server/block: Don't allow liquid removable blocks to replace liquids

server/block/lava.go

@@ -12,7 +12,6 @@ import (
 // Lava is a light-emitting fluid block that causes fire damage.
 type Lava struct {
 	empty
-	replaceable
 
 	// Still makes the lava not spread whenever it is updated. Still lava cannot be acquired in the game
 	// without world editing.
@@ -35,6 +34,16 @@ func neighboursLavaFlammable(pos cube.Pos, tx *world.Tx) bool {
 	return false
 }
 
+// ReplaceableBy ...
+func (l Lava) ReplaceableBy(b world.Block) bool {
+	if _, ok := b.(LiquidRemovable); ok {
+		_, displacer := b.(world.LiquidDisplacer)
+		_, liquid := b.(world.Liquid)
+		return displacer || liquid
+	}
+	return true
+}
+
 // EntityInside ...
 func (l Lava) EntityInside(_ cube.Pos, _ *world.Tx, e world.Entity) {
 	if fallEntity, ok := e.(fallDistanceEntity); ok {

server/block/sea_pickle.go

@@ -29,6 +29,11 @@ func (SeaPickle) canSurvive(pos cube.Pos, tx *world.Tx) bool {
 	if !below.Model().FaceSolid(pos.Side(cube.FaceDown), cube.FaceUp, tx) {
 		return false
 	}
+	if liquid, ok := tx.Liquid(pos); ok {
+		if _, ok = liquid.(Water); !ok || liquid.LiquidDepth() != 8 {
+			return false
+		}
+	}
 	if emitter, ok := below.(LightDiffuser); ok && emitter.LightDiffusionLevel() != 15 {
 		return false
 	}

server/block/water.go

@@ -14,7 +14,6 @@ import (
 // Water is a natural fluid that generates abundantly in the world.
 type Water struct {
 	empty
-	replaceable
 
 	// Still makes the water appear as if it is not flowing.
 	Still bool
@@ -26,6 +25,16 @@ type Water struct {
 	Falling bool
 }
 
+// ReplaceableBy ...
+func (w Water) ReplaceableBy(b world.Block) bool {
+	if _, ok := b.(LiquidRemovable); ok {
+		_, displacer := b.(world.LiquidDisplacer)
+		_, liquid := b.(world.Liquid)
+		return displacer || liquid
+	}
+	return true
+}
+
 // EntityInside ...
 func (w Water) EntityInside(_ cube.Pos, _ *world.Tx, e world.Entity) {
 	if fallEntity, ok := e.(fallDistanceEntity); ok {