Disallow initializing Versions with non-strings

Closes Homebrew/homebrew#23553.

Library/Homebrew/test/test_versions.rb

@@ -1,6 +1,19 @@
 require 'testing_env'
 require 'version'
 
+class VersionTests < Test::Unit::TestCase
+  def test_accepts_objects_responding_to_to_str
+    value = stub(:to_str => '0.1')
+    assert_equal '0.1', Version.new(value).to_s
+  end
+
+  def test_raises_for_non_string_objects
+    assert_raises(TypeError) { Version.new(1.1) }
+    assert_raises(TypeError) { Version.new(1) }
+    assert_raises(TypeError) { Version.new(:symbol) }
+  end
+end
+
 class VersionComparisonTests < Test::Unit::TestCase
   include VersionAssertions
 

Library/Homebrew/version.rb

@@ -163,7 +163,12 @@ class Version
   end
 
   def initialize(val, detected=false)
-    @version = val.to_s
+    if val.respond_to?(:to_str)
+      @version = val.to_str
+    else
+      raise TypeError, "Version value must be a string"
+    end
+
     @detected_from_url = detected
   end