Prevent crash with mods calling getFluidState recursively

The returned fluid is meaningless, but vanilla doesn't crash here

Fixes #238

Author: embeddedt

common/src/main/java/org/embeddedt/modernfix/common/mixin/perf/reduce_blockstate_cache_rebuilds/BlockStateBaseMixin.java

@@ -87,8 +87,19 @@ private FluidState genCacheBeforeGettingFluid(BlockBehaviour.BlockStateBase base
         // don't generate the full cache here as mods will iterate for the fluid state a lot
         // assume blockstates will not change their contained fluidstate at runtime more than once
         // this is how Lithium's implementation used to work, so it should be fine
-        if(this.cacheInvalid && this.fluidState == MFIX$VANILLA_DEFAULT_FLUID)
-            this.fluidState = this.owner.getFluidState(this.asState());
+        if(this.cacheInvalid && this.fluidState == MFIX$VANILLA_DEFAULT_FLUID) {
+            synchronized (BlockBehaviour.BlockStateBase.class) {
+                if(!buildingCache) {
+                    buildingCache = true;
+                    try {
+                        this.fluidState = this.owner.getFluidState(this.asState());
+                    } finally {
+                        buildingCache = false;
+                    }
+                }
+            }
+
+        }
         return this.fluidState;
     }
 

fabric/src/test/java/net/minecraft/world/level/block/state/BlockStateCacheTest.java

@@ -4,6 +4,7 @@
 import net.minecraft.world.level.EmptyBlockGetter;
 import net.minecraft.world.level.block.Block;
 import net.minecraft.world.level.block.Blocks;
+import net.minecraft.world.level.material.FluidState;
 import org.embeddedt.modernfix.duck.IBlockState;
 import org.embeddedt.modernfix.testing.util.BootstrapMinecraft;
 import org.junit.jupiter.api.*;
@@ -74,4 +75,19 @@ public void testExtraFieldCachingCorrect() {
             }
         }
     }
+
+    @Test
+    @Order(5)
+    public void checkRecursiveFluidState() {
+        Block b = new Block(BlockBehaviour.Properties.copy(Blocks.STONE)) {
+            @Override
+            public FluidState getFluidState(BlockState state) {
+                return state.getFluidState();
+            }
+        };
+        BlockState state = b.getStateDefinition().any();
+        ((IBlockState)state).clearCache();
+        // this should not throw
+        state.getFluidState();
+    }
 }