Extract unsatisfied dependency logic from installer

Library/Homebrew/dependency.rb

@@ -42,6 +42,14 @@ class Dependency
     ARGV.formulae.include?(to_formula) rescue false
   end
 
+  def satisfied?
+    installed? && missing_options.empty?
+  end
+
+  def missing_options
+    options - Tab.for_formula(to_formula).used_options
+  end
+
   def universal!
     tags << 'universal' if to_formula.build.has_option? 'universal'
   end

Library/Homebrew/exceptions.rb

@@ -77,6 +77,15 @@ class FormulaInstallationAlreadyAttemptedError < Homebrew::InstallationError
   end
 end
 
+class UnsatisfiedDependencyError < Homebrew::InstallationError
+  def initialize(f, dep)
+    super f, <<-EOS.undent
+    #{f} dependency #{dep} not installed with:
+      #{dep.missing_options * ', '}
+    EOS
+  end
+end
+
 class UnsatisfiedRequirements < Homebrew::InstallationError
   attr :reqs
 

Library/Homebrew/formula_installer.rb

@@ -143,16 +143,10 @@ class FormulaInstaller
             dep.universal! unless dep.build?
           end
 
-          dep_f = dep.to_formula
+          if dep.satisfied?
-          dep_tab = Tab.for_formula(dep)
+            Dependency.prune
-          missing = dep.options - dep_tab.used_options
+          elsif dep.installed?
-
+            raise UnsatisfiedDependencyError.new(f, dep)
-          if dep.installed?
-            if missing.empty?
-              Dependency.prune
-            else
-              raise "#{f} dependency #{dep} not installed with:\n  #{missing*', '}"
-            end
           end
         end
       end