fix: preserve equality when scheduling part ticks

src/test/java/codechicken/multipart/TickSchedulerEqualityRegressionTest.java

@@ -0,0 +1,90 @@
+package codechicken.multipart;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import net.minecraft.world.chunk.Chunk;
+
+import org.junit.jupiter.api.Test;
+
+class TickSchedulerEqualityRegressionTest {
+
+    @Test
+    void equalPartsShareOneEntryAndKeepTheOriginalCallbackTarget() {
+        TickScheduler.ChunkTickScheduler scheduler = scheduler();
+        EqualPart first = new EqualPart("same");
+        EqualPart equal = new EqualPart("same");
+        EqualPart different = new EqualPart("different");
+
+        scheduler.scheduleTick(first, 0, false);
+        scheduler.scheduleTick(equal, 0, false);
+        scheduler.scheduleTick(different, 0, false);
+
+        assertFalse(scheduler.processTicks());
+        assertEquals(1, first.calls);
+        assertEquals(0, equal.calls);
+        assertEquals(1, different.calls);
+    }
+
+    @Test
+    void anEqualPartCanPromoteARandomEntryToAnImmediateScheduledTick() {
+        TickScheduler.ChunkTickScheduler scheduler = scheduler();
+        EqualPart first = new EqualPart("same");
+        EqualPart equal = new EqualPart("same");
+
+        scheduler.scheduleTick(first, 100, true);
+        scheduler.scheduleTick(equal, 0, false);
+
+        assertFalse(scheduler.processTicks());
+        assertEquals(1, first.calls);
+        assertEquals(0, equal.calls);
+    }
+
+    @Test
+    void anEqualPartDoesNotReplaceAnExistingExplicitTick() {
+        TickScheduler.ChunkTickScheduler scheduler = scheduler();
+        EqualPart first = new EqualPart("same");
+        EqualPart equal = new EqualPart("same");
+
+        scheduler.scheduleTick(first, 100, false);
+        scheduler.scheduleTick(equal, 0, false);
+
+        assertTrue(scheduler.processTicks());
+        assertEquals(0, first.calls);
+        assertEquals(0, equal.calls);
+    }
+
+    private static TickScheduler.ChunkTickScheduler scheduler() {
+        return new TickScheduler.ChunkTickScheduler(new Chunk(null, 0, 0), new TickScheduler.WorldTickScheduler(null));
+    }
+
+    private static final class EqualPart extends TMultiPart {
+
+        private final String key;
+        int calls;
+
+        EqualPart(String key) {
+            this.key = key;
+            bind(new TileMultipart());
+        }
+
+        @Override
+        public String getType() {
+            return "test:equal-scheduled";
+        }
+
+        @Override
+        public boolean equals(Object other) {
+            return other instanceof EqualPart && key.equals(((EqualPart) other).key);
+        }
+
+        @Override
+        public int hashCode() {
+            return key.hashCode();
+        }
+
+        @Override
+        public void scheduledTick() {
+            calls++;
+        }
+    }
+}