world: fix deserialize of unpopulated 1.18+ sections

src/world/chunk.rs

@@ -112,27 +112,36 @@ impl<'a> Chunk<'a> {
 		let mut section_map = BTreeMap::new();
 
 		for section in sections {
-			section_map.insert(
+			match &section.section {
-				SectionY(section.y),
+				de::SectionV1_18Variants::V1_18 {
-				(
+					block_states,
-					SectionV1_13::new(
+					biomes,
-						data_version,
+					block_light,
-						section.block_states.data.as_deref(),
+				} => {
-						&section.block_states.palette,
+					section_map.insert(
-						block_types,
+						SectionY(section.y),
-					)
+						(
-					.with_context(|| format!("Failed to load section at Y={}", section.y))?,
+							SectionV1_13::new(
-					BiomesV1_18::new(
+								data_version,
-						section.biomes.data.as_deref(),
+								block_states.data.as_deref(),
-						&section.biomes.palette,
+								&block_states.palette,
-						biome_types,
+								block_types,
-					)
+							)
-					.with_context(|| format!("Failed to load section biomes at Y={}", section.y))?,
+							.with_context(|| {
-					BlockLight::new(section.block_light.as_deref()).with_context(|| {
+								format!("Failed to load section at Y={}", section.y)
-						format!("Failed to load section block light at Y={}", section.y)
+							})?,
-					})?,
+							BiomesV1_18::new(biomes.data.as_deref(), &biomes.palette, biome_types)
-				),
+								.with_context(|| {
-			);
+									format!("Failed to load section biomes at Y={}", section.y)
+								})?,
+							BlockLight::new(block_light.as_deref()).with_context(|| {
+								format!("Failed to load section block light at Y={}", section.y)
+							})?,
+						),
+					);
+				}
+				de::SectionV1_18Variants::Empty {} => {}
+			};
 		}
 
 		Ok(Chunk::V1_18 { section_map })

src/world/de.rs

@@ -28,19 +28,33 @@ pub struct BiomesV1_18 {
 	pub data: Option<fastnbt::LongArray>,
 }
 
+/// Variable part of a [SectionV1_18]
+#[derive(Debug, Deserialize)]
+#[serde(untagged)]
+pub enum SectionV1_18Variants {
+	/// Populated 1.18+ section
+	V1_18 {
+		/// Block type data
+		block_states: BlockStatesV1_18,
+		/// Biome data
+		biomes: BiomesV1_18,
+		/// Block light data
+		#[serde(rename = "BlockLight")]
+		block_light: Option<fastnbt::ByteArray>,
+	},
+	/// Empty section
+	Empty {},
+}
+
 /// Element of the 1.18+ `sections` list found in a [Chunk]
 #[derive(Debug, Deserialize)]
 pub struct SectionV1_18 {
 	/// Y coordinate
 	#[serde(rename = "Y")]
 	pub y: i32,
-	/// Block type data
+	/// Variable part of section
-	pub block_states: BlockStatesV1_18,
+	#[serde(flatten)]
-	/// Biome data
+	pub section: SectionV1_18Variants,
-	pub biomes: BiomesV1_18,
-	/// Block light data
-	#[serde(rename = "BlockLight")]
-	pub block_light: Option<fastnbt::ByteArray>,
 }
 
 /// Version-specific part of a pre-1.18 [Section](SectionV0)