Add Transaction#getCurrentUnsafe and fix mixin fields (#1685)

* Add Transaction#getCurrentUnsafe and fix mixin fields

* Update fabric-transfer-api-v1/src/main/java/net/fabricmc/fabric/impl/transfer/transaction/TransactionManagerImpl.java

Co-authored-by: BasiqueEvangelist <basiqueevangelist@yandex.ru>

Co-authored-by: BasiqueEvangelist <basiqueevangelist@yandex.ru>

fabric-transfer-api-v1/src/main/java/net/fabricmc/fabric/api/transfer/v1/transaction/Transaction.java

@@ -104,6 +104,23 @@ public interface Transaction extends AutoCloseable, TransactionContext {
 		return maybeParent == null ? openOuter() : maybeParent.openNested();
 	}
 
+	/**
+	 * Retrieve the currently open transaction, or null if there is none.
+	 *
+	 * <p><b>Usage of this function is strongly discouraged</b>, this is why it is deprecated and contains {@code unsafe} in its name.
+	 * The transaction may be aborted unbeknownst to you and anything you think that you have committed might be undone.
+	 * Only use it if you have no way to pass the transaction down the stack, for example if you are implementing compat with a simulation-based API,
+	 * and you know what you are doing, for example because you opened the outer transaction.
+	 *
+	 * @throws IllegalStateException If called from a close or outer close callback.
+	 * @deprecated Only use if you absolutely need it, there is almost always a better way.
+	 */
+	@Deprecated
+	@Nullable
+	static TransactionContext getCurrentUnsafe() {
+		return TransactionManagerImpl.MANAGERS.get().getCurrentUnsafe();
+	}
+
 	/**
 	 * Close the current transaction, rolling back all the changes that happened during this transaction and
 	 * the transactions opened with {@link #openNested} from this transaction.

fabric-transfer-api-v1/src/main/java/net/fabricmc/fabric/impl/transfer/transaction/TransactionManagerImpl.java

@@ -18,6 +18,9 @@ package net.fabricmc.fabric.impl.transfer.transaction;
 
 import java.util.ArrayList;
 
+import org.jetbrains.annotations.Nullable;
+
+import net.fabricmc.fabric.api.transfer.v1.transaction.TransactionContext;
 import net.fabricmc.fabric.api.transfer.v1.transaction.Transaction;
 
 public class TransactionManagerImpl {
@@ -40,6 +43,17 @@ public class TransactionManagerImpl {
 		return open();
 	}
 
+	@Nullable
+	public TransactionContext getCurrentUnsafe() {
+		if (currentDepth == -1) {
+			return null;
+		} else if (stack.get(currentDepth).isOpen) {
+			return stack.get(currentDepth);
+		} else {
+			throw new IllegalStateException("May not call getCurrentUnsafe() from a close callback.");
+		}
+	}
+
 	/**
 	 * Open a new transaction, outer or nested, without performing any state check.
 	 */

fabric-transfer-api-v1/src/main/java/net/fabricmc/fabric/mixin/transfer/FluidMixin.java

@@ -31,10 +31,10 @@ import net.fabricmc.fabric.impl.transfer.fluid.FluidVariantCache;
 @SuppressWarnings("unused")
 public class FluidMixin implements FluidVariantCache {
 	@SuppressWarnings("ConstantConditions")
-	private final FluidVariant cachedFluidVariant = new FluidVariantImpl((Fluid) (Object) this, null);
+	private final FluidVariant fabric_cachedFluidVariant = new FluidVariantImpl((Fluid) (Object) this, null);
 
 	@Override
 	public FluidVariant fabric_getCachedFluidVariant() {
-		return cachedFluidVariant;
+		return fabric_cachedFluidVariant;
 	}
 }

fabric-transfer-api-v1/src/main/java/net/fabricmc/fabric/mixin/transfer/ItemMixin.java

@@ -17,7 +17,6 @@
 package net.fabricmc.fabric.mixin.transfer;
 
 import org.spongepowered.asm.mixin.Mixin;
-import org.spongepowered.asm.mixin.Unique;
 
 import net.minecraft.item.Item;
 
@@ -30,11 +29,11 @@ import net.fabricmc.fabric.impl.transfer.item.ItemVariantImpl;
  */
 @Mixin(Item.class)
 public class ItemMixin implements ItemVariantCache {
-	@Unique
-	private final ItemVariant cachedItemVariant = new ItemVariantImpl((Item) (Object) this, null);
+	@SuppressWarnings("ConstantConditions")
+	private final ItemVariant fabric_cachedItemVariant = new ItemVariantImpl((Item) (Object) this, null);
 
 	@Override
 	public ItemVariant fabric_getCachedItemVariant() {
-		return cachedItemVariant;
+		return fabric_cachedItemVariant;
 	}
 }

fabric-transfer-api-v1/src/testmod/java/net/fabricmc/fabric/test/transfer/unittests/TransactionExceptionsTests.java

@@ -60,6 +60,21 @@ class TransactionExceptionsTests {
 		}, "Exceptions in close callbacks should be propagated through the transaction.");
 		if (callbacksInvoked != 4) throw new AssertionError("All 4 callbacks should have been invoked, only so many were: " + callbacksInvoked);
 
+		// Test getCurrentUnsafe.
+		if (Transaction.getCurrentUnsafe() != null) throw new AssertionError("Should have returned null.");
+
+		try (Transaction tx = Transaction.openOuter()) {
+			if (Transaction.getCurrentUnsafe() != tx) throw new AssertionError("Should have returned the current transaction.");
+
+			tx.addCloseCallback(((transaction, result) -> {
+				ensureException(Transaction::getCurrentUnsafe, "Should have thrown an exception in the close callback.");
+			}));
+
+			tx.addOuterCloseCallback((result) -> {
+				ensureException(Transaction::getCurrentUnsafe, "Should have thrown an exception in the outer close callback.");
+			});
+		}
+
 		// Test that transaction state is still OK after these exceptions.
 		try (Transaction tx = Transaction.openOuter()) {
 			tx.commit();