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ZIO Clippy

A Scala compiler plugin for better ZIO type mismatch errors.

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IntelliJ IDEA VSCode / Metals

Zymposium video

Adam Fraser recently interviewed me, and we chatted about ZIO Clippy, how it came to be, and how it works internally. Watch the interview on YouTube!

Getting started

The recommended way to install this plugin is by installing it as a global sbt plugin:

  1. Clone this repository to your local computer
  2. Run sbt +install
  3. In your project, reload sbt/bsp

Running sbt +install builds the plugin jar for all compatible Scala versions and places the ZIOPlugin.scala file in the global ~/.sbt/1.0/plugins directory, allowing any sbt project to load the plugin automatically. To remove, delete the ZIOPlugin.scala file from ~/.sbt/1.0/plugins.

The plugin supports Scala 2.12, 2.13 with Scala 3 support coming soon! The plugin supports both ZIO 1 and ZIO 2.

Additional configuration

Note: The recommended way to specify additional configuration is via a global sbt configuration file, without directly modifying your project's build.sbt.

Create a file clippy.sbt in your global sbt directory, ~/.sbt/1.0. You can specify the options in this file, and they will be loaded automatically by your project.

Original type mismatch error

To render the original type mismatch error in addition to the plugin output, add the following flag to your scalacOptions:

scalacOptions += "-P:clippy:show-original-error"

Additional types for detection

ZIO Clippy support additional, ZIO-like types when parsing type mismatch errors. Any type that has 3 type parameters (e.g. org.company.Saga[R, E, A]) can be specified. To enable, provide a comma-separated fully-qualified list of names to the following option:

scalacOptions += "-P:clippy:additional-types:zio.flow.ZFlow,org.company.Saga"

Technical information

This plugin implements a custom Reporter class, intercepting any type mismatch errors that contain ZIO-specific information (it's all regex!) with all other errors passing through to the underlying reporter.

The plugin tries to extract the found and required dependencies from the error message and performs a set diff to remove the found types from the required ones. This leaves just the type(s) that are missing/were not provided to the effect.

Acknowledgments

The project borrows some ideas from Sam Halliday's excellent Ensime TNG, for both the local development setup and the hack to replace the reporter.

In addition, the ANSI rendering is heavily inspired by Kit Langton's excellent work on zio-magic, which is also part of ZIO 2's default error rendering.

Bugs? Suggestions?

Let us know! Report an issue or send a PR!