[FML 9 Backport] annotate mixin configs with compat level

gradle.properties

@@ -8,7 +8,7 @@ accesstransformers_version=11.0.2
 eventbus_version=8.0.5
 bootstraplauncher_version=1.1.8
 asm_version=9.7
-mixin_version=0.14.0+mixin.0.8.6
+mixin_version=0.16.4+mixin.0.8.7
 terminalconsoleappender_version=1.3.0
 nightconfig_version=3.8.0
 jetbrains_annotations_version=26.0.2

loader/src/main/java/net/neoforged/fml/loading/LoadingModList.java

@@ -83,7 +83,7 @@ public void addMixinConfigs() {
                     final String modId = file.getModInfos().get(0).getModId();
                     for (ModFileParser.MixinConfig potential : file.getMixinConfigs()) {
                         if (potential.requiredMods().stream().allMatch(id -> this.getModFileById(id) != null)) {
-                            DeferredMixinConfigRegistration.addMixinConfig(potential.config(), modId);
+                            DeferredMixinConfigRegistration.addMixinConfig(potential.config(), modId, potential.behaviorVersion());
                         } else {
                             LOGGER.debug("Mixin config {} for mod {} not applied as required mods are missing", potential.config(), modId);
                         }

loader/src/main/java/net/neoforged/fml/loading/mixin/DeferredMixinConfigRegistration.java

@@ -8,6 +8,8 @@
 import java.util.ArrayList;
 import java.util.List;
 import java.util.stream.Collectors;
+import org.apache.maven.artifact.versioning.ArtifactVersion;
+import org.jetbrains.annotations.ApiStatus;
 import org.jetbrains.annotations.Nullable;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -22,7 +24,7 @@ public class DeferredMixinConfigRegistration {
 
     private static boolean added = false;
 
-    record ConfigInfo(String fileName, @Nullable String modId) {}
+    record ConfigInfo(String fileName, @Nullable String modId, int behaviorVersion) {}
 
     private static final List<ConfigInfo> mixinConfigs = new ArrayList<>();
 
@@ -39,11 +41,30 @@ public static void addMixinConfig(String config) {
     }
 
     public static void addMixinConfig(String config, @Nullable String modId) {
+        addMixinConfig(config, modId, null);
+    }
+
+    @ApiStatus.Internal
+    public static void addMixinConfig(String config, @Nullable String modId, @Nullable ArtifactVersion behaviorVersion) {
         if (added) {
             throw new IllegalStateException("Too late to add mixin configs!");
         }
 
-        mixinConfigs.add(new ConfigInfo(config, modId));
+        mixinConfigs.add(new ConfigInfo(config, modId, calculateBehaviorVersion(behaviorVersion)));
+    }
+
+    // Increment to break compatibility; during a BC window, this should be set to the latest version. This is _not_ set
+    // to COMPATIBILITY_LATEST, so that if mixin is bumped past a BC it does not break mods.
+    @ApiStatus.Internal
+    public static final int DEFAULT_BEHAVIOUR_VERSION = FabricUtil.COMPATIBILITY_0_14_0;
+
+    private static int calculateBehaviorVersion(@Nullable ArtifactVersion behaviorVersion) {
+        if (behaviorVersion == null) {
+            return DEFAULT_BEHAVIOUR_VERSION;
+        }
+        return behaviorVersion.getMajorVersion() * (1000 * 1000) +
+                behaviorVersion.getMinorVersion() * 1000 +
+                behaviorVersion.getIncrementalVersion();
     }
 
     static void registerConfigs() {
@@ -59,6 +80,7 @@ static void registerConfigs() {
                 LOG.warn("Config file {} was not registered!", cfg.fileName());
             } else {
                 config.decorate(FabricUtil.KEY_MOD_ID, cfg.modId());
+                config.decorate(FabricUtil.KEY_COMPATIBILITY, cfg.behaviorVersion());
             }
         });
         mixinConfigs.clear();

loader/src/main/java/net/neoforged/fml/loading/moddiscovery/ModFileParser.java

@@ -10,19 +10,25 @@
 import com.electronwill.nightconfig.core.file.FileConfig;
 import com.electronwill.nightconfig.toml.TomlFormat;
 import com.mojang.logging.LogUtils;
+import java.lang.module.ModuleDescriptor;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Optional;
 import net.neoforged.fml.loading.LogMarkers;
+import net.neoforged.fml.loading.mixin.DeferredMixinConfigRegistration;
 import net.neoforged.fml.loading.moddiscovery.readers.JarModsDotTomlModFileReader;
 import net.neoforged.neoforgespi.language.IConfigurable;
 import net.neoforged.neoforgespi.language.IModFileInfo;
 import net.neoforged.neoforgespi.locating.IModFile;
 import net.neoforged.neoforgespi.locating.InvalidModFileException;
 import net.neoforged.neoforgespi.locating.ModFileInfoParser;
+import org.apache.maven.artifact.versioning.ArtifactVersion;
+import org.apache.maven.artifact.versioning.DefaultArtifactVersion;
+import org.jetbrains.annotations.Nullable;
 import org.slf4j.Logger;
+import org.spongepowered.asm.mixin.FabricUtil;
 
 public class ModFileParser {
     private static final Logger LOGGER = LogUtils.getLogger();
@@ -63,10 +69,32 @@ private static UnmodifiableConfig copyConfig(ConcurrentConfig config) {
     /**
      * Represents a potential mixin configuration.
      *
-     * @param config       The name of the mixin configuration.
-     * @param requiredMods The mod ids that are required for this mixin configuration to be loaded. If empty, will be loaded regardless.
+     * @param config          The name of the mixin configuration.
+     * @param requiredMods    The mod ids that are required for this mixin configuration to be loaded. If empty, will be loaded regardless.
+     * @param behaviorVersion The mixin version whose behavior this configuration requests; if unspecified, the default is provided by FML.
      */
-    public record MixinConfig(String config, List<String> requiredMods) {}
+    public record MixinConfig(String config, List<String> requiredMods, @Nullable ArtifactVersion behaviorVersion) {
+        public MixinConfig(String config, List<String> requiredMods) {
+            this(config, requiredMods, null);
+        }
+    }
+
+    private static final ArtifactVersion HIGHEST_MIXIN_VERSION;
+    private static final ArtifactVersion LOWEST_MIXIN_VERSION;
+
+    static {
+        HIGHEST_MIXIN_VERSION = new DefaultArtifactVersion(Optional.ofNullable(FabricUtil.class.getModule().getDescriptor())
+                .flatMap(ModuleDescriptor::version).map(ModuleDescriptor.Version::toString)
+                .or(() -> Optional.ofNullable(FabricUtil.class.getPackage().getImplementationVersion()))
+                .orElseThrow(() -> new IllegalStateException("Cannot determine version of currently running mixin")));
+        int defaultMixinVersion = DeferredMixinConfigRegistration.DEFAULT_BEHAVIOUR_VERSION;
+        int patch = defaultMixinVersion % 1000;
+        defaultMixinVersion /= 1000;
+        int minor = defaultMixinVersion % 1000;
+        defaultMixinVersion /= 1000;
+        int major = defaultMixinVersion;
+        LOWEST_MIXIN_VERSION = new DefaultArtifactVersion(major + "." + minor + "." + patch);
+    }
 
     protected static List<MixinConfig> getMixinConfigs(IModFileInfo modFileInfo) {
         try {
@@ -78,7 +106,21 @@ protected static List<MixinConfig> getMixinConfigs(IModFileInfo modFileInfo) {
                 var name = mixinsEntry.<String>getConfigElement("config")
                         .orElseThrow(() -> new InvalidModFileException("Missing \"config\" in [[mixins]] entry", modFileInfo));
                 var requiredModIds = mixinsEntry.<List<String>>getConfigElement("requiredMods").orElse(List.of());
-                potentialMixins.add(new MixinConfig(name, requiredModIds));
+                var behaviorVersion = mixinsEntry.<String>getConfigElement("behaviorVersion")
+                        .map(DefaultArtifactVersion::new)
+                        .orElse(null);
+                if (behaviorVersion != null) {
+                    if (behaviorVersion.compareTo(HIGHEST_MIXIN_VERSION) > 0) {
+                        throw new InvalidModFileException("Specified mixin behavior version " + behaviorVersion
+                                + " is higher than the current mixin version " + HIGHEST_MIXIN_VERSION + "; this may be fixable by updating neoforge",
+                                modFileInfo);
+                    } else if (behaviorVersion.compareTo(LOWEST_MIXIN_VERSION) < 0) {
+                        throw new InvalidModFileException("Specified mixin behavior version " + behaviorVersion
+                                + " is lower than the minimum supported behavior version " + LOWEST_MIXIN_VERSION,
+                                modFileInfo);
+                    }
+                }
+                potentialMixins.add(new MixinConfig(name, requiredModIds, behaviorVersion));
             }
 
             return potentialMixins;