pathname.rb: fix a Pathname#relative_path_from crash on

* ext/pathname/lib/pathname.rb (SAME_PATHS):
  Pathname#relative_path_from uses String#casecmp to compare strings
  on case-insensitive filesystem platforms (e.g., Windows). This can
  return nil for strings with different encodings, and the code
  previously assumed that it always returned a Fixnum.  [Fix GH-713]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47591 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,11 @@
+Mon Sep 15 10:29:25 2014  Natalie Weizenbaum  <nweiz@google.com>
+
+	* ext/pathname/lib/pathname.rb (SAME_PATHS):
+	  Pathname#relative_path_from uses String#casecmp to compare strings
+	  on case-insensitive filesystem platforms (e.g., Windows). This can
+	  return nil for strings with different encodings, and the code
+	  previously assumed that it always returned a Fixnum.  [Fix GH-713]
+
 Mon Sep 15 09:43:18 2014  Sho Hashimoto  <sho.hsmt@gmail.com>
 
 	* ext/fiddle/lib/fiddle/import.rb (Fiddle::Importer#sizeof): fix typo,

ext/pathname/lib/pathname.rb

@@ -22,7 +22,8 @@ class Pathname
   end
 
   SAME_PATHS = if File::FNM_SYSCASE.nonzero?
-    proc {|a, b| a.casecmp(b).zero?}
+    # Avoid #zero? here because #casecmp can return nil.
+    proc {|a, b| a.casecmp(b) == 0}
   else
     proc {|a, b| a == b}
   end

test/pathname/test_pathname.rb

@@ -1374,4 +1374,17 @@ class TestPathname < Test::Unit::TestCase
       assert_equal("foo/bar", File.join(Pathname.new("foo"), Pathname.new("bar").taint))
     }.call
   end
+
+  def test_relative_path_from_casefold
+    assert_separately([], <<-'end;') #    do
+      module File::Constants
+        remove_const :FNM_SYSCASE
+        FNM_SYSCASE = FNM_CASEFOLD
+      end
+      require 'pathname'
+      foo = Pathname.new("fo\u{f6}")
+      bar = Pathname.new("b\u{e4}r".encode("ISO-8859-1"))
+      assert_instance_of(Pathname, foo.relative_path_from(bar))
+    end;
+  end
 end