Function to return a binary's Mach-O architectures

Added a utility method to get an array of architecture names for
a given executable.

This will be useful for, say, figuring out what Python was compiled for,
to know what to compile a C-based module as.

Signed Off By: Max Howell <max@methylblue.com>

I added a test and made the function use `which` if the path provided is not
absolute. I considered allowing relative paths, but then it is possible for
the function to take eg. the svn binary from the current directory when you
meant the one in the path, and that could be a confusing bug.

Library/Homebrew/unittest.rb

@@ -415,6 +415,15 @@ class BeerTasting <Test::Unit::TestCase
     assert_equal 10.7, f+0.1
   end
 
+  def test_arch_for_command
+    # NOTE only works on Snow Leopard I bet, pick a better file!
+    arches=arch_for_command '/usr/bin/svn'
+    assert_equal 3, arches.count
+    assert arches.include?(:x86_64)
+    assert arches.include?(:i386)
+    assert arches.include?(:ppc7400)
+  end
+
   def test_pathname_plus_yeast
     nostdout do
       assert_nothing_raised do

Library/Homebrew/utils.rb

@@ -99,3 +99,24 @@ def exec_editor *args
   # we don't have to escape args, and escaping 100% is tricky
   exec *(editor.split+args)
 end
+
+# provide an absolute path to a command or this function will search the PATH
+def arch_for_command cmd
+    archs = []
+    cmd = `which #{cmd}` if not Pathname.new(cmd).absolute?
+
+    IO.popen("file #{cmd}").readlines.each do |line|
+      case line
+      when /Mach-O executable ppc/
+        archs << :ppc7400
+      when /Mach-O 64-bit executable ppc64/
+        archs << :ppc64
+      when /Mach-O executable i386/
+        archs << :i386
+      when /Mach-O 64-bit executable x86_64/
+        archs << :x86_64
+      end
+    end
+
+    return archs
+end