Fix EitherCodec dropping partial results

gradle.properties

@@ -1 +1 @@
-majorMinor: 7.0
+majorMinor: 7.1

src/main/java/com/mojang/serialization/DataResult.java

@@ -67,6 +67,8 @@ static String appendMessages(final String first, final String second) {
 
     Lifecycle lifecycle();
 
+    boolean hasResultOrPartial();
+
     Optional<R> resultOrPartial(Consumer<String> onError);
 
     Optional<R> resultOrPartial();
@@ -143,6 +145,11 @@ public Optional<Error<R>> error() {
             return Optional.empty();
         }
 
+        @Override
+        public boolean hasResultOrPartial() {
+            return true;
+        }
+
         @Override
         public Optional<R> resultOrPartial(final Consumer<String> onError) {
             return Optional.of(value);
@@ -259,6 +266,11 @@ public Optional<Error<R>> error() {
             return Optional.of(this);
         }
 
+        @Override
+        public boolean hasResultOrPartial() {
+            return partialValue.isPresent();
+        }
+
         @Override
         public Optional<R> resultOrPartial(final Consumer<String> onError) {
             onError.accept(messageSupplier.get());

src/main/java/com/mojang/serialization/KeyCompressor.java

@@ -46,7 +46,7 @@ public int compress(final String key) {
     }
 
     public int compress(final T key) {
-        return compress.get(key);
+        return compress.getInt(key);
     }
 
     public int size() {

src/main/java/com/mojang/serialization/codecs/EitherCodec.java

@@ -19,7 +19,13 @@ public <T> DataResult<Pair<Either<F, S>, T>> decode(final DynamicOps<T> ops, fin
         if (secondRead.isSuccess()) {
             return secondRead;
         }
-        return firstRead.apply2((f, s) -> s, secondRead);
+        if (firstRead.hasResultOrPartial()) {
+            return firstRead;
+        }
+        if (secondRead.hasResultOrPartial()) {
+            return secondRead;
+        }
+        return DataResult.error(() -> "Failed to parse either. First: " + firstRead.error().orElseThrow().message() + "; Second: " + secondRead.error().orElseThrow().message());
     }
 
     @Override

src/test/java/com/mojang/serialization/CodecTests.java

@@ -32,6 +32,10 @@ private static <T> T fromJavaOrPartial(final Codec<T> codec, final Object value)
         return codec.parse(JavaOps.INSTANCE, value).getPartialOrThrow(AssertionError::new);
     }
 
+    private static String fromJavaErrorMessage(final Codec<String> codec, final Object value) {
+        return codec.parse(JavaOps.INSTANCE, value).error().orElseThrow(AssertionError::new).message();
+    }
+
     private static void assertFromJavaFails(final Codec<?> codec, final Object value) {
         final DataResult<?> result = codec.parse(JavaOps.INSTANCE, value);
         assertTrue("Expected data result error, but got: " + result.result(), result.isError());
@@ -249,6 +253,69 @@ public void withAlternative_simple() {
         assertFromJavaFails(codec, false);
     }
 
+    public static final Codec<String> NEVER_PRIMARY = Codec.STRING.validate(s -> DataResult.error(() -> "Failed Primary"));
+    public static final Codec<String> NEVER_ALTERNATIVE = Codec.STRING.validate(s -> DataResult.error(() -> "Failed Alternative"));
+    public static final Codec<String> NEVER_WITH_PARTIAL_PRIMARY = Codec.STRING.validate(s -> DataResult.error(() -> "Failed Primary with partial", "Partial Primary: " + s));
+    public static final Codec<String> NEVER_WITH_PARTIAL_ALTERNATIVE = Codec.STRING.validate(s -> DataResult.error(() -> "Failed Alternative with partial", "Partial Alternative: " + s));
+
+    @Test
+    public void withAlternative_primaryPartialAlternativeFails() {
+        final Codec<String> codec = Codec.withAlternative(
+            NEVER_WITH_PARTIAL_PRIMARY,
+            NEVER_ALTERNATIVE
+        );
+        assertEquals(
+            "Partial Primary: value",
+            fromJavaOrPartial(codec, "value")
+        );
+
+        assertEquals(
+            "Failed Primary with partial",
+            fromJavaErrorMessage(codec, "value")
+        );
+    }
+
+    @Test
+    public void withAlternative_primaryFailsAlternativePartial() {
+        final Codec<String> codec = Codec.withAlternative(
+            NEVER_PRIMARY,
+            NEVER_WITH_PARTIAL_ALTERNATIVE
+        );
+        assertEquals(
+            "Partial Alternative: value",
+            fromJavaOrPartial(codec, "value")
+        );
+
+        assertEquals(
+            "Failed Alternative with partial",
+            fromJavaErrorMessage(codec, "value")
+        );
+    }
+
+    @Test
+    public void withAlternative_bothPartialPrefersPrimary() {
+        final Codec<String> codec = Codec.withAlternative(
+            NEVER_WITH_PARTIAL_PRIMARY,
+            NEVER_WITH_PARTIAL_ALTERNATIVE
+        );
+        assertEquals(
+            "Partial Primary: value",
+            fromJavaOrPartial(codec, "value")
+        );
+    }
+
+    @Test
+    public void withAlternative_bothFail() {
+        final Codec<String> codec = Codec.withAlternative(
+            NEVER_PRIMARY,
+            NEVER_ALTERNATIVE
+        );
+        assertEquals(
+            "Failed to parse either. First: Failed Primary; Second: Failed Alternative",
+            fromJavaErrorMessage(codec, "value")
+        );
+    }
+
     @Test
     public void withAlternative_bothSuccessful() {
         final Codec<String> codec = Codec.withAlternative(Codec.STRING, TO_LOWER_CASE);