README.md

Compiler Plugin SPI

Thrifty exposes two post-processing interfaces: TypeProcessor, and KotlinTypeProcessor. Using the standard Java SPI, you can modify the classes generated from Thrift IDL by implementing one of these interfaces and making it available in the compiler's classpath. The interface you implement depends on the target language, Java or Kotlin, respectively.

Java Example

Thrifty generated classes are not Serializable by default. If you wanted to change that, you could modify the compiler - or, you could implement a TypeProcessor to do it for you, much more easily:

public class SerializableTypeProcessor implements TypeProcessor {
    @Override
    public TypeSpec process(TypeSpec type) {
        TypeSpec.Builder builder = type.toBuilder();

        builder.addSuperinterface(Serializable.class);
        builder.addField(FieldSpec.builder(long.class, "serialVersionUID")
                .addModifiers(Modifier.PRIVATE, Modifier.STATIC, Modifier.FINAL)
                .initializer("$L", -1)
                .build());

        return builder.build();
    }
}

Kotlin Example

Kotlin data classes (which Thrifty-generated structs are) are also not Serializable by default. As in the Java example above, you can change this by providing a KotlinTypeProcessor:

class SerializableKotlinProcessor : KotlinTypeProcessor {
  override fun process(spec: TypeSpec): TypeSpec? {
    return spec.toBuilder().run {
      addSuperinterface(Serializable::class)
      
      // Static fields in Kotlin go in a companion object;
      // we'll assume here that `spec` does not already
      // have one.
      val companionType = TypeSpec.companionObjectBuilder()
          .addProperty(PropertySpec.builder("serialVersionUID", Long::class)
              .addModifiers(KModifier.PRIVATE, KModifier.CONST) // const vals in companions are static
              .initializer("%L", -1L)
              .build())
          .build()
      
      addType(companionType)
      build()
    }
  }
}

Usage

The minimal project to implement this processor looks like the following:

src/

• main/
  • java/
    • com/
      • corp/
        • SerializableTypeProcessor.java
  • resources/
    • META-INF/
      • services/
        • com.microsoft.thrifty.compiler.spi.TypeProcessor // For a Java processor
        • com.microsoft.thrifty.compiler.spi.KotlinTypeProcessor // for a Kotlin processor

The file under META-INF is how Java services are identified. The file should contain the full name of your processor class:

For Java:

com.corp.SerializableTypeProcessor

For Kotlin:

com.corp.SerializableKotlinProcessor

Once this project is built into a JAR, you can include it in the classpath on the command line like so:

java -cp thrifty-compiler.jar:your-processor.jar com.microsoft.thrifty.compiler.ThriftyCompiler # compiler args as usual

This is a little wordy. An easier but less-flexible approach could be to build an uberjar including the compiler along with your processor. See thrifty-example-postprocessor/build.gradle for one way to do it.