ruby · nobu · Jun 14, 2012
diff --git a/NEWS b/NEWS
@@ -25,6 +25,10 @@ with all sufficient information, see the ChangeLog file.
     * aliased method:
       * ENV.to_h is a new alias for ENV.to_hash
 
+  * File
+    * added method:
+      * added File.rootname returns root part of file name.
+
   * Hash
     * added method:
       * added Hash#to_h as explicit conversion method, like Array#to_a.

diff --git a/file.c b/file.c
@@ -3765,6 +3765,48 @@ rb_file_dirname(VALUE fname)
     return dirname;
 }
 
+/*
+ *  call-seq:
+ *     File.rootname(file_name )  ->  root_name
+ *
+ *  Returns root part of the filename given in <i>file_name</i>.
+ *  Returns an empty string if <i>file_name</i> is not an absolute
+ *  path.
+ *
+ *  * On Unix
+ *     File.rootname("/home/gumby/work/ruby.rb")        #=> "/"
+ *     File.rootname("home/gumby/work/ruby.rb")         #=> ""
+ *
+ *  * On Windows
+ *     File.rootname("c:/Users/gumby/work/ruby.rb")     #=> "c:/"
+ *     File.rootname("//host/share/gumby/work/ruby.rb") #=> "//host/share/"
+ *     File.rootname("home/gumby/work/ruby.rb")         #=> ""
+ */
+
+static VALUE
+rb_file_s_rootname(VALUE klass, VALUE fname)
+{
+    const char *name, *root, *end;
+    VALUE rootname;
+    rb_encoding *enc;
+
+    FilePathStringValue(fname);
+    name = StringValueCStr(fname);
+    end = name + RSTRING_LEN(fname);
+    enc = rb_enc_get(fname);
+    root = skipprefix(name, end, enc);
+    if (root < end && isdirsep(*root)) root++;
+#if defined(DOSISH_UNC) || defined(DOSISH_DRIVE_LETTER)
+    if (root == name + 2 && name[1] == ':') root = name;
+# ifndef __CYGWIN__
+    else if (root == name + 1) root = name;
+# endif
+#endif
+    rootname = rb_enc_str_new(name, root - name, enc);
+    OBJ_INFECT(rootname, fname);
+    return rootname;
+}
+
 /*
  * accept a String, and return the pointer of the extension.
  * if len is passed, set the length of extension to it.
@@ -5460,6 +5502,7 @@ Init_File(void)
     rb_define_singleton_method(rb_cFile, "basename", rb_file_s_basename, -1);
     rb_define_singleton_method(rb_cFile, "dirname", rb_file_s_dirname, 1);
     rb_define_singleton_method(rb_cFile, "extname", rb_file_s_extname, 1);
+    rb_define_singleton_method(rb_cFile, "rootname", rb_file_s_rootname, 1);
     rb_define_singleton_method(rb_cFile, "path", rb_file_s_path, 1);
 
     separator = rb_obj_freeze(rb_usascii_str_new2("/"));

diff --git a/test/ruby/test_file_exhaustive.rb b/test/ruby/test_file_exhaustive.rb
@@ -522,6 +522,30 @@ def test_extname
     assert_incompatible_encoding {|d| File.extname(d)}
   end
 
+  def assert_rootname(expect, path, *rest)
+    assert_equal(expect, File.rootname(path), *rest)
+  end
+
+  if /cygwin|mswin|bccwin|mingw|emx/ =~ RUBY_PLATFORM
+    alias assert_rootname_slash assert_rootname
+    def assert_rootname(expect, path, *rest)
+      assert_rootname_slash(expect, path, *rest)
+      assert_rootname_slash(expect.tr("/", "\\"), path.tr("/", "\\"), *rest)
+    end
+  end
+
+  def test_rootname
+    if /cygwin|mswin|bccwin|mingw|emx/ =~ RUBY_PLATFORM
+      assert_rootname("c:/", "c:/Users/gumby/work/ruby.rb")
+      assert_rootname("//host/share/", "//host/share/gumby/work/ruby.rb")
+      assert_rootname("//./device/", "//./device/foo")
+      assert_rootname("", "c:gumby/work/ruby.rb")
+    end
+    root = /mswin|bccwin|mingw|emx/ =~ RUBY_PLATFORM ? "" : "/"
+    assert_rootname(root, "/Users/gumby/work/ruby.rb")
+    assert_rootname("", "home/gumby/work/ruby.rb")
+  end
+
   def test_split
     d, b = File.split(@file)
     assert_equal(File.dirname(@file), d)