Scalafix - Detailed Review

Here are some frequently asked questions about Scalafix, along with detailed responses to each:

Q: What is Scalafix and what does it do?

Scalafix is a code refactoring and linting tool specifically designed for Scala code. It automatically spots and fixes code issues, updates old code patterns to modern syntax, enforces consistent code style, and helps with Scala version migrations.

Q: How do I install Scalafix in my Scala project?

To install Scalafix, you need to add the Scalafix plugin to your project/plugins.sbt file. Here is an example:

addSbtPlugin("ch.epfl.scala" % "sbt-scalafix" % "0.14.0")

You also need to enable the SemanticDB compiler plugin in your build.sbt file if you plan to use semantic rules:

inThisBuild(List(
  scalaVersion := "2.12.20",
  semanticdbEnabled := true,
  semanticdbVersion := scalafixSemanticdb.revision
))

For command-line installation, you can use Coursier to install the Scalafix CLI.

Q: What types of rules does Scalafix support?

Scalafix supports two main types of rules: syntactic and semantic rules. Syntactic rules check code structure and can run without compilation, while semantic rules analyze the code meaning and require compilation with the SemanticDB compiler plugin. Additionally, Scalafix includes built-in rules and allows you to create custom rules.

Q: How do I configure Scalafix rules?

You configure Scalafix rules using a .scalafix.conf file in the root of your project. This file uses the HOCON format and allows you to specify which rules to run and their options. For example:

rules = [
  DisableSyntax,
  ExplicitResultTypes
]

DisableSyntax.noFinalize = true
ExplicitResultTypes.skipSimpleDefinitions = false

You can also specify rules and options via command-line arguments.

Q: How do I run Scalafix on my project?

To run Scalafix, you can use sbt commands. For example, to run a specific rule on one project:

sbt "scalafix RemoveUnused"

To run Scalafix on all projects:

sbt scalafixAll

You can also use the --check option to ensure all files have been fixed without writing changes to the files.

Q: Can I integrate Scalafix with Continuous Integration (CI) pipelines?

Yes, you can integrate Scalafix with CI pipelines. You can use the --check option to fail the build if any files need fixing. This ensures that all code changes are compliant with your Scalafix rules before they are merged. You can also configure Scalafix to run automatically in your CI workflows.

Q: How do I create custom Scalafix rules?

To create custom rules, you need to write Scala code for your rules and place them in the rules/ directory of your project. You can then configure these rules in your .scalafix.conf file. Here is an example of setting up custom rules:

rules = [
  CustomLint
]

Ensure your custom rules are properly tested in the tests/ directory.

Q: Are there any specific requirements for using semantic rules in Scalafix?

Yes, semantic rules require that your code is compiled with the SemanticDB compiler plugin. This plugin generates additional metadata that semantic rules need to analyze the code meaning. You need to specify the correct Scala version and classpath when running semantic rules.

Q: How do I exclude certain files or directories from Scalafix?

You can exclude files or directories using the --exclude option. This option allows you to specify Unix-style glob patterns for files or directories that you want to exclude from the fixing process.

Q: Can Scalafix be used with other build tools besides sbt?

Yes, Scalafix supports integration with other build tools such as scala-cli, Mill, Gradle, and Maven through externally maintained plugins. This allows you to use Scalafix regardless of your build tool of choice.

Q: How do I get help or see the available options for the Scalafix command-line interface?

You can get help and see the available options by running the --help or -h command with the Scalafix CLI:

./scalafix --help

This will display all the available options and their usage.