Add depends property to Mod annotation for conditional entrypoints

loader/src/main/java/net/neoforged/fml/common/Mod.java

@@ -16,6 +16,7 @@
  * <p>
  * Any class found with this annotation applied will be loaded as a mod entrypoint for the mod with the given {@linkplain #value() ID}. <br>
  * A mod loaded with the {@code javafml} language loader may have multiple entrypoints.
+ * Entrypoints with the least {@link #depends} are run first.
  * Entrypoints for all {@link #dist}s are always run before entrypoints for a single {@link #dist}.
  */
 @Retention(RetentionPolicy.RUNTIME)
@@ -34,4 +35,9 @@
      * {@return the side to load this mod entrypoint on}
      */
     Dist[] dist() default { Dist.CLIENT, Dist.DEDICATED_SERVER };
+
+    /**
+     * A list of mod IDs which are all required to be present in order to load this mod entrypoint.
+     */
+    String[] depends() default {};
 }

loader/src/main/java/net/neoforged/fml/javafmlmod/FMLJavaModLanguageProvider.java

@@ -7,8 +7,10 @@
 
 import java.lang.annotation.ElementType;
 import java.util.Collection;
+import java.util.Collections;
 import java.util.Comparator;
 import java.util.HashSet;
+import java.util.List;
 import java.util.Set;
 import net.neoforged.fml.ModContainer;
 import net.neoforged.fml.ModLoadingIssue;
@@ -33,7 +35,9 @@ public ModContainer loadMod(IModInfo info, ModFileScanData modFileScanResults, M
         var modClasses = modFileScanResults.getAnnotatedBy(Mod.class, ElementType.TYPE)
                 .filter(data -> data.annotationData().get("value").equals(info.getModId()))
                 .filter(ad -> AutomaticEventSubscriber.getSides(ad.annotationData().get("dist")).contains(FMLLoader.getCurrent().getDist()))
-                .sorted(Comparator.comparingInt(ad -> -AutomaticEventSubscriber.getSides(ad.annotationData().get("dist")).size()))
+                .filter(ad -> getDepends(ad).stream().allMatch(otherMod -> FMLLoader.getCurrent().getLoadingModList().getModFileById(otherMod) != null))
+                .sorted(Comparator.<ModFileScanData.AnnotationData>comparingInt(ad -> getDepends(ad).size())
+                        .thenComparingInt(ad -> -AutomaticEventSubscriber.getSides(ad.annotationData().get("dist")).size()))
                 .map(ad -> ad.clazz().getClassName())
                 .toList();
         return new FMLModContainer(info, modClasses, modFileScanResults, layer);
@@ -57,4 +61,10 @@ public void validate(IModFile file, Collection<ModContainer> loadedContainers, I
                     reporter.addIssue(issue);
                 });
     }
+
+    @SuppressWarnings("unchecked")
+    private static List<String> getDepends(ModFileScanData.AnnotationData data) {
+        var depends = data.annotationData().get("depends");
+        return depends != null ? (List<String>) depends : Collections.emptyList();
+    }
 }

loader/src/test/java/net/neoforged/fml/javafmlmod/FMLJavaModLanguageProviderTest.java

@@ -127,6 +127,61 @@ public ClientEntryPoint() {
         assertThat(MESSAGES).isEqualTo(List.of("common", "client"));
     }
 
+    @Test
+    void testDependsEntrypointDoesntFire() throws Exception {
+        installation.setupProductionClient();
+
+        installation.buildModJar("test.jar")
+                .withTestmodModsToml()
+                .addClass("testmod.DependsEntryPoint", """
+                        @net.neoforged.fml.common.Mod(value = "testmod", depends = "othermod")
+                        public class DependsEntryPoint {
+                            public DependsEntryPoint() {
+                                net.neoforged.fml.javafmlmod.FMLJavaModLanguageProviderTest.MESSAGES.add("fired");
+                            }
+                        }
+                        """)
+                .build();
+
+        launchAndLoad("neoforgeclient");
+
+        assertThat(MESSAGES).isEmpty();
+    }
+
+    @Test
+    void testDependsEntrypointOrdering() throws Exception {
+        installation.setupProductionClient();
+
+        installation.buildModJar("othermod.jar").withMod("othermod", "1.0").build();
+        installation.buildModJar("test.jar")
+                .withTestmodModsToml(builder -> {
+                    builder.addDependency("testmod", "othermod", "[1,)", config -> {
+                        config.set("type", "optional");
+                    });
+                })
+                .addClass("testmod.EntryPoint", """
+                        @net.neoforged.fml.common.Mod("testmod")
+                        public class EntryPoint {
+                            public EntryPoint() {
+                                net.neoforged.fml.javafmlmod.FMLJavaModLanguageProviderTest.MESSAGES.add("common");
+                            }
+                        }
+                        """)
+                .addClass("testmod.DependsEntryPoint", """
+                        @net.neoforged.fml.common.Mod(value = "testmod", depends = "othermod")
+                        public class DependsEntryPoint {
+                            public DependsEntryPoint() {
+                                net.neoforged.fml.javafmlmod.FMLJavaModLanguageProviderTest.MESSAGES.add("dependency");
+                            }
+                        }
+                        """)
+                .build();
+
+        launchAndLoad("neoforgeclient");
+
+        assertThat(MESSAGES).isEqualTo(List.of("common", "dependency"));
+    }
+
     @Test
     void testErrorDuringEventDispatch() throws Exception {
         installation.setupProductionClient();