load tap formula through direct search

Library/Homebrew/exceptions.rb

@@ -65,6 +65,25 @@ class TapFormulaUnavailableError < FormulaUnavailableError
   end
 end
 
+class TapFormulaAmbiguityError < RuntimeError
+  attr_reader :name, :paths, :formulae
+
+  def initialize name, paths
+    @name = name
+    @paths = paths
+    @formulae = paths.map do |path|
+      path.to_s =~ HOMEBREW_TAP_PATH_REGEX
+      "#{$1}/#{$2.sub("homebrew-", "")}/#{path.basename(".rb")}"
+    end
+
+    super <<-EOS.undent
+      Formulae found in multiple taps: #{formulae.map { |f| "\n       * #{f}" }.join}
+
+      Please use the fully-qualified name e.g. #{formulae.first} to refer the formula.
+    EOS
+  end
+end
+
 class OperationInProgressError < RuntimeError
   def initialize name
     message = <<-EOS.undent

Library/Homebrew/formulary.rb

@@ -232,6 +232,13 @@ class Formulary
       return AliasLoader.new(possible_alias)
     end
 
+    possible_tap_formulae = tap_paths(ref)
+    if possible_tap_formulae.size > 1
+      raise TapFormulaAmbiguityError.new(ref, possible_tap_formulae)
+    elsif possible_tap_formulae.size == 1
+      return FormulaLoader.new(ref, possible_tap_formulae.first)
+    end
+
     possible_cached_formula = Pathname.new("#{HOMEBREW_CACHE_FORMULA}/#{ref}.rb")
     if possible_cached_formula.file?
       return FormulaLoader.new(ref, possible_cached_formula)
@@ -243,4 +250,12 @@ class Formulary
   def self.core_path(name)
     Pathname.new("#{HOMEBREW_LIBRARY}/Formula/#{name.downcase}.rb")
   end
+
+  def self.tap_paths(name)
+    name = name.downcase
+    Dir["#{HOMEBREW_LIBRARY}/Taps/*/*/"].map do |tap|
+      Pathname.glob(["#{tap}#{name}.rb", "#{tap}Formula/#{name}.rb",
+                     "#{tap}HomebrewFormula/#{name}.rb"])
+    end.flatten.select(&:file?)
+  end
 end