Item-from-string parsing no longer depends on ItemIds

after this is done I'm banning the constant() function.

src/item/Item.php

@@ -667,7 +667,7 @@ class Item implements \JsonSerializable{
 			$item = ItemFactory::getInstance()->get($idTag->getValue(), $meta, $count);
 		}elseif($idTag instanceof StringTag){ //PC item save format
 			try{
-				$item = ItemFactory::getInstance()->fromString($idTag->getValue() . ":$meta");
+				$item = LegacyStringToItemParser::getInstance()->parse($idTag->getValue() . ":$meta");
 			}catch(\InvalidArgumentException $e){
 				//TODO: improve error handling
 				return ItemFactory::air();

src/item/ItemFactory.php

@@ -34,14 +34,7 @@ use pocketmine\entity\Living;
 use pocketmine\inventory\ArmorInventory;
 use pocketmine\nbt\tag\CompoundTag;
 use pocketmine\utils\SingletonTrait;
-use function constant;
-use function defined;
-use function explode;
 use function is_a;
-use function is_numeric;
-use function str_replace;
-use function strtoupper;
-use function trim;
 
 /**
  * Manages Item instance creation and registration
@@ -431,37 +424,6 @@ class ItemFactory{
 		return $item;
 	}
 
-	/**
-	 * Tries to parse the specified string into Item types.
-	 *
-	 * Example accepted formats:
-	 * - `diamond_pickaxe:5`
-	 * - `minecraft:string`
-	 * - `351:4 (lapis lazuli ID:meta)`
-	 *
-	 * @throws \InvalidArgumentException if the given string cannot be parsed as an item identifier
-	 */
-	public function fromString(string $str) : Item{
-		$b = explode(":", str_replace([" ", "minecraft:"], ["_", ""], trim($str)));
-		if(!isset($b[1])){
-			$meta = 0;
-		}elseif(is_numeric($b[1])){
-			$meta = (int) $b[1];
-		}else{
-			throw new \InvalidArgumentException("Unable to parse \"" . $b[1] . "\" from \"" . $str . "\" as a valid meta value");
-		}
-
-		if(is_numeric($b[0])){
-			$item = $this->get((int) $b[0], $meta);
-		}elseif(defined(ItemIds::class . "::" . strtoupper($b[0]))){
-			$item = $this->get(constant(ItemIds::class . "::" . strtoupper($b[0])), $meta);
-		}else{
-			throw new \InvalidArgumentException("Unable to resolve \"" . $str . "\" to a valid item");
-		}
-
-		return $item;
-	}
-
 	public static function air() : Item{
 		return self::$air ?? (self::$air = self::getInstance()->get(ItemIds::AIR, 0, 0));
 	}

src/item/LegacyStringToItemParser.php

@@ -0,0 +1,117 @@
+<?php
+
+/*
+ *
+ *  ____            _        _   __  __ _                  __  __ ____
+ * |  _ \ ___   ___| | _____| |_|  \/  (_)_ __   ___      |  \/  |  _ \
+ * | |_) / _ \ / __| |/ / _ \ __| |\/| | | '_ \ / _ \_____| |\/| | |_) |
+ * |  __/ (_) | (__|   <  __/ |_| |  | | | | | |  __/_____| |  | |  __/
+ * |_|   \___/ \___|_|\_\___|\__|_|  |_|_|_| |_|\___|     |_|  |_|_|
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * @author PocketMine Team
+ * @link http://www.pocketmine.net/
+ *
+ *
+*/
+
+declare(strict_types=1);
+
+namespace pocketmine\item;
+
+use pocketmine\utils\AssumptionFailedError;
+use pocketmine\utils\SingletonTrait;
+use function explode;
+use function file_get_contents;
+use function is_array;
+use function is_int;
+use function is_numeric;
+use function is_string;
+use function json_decode;
+use function str_replace;
+use function strtolower;
+use function trim;
+
+/**
+ * This class fills in as a substitute for all the stuff that used to make ItemFactory::fromString()
+ * work. Since legacy item IDs are on their way out, we can't keep using their constants as stringy
+ * IDs (especially not considering the unnoticed BC-break potential posed by such a stupid idea).
+ */
+final class LegacyStringToItemParser{
+	use SingletonTrait;
+
+	/** @var ItemFactory */
+	private $itemFactory;
+
+	private static function make() : self{
+		$result = new self(ItemFactory::getInstance());
+
+		$mappingsRaw = @file_get_contents(\pocketmine\RESOURCE_PATH . '/item_from_string_bc_map.json');
+		if($mappingsRaw === false) throw new AssumptionFailedError("Missing required resource file");
+
+		$mappings = json_decode($mappingsRaw, true);
+		if(!is_array($mappings)) throw new AssumptionFailedError("Invalid mappings format, expected array");
+
+		foreach($mappings as $name => $id){
+			if(!is_string($name) or !is_int($id)) throw new AssumptionFailedError("Invalid mappings format, expected string keys and int values");
+			$result->addMapping($name, $id);
+		}
+
+		return $result;
+	}
+
+	/**
+	 * @var int[]
+	 * @phpstan-var array<string, int>
+	 */
+	private $map = [];
+
+	public function __construct(ItemFactory $itemFactory){
+		$this->itemFactory = $itemFactory;
+	}
+
+	public function addMapping(string $alias, int $id) : void{
+		$this->map[$alias] = $id;
+	}
+
+	/**
+	 * Tries to parse the specified string into Item types.
+	 *
+	 * Example accepted formats:
+	 * - `diamond_pickaxe:5`
+	 * - `minecraft:string`
+	 * - `351:4 (lapis lazuli ID:meta)`
+	 *
+	 * @throws \InvalidArgumentException if the given string cannot be parsed as an item identifier
+	 */
+	public function parse(string $input) : Item{
+		$key = $this->reprocess($input);
+		$b = explode(":", $key);
+
+		if(!isset($b[1])){
+			$meta = 0;
+		}elseif(is_numeric($b[1])){
+			$meta = (int) $b[1];
+		}else{
+			throw new \InvalidArgumentException("Unable to parse \"" . $b[1] . "\" from \"" . $input . "\" as a valid meta value");
+		}
+
+		if(is_numeric($b[0])){
+			$item = $this->itemFactory->get((int) $b[0], $meta);
+		}elseif(isset($this->map[strtolower($b[0])])){
+			$item = $this->itemFactory->get($this->map[strtolower($b[0])], $meta);
+		}else{
+			throw new \InvalidArgumentException("Unable to resolve \"" . $input . "\" to a valid item");
+		}
+
+		return $item;
+	}
+
+	protected function reprocess(string $input) : string{
+		return str_replace([" ", "minecraft:"], ["_", ""], trim($input));
+	}
+}