Fix conflicts with other mods replacing reach distance

projects/fabric/src/main/java/dan200/computercraft/mixin/ItemMixin.java

@@ -9,24 +9,38 @@
 import net.minecraft.world.item.Item;
 import net.minecraft.world.level.ClipContext;
 import net.minecraft.world.level.Level;
+import net.minecraft.world.phys.BlockHitResult;
 import org.spongepowered.asm.mixin.Mixin;
-import org.spongepowered.asm.mixin.injection.Constant;
-import org.spongepowered.asm.mixin.injection.ModifyConstant;
+import org.spongepowered.asm.mixin.Unique;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfoReturnable;
 
 @Mixin(Item.class)
 class ItemMixin {
     /**
      * Replace the reach distance in {@link Item#getPlayerPOVHitResult(Level, Player, ClipContext.Fluid)}.
      *
-     * @param reach  The original reach distance.
-     * @param level  The current level.
-     * @param player The current player.
-     * @return The new reach distance.
+     * @param level     The current level.
+     * @param player    The current player.
+     * @param fluidMode The current clip-context fluid mode.
+     * @param cir       Callback info to store the new reach distance.
      * @see FakePlayer#getBlockReach()
      */
-    @ModifyConstant(method = "getPlayerPOVHitResult", constant = @Constant(doubleValue = 5))
+    @Inject(method = "getPlayerPOVHitResult", at = @At("HEAD"), cancellable = true)
     @SuppressWarnings("UnusedMethod")
-    private static double getReachDistance(double reach, Level level, Player player) {
-        return player instanceof FakePlayer fp ? fp.getBlockReach() : reach;
+    private static void getReachDistance(Level level, Player player, ClipContext.Fluid fluidMode, CallbackInfoReturnable<BlockHitResult> cir) {
+        // It would theoretically be cleaner to use @ModifyConstant here, but as it's treated as a @Redirect, it doesn't
+        // compose with other mods. Instead, we replace the method when working with our fake player.
+        if (player instanceof FakePlayer fp) cir.setReturnValue(getHitResult(level, fp, fluidMode));
+    }
+
+    @Unique
+    private static BlockHitResult getHitResult(Level level, FakePlayer player, ClipContext.Fluid fluidMode) {
+        var start = player.getEyePosition();
+        var reach = player.getBlockReach();
+        var direction = player.getViewVector(1.0f);
+        var end = start.add(direction.x() * reach, direction.y() * reach, direction.z() * reach);
+        return level.clip(new ClipContext(start, end, ClipContext.Block.OUTLINE, fluidMode, player));
     }
 }