Add support of aliases for Method

Fix issue #367 (stat command should display the list of aliases for a
given method).

You can get a list of aliases for a method like this:

  pry(main)> stat Array#map
  Method Information:
  --
  Name: map
  Alias: collect
  Owner: Array
  Visibility: public
  Type: Unbound
  Arity: 0
  Method Signature: map()
  Source Location: Not found.

Note that `Method#aliases` returns an Array of strings on MRI 1.8 and
friends, while on MRI 1.9 it returns an Array of symbols.

Signed-off-by: Kyrylo Silin <kyrylosilin@gmail.com>

lib/pry/commands/stat.rb

@@ -16,10 +16,13 @@ class Pry
 
     def process
       meth = method_object
+      aliases = meth.aliases
+
       output.puts unindent <<-EOS
         Method Information:
         --
         Name: #{meth.name}
+        Alias#{ "es" if aliases.length > 1 }: #{ aliases.any? ? aliases.join(", ") : "None." }
         Owner: #{meth.owner ? meth.owner : "Unknown"}
         Visibility: #{meth.visibility}
         Type: #{meth.is_a?(::Method) ? "Bound" : "Unbound"}

lib/pry/method.rb

@@ -403,6 +403,23 @@ class Pry
       source_file == Pry.eval_path
     end
 
+    # @return [Array<Symbol>] All known aliases for the method. For Ruby 1.8 and
+    #   friends returns [Array<String>].
+    def aliases
+      owner = @method.owner
+      # Avoid using `to_sym` on {Method#name}, which returns a `String`, because
+      # it won't be garbage collected.
+      name = @method.name
+
+      alias_list = owner.instance_methods.combination(2).select do |pair|
+        owner.instance_method(pair.first) == owner.instance_method(pair.last) &&
+          pair.include?(name)
+      end.flatten
+      alias_list.delete(name)
+
+      alias_list
+    end
+
     # @return [Boolean] Is the method definitely an alias?
     def alias?
       name != original_name

test/test_method.rb

@@ -397,5 +397,50 @@ describe Pry::Method do
       meth.send(:method_name_from_first_line, "def obj_name.x").should == "x"
     end
   end
+
+  describe 'method aliases' do
+    before do
+      @class = Class.new {
+        def eat
+        end
+
+        alias fress eat
+        alias_method :omnomnom, :fress
+
+        def eruct
+        end
+      }
+    end
+
+    it 'should be able to find method aliases' do
+      meth = Pry::Method(@class.new.method(:eat))
+
+      if Pry::Helpers::BaseHelpers.mri_19?
+        meth.aliases.should == [:fress, :omnomnom]
+      else
+        meth.aliases.sort.map(&:to_sym).should == [:fress, :omnomnom]
+      end
+    end
+
+    it 'should return an empty Array if cannot find aliases' do
+      meth = Pry::Method(@class.new.method(:eruct))
+      meth.aliases.should.be.empty
+    end
+
+    it 'should not include the own name in the list of aliases' do
+      meth = Pry::Method(@class.new.method(:eat))
+
+      meth.aliases.should.not.include :eat
+      meth.aliases.should.not.include "eat" # For Ruby 1.8 and friends.
+    end
+
+    if Pry::Helpers::BaseHelpers.mri_18? || Pry::Helpers::BaseHelpers.mri_19?
+      it 'should be able to find aliases for methods implemented in C' do
+        meth = Pry::Method(Hash.new.method(:key?))
+        meth.aliases.should == [:include?, :member?, :has_key?]
+      end
+    end
+
+  end
 end