Improve the dispatched map codec error messages

Author: ErrorCraft

src/main/java/net/errorcraft/codecium/mixin/mojang/serialization/codecs/DispatchedMapCodecExtender.java

@@ -0,0 +1,58 @@
+package net.errorcraft.codecium.mixin.mojang.serialization.codecs;
+
+import com.llamalad7.mixinextras.injector.ModifyReturnValue;
+import com.llamalad7.mixinextras.sugar.Local;
+import com.mojang.datafixers.util.Pair;
+import com.mojang.datafixers.util.Unit;
+import com.mojang.serialization.Codec;
+import com.mojang.serialization.DataResult;
+import com.mojang.serialization.DynamicOps;
+import com.mojang.serialization.codecs.DispatchedMapCodec;
+import net.errorcraft.codecium.util.StringUtil;
+import org.spongepowered.asm.mixin.Final;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Shadow;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.ModifyArg;
+
+import java.util.Optional;
+import java.util.function.Supplier;
+import java.util.function.UnaryOperator;
+
+@Mixin(value = DispatchedMapCodec.class, remap = false)
+public class DispatchedMapCodecExtender<K, V> {
+    @Shadow
+    @Final
+    private Codec<K> keyCodec;
+
+    @ModifyArg(
+        method = "parseEntry",
+        at = @At(
+            value = "INVOKE",
+            target = "Lcom/mojang/serialization/DataResult;error(Ljava/util/function/Supplier;)Lcom/mojang/serialization/DataResult;"
+        )
+    )
+    @SuppressWarnings({ "OptionalUsedAsFieldOrParameterType", "OptionalGetWithoutIsPresent" })
+    private <T> Supplier<String> duplicateFieldUseBetterErrorMessage(Supplier<String> message, @Local(argsOnly = true) final DynamicOps<T> ops, @Local(argsOnly = true) final Pair<T, T> pair, @Local final Optional<Pair<K, V>> entry) {
+        return () -> "Duplicate field " + this.keyCodec.encodeStart(ops, entry.get().getFirst()).getOrThrow() + ": " + pair.getFirst();
+    }
+
+    @ModifyReturnValue(
+        method = "parseEntry",
+        at = @At("TAIL")
+    )
+    private <T> DataResult<Unit> duplicateFieldUseBetterErrorMessage(DataResult<Unit> original, @Local(argsOnly = true) final Pair<T, T> input) {
+        return original.mapError(message -> "For field " + input.getFirst() + ": " + message);
+    }
+
+    @ModifyArg(
+        method = "lambda$decode$5",
+        at = @At(
+            value = "INVOKE",
+            target = "Lcom/mojang/serialization/DataResult;mapError(Ljava/util/function/UnaryOperator;)Lcom/mojang/serialization/DataResult;"
+        )
+    )
+    private UnaryOperator<String> mapErrorsUseBetterErrorMessage(UnaryOperator<String> function) {
+        return message -> "Map has errors:\n" + StringUtil.indent(message);
+    }
+}

src/main/resources/codecium.mixins.json

@@ -14,6 +14,7 @@
     "mojang.serialization.JsonOpsExtender$MapLikeExtender",
     "mojang.serialization.MapLikeExtender$ForMapExtender",
     "mojang.serialization.codecs.BaseMapCodecExtender",
+    "mojang.serialization.codecs.DispatchedMapCodecExtender",
     "mojang.serialization.codecs.EitherCodecExtender",
     "mojang.serialization.codecs.FieldDecoderExtender",
     "mojang.serialization.codecs.KeyDispatchCodecExtender",