated/uninstalled. I think this makes sense as they will likely be heavily modified.

Recipe PR: symfony/recipes#1088

Test:

symfony new project
cd project
export SYMFONY_ENDPOINT=https://raw.githubusercontent.com/symfony/recipes/flex/pull-1088/index.json
composer config repositories.homepage vcs [email protected]:kbond/homepage-scaffold
composer config repositories.flex vcs [email protected]:kbond/flex
composer require symfony/flex:dev-pack-recipes
composer require kbond/homepage-scaffold # installs the "scaffold"
vendor/bin/phpunit # 1 test should run & pass

TODO:

• If installing a scaffold with --dev, you get all the deps in require-dev.
• Way to determine if a recipe is a pack on unconfigure.
• Higher priority for pack recipes. This will allow files in pack recipes to take precedence over their dependency recipes (like metapackages do now).

[kbond]

I could not figure out how to determine if the recipe is a pack or not here. $recipe->getPackage()->getType === null.

[kbond]

Closing in favour of #923.