Fix PHP 8.4 compatibility / drop support for PHP < 7.1

PHP 8.4 deprecates implicitly nullable parameters, i.e. typed parameter with a `null` default value, which are not explicitly declared as nullable.
Ref: https://wiki.php.net/rfc/deprecate-implicitly-nullable-types

There are multiple ways to fix this, though most involve breaking changes:
1. Remove the type declaration and do in-method type validation.
    As this is not a `final` class, nor are these `final` or `private` methods, this would be a breaking change for any class extending the `Parser` class as parameter types are contra-variant, so this would cause a signature mismatch.
2. Remove the `null` default value.
    This, again, would be a breaking change and an even bigger one as it turns an optional parameter into a required one, so this wouldn't just have an impact on overloaded methods, but on all _calls_ to the methods too.
3. Declare the parameters as nullable.
    This would not cause a signature mismatch.
    This is the change with the least impact, although it does require PHP 7.1. If this is released as a next _minor_ though, the impact will be minimal as Composer can handle the version negotiations and will just install an older version for PHP 5.6/7.0.
    Also note that based on the Packagist stats, this version negotiation would rarely be needed as the users of this package hardly use PHP 5.6/7.0 anymore: https://packagist.org/packages/mf2/mf2/php-stats

With this in mind, I'm proposing dropping support for PHP < 7.1 and fixing the PHP 8.4 deprecations by making the relevant parameters explicitly nullable.

Includes updating CI and the PHPCS config.

Author: jrfnl

.github/workflows/main.yml

@@ -43,7 +43,7 @@ jobs:
 
     strategy:
       matrix:
-        php: ['5.6', '7.3', '7.4', '8.0', '8.1', '8.2', '8.3', '8.4']
+        php: ['7.1', '7.3', '7.4', '8.0', '8.1', '8.2', '8.3', '8.4']
 
     runs-on: ubuntu-latest
 

Mf2/Parser.php

@@ -1383,7 +1383,7 @@ public function upgradeRelTagToCategory(DOMElement $el) {
 	 * @param DOMElement $context optionally specify an element from which to parse microformats
 	 * @return array An array containing all the microformats found in the current document
 	 */
-	public function parse($convertClassic = true, DOMElement $context = null) {
+	public function parse($convertClassic = true, ?DOMElement $context = null) {
 		$this->convertClassic = $convertClassic;
 		$mfs = $this->parse_recursive($context);
 
@@ -1411,7 +1411,7 @@ public function parse($convertClassic = true, DOMElement $context = null) {
 	 * @param int $depth: recursion depth
 	 * @return array
 	 */
-	public function parse_recursive(DOMElement $context = null, $depth = 0) {
+	public function parse_recursive(?DOMElement $context = null, $depth = 0) {
 		$mfs = array();
 		$mfElements = $this->getRootMF($context);
 
@@ -1516,7 +1516,7 @@ public function parseFromId($id, $convertClassic=true) {
 	 * @param DOMElement $context
 	 * @return DOMNodeList
 	 */
-	public function getRootMF(DOMElement $context = null) {
+	public function getRootMF(?DOMElement $context = null) {
 		// start with mf2 root class name xpath
 		$xpaths = array(
 			'(php:function("\\Mf2\\classHasMf2RootClassname", normalize-space(@class)))'

composer.json

@@ -11,7 +11,7 @@
     ],
     "bin": ["bin/fetch-mf2", "bin/parse-mf2"],
     "require": {
-        "php": ">=5.6.0"
+        "php": ">=7.1.0"
     },
     "config": {
         "platform": {

phpcs.xml

@@ -3,5 +3,5 @@
 	<description>PHP-MF2 Standards</description>
 	<file>./Mf2/Parser.php</file>
 	<rule ref="PHPCompatibility"/>
-	<config name="testVersion" value="5.6-"/>
+	<config name="testVersion" value="7.1-"/>
 </ruleset>