Fix some of the implicit immutability issues of EmptySubChunk

it's useful to have an immutable stub around for the sake of feeding back dummy read values, but for write values it has to barf instead of being quiet.
There's still some issues with LightArray which I don't currently have a solution for, but I'm thinking about separating light storage from chunks anyway.

src/world/format/Chunk.php

@@ -152,7 +152,7 @@ class Chunk{
 	 * Sets the blockstate at the given coordinate by internal ID.
 	 */
 	public function setFullBlock(int $x, int $y, int $z, int $block) : void{
-		$this->getSubChunk($y >> 4)->setFullBlock($x, $y & 0xf, $z, $block);
+		$this->getWritableSubChunk($y >> 4)->setFullBlock($x, $y & 0xf, $z, $block);
 		$this->dirtyFlags |= self::DIRTY_FLAG_TERRAIN;
 	}
 
@@ -178,12 +178,12 @@ class Chunk{
 	 * @param int $level 0-15
 	 */
 	public function setBlockSkyLight(int $x, int $y, int $z, int $level) : void{
-		$this->getSubChunk($y >> 4)->getBlockSkyLightArray()->set($x & 0xf, $y & 0x0f, $z & 0xf, $level);
+		$this->getWritableSubChunk($y >> 4)->getBlockSkyLightArray()->set($x & 0xf, $y & 0x0f, $z & 0xf, $level);
 	}
 
 	public function setAllBlockSkyLight(int $level) : void{
 		for($y = $this->subChunks->count() - 1; $y >= 0; --$y){
-			$this->getSubChunk($y)->setBlockSkyLightArray(LightArray::fill($level));
+			$this->getWritableSubChunk($y)->setBlockSkyLightArray(LightArray::fill($level));
 		}
 	}
 
@@ -209,12 +209,12 @@ class Chunk{
 	 * @param int $level 0-15
 	 */
 	public function setBlockLight(int $x, int $y, int $z, int $level) : void{
-		$this->getSubChunk($y >> 4)->getBlockLightArray()->set($x & 0xf, $y & 0x0f, $z & 0xf, $level);
+		$this->getWritableSubChunk($y >> 4)->getBlockLightArray()->set($x & 0xf, $y & 0x0f, $z & 0xf, $level);
 	}
 
 	public function setAllBlockLight(int $level) : void{
 		for($y = $this->subChunks->count() - 1; $y >= 0; --$y){
-			$this->getSubChunk($y)->setBlockLightArray(LightArray::fill($level));
+			$this->getWritableSubChunk($y)->setBlockLightArray(LightArray::fill($level));
 		}
 	}
 
@@ -340,10 +340,10 @@ class Chunk{
 		$highestHeightMap = max($this->heightMap->getValues());
 		$lowestFullyLitSubChunk = ($highestHeightMap >> 4) + (($highestHeightMap & 0xf) !== 0 ? 1 : 0);
 		for($y = 0; $y < $lowestFullyLitSubChunk; $y++){
-			$this->getSubChunk($y)->setBlockSkyLightArray(LightArray::fill(0));
+			$this->getWritableSubChunk($y)->setBlockSkyLightArray(LightArray::fill(0));
 		}
 		for($y = $lowestFullyLitSubChunk, $yMax = $this->subChunks->count(); $y < $yMax; $y++){
-			$this->getSubChunk($y)->setBlockSkyLightArray(LightArray::fill(15));
+			$this->getWritableSubChunk($y)->setBlockSkyLightArray(LightArray::fill(15));
 		}
 
 		for($x = 0; $x < 16; ++$x){
@@ -623,6 +623,13 @@ class Chunk{
 		return $this->subChunks[$y];
 	}
 
+	public function getWritableSubChunk(int $y) : SubChunk{
+		if($y < 0 || $y >= $this->subChunks->getSize()){
+			throw new \InvalidArgumentException("Cannot get subchunk $y for writing");
+		}
+		return $this->subChunks[$y];
+	}
+
 	/**
 	 * Sets a subchunk in the chunk index
 	 */

src/world/format/EmptySubChunk.php

@@ -47,10 +47,6 @@ class EmptySubChunk implements SubChunkInterface{
 		return 0;
 	}
 
-	public function setFullBlock(int $x, int $y, int $z, int $block) : void{
-
-	}
-
 	public function getBlockLayers() : array{
 		return [];
 	}
@@ -63,15 +59,7 @@ class EmptySubChunk implements SubChunkInterface{
 		return new LightArray(LightArray::ZERO);
 	}
 
-	public function setBlockLightArray(LightArray $data) : void{
-
-	}
-
 	public function getBlockSkyLightArray() : LightArray{
 		return new LightArray(LightArray::FIFTEEN);
 	}
-
-	public function setBlockSkyLightArray(LightArray $data) : void{
-
-	}
 }

src/world/format/SubChunkInterface.php

@@ -40,8 +40,6 @@ interface SubChunkInterface{
 
 	public function getFullBlock(int $x, int $y, int $z) : int;
 
-	public function setFullBlock(int $x, int $y, int $z, int $block) : void;
-
 	/**
 	 * @return PalettedBlockArray[]
 	 */
@@ -51,9 +49,5 @@ interface SubChunkInterface{
 
 	public function getBlockSkyLightArray() : LightArray;
 
-	public function setBlockSkyLightArray(LightArray $data) : void;
-
 	public function getBlockLightArray() : LightArray;
-
-	public function setBlockLightArray(LightArray $data) : void;
 }

src/world/generator/Flat.php

@@ -156,7 +156,7 @@ class Flat extends Generator{
 
 		$count = count($this->structure);
 		for($sy = 0; $sy < $count; $sy += 16){
-			$subchunk = $this->chunk->getSubChunk($sy >> 4);
+			$subchunk = $this->chunk->getWritableSubChunk($sy >> 4);
 			for($y = 0; $y < 16 and isset($this->structure[$y | $sy]); ++$y){
 				$id = $this->structure[$y | $sy];
 

src/world/light/LightPopulationTask.php

@@ -94,10 +94,10 @@ class LightPopulationTask extends AsyncTask{
 			$blockLightArrays = igbinary_unserialize($this->resultBlockLightArrays);
 
 			foreach($skyLightArrays as $y => $array){
-				$chunk->getSubChunk($y)->setBlockSkyLightArray($array);
+				$chunk->getWritableSubChunk($y)->setBlockSkyLightArray($array);
 			}
 			foreach($blockLightArrays as $y => $array){
-				$chunk->getSubChunk($y)->setBlockLightArray($array);
+				$chunk->getWritableSubChunk($y)->setBlockLightArray($array);
 			}
 			$chunk->setLightPopulated();
 		}

tests/phpstan/configs/l8-baseline.neon

@@ -760,6 +760,11 @@ parameters:
 			count: 1
 			path: ../../../src/world/format/Chunk.php
 
+		-
+			message: "#^Method pocketmine\\\\world\\\\format\\\\Chunk\\:\\:getWritableSubChunk\\(\\) should return pocketmine\\\\world\\\\format\\\\SubChunk but returns pocketmine\\\\world\\\\format\\\\SubChunk\\|null\\.$#"
+			count: 1
+			path: ../../../src/world/format/Chunk.php
+
 		-
 			message: "#^Method pocketmine\\\\world\\\\format\\\\HeightArray\\:\\:get\\(\\) should return int but returns int\\|null\\.$#"
 			count: 1