Dependency.expand_dependencies

Move Formula.expand_dependencies into the Dependency class, and extend
it to allow arbitrary filters to be applied when enumerating deps.

When supplied with a block, expand_dependencies will yield a [dependent,
dependency] pair for each dependency, allowing callers to filter out
dependencies that may not be applicable or useful in a given situation.

Deps can be skipped by simple calling Dependency.prune in the block,
e.g.:

  Dependency.expand_dependencies do |f, dep|
    Dependency.prune if dep.to_formula.installed?
  end

The return value of the method is the filtered list.

If no block is supplied, a default filter that omits optional or
recommended deps based on what the dependent formula has requested is
applied.

Formula#recursive_dependencies is now implemented on top of this,
allowing FormulaInstaller to exact detailed control over what deps are
installed. `brew missing` and `brew upgrade` can learn to use this to
apply the installed options set when expanding dependencies.

Move Formula.expand_deps and Formula#recursive_deps into compat, because
these methods do not respect the new optional and recommended tags and
thus should no longer be used.

Library/Homebrew/compat/compatibility.rb

@@ -99,6 +99,21 @@ class Formula
       val.nil? ? @bottle_sha1 : @bottle_sha1 = val
     end
   end
+
+  # These methods return lists of Formula objects.
+  # They are eprecated in favor of Dependency::expand_dependencies
+  # and Formula#recursive_dependencies, which return lists of
+  # Dependency objects instead.
+  def self.expand_deps f
+    f.deps.map do |dep|
+      f_dep = Formula.factory dep.to_s
+      expand_deps(f_dep) << f_dep
+    end
+  end
+
+  def recursive_deps
+    Formula.expand_deps(self).flatten.uniq
+  end
 end
 
 class UnidentifiedFormula < Formula

Library/Homebrew/dependencies.rb

@@ -177,6 +177,32 @@ class Dependency
   def requested?
     ARGV.formulae.include?(to_formula) rescue false
   end
+
+  # Expand the dependencies of f recursively, optionally yielding
+  # [f, dep] to allow callers to apply arbitrary filters to the list.
+  # The default filter, which is used when a block is not supplied,
+  # omits optionals and recommendeds based on what the dependent has
+  # asked for.
+  def self.expand(dependent, &block)
+    dependent.deps.map do |dep|
+      prune = catch(:prune) do
+        if block_given?
+          yield dependent, dep
+        elsif dep.optional? || dep.recommended?
+          Dependency.prune unless dependent.build.with?(dep.name)
+        end
+      end
+
+      next if prune
+
+      expand(dep.to_formula, &block) << dep
+    end.flatten.compact.uniq
+  end
+
+  # Used to prune dependencies when calling expand_dependencies with a block.
+  def self.prune
+    throw(:prune, true)
+  end
 end
 
 # A base class for non-formula requirements needed by formulae.

Library/Homebrew/formula.rb

@@ -457,32 +457,10 @@ class Formula
     requirements.select { |r| r.is_a? ConflictRequirement }
   end
 
-  # for Formula objects
-  def self.expand_deps f
-    f.deps.map do |dep|
-      f_dep = Formula.factory dep.to_s
-      expand_deps(f_dep) << f_dep
-    end
-  end
-
-  # for Dependency objects
-  def self.expand_dependencies f
-    f.deps.map do |dep|
-      f_dep = Formula.factory dep.to_s
-      expand_dependencies(f_dep) << dep
-    end
-  end
-
-  # deps are in an installable order
-  # which means if a depends on b then b will be ordered before a in this list
-  def recursive_deps
-    Formula.expand_deps(self).flatten.uniq
-  end
-
-  # Like recursive_deps, but returns a list of Dependency objects instead
-  # of Formula objects.
-  def recursive_dependencies
-    Formula.expand_dependencies(self).flatten.uniq
+  # Returns a list of Dependency objects in an installable order, which
+  # means if a depends on b then b will be ordered before a in this list
+  def recursive_dependencies(&block)
+    Dependency.expand(self, &block)
   end
 
   # The full set of Requirements for this formula's dependency tree.