Player Feedback, Part I

src/main/java/com/simibubi/create/content/contraptions/components/structureMovement/AssemblyException.java

@@ -0,0 +1,23 @@
+package com.simibubi.create.content.contraptions.components.structureMovement;
+
+import net.minecraft.block.BlockState;
+import net.minecraft.util.math.BlockPos;
+import net.minecraft.util.text.ITextComponent;
+import net.minecraft.util.text.TranslationTextComponent;
+
+public class AssemblyException extends RuntimeException {
+	public final ITextComponent message;
+
+	public AssemblyException(ITextComponent message) {
+		this.message = message;
+	}
+
+	public AssemblyException(String langKey, Object... objects) {
+		this(new TranslationTextComponent("gui.goggles.contraptions." + langKey, objects));
+	}
+
+	public static AssemblyException unmovableBlock(BlockPos pos, BlockState state) {
+		return new AssemblyException("unmovableBlock", pos.getX(), pos.getY(), pos.getZ(),
+				new TranslationTextComponent(state.getBlock().getTranslationKey()));
+	}
+}

src/main/java/com/simibubi/create/content/contraptions/components/structureMovement/Contraption.java

@@ -135,7 +135,7 @@ public abstract class Contraption {
 		stabilizedSubContraptions = new HashMap<>();
 	}
 
-	public abstract boolean assemble(World world, BlockPos pos);
+	public abstract boolean assemble(World world, BlockPos pos) throws AssemblyException;
 
 	protected abstract boolean canAxisBeStabilized(Axis axis);
 
@@ -180,7 +180,7 @@ public abstract class Contraption {
 			if (!moveBlock(world, forcedDirection, frontier, visited))
 				return false;
 		}
-		return false;
+		throw new AssemblyException("structureTooLarge");
 	}
 
 	public void onEntityCreated(AbstractContraptionEntity entity) {
@@ -192,8 +192,12 @@ public abstract class Contraption {
 			StabilizedContraption subContraption = new StabilizedContraption(face);
 			World world = entity.world;
 			BlockPos pos = blockFace.getPos();
+			try {
 				if (!subContraption.assemble(world, pos))
 					continue;
+			} catch (AssemblyException e) {
+				continue;
+			}
 			subContraption.removeBlocksFromWorld(world, BlockPos.ZERO);
 			OrientedContraptionEntity movedContraption =
 				OrientedContraptionEntity.create(world, subContraption, Optional.of(face));
@@ -243,6 +247,7 @@ public abstract class Contraption {
 		fluidStorage.forEach((pos, mfs) -> mfs.tick(entity, pos, world.isRemote));
 	}
 
+	/** move the first block in frontier queue */
 	protected boolean moveBlock(World world, @Nullable Direction forcedDirection, Queue<BlockPos> frontier,
 		Set<BlockPos> visited) {
 		BlockPos pos = frontier.poll();
@@ -250,15 +255,17 @@ public abstract class Contraption {
 			return false;
 		visited.add(pos);
 
+		if (World.isOutsideBuildHeight(pos))
+			return true;
 		if (!world.isBlockPresent(pos))
-			return false;
+			throw new AssemblyException("chunkNotLoaded");
 		if (isAnchoringBlockAt(pos))
 			return true;
 		BlockState state = world.getBlockState(pos);
 		if (!BlockMovementTraits.movementNecessary(state, world, pos))
 			return true;
 		if (!movementAllowed(state, world, pos))
-			return false;
+			throw AssemblyException.unmovableBlock(pos, state);
 		if (state.getBlock() instanceof AbstractChassisBlock
 			&& !moveChassis(world, pos, forcedDirection, frontier, visited))
 			return false;
@@ -309,7 +316,7 @@ public abstract class Contraption {
 				continue;
 			if (!movementAllowed(blockState, world, offsetPos)) {
 				if (offset == forcedDirection)
-					return false;
+					throw AssemblyException.unmovableBlock(pos, state);
 				continue;
 			}
 
@@ -338,7 +345,10 @@ public abstract class Contraption {
 		}
 
 		addBlock(pos, capture(world, pos));
-		return blocks.size() <= AllConfigs.SERVER.kinetics.maxBlocksMoved.get();
+		if (blocks.size() <= AllConfigs.SERVER.kinetics.maxBlocksMoved.get())
+			return true;
+		else
+			throw new AssemblyException("structureTooLarge");
 	}
 
 	private void moveBearing(BlockPos pos, Queue<BlockPos> frontier, Set<BlockPos> visited, BlockState state) {
@@ -414,7 +424,7 @@ public abstract class Contraption {
 				break;
 			}
 			if (limit <= -1)
-				return false;
+				throw new AssemblyException("tooManyPistonPoles");
 		}
 
 		BlockPos searchPos = pos;
@@ -433,7 +443,7 @@ public abstract class Contraption {
 		}
 
 		if (limit <= -1)
-			return false;
+			throw new AssemblyException("tooManyPistonPoles");
 		return true;
 	}
 

src/main/java/com/simibubi/create/content/contraptions/components/structureMovement/bearing/BearingContraption.java

@@ -4,6 +4,7 @@ import org.apache.commons.lang3.tuple.Pair;
 
 import com.simibubi.create.AllTags.AllBlockTags;
 import com.simibubi.create.content.contraptions.components.structureMovement.AllContraptionTypes;
+import com.simibubi.create.content.contraptions.components.structureMovement.AssemblyException;
 import com.simibubi.create.content.contraptions.components.structureMovement.Contraption;
 
 import net.minecraft.nbt.CompoundNBT;
@@ -29,7 +30,7 @@ public class BearingContraption extends Contraption {
 	}
 
 	@Override
-	public boolean assemble(World world, BlockPos pos) {
+	public boolean assemble(World world, BlockPos pos) throws AssemblyException {
 		BlockPos offset = pos.offset(facing);
 		if (!searchMovedStructure(world, offset, null))
 			return false;

src/main/java/com/simibubi/create/content/contraptions/components/structureMovement/bearing/ClockworkBearingTileEntity.java

@@ -6,6 +6,7 @@ import org.apache.commons.lang3.tuple.Pair;
 
 import com.simibubi.create.content.contraptions.base.KineticTileEntity;
 import com.simibubi.create.content.contraptions.components.structureMovement.AbstractContraptionEntity;
+import com.simibubi.create.content.contraptions.components.structureMovement.AssemblyException;
 import com.simibubi.create.content.contraptions.components.structureMovement.ControlledContraptionEntity;
 import com.simibubi.create.content.contraptions.components.structureMovement.bearing.ClockworkContraption.HandType;
 import com.simibubi.create.foundation.advancement.AllTriggers;
@@ -25,6 +26,7 @@ import net.minecraft.util.Direction;
 import net.minecraft.util.Direction.Axis;
 import net.minecraft.util.math.BlockPos;
 import net.minecraft.util.math.MathHelper;
+import net.minecraft.util.text.ITextComponent;
 
 public class ClockworkBearingTileEntity extends KineticTileEntity implements IBearingTileEntity {
 
@@ -37,6 +39,7 @@ public class ClockworkBearingTileEntity extends KineticTileEntity implements IBe
 
 	protected boolean running;
 	protected boolean assembleNextTick;
+	protected ITextComponent lastException;
 
 	protected ScrollOptionBehaviour<ClockHands> operationMode;
 
@@ -199,8 +202,14 @@ public class ClockworkBearingTileEntity extends KineticTileEntity implements IBe
 		Direction direction = getBlockState().get(BlockStateProperties.FACING);
 
 		// Collect Construct
-		Pair<ClockworkContraption, ClockworkContraption> contraption =
+		Pair<ClockworkContraption, ClockworkContraption> contraption;
-			ClockworkContraption.assembleClockworkAt(world, pos, direction);
+		try {
+			contraption = ClockworkContraption.assembleClockworkAt(world, pos, direction);
+			lastException = null;
+		} catch (AssemblyException e) {
+			lastException = e.message;
+			return;
+		}
 		if (contraption == null)
 			return;
 		if (contraption.getLeft() == null)
@@ -284,6 +293,8 @@ public class ClockworkBearingTileEntity extends KineticTileEntity implements IBe
 		compound.putBoolean("Running", running);
 		compound.putFloat("HourAngle", hourAngle);
 		compound.putFloat("MinuteAngle", minuteAngle);
+		if (lastException != null)
+			compound.putString("LastException", ITextComponent.Serializer.toJson(lastException));
 		super.write(compound, clientPacket);
 	}
 
@@ -295,6 +306,10 @@ public class ClockworkBearingTileEntity extends KineticTileEntity implements IBe
 		running = compound.getBoolean("Running");
 		hourAngle = compound.getFloat("HourAngle");
 		minuteAngle = compound.getFloat("MinuteAngle");
+		if (compound.contains("LastException"))
+			lastException = ITextComponent.Serializer.fromJson(compound.getString("LastException"));
+		else
+			lastException = null;
 		super.read(compound, clientPacket);
 
 		if (!clientPacket)
@@ -393,4 +408,12 @@ public class ClockworkBearingTileEntity extends KineticTileEntity implements IBe
 		return pos;
 	}
 
+	@Override
+	public boolean addToGoggleTooltip(List<String> tooltip, boolean isPlayerSneaking) {
+		boolean added = super.addToGoggleTooltip(tooltip, isPlayerSneaking);
+		if (lastException != null)
+			tooltip.add(lastException.getFormattedText());
+		return lastException != null || added;
+	}
+
 }

src/main/java/com/simibubi/create/content/contraptions/components/structureMovement/bearing/ClockworkContraption.java

@@ -7,6 +7,7 @@ import java.util.Set;
 import org.apache.commons.lang3.tuple.Pair;
 
 import com.simibubi.create.content.contraptions.components.structureMovement.AllContraptionTypes;
+import com.simibubi.create.content.contraptions.components.structureMovement.AssemblyException;
 import com.simibubi.create.content.contraptions.components.structureMovement.Contraption;
 import com.simibubi.create.foundation.utility.NBTHelper;
 
@@ -39,7 +40,7 @@ public class ClockworkContraption extends Contraption {
 	}
 
 	public static Pair<ClockworkContraption, ClockworkContraption> assembleClockworkAt(World world, BlockPos pos,
-		Direction direction) {
+		Direction direction) throws AssemblyException {
 		int hourArmBlocks = 0;
 
 		ClockworkContraption hourArm = new ClockworkContraption();
@@ -82,7 +83,7 @@ public class ClockworkContraption extends Contraption {
 	}
 	
 	@Override
-	public boolean assemble(World world, BlockPos pos) {
+	public boolean assemble(World world, BlockPos pos) throws AssemblyException {
 		return searchMovedStructure(world, pos, facing);
 	}
 

src/main/java/com/simibubi/create/content/contraptions/components/structureMovement/bearing/MechanicalBearingTileEntity.java

@@ -6,6 +6,7 @@ import java.util.List;
 
 import com.simibubi.create.content.contraptions.base.GeneratingKineticTileEntity;
 import com.simibubi.create.content.contraptions.components.structureMovement.AbstractContraptionEntity;
+import com.simibubi.create.content.contraptions.components.structureMovement.AssemblyException;
 import com.simibubi.create.content.contraptions.components.structureMovement.ControlledContraptionEntity;
 import com.simibubi.create.foundation.advancement.AllTriggers;
 import com.simibubi.create.foundation.item.TooltipHelper;
@@ -22,6 +23,7 @@ import net.minecraft.tileentity.TileEntityType;
 import net.minecraft.util.Direction;
 import net.minecraft.util.math.BlockPos;
 import net.minecraft.util.math.MathHelper;
+import net.minecraft.util.text.ITextComponent;
 
 public class MechanicalBearingTileEntity extends GeneratingKineticTileEntity implements IBearingTileEntity {
 
@@ -31,6 +33,7 @@ public class MechanicalBearingTileEntity extends GeneratingKineticTileEntity imp
 	protected boolean running;
 	protected boolean assembleNextTick;
 	protected float clientAngleDiff;
+	protected ITextComponent lastException;
 
 	public MechanicalBearingTileEntity(TileEntityType<? extends MechanicalBearingTileEntity> type) {
 		super(type);
@@ -62,6 +65,8 @@ public class MechanicalBearingTileEntity extends GeneratingKineticTileEntity imp
 	public void write(CompoundNBT compound, boolean clientPacket) {
 		compound.putBoolean("Running", running);
 		compound.putFloat("Angle", angle);
+		if (lastException != null)
+			compound.putString("LastException", ITextComponent.Serializer.toJson(lastException));
 		super.write(compound, clientPacket);
 	}
 
@@ -70,6 +75,10 @@ public class MechanicalBearingTileEntity extends GeneratingKineticTileEntity imp
 		float angleBefore = angle;
 		running = compound.getBoolean("Running");
 		angle = compound.getFloat("Angle");
+		if (compound.contains("LastException"))
+			lastException = ITextComponent.Serializer.fromJson(compound.getString("LastException"));
+		else
+			lastException = null;
 		super.read(compound, clientPacket);
 		if (!clientPacket)
 			return;
@@ -120,8 +129,14 @@ public class MechanicalBearingTileEntity extends GeneratingKineticTileEntity imp
 
 		Direction direction = getBlockState().get(FACING);
 		BearingContraption contraption = new BearingContraption(isWindmill(), direction);
+		try {
+			lastException = null;
 			if (!contraption.assemble(world, pos))
 				return;
+		} catch (AssemblyException e) {
+			lastException = e.message;
+			return;
+		}
 
 		if (isWindmill())
 			AllTriggers.triggerForNearbyPlayers(AllTriggers.WINDMILL, world, pos, 5);
@@ -282,4 +297,11 @@ public class MechanicalBearingTileEntity extends GeneratingKineticTileEntity imp
 		return true;
 	}
 
+	@Override
+	public boolean addToGoggleTooltip(List<String> tooltip, boolean isPlayerSneaking) {
+		boolean added = super.addToGoggleTooltip(tooltip, isPlayerSneaking);
+		if (lastException != null)
+			tooltip.add(lastException.getFormattedText());
+		return lastException != null || added;
+	}
 }

src/main/java/com/simibubi/create/content/contraptions/components/structureMovement/bearing/StabilizedContraption.java

@@ -1,6 +1,7 @@
 package com.simibubi.create.content.contraptions.components.structureMovement.bearing;
 
 import com.simibubi.create.content.contraptions.components.structureMovement.AllContraptionTypes;
+import com.simibubi.create.content.contraptions.components.structureMovement.AssemblyException;
 import com.simibubi.create.content.contraptions.components.structureMovement.Contraption;
 
 import net.minecraft.nbt.CompoundNBT;
@@ -20,7 +21,7 @@ public class StabilizedContraption extends Contraption {
 	}
 
 	@Override
-	public boolean assemble(World world, BlockPos pos) {
+	public boolean assemble(World world, BlockPos pos) throws AssemblyException {
 		BlockPos offset = pos.offset(facing);
 		if (!searchMovedStructure(world, offset, null))
 			return false;

src/main/java/com/simibubi/create/content/contraptions/components/structureMovement/mounted/CartAssemblerBlock.java

@@ -3,6 +3,7 @@ package com.simibubi.create.content.contraptions.components.structureMovement.mo
 import com.simibubi.create.AllBlocks;
 import com.simibubi.create.AllShapes;
 import com.simibubi.create.AllTileEntities;
+import com.simibubi.create.content.contraptions.components.structureMovement.AssemblyException;
 import com.simibubi.create.content.contraptions.components.structureMovement.OrientedContraptionEntity;
 import com.simibubi.create.content.contraptions.components.structureMovement.mounted.CartAssemblerTileEntity.CartMovementMode;
 import com.simibubi.create.content.contraptions.components.structureMovement.train.CouplingHandler;
@@ -229,13 +230,20 @@ public class CartAssemblerBlock extends AbstractRailBlock
 			.isCoupledThroughContraption())
 			return;
 
-		CartMovementMode mode =
+		
-			getTileEntityOptional(world, pos).map(te -> CartMovementMode.values()[te.movementMode.value])
+		Optional<CartAssemblerTileEntity> assembler = getTileEntityOptional(world, pos);
+		CartMovementMode mode = assembler.map(te -> CartMovementMode.values()[te.movementMode.value])
 				.orElse(CartMovementMode.ROTATE);
 
 		MountedContraption contraption = new MountedContraption(mode);
+		try {
+			assembler.ifPresent(te -> te.lastException = null);
 			if (!contraption.assemble(world, pos))
 				return;
+		} catch (AssemblyException e) {
+			assembler.ifPresent(te -> te.lastException = e.message);
+			return;
+		}
 
 		boolean couplingFound = contraption.connectedCart != null;
 		Optional<Direction> initialOrientation = cart.getMotion()

src/main/java/com/simibubi/create/content/contraptions/components/structureMovement/mounted/CartAssemblerTileEntity.java

@@ -2,6 +2,7 @@ package com.simibubi.create.content.contraptions.components.structureMovement.mo
 
 import java.util.List;
 
+import com.simibubi.create.content.contraptions.goggles.IHaveGoggleInformation;
 import com.simibubi.create.foundation.gui.AllIcons;
 import com.simibubi.create.foundation.tileEntity.SmartTileEntity;
 import com.simibubi.create.foundation.tileEntity.TileEntityBehaviour;
@@ -16,12 +17,14 @@ import net.minecraft.state.properties.RailShape;
 import net.minecraft.tileentity.TileEntityType;
 import net.minecraft.util.Direction.Axis;
 import net.minecraft.util.math.Vec3d;
+import net.minecraft.util.text.ITextComponent;
 
-public class CartAssemblerTileEntity extends SmartTileEntity {
+public class CartAssemblerTileEntity extends SmartTileEntity implements IHaveGoggleInformation {
 	private static final int assemblyCooldown = 8;
 
 	protected ScrollOptionBehaviour<CartMovementMode> movementMode;
 	private int ticksSinceMinecartUpdate;
+	protected ITextComponent lastException; //TODO
 
 	public CartAssemblerTileEntity(TileEntityType<? extends CartAssemblerTileEntity> type) {
 		super(type);
@@ -104,4 +107,10 @@ public class CartAssemblerTileEntity extends SmartTileEntity {
 		return ticksSinceMinecartUpdate >= assemblyCooldown;
 	}
 
+	@Override
+	public boolean addToGoggleTooltip(List<String> tooltip, boolean isPlayerSneaking) {
+		if (lastException != null)
+			tooltip.add(lastException.getFormattedText());
+		return lastException != null;
+	}
 }

src/main/java/com/simibubi/create/content/contraptions/components/structureMovement/mounted/MountedContraption.java

@@ -8,6 +8,7 @@ import org.apache.commons.lang3.tuple.Pair;
 
 import com.simibubi.create.AllBlocks;
 import com.simibubi.create.content.contraptions.components.structureMovement.AllContraptionTypes;
+import com.simibubi.create.content.contraptions.components.structureMovement.AssemblyException;
 import com.simibubi.create.content.contraptions.components.structureMovement.Contraption;
 import com.simibubi.create.content.contraptions.components.structureMovement.mounted.CartAssemblerTileEntity.CartMovementMode;
 import com.simibubi.create.foundation.utility.Iterate;
@@ -52,7 +53,7 @@ public class MountedContraption extends Contraption {
 	}
 	
 	@Override
-	public boolean assemble(World world, BlockPos pos) {
+	public boolean assemble(World world, BlockPos pos) throws AssemblyException {
 		BlockState state = world.getBlockState(pos);
 		if (!state.has(RAIL_SHAPE))
 			return false;

src/main/java/com/simibubi/create/content/contraptions/components/structureMovement/piston/LinearActuatorTileEntity.java

@@ -4,6 +4,7 @@ import java.util.List;
 
 import com.simibubi.create.content.contraptions.base.KineticTileEntity;
 import com.simibubi.create.content.contraptions.components.structureMovement.AbstractContraptionEntity;
+import com.simibubi.create.content.contraptions.components.structureMovement.AssemblyException;
 import com.simibubi.create.content.contraptions.components.structureMovement.ControlledContraptionEntity;
 import com.simibubi.create.content.contraptions.components.structureMovement.IControlContraption;
 import com.simibubi.create.foundation.tileEntity.TileEntityBehaviour;
@@ -17,6 +18,7 @@ import net.minecraft.tileentity.TileEntityType;
 import net.minecraft.util.math.BlockPos;
 import net.minecraft.util.math.MathHelper;
 import net.minecraft.util.math.Vec3d;
+import net.minecraft.util.text.ITextComponent;
 
 public abstract class LinearActuatorTileEntity extends KineticTileEntity implements IControlContraption {
 
@@ -27,6 +29,7 @@ public abstract class LinearActuatorTileEntity extends KineticTileEntity impleme
 	protected boolean forceMove;
 	protected ScrollOptionBehaviour<MovementMode> movementMode;
 	protected boolean waitingForSpeedChange;
+	protected ITextComponent lastException;
 
 	// Custom position sync
 	protected float clientOffsetDiff;
@@ -80,7 +83,12 @@ public abstract class LinearActuatorTileEntity extends KineticTileEntity impleme
 				return;
 			} else {
 				if (getSpeed() != 0)
+					try {
 						assemble();
+						lastException = null;
+					} catch (AssemblyException e) {
+						lastException = e.message;
+					}
 			}
 			return;
 		}
@@ -153,6 +161,8 @@ public abstract class LinearActuatorTileEntity extends KineticTileEntity impleme
 		compound.putBoolean("Running", running);
 		compound.putBoolean("Waiting", waitingForSpeedChange);
 		compound.putFloat("Offset", offset);
+		if (lastException != null)
+			compound.putString("LastException", ITextComponent.Serializer.toJson(lastException));
 		super.write(compound, clientPacket);
 		
 		if (clientPacket && forceMove) {
@@ -169,6 +179,10 @@ public abstract class LinearActuatorTileEntity extends KineticTileEntity impleme
 		running = compound.getBoolean("Running");
 		waitingForSpeedChange = compound.getBoolean("Waiting");
 		offset = compound.getFloat("Offset");
+		if (compound.contains("LastException"))
+			lastException = ITextComponent.Serializer.fromJson(compound.getString("LastException"));
+		else
+			lastException = null;
 		super.read(compound, clientPacket);
 
 		if (!clientPacket)
@@ -185,7 +199,7 @@ public abstract class LinearActuatorTileEntity extends KineticTileEntity impleme
 
 	public abstract void disassemble();
 
-	protected abstract void assemble();
+	protected abstract void assemble() throws AssemblyException;
 
 	protected abstract int getExtensionRange();
 
@@ -289,4 +303,12 @@ public abstract class LinearActuatorTileEntity extends KineticTileEntity impleme
 		return pos;
 	}
 
+	@Override
+	public boolean addToGoggleTooltip(List<String> tooltip, boolean isPlayerSneaking) {
+		boolean added = super.addToGoggleTooltip(tooltip, isPlayerSneaking);
+		if (lastException != null)
+			tooltip.add(lastException.getFormattedText());
+		return lastException != null || added;
+	}
+
 }

src/main/java/com/simibubi/create/content/contraptions/components/structureMovement/piston/MechanicalPistonTileEntity.java

@@ -2,6 +2,7 @@ package com.simibubi.create.content.contraptions.components.structureMovement.pi
 
 import com.simibubi.create.AllBlocks;
 import com.simibubi.create.content.contraptions.base.IRotate;
+import com.simibubi.create.content.contraptions.components.structureMovement.AssemblyException;
 import com.simibubi.create.content.contraptions.components.structureMovement.ContraptionCollider;
 import com.simibubi.create.content.contraptions.components.structureMovement.ControlledContraptionEntity;
 import com.simibubi.create.content.contraptions.components.structureMovement.DirectionalExtenderScrollOptionSlot;
@@ -41,7 +42,7 @@ public class MechanicalPistonTileEntity extends LinearActuatorTileEntity {
 	}
 
 	@Override
-	public void assemble() {
+	public void assemble() throws AssemblyException {
 		if (!(world.getBlockState(pos)
 			.getBlock() instanceof MechanicalPistonBlock))
 			return;

src/main/java/com/simibubi/create/content/contraptions/components/structureMovement/piston/PistonContraption.java

@@ -1,6 +1,7 @@
 package com.simibubi.create.content.contraptions.components.structureMovement.piston;
 
 import com.simibubi.create.content.contraptions.components.structureMovement.AllContraptionTypes;
+import com.simibubi.create.content.contraptions.components.structureMovement.AssemblyException;
 import com.simibubi.create.content.contraptions.components.structureMovement.BlockMovementTraits;
 import com.simibubi.create.content.contraptions.components.structureMovement.TranslatingContraption;
 import com.simibubi.create.content.contraptions.components.structureMovement.piston.MechanicalPistonBlock.*;
@@ -52,7 +53,7 @@ public class PistonContraption extends TranslatingContraption {
 	}
 
 	@Override
-	public boolean assemble(World world, BlockPos pos) {
+	public boolean assemble(World world, BlockPos pos) throws AssemblyException {
 		if (!collectExtensions(world, pos, orientation))
 			return false;
 		int count = blocks.size();
@@ -90,7 +91,7 @@ public class PistonContraption extends TranslatingContraption {
 
 				nextBlock = world.getBlockState(actualStart.offset(direction));
 				if (extensionsInFront > MechanicalPistonBlock.maxAllowedPistonPoles())
-					return false;
+					throw new AssemblyException("tooManyPistonPoles");
 			}
 		}
 
@@ -113,7 +114,7 @@ public class PistonContraption extends TranslatingContraption {
 			nextBlock = world.getBlockState(end.offset(direction.getOpposite()));
 
 			if (extensionsInFront + extensionsInBack > MechanicalPistonBlock.maxAllowedPistonPoles())
-				return false;
+				throw new AssemblyException("tooManyPistonPoles");
 		}
 
 		anchor = pos.offset(direction, initialExtensionProgress + 1);
@@ -125,7 +126,7 @@ public class PistonContraption extends TranslatingContraption {
 						1, 1);
 
 		if (extensionLength == 0)
-			return false;
+			throw new AssemblyException("noPistonPoles");
 
 		bounds = new AxisAlignedBB(0, 0, 0, 0, 0, 0);
 
@@ -155,8 +156,10 @@ public class PistonContraption extends TranslatingContraption {
 			if (offset == 1 && retracting)
 				return true;
 			BlockPos currentPos = pos.offset(orientation, offset + initialExtensionProgress);
+			if (retracting && World.isOutsideBuildHeight(currentPos))
+				return true;
 			if (!world.isBlockPresent(currentPos))
-				return false;
+				throw new AssemblyException("chunkNotLoaded");
 			BlockState state = world.getBlockState(currentPos);
 			if (!BlockMovementTraits.movementNecessary(state, world, currentPos))
 				return true;
@@ -165,7 +168,10 @@ public class PistonContraption extends TranslatingContraption {
 			if (isPistonHead(state) && state.get(FACING) == direction.getOpposite())
 				return true;
 			if (!BlockMovementTraits.movementAllowed(state, world, currentPos))
-				return retracting;
+				if (retracting)
+					return true;
+				else
+					throw AssemblyException.unmovableBlock(currentPos, state);
 			if (retracting && state.getPushReaction() == PushReaction.PUSH_ONLY)
 				return true;
 			frontier.add(currentPos);

src/main/java/com/simibubi/create/content/contraptions/components/structureMovement/pulley/PulleyContraption.java

@@ -1,6 +1,7 @@
 package com.simibubi.create.content.contraptions.components.structureMovement.pulley;
 
 import com.simibubi.create.content.contraptions.components.structureMovement.AllContraptionTypes;
+import com.simibubi.create.content.contraptions.components.structureMovement.AssemblyException;
 import com.simibubi.create.content.contraptions.components.structureMovement.TranslatingContraption;
 
 import net.minecraft.nbt.CompoundNBT;
@@ -23,7 +24,7 @@ public class PulleyContraption extends TranslatingContraption {
 	}
 
 	@Override
-	public boolean assemble(World world, BlockPos pos) {
+	public boolean assemble(World world, BlockPos pos) throws AssemblyException {
 		if (!searchMovedStructure(world, pos, null))
 			return false;
 		startMoving(world);

src/main/java/com/simibubi/create/content/contraptions/components/structureMovement/pulley/PulleyTileEntity.java

@@ -1,6 +1,7 @@
 package com.simibubi.create.content.contraptions.components.structureMovement.pulley;
 
 import com.simibubi.create.AllBlocks;
+import com.simibubi.create.content.contraptions.components.structureMovement.AssemblyException;
 import com.simibubi.create.content.contraptions.components.structureMovement.BlockMovementTraits;
 import com.simibubi.create.content.contraptions.components.structureMovement.ContraptionCollider;
 import com.simibubi.create.content.contraptions.components.structureMovement.ControlledContraptionEntity;
@@ -22,6 +23,7 @@ import net.minecraft.util.math.AxisAlignedBB;
 import net.minecraft.util.math.BlockPos;
 import net.minecraft.util.math.MathHelper;
 import net.minecraft.util.math.Vec3d;
+import net.minecraft.util.text.ITextComponent;
 
 public class PulleyTileEntity extends LinearActuatorTileEntity {
 
@@ -42,7 +44,7 @@ public class PulleyTileEntity extends LinearActuatorTileEntity {
 	}
 
 	@Override
-	protected void assemble() {
+	protected void assemble() throws AssemblyException {
 		if (!(world.getBlockState(pos)
 			.getBlock() instanceof PulleyBlock))
 			return;
@@ -189,12 +191,18 @@ public class PulleyTileEntity extends LinearActuatorTileEntity {
 	@Override
 	protected void read(CompoundNBT compound, boolean clientPacket) {
 		initialOffset = compound.getInt("InitialOffset");
+		if (compound.contains("LastException"))
+			lastException = ITextComponent.Serializer.fromJson(compound.getString("LastException"));
+		else
+			lastException = null;
 		super.read(compound, clientPacket);
 	}
 
 	@Override
 	public void write(CompoundNBT compound, boolean clientPacket) {
 		compound.putInt("InitialOffset", initialOffset);
+		if (lastException != null)
+			compound.putString("LastException", ITextComponent.Serializer.toJson(lastException));
 		super.write(compound, clientPacket);
 	}