Allow requirements to specify a default formula.

This allows default resolution of requirements without user intervention.

Closes Homebrew/homebrew#19627.

1 files changed, 12 insertions, 0 deletions

diff --git a/Library/Homebrew/requirement.rb b/Library/Homebrew/requirement.rb
index c20273895..4cae1f246 100644
--- a/Library/Homebrew/requirement.rb
+++ b/Library/Homebrew/requirement.rb
@@ -75,6 +75,11 @@ class Requirement
   end
 
   class << self
+    # The default formula to install to satisfy this requirement.
+    def default_formula(val=nil)
+      val.nil? ? @default_formula : @default_formula = val.to_s
+    end
+
     def fatal(val=nil)
       val.nil? ? @fatal : @fatal = val
     end
@@ -138,6 +143,13 @@ class Requirement
 
         next if prune
 
+        # TODO: Do this in a cleaner way, perhaps with another type of
+        # dependency type.
+        if req.class.default_formula
+          dependent.class.depends_on(req.class.default_formula)
+          next
+        end
+
         reqs << req
       end
     end