Extension APIs

[jbgi]

Derive4J should allow two types for extension mechanisms:

1. for type class derivations.
2. for modification / enhancement of generated code before writing the main class file.

Eg. demonstration of an extension that remove the private modifier of implementation classes:

import com.google.auto.service.AutoService;
import com.squareup.javapoet.TypeSpec;
import java.util.List;
import java.util.Set;
import javax.lang.model.element.Modifier;
import org.derive4j.processor.api.DeriveResult;
import org.derive4j.processor.api.DeriveUtils;
import org.derive4j.processor.api.Extension;
import org.derive4j.processor.api.ExtensionFactory;
import org.derive4j.processor.api.TypeSpecModifier;
import org.derive4j.processor.api.model.DataConstructor;

import static java.util.Collections.singletonList;
import static java.util.stream.Collectors.toList;
import static java.util.stream.Collectors.toSet;

@AutoService(ExtensionFactory.class)
public final class ExtensionFactoryImpl implements ExtensionFactory {
  @Override
  public List<Extension> extensions(DeriveUtils deriveUtils) {
    return singletonList((adtModel, codeGenSpec) -> {

      Set<String> strictConstructors = adtModel.dataConstruction()
          .constructors()
          .stream()
          .map(DataConstructor::name)
          .map(String::toLowerCase)
          .collect(toSet());

      return DeriveResult.result(new TypeSpecModifier(codeGenSpec).modTypes(typeSpecs ->
          typeSpecs.stream().map(ts ->
              strictConstructors.contains(ts.name.toLowerCase())
                ? removePrivateModifier(ts)
                : ts)
          .collect(toList())).build());

    });
  }

  private static TypeSpec removePrivateModifier(TypeSpec ts) {
    return new TypeSpecModifier(ts).modModifiers(
        modifiers -> modifiers.stream().filter(m -> m != Modifier.PRIVATE).collect(toSet())
    ).build();
  }
}

[jbgi]

implemented by 7795795