Update URI::Generic.build/build2 to use RFC3986_PARSER

In bb83f32, a new URI parser was introduced to support RFC3986, where
previously support was limited to RFC2396. The default parser used by
URI() was updated to point to the new parser.

However, the parser used by URI::Generic.build and build2 still points
at the old parser. Among other things this means that hostnames with
underscores can't correctly be parsed by this method.

This commit switches to explicitly use the newer parser for these
methods, and adds a previously failing test that now passes.

lib/uri/generic.rb

@@ -158,7 +158,7 @@ def self.build(args)
     # +fragment+::
     #   Part of the URI after '#' character.
     # +parser+::
-    #   Parser for internal use [URI::DEFAULT_PARSER by default].
+    #   Parser for internal use [URI::RFC3986_PARSER by default].
     # +arg_check+::
     #   Check arguments [false by default].
     #
@@ -171,7 +171,7 @@ def initialize(scheme,
                    path, opaque,
                    query,
                    fragment,
-                   parser = DEFAULT_PARSER,
+                   parser = RFC3986_PARSER,
                    arg_check = false)
       @scheme = nil
       @user = nil
@@ -182,7 +182,7 @@ def initialize(scheme,
       @query = nil
       @opaque = nil
       @fragment = nil
-      @parser = parser == DEFAULT_PARSER ? nil : parser
+      @parser = parser == RFC3986_PARSER ? nil : parser
 
       if arg_check
         self.scheme = scheme
@@ -284,13 +284,13 @@ def registry # :nodoc:
 
     # Returns the parser to be used.
     #
-    # Unless a URI::Parser is defined, DEFAULT_PARSER is used.
+    # Unless a URI::Parser is defined, RFC3986_PARSER is used.
     #
     def parser
       if !defined?(@parser) || !@parser
-        DEFAULT_PARSER
+        RFC3986_PARSER
       else
-        @parser || DEFAULT_PARSER
+        @parser || RFC3986_PARSER
       end
     end
 

test/uri/test_generic.rb

@@ -841,6 +841,10 @@ def test_build
     assert_equal(":5432", u.to_s)
     assert_equal(5432, u.port)
 
+    u = URI::Generic.build(:host => "underscore_host.test")
+    assert_equal("//underscore_host.test", u.to_s)
+    assert_equal("underscore_host.test", u.host)
+
     u = URI::Generic.build(:scheme => "http", :host => "::1", :path => "/bar/baz")
     assert_equal("http://[::1]/bar/baz", u.to_s)
     assert_equal("[::1]", u.host)