Avoid recursion as much as possible when searching for a spawn

src/mixins/java/org/spongepowered/common/mixin/core/server/level/PlayerSpawnFinderMixin.java

@@ -0,0 +1,160 @@
+/*
+ * This file is part of Sponge, licensed under the MIT License (MIT).
+ *
+ * Copyright (c) SpongePowered <https://www.spongepowered.org>
+ * Copyright (c) contributors
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package org.spongepowered.common.mixin.core.server.level;
+
+import net.minecraft.CrashReport;
+import net.minecraft.CrashReportCategory;
+import net.minecraft.ReportedException;
+import net.minecraft.core.BlockPos;
+import net.minecraft.core.SectionPos;
+import net.minecraft.server.MinecraftServer;
+import net.minecraft.server.level.PlayerSpawnFinder;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.server.level.TicketType;
+import net.minecraft.world.level.ChunkPos;
+import net.minecraft.world.level.CollisionGetter;
+import net.minecraft.world.phys.Vec3;
+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.Optional;
+import java.util.concurrent.CompletableFuture;
+import java.util.function.Supplier;
+
+import javax.annotation.Nullable;
+
+@Mixin(PlayerSpawnFinder.class)
+public abstract class PlayerSpawnFinderMixin {
+
+    @Shadow @Final private CompletableFuture<Vec3> finishedFuture;
+    @Shadow @Final private ServerLevel level;
+    @Shadow @Final private BlockPos spawnSuggestion;
+    @Shadow @Final private int radius;
+    @Shadow @Final private int candidateCount;
+    @Shadow private int nextCandidateIndex;
+    @Shadow @Final private int offset;
+    @Shadow @Final private int coprime;
+
+    @Shadow
+    private static Vec3 fixupSpawnHeight(CollisionGetter $$0, BlockPos $$1) {
+        throw new IllegalStateException();
+    }
+
+    @Shadow
+    @Nullable
+    protected static BlockPos getOverworldRespawnPos(ServerLevel $$0, int $$1, int $$2) {
+        throw new IllegalStateException();
+    }
+
+    @Shadow
+    private static boolean noCollisionNoLiquid(CollisionGetter $$0, BlockPos $$1) {
+        throw new IllegalStateException();
+    }
+
+    /**
+     * A mix of loop and recursion.
+     * Loop is preferred when possible.
+     *
+     * @author Yeregorix
+     * @reason Fix <a href="https://bugs.mojang.com/browse/MC/issues/MC-304426">MC-304426</a>.
+     */
+    @Overwrite
+    private void scheduleNext() {
+        int i;
+        while ((i = this.nextCandidateIndex++) < this.candidateCount) {
+            if (this.finishedFuture.isDone()) {
+                return;
+            }
+
+            final int candidate = (this.offset + this.coprime * i) % this.candidateCount;
+            final int relX = candidate % (this.radius * 2 + 1);
+            final int relZ = candidate / (this.radius * 2 + 1);
+            final int x = this.spawnSuggestion.getX() + relX - this.radius;
+            final int z = this.spawnSuggestion.getZ() + relZ - this.radius;
+
+            if (this.scheduleCandidate(x, z, i, () -> {
+                final BlockPos pos = getOverworldRespawnPos(this.level, x, z);
+                return pos != null && noCollisionNoLiquid(this.level, pos) ? Optional.of(Vec3.atBottomCenterOf(pos)) : Optional.empty();
+            })) {
+                return;
+            }
+        }
+
+        if (this.finishedFuture.isDone()) {
+            return;
+        }
+
+        scheduleCandidate(this.spawnSuggestion.getX(), this.spawnSuggestion.getZ(), i, () -> Optional.of(PlayerSpawnFinderMixin.fixupSpawnHeight(this.level, this.spawnSuggestion)));
+    }
+
+    private boolean scheduleCandidate(int x, int z, int index, Supplier<Optional<Vec3>> supplier) {
+        int chunkX = SectionPos.blockToSectionCoord(x);
+        int chunkZ = SectionPos.blockToSectionCoord(z);
+        final CompletableFuture<?> future = this.level.getChunkSource().addTicketAndLoadWithRadius(TicketType.SPAWN_SEARCH, new ChunkPos(chunkX, chunkZ), 0);
+        final MinecraftServer server = this.level.getServer();
+
+        if (future.isDone() && server.isSameThread()) {
+            try {
+                future.get();
+                supplier.get().ifPresent(this.finishedFuture::complete);
+            } catch (Throwable error) {
+                this.crash(x, z, index, error);
+            }
+            return false; // stay on loop
+        }
+
+        future.whenCompleteAsync((chunk, error) -> {
+            if (error == null) {
+                try {
+                    Optional<Vec3> result = supplier.get();
+                    if (result.isPresent()) {
+                        this.finishedFuture.complete(result.get());
+                    } else {
+                        this.scheduleNext();
+                    }
+                } catch (Exception exception) {
+                    error = exception;
+                }
+            }
+
+            if (error != null) {
+                this.crash(x, z, index, error);
+            }
+        }, server);
+        return true; // exit loop
+    }
+
+    private void crash(final int x, final int z, final int index, final Throwable error) {
+        CrashReport report = CrashReport.forThrowable(error, "Searching for spawn");
+        CrashReportCategory category = report.addCategory("Spawn Lookup");
+        category.setDetail("Origin", this.spawnSuggestion::toString);
+        category.setDetail("Radius", () -> Integer.toString(this.radius));
+        category.setDetail("Candidate", () -> "[" + x + "," + z + "]");
+        category.setDetail("Progress", () -> index + " out of " + this.candidateCount);
+        this.finishedFuture.completeExceptionally(new ReportedException(report));
+    }
+}

src/mixins/resources/mixins.sponge.core.json

@@ -76,6 +76,7 @@
     "server.level.ChunkMapMixin",
     "server.level.DistanceManagerMixin",
     "server.level.GenerationChunkHolderMixin",
+    "server.level.PlayerSpawnFinderMixin",
     "server.level.ServerBossEventMixin",
     "server.level.ServerChunkCacheMixin",
     "server.level.ServerEntityMixin",
@@ -130,7 +131,6 @@
     "world.entity.LightningBoltMixin",
     "world.entity.LivingEntityMixin",
     "world.entity.LivingEntityMixin_Damage",
-    "world.entity.decoration.MannequinMixin",
     "world.entity.MobMixin",
     "world.entity.MobMixin_Attack",
     "world.entity.PortalProcessorMixin",
@@ -156,6 +156,7 @@
     "world.entity.decoration.BlockAttachedEntityMixin",
     "world.entity.decoration.HangingEntityMixin",
     "world.entity.decoration.ItemFrameMixin",
+    "world.entity.decoration.MannequinMixin",
     "world.entity.item.ItemEntityMixin",
     "world.entity.item.PrimedTntMixin",
     "world.entity.monster.Blaze_BlazeAttackGoalMixin",