Add the spec from the possible list to specs and process
the spec’s dependencies by adding them to needed.
# File lib/rubygems/resolver.rb, line 384
def resolve_for_single needed, specs, dep, possible # :nodoc:
spec, act = activation_request dep, possible
specs = Gem::List.prepend specs, act
# Put the deps for at the beginning of needed
# rather than the end to match the depth first
# searching done by the multiple case code below.
#
# This keeps the error messages consistent.
needed = requests spec, act, needed
return needed, specs
end