multiple default_sources should have a configurable priority for automatic preferred_for behavior

[lamont-granquist]

The default behavior should not change, but users really want to be able to say "use all my :chef_repo cookbooks first, then use :supermarket second, and i don't want to tell you that my version of build-essentials should always take priority"

Right now that looks something like:

default_source :chef_repo, “./cookbooks” do |s|
  s.preferred_for *(Dir.entries(‘./cookbooks’) - [‘.’, ‘..’] & self.run_list.map {|c| c.split(‘::’).first})
end

The new DSL code should behave the same way so that if the :chef_repo takes priority over :supermaket then the presence of a build-essential-0.0.1 cookbook in the :chef_repo would take precedence over any version of build-essential in supermarket and there would be no crazy merging of actual versions -- presence of any version in a higher priority repo would knock out all versions in a lower priority repo.

[lamont-granquist]

And I swear this is a dup of a conversation that I've had with @danielsdeleo before, but this one has a better title with SEO for the keywords I was trying to search on, plus it has the existing workaround.

[lamont-granquist]

And the workaround obviously relies on ruby local pathing hacks so won't work for private-supermarket-overriding-public-supermarket or any other use case outside of :chef_repo I think.

[danielsdeleo]

Yeah, if it's opt-in it's probably ok, especially since folks will just hack around it if we don't provide something. It would be extra awesome if we could detect in chef update if a cookbook moved from one default source to another and make that really clear. Or even have a mode where you have to explicitly allow cookbooks to move between sources, e.g.,

chef update
=> Error: you've been getting cookbook build-essentials from the public supermarket but now it's gonna come from private supermarket. Use `chef update --nah-its-fine` if this is cool
chef update --nah-its-fine
=> (success)

[danielsdeleo]

In terms of hacks you could do with the current code, if you wanted one source to win for everything, I think this would work:

all_the_things = Object.new
def all_the_things.==(other); true; end
s.preferred_for all_the_things

But I haven't tried it so caveat emptor.