Restore EMAIL_PREFIX from WHATWG HTML LS

Effectively reverts 3233592 and
7363a13.

The original regex intentionally allowed consecutive dots (..) in the
local part.

Author: osyoyu

lib/uri/mailto.rb

@@ -52,11 +52,7 @@ class MailTo < Generic
     HEADER_REGEXP  = /\A(?<hfield>(?:%\h\h|[!$'-.0-;@-Z_a-z~])*=(?:%\h\h|[!$'-.0-;@-Z_a-z~])*)(?:&\g<hfield>)*\z/
     # practical regexp for email address
     # https://html.spec.whatwg.org/multipage/input.html#valid-e-mail-address
-    EMAIL_REGEXP = %r[\A#{
-      atext = %q[(?:[a-zA-Z0-9!\#$%&'*+\/=?^_`{|}~-]+)]
-    }(?:\.#{atext})*@#{
-      label = %q[(?:[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)]
-    }(?:\.#{label})*\z]
+    EMAIL_REGEXP = /\A(?!\.)[a-zA-Z0-9.!\#$%&'*+\/=?^_`{|}~-]+(?<!\.)@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(?:\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*\z/
     # :startdoc:
 
     #

test/uri/test_mailto.rb

@@ -145,6 +145,10 @@ def test_check_to
     u.to = 'a@valid.com'
     assert_equal(u.to, 'a@valid.com')
 
+    # Intentionally allowed violations of RFC 5322
+    u.to = 'a..a@valid.com'
+    assert_equal(u.to, 'a..a@valid.com')
+
     # Invalid emails
     assert_raise(URI::InvalidComponentError) do
       u.to = '#1@mail.com'
@@ -166,10 +170,6 @@ def test_check_to
       u.to = 'n.@invalid.email'
     end
 
-    assert_raise(URI::InvalidComponentError) do
-      u.to = 'n..t@invalid.email'
-    end
-
     # Invalid host emails
     assert_raise(URI::InvalidComponentError) do
       u.to = 'a@.invalid.email'