Merge 1.20 into 1.20.4

Author: embeddedt

common/src/main/java/org/embeddedt/modernfix/common/mixin/perf/ticking_chunk_alloc/ChunkAccessMixin.java

@@ -0,0 +1,36 @@
+package org.embeddedt.modernfix.common.mixin.perf.ticking_chunk_alloc;
+
+import net.minecraft.world.level.chunk.ChunkAccess;
+import org.spongepowered.asm.mixin.Final;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Overwrite;
+import org.spongepowered.asm.mixin.Shadow;
+
+import java.util.Collections;
+import java.util.Map;
+
+@Mixin(value = ChunkAccess.class, priority = 800)
+public class ChunkAccessMixin {
+    @Shadow @Final private Map<?, ?> structuresRefences;
+    private Map<?, ?> mfix$structureRefsView;
+
+    /**
+     * @author embeddedt
+     * @reason Cache returned map view to avoid allocations, return empty map when possible
+     * so that iterator() calls don't allocate
+     * <p></p>
+     * Note: technically, this introduces an API change, as the return value may no longer be a live view
+     * of the structure references of the chunk. It's unlikely this will affect anything in practice.
+     */
+    @Overwrite
+    public Map<?, ?> getAllReferences() {
+        if(this.structuresRefences.isEmpty()) {
+            return Collections.emptyMap();
+        }
+        Map<?, ?> view = this.mfix$structureRefsView;
+        if(view == null) {
+            this.mfix$structureRefsView = view = Collections.unmodifiableMap(this.structuresRefences);
+        }
+        return view;
+    }
+}