zio-blocks-codegen: Generic Scala code generation IR and emitter

[987Nabil]

Summary

Add a code generation module (zio-blocks-codegen) providing a generic IR (intermediate representation) ADT for Scala data types and a code emitter that generates Scala source files from it.

Motivation

zio-http currently contains zio-http-gen, which generates Scala code from OpenAPI specifications. However, the core concept — an IR representing Scala types (case classes, sealed traits, objects, enums) and emitting formatted source code — is not HTTP-specific. Multiple generators (OpenAPI → Scala, Smithy → Scala, Protobuf → Scala, JSON Schema → Scala) share the same output concern.

By extracting this into zio-blocks, we enable:

• Reuse across generators (OpenAPI, Smithy, Protobuf, etc.)
• A single, well-tested code emitter
• Consistent code style across all generated code
• Other ZIO ecosystem libraries to leverage codegen without depending on zio-http

Scope

• IR ADT: Type-safe representation of Scala code structures:
  • File, Package, Import
  • CaseClass, SealedTrait, Object, Enum
  • Field, Method, TypeRef, Annotation
  • Newtype (zio-prelude wrapper types)
• Emitter: IR → formatted Scala source string
• Scalafmt integration (optional): Format emitted code
• No domain-specific logic: The IR is generic — OpenAPI-to-IR conversion stays in zio-http (or zio-blocks-openapi), Smithy-to-IR stays in zio-blocks-smithy, etc.

Related

• Add OpenAPI micro-library #918 — OpenAPI micro-library (consumer of codegen)
• zio-http zio-http-gen module — current implementation to extract from
• zio-http 4.0 migration: codegen moves from zio-http → zio-blocks