Add missing structure set seed configs

The 4 missing structure set seed configs are strongholds, mineshafts,
buried treasure, and ancient cities.

Strongholds use a ring placement scheme which isn't random so they
utilize the world seed by default, this adds a config to override it
for just generating the ring positions.

Mineshafts and Buried Treasure structure sets are special cases
where the "salt" that can be defined for them via datapacks has 0
effect because the difference between the spacing and separation is 1
which is used as the upper bound in the random with salt. So the random
always returns the same int (0) so the salt has no effect. This adds
seeds/salts to the frequency reducer which has a similar effect.

Co-authored-by: William Blake Galbreath <blake.galbreath@gmail.com>

paper-server/patches/sources/net/minecraft/world/level/levelgen/structure/StructureCheck.java.patch

@@ -18,3 +18,33 @@
          ChunkGenerator chunkGenerator,
          RandomState noiseConfig,
          LevelHeightAccessor world,
+@@ -74,6 +74,20 @@
+         this.fixerUpper = dataFixer;
+     }
+ 
++    // Paper start - add missing structure salt configs
++    @Nullable
++    private Integer getSaltOverride(Structure type) {
++        if (this.heightAccessor instanceof net.minecraft.server.level.ServerLevel serverLevel) {
++            if (type instanceof net.minecraft.world.level.levelgen.structure.structures.MineshaftStructure) {
++                return serverLevel.spigotConfig.mineshaftSeed;
++            } else if (type instanceof net.minecraft.world.level.levelgen.structure.structures.BuriedTreasureStructure) {
++                return serverLevel.spigotConfig.buriedTreasureSeed;
++            }
++        }
++        return null;
++    }
++    // Paper end - add missing structure seed configs
++
+     public StructureCheckResult checkStart(ChunkPos pos, Structure type, StructurePlacement placement, boolean skipReferencedStructures) {
+         long l = pos.toLong();
+         Object2IntMap<Structure> object2IntMap = this.loadedChunks.get(l);
+@@ -83,7 +97,7 @@
+             StructureCheckResult structureCheckResult = this.tryLoadFromStorage(pos, type, skipReferencedStructures, l);
+             if (structureCheckResult != null) {
+                 return structureCheckResult;
+-            } else if (!placement.applyAdditionalChunkRestrictions(pos.x, pos.z, this.seed)) {
++            } else if (!placement.applyAdditionalChunkRestrictions(pos.x, pos.z, this.seed, this.getSaltOverride(type))) { // Paper - add missing structure seed configs
+                 return StructureCheckResult.START_NOT_PRESENT;
+             } else {
+                 boolean bl = this.featureChecks

paper-server/patches/sources/net/minecraft/world/level/levelgen/structure/placement/StructurePlacement.java.patch

@@ -0,0 +1,93 @@
+--- a/net/minecraft/world/level/levelgen/structure/placement/StructurePlacement.java
++++ b/net/minecraft/world/level/levelgen/structure/placement/StructurePlacement.java
+@@ -79,14 +79,30 @@
+         return this.exclusionZone;
+     }
+ 
++    @Deprecated @io.papermc.paper.annotation.DoNotUse // Paper - Add missing structure set seed configs
+     public boolean isStructureChunk(ChunkGeneratorStructureState calculator, int chunkX, int chunkZ) {
++        // Paper start - Add missing structure set seed configs
++        return this.isStructureChunk(calculator, chunkX, chunkZ, null);
++    }
++    public boolean isStructureChunk(ChunkGeneratorStructureState calculator, int chunkX, int chunkZ, @org.jetbrains.annotations.Nullable net.minecraft.resources.ResourceKey<StructureSet> structureSetKey) {
++        Integer saltOverride = null;
++        if (structureSetKey != null) {
++            if (structureSetKey == net.minecraft.world.level.levelgen.structure.BuiltinStructureSets.MINESHAFTS) {
++                saltOverride = calculator.conf.mineshaftSeed;
++            } else if (structureSetKey == net.minecraft.world.level.levelgen.structure.BuiltinStructureSets.BURIED_TREASURES) {
++                saltOverride = calculator.conf.buriedTreasureSeed;
++            }
++        }
++        // Paper end - Add missing structure set seed configs
+         return this.isPlacementChunk(calculator, chunkX, chunkZ)
+-            && this.applyAdditionalChunkRestrictions(chunkX, chunkZ, calculator.getLevelSeed())
++            && this.applyAdditionalChunkRestrictions(chunkX, chunkZ, calculator.getLevelSeed(), saltOverride) // Paper - Add missing structure set seed configs
+             && this.applyInteractionsWithOtherStructures(calculator, chunkX, chunkZ);
+     }
+ 
+-    public boolean applyAdditionalChunkRestrictions(int chunkX, int chunkZ, long seed) {
+-        return !(this.frequency < 1.0F) || this.frequencyReductionMethod.shouldGenerate(seed, this.salt, chunkX, chunkZ, this.frequency);
++    // Paper start - Add missing structure set seed configs
++    public boolean applyAdditionalChunkRestrictions(int chunkX, int chunkZ, long seed, @org.jetbrains.annotations.Nullable Integer saltOverride) {
++        return !(this.frequency < 1.0F) || this.frequencyReductionMethod.shouldGenerate(seed, this.salt, chunkX, chunkZ, this.frequency, saltOverride);
++        // Paper end - Add missing structure set seed configs
+     }
+ 
+     public boolean applyInteractionsWithOtherStructures(ChunkGeneratorStructureState calculator, int centerChunkX, int centerChunkZ) {
+@@ -101,25 +117,31 @@
+ 
+     public abstract StructurePlacementType<?> type();
+ 
+-    private static boolean probabilityReducer(long seed, int salt, int chunkX, int chunkZ, float frequency) {
++    private static boolean probabilityReducer(long seed, int salt, int chunkX, int chunkZ, float frequency, @org.jetbrains.annotations.Nullable Integer saltOverride) { // Paper - Add missing structure set seed configs; ignore here
+         WorldgenRandom worldgenRandom = new WorldgenRandom(new LegacyRandomSource(0L));
+         worldgenRandom.setLargeFeatureWithSalt(seed, salt, chunkX, chunkZ);
+         return worldgenRandom.nextFloat() < frequency;
+     }
+ 
+-    private static boolean legacyProbabilityReducerWithDouble(long seed, int salt, int chunkX, int chunkZ, float frequency) {
++    private static boolean legacyProbabilityReducerWithDouble(long seed, int salt, int chunkX, int chunkZ, float frequency, @org.jetbrains.annotations.Nullable Integer saltOverride) { // Paper - Add missing structure set seed configs
+         WorldgenRandom worldgenRandom = new WorldgenRandom(new LegacyRandomSource(0L));
++        if (saltOverride == null) { // Paper - Add missing structure set seed configs
+         worldgenRandom.setLargeFeatureSeed(seed, chunkX, chunkZ);
++        // Paper start - Add missing structure set seed configs
++        } else {
++            worldgenRandom.setLargeFeatureWithSalt(seed, chunkX, chunkZ, saltOverride);
++        }
++        // Paper end - Add missing structure set seed configs
+         return worldgenRandom.nextDouble() < (double)frequency;
+     }
+ 
+-    private static boolean legacyArbitrarySaltProbabilityReducer(long seed, int salt, int chunkX, int chunkZ, float frequency) {
++    private static boolean legacyArbitrarySaltProbabilityReducer(long seed, int salt, int chunkX, int chunkZ, float frequency, @org.jetbrains.annotations.Nullable Integer saltOverride) { // Paper - Add missing structure set seed configs
+         WorldgenRandom worldgenRandom = new WorldgenRandom(new LegacyRandomSource(0L));
+-        worldgenRandom.setLargeFeatureWithSalt(seed, chunkX, chunkZ, 10387320);
++        worldgenRandom.setLargeFeatureWithSalt(seed, chunkX, chunkZ, saltOverride != null ? saltOverride : HIGHLY_ARBITRARY_RANDOM_SALT); // Paper - Add missing structure set seed configs
+         return worldgenRandom.nextFloat() < frequency;
+     }
+ 
+-    private static boolean legacyPillagerOutpostReducer(long seed, int salt, int chunkX, int chunkZ, float frequency) {
++    private static boolean legacyPillagerOutpostReducer(long seed, int salt, int chunkX, int chunkZ, float frequency, @org.jetbrains.annotations.Nullable Integer saltOverride) { // Paper - Add missing structure set seed configs; ignore here
+         int i = chunkX >> 4;
+         int j = chunkZ >> 4;
+         WorldgenRandom worldgenRandom = new WorldgenRandom(new LegacyRandomSource(0L));
+@@ -147,7 +169,7 @@
+ 
+     @FunctionalInterface
+     public interface FrequencyReducer {
+-        boolean shouldGenerate(long seed, int salt, int chunkX, int chunkZ, float chance);
++        boolean shouldGenerate(long seed, int salt, int chunkX, int chunkZ, float chance, @org.jetbrains.annotations.Nullable Integer saltOverride); // Paper - Add missing structure set seed configs
+     }
+ 
+     public static enum FrequencyReductionMethod implements StringRepresentable {
+@@ -167,8 +189,8 @@
+             this.reducer = generationPredicate;
+         }
+ 
+-        public boolean shouldGenerate(long seed, int salt, int chunkX, int chunkZ, float chance) {
+-            return this.reducer.shouldGenerate(seed, salt, chunkX, chunkZ, chance);
++        public boolean shouldGenerate(long seed, int salt, int chunkX, int chunkZ, float chance, @org.jetbrains.annotations.Nullable Integer saltOverride) { // Paper - Add missing structure set seed configs
++            return this.reducer.shouldGenerate(seed, salt, chunkX, chunkZ, chance, saltOverride); // Paper - Add missing structure set seed configs
+         }
+ 
+         @Override