Pin feature ordering to vanilla runtime

tools/VanillaFeatureSorterVectors.java

@@ -0,0 +1,81 @@
+import java.lang.reflect.Constructor;
+import java.util.ArrayList;
+import java.util.IdentityHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.function.Function;
+
+import net.minecraft.SharedConstants;
+import net.minecraft.core.Holder;
+import net.minecraft.core.HolderSet;
+import net.minecraft.server.Bootstrap;
+import net.minecraft.world.level.biome.BiomeGenerationSettings;
+import net.minecraft.world.level.biome.FeatureSorter;
+import net.minecraft.world.level.levelgen.feature.ConfiguredFeature;
+import net.minecraft.world.level.levelgen.feature.Feature;
+import net.minecraft.world.level.levelgen.feature.configurations.NoneFeatureConfiguration;
+import net.minecraft.world.level.levelgen.placement.CountPlacement;
+import net.minecraft.world.level.levelgen.placement.PlacedFeature;
+
+// Emits FeatureSorter vectors from the official 26.1.2 runtime. The graph is
+// synthetic so this helper verifies ordering and identity without booting a
+// world or depending on registry datapack loading.
+public final class VanillaFeatureSorterVectors {
+    private static final Map<PlacedFeature, String> NAMES = new IdentityHashMap<>();
+
+    public static void main(String[] args) throws Exception {
+        SharedConstants.tryDetectVersion();
+        Bootstrap.bootStrap();
+
+        PlacedFeature f1 = feature("f1", 1);
+        PlacedFeature f2 = feature("f2", 2);
+        PlacedFeature f3 = feature("f3", 3);
+        PlacedFeature f4 = feature("f4", 4);
+        PlacedFeature f5 = feature("f5", 5);
+
+        BiomeGenerationSettings a = settings(
+                List.of(List.of(f1), List.of(f3, f4)));
+        BiomeGenerationSettings b = settings(
+                List.of(List.of(f2, f1), List.of(f5, f4)));
+
+        dump("ab", List.of(a, b));
+        dump("ba", List.of(b, a));
+    }
+
+    private static PlacedFeature feature(String name, int count) {
+        ConfiguredFeature<NoneFeatureConfiguration, Feature<NoneFeatureConfiguration>> configured =
+                new ConfiguredFeature<>(Feature.NO_OP, NoneFeatureConfiguration.INSTANCE);
+        PlacedFeature placed = new PlacedFeature(Holder.direct(configured), List.of(CountPlacement.of(count)));
+        NAMES.put(placed, name);
+        return placed;
+    }
+
+    @SuppressWarnings("unchecked")
+    private static BiomeGenerationSettings settings(List<List<PlacedFeature>> stages) throws Exception {
+        List<HolderSet<PlacedFeature>> holders = new ArrayList<>();
+        for (List<PlacedFeature> stage : stages) {
+            Holder<PlacedFeature>[] values = stage.stream().map(Holder::direct).toArray(Holder[]::new);
+            holders.add(HolderSet.direct(values));
+        }
+        Constructor<BiomeGenerationSettings> constructor = BiomeGenerationSettings.class
+                .getDeclaredConstructor(HolderSet.class, List.class);
+        constructor.setAccessible(true);
+        return constructor.newInstance(HolderSet.empty(), holders);
+    }
+
+    private static void dump(String label, List<BiomeGenerationSettings> biomes) {
+        Function<BiomeGenerationSettings, List<HolderSet<PlacedFeature>>> stages =
+                BiomeGenerationSettings::features;
+        List<FeatureSorter.StepFeatureData> steps =
+                FeatureSorter.buildFeaturesPerStep(biomes, stages, true);
+        for (int stage = 0; stage < steps.size(); stage++) {
+            FeatureSorter.StepFeatureData step = steps.get(stage);
+            List<String> values = new ArrayList<>();
+            for (int index = 0; index < step.features().size(); index++) {
+                PlacedFeature feature = step.features().get(index);
+                values.add(NAMES.get(feature) + "@" + step.indexMapping().applyAsInt(feature));
+            }
+            System.out.println(label + ".stage" + stage + "=" + String.join(",", values));
+        }
+    }
+}