minor #454 Conform to IDNA version 15.1.0 revision 31 (TRowbotham)

This PR was merged into the 1.x branch.

Discussion
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Conform to IDNA version 15.1.0 revision 31

This adds the necessary changes to conform to [IDNA version 15.1.0 revision 31](https://www.unicode.org/reports/tr46/tr46-31.html#Modifications).

Notable Changes

* Transitional processing (the default in PHP) is now deprecated. No deprecation notices were added as PHP does not yet report a deprecation notice in this case.
* An error is no longer recorded for characters with a status of disallowed.
* When performing code point mapping and transitional processing is enabled the code point U+1E9E capital sharp s (ẞ), is replaced by the string “ss”
* A new internal option "IgnoreInvalidPunycode" was added, which is supposed to allow for an all-ASCII fast-path, however, the official tests do not test this configuration option.

Commits
-------

385d1d5 Conform to IDNA version 15.1.0 revision 31

src/Intl/Idn/Idn.php

@@ -280,10 +280,6 @@ private static function mapCodePoints($input, array $options, Info $info)
 
             switch ($data['status']) {
                 case 'disallowed':
-                    $info->errors |= self::ERROR_DISALLOWED;
-
-                    // no break.
-
                 case 'valid':
                     $str .= mb_chr($codePoint, 'utf-8');
 
@@ -294,7 +290,7 @@ private static function mapCodePoints($input, array $options, Info $info)
                     break;
 
                 case 'mapped':
-                    $str .= $data['mapping'];
+                    $str .= $transitional && 0x1E9E === $codePoint ? 'ss' : $data['mapping'];
 
                     break;
 
@@ -346,6 +342,18 @@ private static function process($domain, array $options, Info $info)
             $validationOptions = $options;
 
             if ('xn--' === substr($label, 0, 4)) {
+                // Step 4.1. If the label contains any non-ASCII code point (i.e., a code point greater than U+007F),
+                // record that there was an error, and continue with the next label.
+                if (preg_match('/[^\x00-\x7F]/', $label)) {
+                    $info->errors |= self::ERROR_PUNYCODE;
+
+                    continue;
+                }
+
+                // Step 4.2. Attempt to convert the rest of the label to Unicode according to Punycode [RFC3492]. If
+                // that conversion fails, record that there was an error, and continue
+                // with the next label. Otherwise replace the original label in the string by the results of the
+                // conversion.
                 try {
                     $label = self::punycodeDecode(substr($label, 4));
                 } catch (\Exception $e) {
@@ -516,6 +524,8 @@ private static function validateLabel($label, Info $info, array $options, $canBe
             if ('-' === substr($label, -1, 1)) {
                 $info->errors |= self::ERROR_TRAILING_HYPHEN;
             }
+        } elseif ('xn--' === substr($label, 0, 4)) {
+            $info->errors |= self::ERROR_PUNYCODE;
         }
 
         // Step 4. The label must not contain a U+002E (.) FULL STOP.

tests/Intl/Idn/IdnTest.php

@@ -284,6 +284,55 @@ public function testEncodePhp53($decoded, $encoded)
         $this->assertSame($encoded, $result);
     }
 
+    /**
+     * IDNA 15.1.0 revision 31
+     *
+     * This tests the change in "Section 4 Processing step 1. Map" which conditionally maps U+1E9E capital sharp s to
+     * "ss" if Transitional_Processing is used.
+     *
+     * @dataProvider captialSharpSProvider
+     */
+    public function testCapitalSharpSProcessing($input, $expected, $flags)
+    {
+        idn_to_utf8($input, $flags, \INTL_IDNA_VARIANT_UTS46, $info);
+        $this->assertSame($expected, $info['result']);
+    }
+
+    /**
+     * IDNA 15.1.0 revision 31
+     *
+     * This tests the additional validity check in "Section 4.1 Validity Criteria Processing step 4", which is used to
+     * disallow labels that do not round trip.
+     */
+    public function testLabelsThatDoNotRoundTripAreDisallowed()
+    {
+        idn_to_utf8('xn--xn---epa.', \IDNA_DEFAULT, \INTL_IDNA_VARIANT_UTS46, $info1);
+        idn_to_ascii($info1['result'], \IDNA_DEFAULT, \INTL_IDNA_VARIANT_UTS46, $info2);
+        $this->assertSame(\IDNA_ERROR_PUNYCODE, \IDNA_ERROR_PUNYCODE & $info2['errors']);
+    }
+
+    /**
+     * IDNA 15.1.0 revision 31
+     *
+     * This tests the the additional condition in "Section 4 Processing step 4.1" where a label that starts with "xn--"
+     * and contains a non-ASCII codepoint records an error and the processing steps continue with the next label.
+     */
+    public function testLabelStartingWithPunycodePrefixWithNonAsciiCharacterRecordsErrorAndIsSkipped()
+    {
+        \idn_to_utf8('xn--🌈.xn--fa-hia.de', \IDNA_DEFAULT, \INTL_IDNA_VARIANT_UTS46, $info);
+        $this->assertSame(\IDNA_ERROR_PUNYCODE, \IDNA_ERROR_PUNYCODE & $info['errors']);
+        $this->assertSame('xn--🌈.faß.de', $info['result']);
+    }
+
+    public static function captialSharpSProvider()
+    {
+        return [
+            ['Faß.de', 'fass.de', \IDNA_DEFAULT],
+            ['Faß.de', 'faß.de', \IDNA_NONTRANSITIONAL_TO_UNICODE],
+        ];
+    }
+
+
     public static function domainNamesProvider()
     {
         return [