Fix signs being empty when placed

As of 1.20, sign messages are immutable - we need to do
text = text.setMesssage(...) instead. Also do a tiny bit of cleanup to
this function while we're here.

Probably not the best use of my lunch break :D:.

Fixes #1611.

projects/common/src/main/java/dan200/computercraft/shared/turtle/core/TurtlePlaceCommand.java

@@ -27,7 +27,6 @@
 import net.minecraft.world.item.context.UseOnContext;
 import net.minecraft.world.level.Level;
 import net.minecraft.world.level.block.Block;
-import net.minecraft.world.level.block.entity.BlockEntity;
 import net.minecraft.world.level.block.entity.SignBlockEntity;
 import net.minecraft.world.level.block.entity.SignText;
 import net.minecraft.world.level.block.state.BlockState;
@@ -186,7 +185,7 @@ private static boolean deployOnBlock(
                 tile = world.getBlockEntity(position.relative(side));
             }
 
-            if (tile instanceof SignBlockEntity) setSignText(world, tile, message);
+            if (tile instanceof SignBlockEntity sign) setSignText(world, sign, message);
         }
 
         return placed;
@@ -220,23 +219,20 @@ private static InteractionResult doDeployOnBlock(ItemStack stack, TurtlePlayer t
         return InteractionResult.PASS;
     }
 
-    private static void setSignText(Level world, BlockEntity tile, String message) {
-        var signTile = (SignBlockEntity) tile;
-        var split = Splitter.on('\n').splitToList(message);
-        var firstLine = split.size() <= 2 ? 1 : 0;
+    private static void setSignText(Level world, SignBlockEntity sign, String message) {
+        var lines = Splitter.on('\n').splitToList(message);
+        var firstLine = lines.size() <= 2 ? 1 : 0;
 
         var signText = new SignText();
-        for (var i = 0; i < 4; i++) {
-            if (i >= firstLine && i < firstLine + split.size()) {
-                var line = split.get(i - firstLine);
-                signText.setMessage(i, line.length() > 15
-                    ? Component.literal(line.substring(0, 15))
-                    : Component.literal(line)
-                );
-            }
+        for (int i = 0, len = Math.min(lines.size(), 4); i < len; i++) {
+            var line = lines.get(i);
+            signText = signText.setMessage(i + firstLine, line.length() > 15
+                ? Component.literal(line.substring(0, 15))
+                : Component.literal(line)
+            );
         }
-        signTile.setText(signText, true);
-        world.sendBlockUpdated(tile.getBlockPos(), tile.getBlockState(), tile.getBlockState(), Block.UPDATE_ALL);
+        sign.setText(signText, true);
+        world.sendBlockUpdated(sign.getBlockPos(), sign.getBlockState(), sign.getBlockState(), Block.UPDATE_ALL);
     }
 
     private static final class ErrorMessage {

projects/common/src/testMod/kotlin/dan200/computercraft/gametest/Turtle_Test.kt

@@ -37,6 +37,7 @@ import net.minecraft.world.item.Items
 import net.minecraft.world.item.enchantment.Enchantments
 import net.minecraft.world.level.block.Blocks
 import net.minecraft.world.level.block.FenceBlock
+import net.minecraft.world.level.block.entity.BlockEntityType
 import net.minecraft.world.level.block.state.properties.BlockStateProperties
 import org.hamcrest.MatcherAssert.assertThat
 import org.hamcrest.Matchers.array
@@ -86,6 +87,26 @@ class Turtle_Test {
         thenExecute { helper.assertBlockPresent(Blocks.LAVA, BlockPos(2, 2, 2)) }
     }
 
+    /**
+     * Checks turtles can write to signs.
+     *
+     * @see [#1611](https://github.com/cc-tweaked/CC-Tweaked/issues/1611)
+     */
+    @GameTest
+    fun Place_sign(helper: GameTestHelper) = helper.sequence {
+        thenOnComputer {
+            turtle.place(ObjectArguments("Test\nmessage")).await()
+                .assertArrayEquals(true, message = "Placed sign")
+        }
+        thenExecute {
+            val sign = helper.getBlockEntity(BlockPos(2, 2, 1), BlockEntityType.SIGN)
+            val lines = listOf("", "Test", "message", "")
+            for ((i, line) in lines.withIndex()) {
+                assertEquals(line, sign.frontText.getMessage(i, false).string, "Line $i")
+            }
+        }
+    }
+
     /**
      * Checks that calling [net.minecraft.world.item.Item.use] will not place blocks too far away.
      *