Add inline classes support for scalars

[BoD]

This adds 2 things:

1. Scalar mappings can indicate the target is an inline class, and the name of the wrapped property.
   When doing so, the generated adapter calls the primitive adapter on the wrapped property to avoid boxing/unboxing.
   To do this, new versions of mapScalarToKotlinXyz() are added that take the inline class target name and property name.

2. Ability to generate inline classes for scalars.
   Done by applying a new @inlineClass directive, e.g. extend scalar Length @inlineClass(coercion: Long)
   This will generate:

package com.example.xyz.type.scalar

@JvmInline
public value class Length(
  public val `value`: Long,
)

When doing so, the mapping is also added (no need to call mapScalarToXyz()).

Related to #6332.

[svc-apollo-docs]

✅ Docs preview has no changes

The preview was not built because there were no changes.

Build ID: d17423f264760e0c34caa9dd

[martinbonnin]

Looks cool! I'm curious at the generated bytecode. Can you dump the adapters bytecode for a simple scalar/list primitive case ? Make sure there's no boxing?

[martinbonnin]

FWIW, this is expected:

[martinbonnin]

Nice!

[martinbonnin]

Also reminder to add the matching definition on https://github.com/apollographql/specs if we agree on this

[martinbonnin]

Also reminder to add support in the IDE plugin

[BoD]

Generated Kotlin

public object InlineClassQuery_ResponseAdapter {
  public object Data : Adapter<InlineClassQuery.Data> {
    public val RESPONSE_NAMES: List<String> = listOf("nonNullableLength")

    override fun fromJson(reader: JsonReader, customScalarAdapters: CustomScalarAdapters): InlineClassQuery.Data {
      var _nonNullableLength: Length? = null

      while (true) {
        when (reader.selectName(RESPONSE_NAMES)) {
          0 -> _nonNullableLength = custom.scalars.type.scalar.Length(com.apollographql.apollo.api.LongAdapter.fromJson(reader, customScalarAdapters))
          else -> break
        }
      }

      return InlineClassQuery.Data(
        nonNullableLength = _nonNullableLength ?: missingField(reader, "nonNullableLength")
      )
    }

    override fun toJson(
      writer: JsonWriter,
      customScalarAdapters: CustomScalarAdapters,
      `value`: InlineClassQuery.Data,
    ) {
      writer.name("nonNullableLength")
      com.apollographql.apollo.api.LongAdapter.toJson(writer, customScalarAdapters, value.nonNullableLength.value)
    }
  }
}

Decompiled Java equivalent

  @NotNull
  public InlineClassQuery.Data fromJson(@NotNull JsonReader reader, @NotNull CustomScalarAdapters customScalarAdapters) {
     Intrinsics.checkNotNullParameter(reader, "reader");
     Intrinsics.checkNotNullParameter(customScalarAdapters, "customScalarAdapters");
     Length _nonNullableLength = null;

     while(true) {
        int var4 = reader.selectName(RESPONSE_NAMES);
        if (var4 != 0) {
           InlineClassQuery.Data var10000 = new InlineClassQuery.Data;
           if (_nonNullableLength != null) {
              var10000.<init>(_nonNullableLength.unbox-impl(), (DefaultConstructorMarker)null);
              return var10000;
           } else {
              Assertions.missingField(reader, "nonNullableLength");
              throw new KotlinNothingValueException();
           }
        }

        _nonNullableLength = Length.box-impl(Length.constructor-impl(((Number)Adapters.LongAdapter.fromJson(reader, customScalarAdapters)).longValue()));
     }
  }

  public void toJson(@NotNull JsonWriter writer, @NotNull CustomScalarAdapters customScalarAdapters, @NotNull InlineClassQuery.Data value) {
     Intrinsics.checkNotNullParameter(writer, "writer");
     Intrinsics.checkNotNullParameter(customScalarAdapters, "customScalarAdapters");
     Intrinsics.checkNotNullParameter(value, "value");
     writer.name("nonNullableLength");
     Adapters.LongAdapter.toJson(writer, customScalarAdapters, value.getNonNullableLength-7cMOgQw());
  }

• In fromJson, _nonNullableLength is a nullable Length and boxing/unboxing happens :( I wonder if we could avoid it, while keeping the missingField behavior...

• In toJson, value.getNonNullableLength-7cMOgQw() returns a long: no boxing 👍

[martinbonnin]

In fromJson, _nonNullableLength is a nullable Length and boxing/unboxing happens :( I wonder if we could avoid it, while keeping the missingField behavior...

I guess we could do it by using a separate boolean. No idea if it's worth the added complexity without additional benchmarks though.

[BoD]

I guess we could do it by using a separate boolean.

Yeah thought of using booleans... honestly I'm not convinced it's worth it.

I think this is still useful even with this un/boxing?

[martinbonnin]

Superseded by #6404