FormulaInstaller: split up big method

Library/Homebrew/formula_installer.rb

@@ -140,21 +140,16 @@ class FormulaInstaller
     end
   end
 
-  def effective_deps
-    @deps ||= begin
-      deps = Set.new
-
-      # If a dep was also requested on the command line, we let it honor
-      # any influential flags (--HEAD, --devel, etc.) the user has passed
-      # when we check the installed status.
-      requested_deps = f.recursive_dependencies.select do |dep|
-        dep.requested? && !dep.installed?
+  # Dependencies of f that were also explicitly requested on the command line.
+  # These honor options like --HEAD and --devel.
+  def requested_deps
+    f.recursive_dependencies.select { |dep| dep.requested? && !dep.installed? }
   end
 
-      # Otherwise, we filter these influential flags so that they do not
-      # affect installation prefixes and other properties when we decide
-      # whether or not the dep is needed.
-      necessary_deps = ARGV.filter_for_dependencies do
+  # All dependencies that we must install before installing f.
+  # These do not honor flags like --HEAD and --devel.
+  def necessary_deps
+    ARGV.filter_for_dependencies do
       f.recursive_dependencies do |dependent, dep|
         if dep.optional? || dep.recommended?
           Dependency.prune unless dependent.build.with?(dep.name)
@@ -173,14 +168,16 @@ class FormulaInstaller
         end
       end
     end
+  end
 
-      deps.merge(requested_deps)
-      deps.merge(necessary_deps)
-
-      # Now that we've determined which deps we need, map them back
-      # onto recursive_dependencies to preserve installation order
+  # Combine requested_deps and necessary deps.
+  def filter_deps
+    deps = Set.new.merge(requested_deps).merge(necessary_deps)
     f.recursive_dependencies.select { |d| deps.include? d }
   end
+
+  def effective_deps
+    @effective_deps ||= filter_deps
   end
 
   def install_dependencies