[Data Liberation] Merge both XML processors into a single WP_XML_Processor (#1960)

Merge `WP_XML_Tag_Processor` and `WP_XML_Processor` into a single
`WP_XML_Processor` class. This reduces abstractions, enables keeping
more properties as private, and simplifies the code.

Related to #1894
and WordPress/wordpress-develop#6713

 ## Testing instructions

Confirm the CI tests pass.

Author: adamziel

packages/playground/data-liberation/bootstrap.php

@@ -30,16 +30,14 @@
 require_once __DIR__ . '/src/WP_URL.php';
 
 require_once __DIR__ . '/src/xml-api/WP_XML_Decoder.php';
-require_once __DIR__ . '/src/xml-api/WP_XML_Tag_Processor.php';
 require_once __DIR__ . '/src/xml-api/WP_XML_Processor.php';
 require_once __DIR__ . '/src/WP_WXR_URL_Rewrite_Processor.php';
 
 require_once __DIR__ . '/vendor/autoload.php';
 
 
 // Polyfill WordPress core functions
-function _doing_it_wrong() {
-
+function _doing_it_wrong($method, $message, $version) {
 }
 
 function __($input) {

packages/playground/data-liberation/phpunit.xml

@@ -9,7 +9,6 @@
       <file>tests/WPBlockMarkupUrlProcessorTests.php</file>
       <file>tests/URLParserWHATWGComplianceTests.php</file>
       <file>tests/WPXMLProcessorTests.php</file>
-      <file>tests/WPXMLTagProcessorTests.php</file>
       <file>tests/UrldecodeNTests.php</file>
     </testsuite>
   </testsuites>

packages/playground/data-liberation/src/WP_WXR_URL_Rewrite_Processor.php

@@ -3,8 +3,8 @@
 class WP_WXR_URL_Rewrite_Processor {
 
 
-	public static function stream( $current_site_url, $new_site_url ) {
-		return WP_XML_Processor::stream(
+	public static function create_stream_processor( $current_site_url, $new_site_url ) {
+		return WP_XML_Processor::create_stream_processor(
 			function ( $processor ) use ( $current_site_url, $new_site_url ) {
 				if ( static::is_wxr_content_node( $processor ) ) {
 					$text         = $processor->get_modifiable_text();

packages/playground/data-liberation/src/stream-api/WP_File_Byte_Stream.php

@@ -11,6 +11,7 @@ public function __construct( $file_path, $chunk_size = 8096 ) {
 		$this->file_path  = $file_path;
 		$this->chunk_size = $chunk_size;
 		parent::__construct();
+		$this->append_eof();
 	}
 
 	public function pause() {

packages/playground/data-liberation/src/stream-api/WP_Stream_Chain.php

@@ -16,6 +16,11 @@
  * Consult it for reasoning and usage examples:
  *
  * https://github.com/adamziel/wxr-normalize/pull/1
+ *
+ * @TODO: Allow each stream to indicate its output reached EOF
+ *        and propagate that information downstream. Otherwise,
+ *        WP_XML_Processor will always end in an "incomplete input"
+ *        state.
  */
 class WP_Stream_Chain extends WP_Byte_Stream implements ArrayAccess, Iterator {
 	private $first_stream;

packages/playground/data-liberation/src/stream-api/WP_Stream_Processor.php

@@ -2,6 +2,7 @@
 
 interface WP_Stream_Processor {
 	public function append_bytes( string $bytes );
+	public function input_finished(): void;
 	public function is_finished(): bool;
 	public function is_paused_at_incomplete_input(): bool;
 	public function get_last_error(): ?string;