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scalafix-maven-plugin

scalafix-maven-plugin enables automatic refactoring and linting of Maven projects written in Scala using Scalafix.

Installation

Add plugin into plugins node of pom.xml:

<plugins>
    <plugin>
        <groupId>io.github.evis</groupId>
        <artifactId>scalafix-maven-plugin_2.13</artifactId>
        <version>0.1.9_0.12.1</version>
    </plugin>
</plugins>

Where 0.1.9 is version of the plugin itself, and 0.12.1 is version of Scalafix invoked by the plugin.

Notes about Scala versions:

  1. It should be OK to use scalafix-maven-plugin_2.13 for Scala 3. Though, if you encounter any problems with such usage, create an issue.
  2. Use scalafix-maven-plugin_2.12 for Scala 2.12, if you need semantic rules.
  3. Scala 2.11 and older aren't supported.

Then, you need to setup a file .scalafix.conf in the root directory of your Maven project (note the dot at the start of filename). You can find .scalafix.conf guide here.

You don't need to care about passing Scala version and Scalac options to this plugin specifically. Plugin finds them automatically from your build info.

Semantic rules with SemanticDB

In order to execute semantic rules (e.g., RemoveUnused), you need to enable SemanticDB.

For Scala 2, you should add compiler plugin. 
<plugin>
    <groupId>net.alchim31.maven</groupId>
    <artifactId>scala-maven-plugin_${scala.binary.version}</artifactId>
    <version>${scala-maven-plugin.version}</version>
    <executions>
        <execution>
            <goals>
                <goal>compile</goal>
                <goal>testCompile</goal>
            </goals>
        </execution>
    </executions>
    <configuration>
        <args>
            <arg>-Ywarn-unused</arg> <!-- if you need exactly RemoveUnused -->
        </args>
        <compilerPlugins>
            <compilerPlugin>
                <groupId>org.scalameta</groupId>
                <artifactId>semanticdb-scalac_${scala.binary.version}</artifactId>
                <version>${semanticdb.version}</version>
            </compilerPlugin>
        </compilerPlugins>
    </configuration>
</plugin>
For Scala 3, you just need to enable it with compiler flag. 
<plugin>
    <groupId>net.alchim31.maven</groupId>
    <artifactId>scala-maven-plugin_${scala.binary.version}</artifactId>
    <version>${scala-maven-plugin.version}</version>
    <executions>
        <execution>
            <goals>
                <goal>compile</goal>
                <goal>testCompile</goal>
            </goals>
        </execution>
    </executions>
    <configuration>
        <args>
            <arg>-Ywarn-unused</arg> <!-- if you need exactly RemoveUnused -->
            <arg>-Ysemanticdb</arg>
        </args>
    </configuration>
</plugin>

Overriding sources location

By default, sources should be located inside src/main/scala directory. Though, you may change it using sourceDirectory build option, plugin respects this, e.g.:

<build>
    <sourceDirectory>src/main/my-sources-dir</sourceDirectory>
    <!-- another build settings... -->
</build>

Or using mainSourceDirectories configuration option of the plugin, e.g.:

<plugin>
    <groupId>io.github.evis</groupId>
    <artifactId>scalafix-maven-plugin_2.13</artifactId>
    <version>0.1.9_0.12.1</version>
    <configuration>
        <mainSourceDirectories>
            <directory>src/main/my-sources-dir</directory>
            <directory>src/main/my-another-dir</directory>
            <!-- and so on, you can list several directories here... -->
        </mainSourceDirectories>
    </configuration>
</plugin>

Usage

There is one Maven goal in this plugin called scalafix:scalafix. It executes Scalafix with given config on your sources.

First of all, you can invoke it via CLI:

mvn scalafix:scalafix

If there are some errors while running Scalafix, then the build will fail. Otherwise, it will succeed.

In order to execute semantic rules (e.g., RemoveUnused), you also need to compile sources beforehand, e.g.:

mvn compile test-compile scalafix:scalafix

You can tweak plugin execution using some parameters, e.g.:

mvn scalafix:scalafix -Dscalafix.mode=CHECK -Dscalafix.skipTest=true

Also, you can pass parameters via pom.xml:

<plugins>
    <plugin>
        <groupId>io.github.evis</groupId>
        <artifactId>scalafix-maven-plugin_2.13</artifactId>
        <version>0.1.9_0.12.1</version>
        <configuration>
            <mode>CHECK</mode>
            <skipTest>true</skipTest>
        </configuration>
    </plugin>
</plugins>

If you want to use external rules, add jars containing rules to dependencies of the plugin:

<plugin>
    <groupId>io.github.evis</groupId>
    <artifactId>scalafix-maven-plugin_2.13</artifactId>
    <version>0.1.9_0.12.1</version>
    <dependencies>
        <dependency>
            <groupId>com.nequissimus</groupId>
            <artifactId>sort-imports_2.13</artifactId>
            <version>0.6.1</version>
        </dependency>
    </dependencies>
</plugin>

Plugin parameters

CLI name Maven configuration name Maven type Description
scalafix.mode mode ScalafixMainMode: either IN_PLACE, CHECK, STDOUT or AUTO_SUPPRESS_LINTER_ERRORS (default: IN_PLACE) Describes mode in which Scalafix runs. Description of different parameter values can be found in Scalafix javadoc.
scalafix.command.line.args commandLineArgs List[String] (default: empty) Custom CLI arguments to pass into Scalafix. Description of available arguments can be found in Scalafix CLI documentation.
scalafix.skip skip Boolean (default: false) Whether we should skip all formatting.
scalafix.skip.main skipMain Boolean (default: false) Whether we should skip formatting of application/library sources (by default located in main/scala).
scalafix.skip.test skipTest Boolean (default: false) Whether we should skip formatting of test sources (by default located in /test/scala).
scalafix.config config File (default: .scalafix.conf) Configuration with rules to invoke for Scalafix.
scalafix.mainSourceDirectories mainSourceDirectories List[File] (default: see below) Which main source directories to format.
scalafix.testSourceDirectories testSourceDirectories List[File] (default: see below) Which test source directories to format.

The plugin determines code paths to process the same way the compiler would; by default, from build.sourceDirectory property, but could be added by another plugin (e.g., build-helper-maven-plugin and scala-maven-plugin have a way to define multiple paths).

If a plugin defines those paths, be sure to invoke mvn with the phase in which that happens; for instance: mvn initialize scalafix:scalafix.

Tips and tricks

  1. scalafix.mode=AUTO_SUPPRESS_LINTER_ERRORS is useful on the first execution of Scalafix: it allows to effectively ignore warnings in existing large codebase.
  2. scalafix.mode=CHECK is convenient to use in continuous integration builds: e.g., to disallow merging code with identified problems.
  3. scalafix.skip=true is especially useful for Maven modules which don't contain Scala sources at all.
  4. scalafix.command.line is great for applying those Scalafix parameters which aren't directly supported by plugin yet.
  5. SemanticDB compiler plugin may slow down compilation a little bit. If you want to use it only for Scalafix, you can make separate Maven profile, e.g.:
<profiles>
    <profile>
        <id>semanticdb</id>
        <build>
            <pluginManagement>
                <plugins>
                    <plugin>
                        <groupId>net.alchim31.maven</groupId>
                        <artifactId>scala-maven-plugin_${scala.binary.version}</artifactId>
                        <version>${scala-maven-plugin.version}</version>
                        <configuration>
                            <compilerPlugins>
                                <compilerPlugin>
                                    <groupId>org.scalameta</groupId>
                                    <artifactId>semanticdb-scalac_${scala.binary.version}</artifactId>
                                    <version>${semanticdb.version}</version>
                                </compilerPlugin>
                            </compilerPlugins>
                        </configuration>
                    </plugin>
                </plugins>
            </pluginManagement>
        </build>
    </profile>
</profiles>

Then, run Scalafix like this:

mvn clean compile test-compile scalafix:scalafix -Psemanticdb

So, when you run compilation with profile turned off, then SemanticDB compiler plugin doesn't affect compilation time at all.

  1. Sometimes it makes sense to make different requirements about main and test code quality. To achieve it you can make separate test config, and invoke plugin twice, e.g.:
mvn clean compile scalafix:scalafix # this invocation uses .scalafix.conf
mvn test-compile scalafix:scalafix -Dscalafix.config=.scalafix.test.conf # means that rules for test code are located in file .scalafix.test.conf
  1. If you need to run a rule from Github, add it to the list of rules inside .scalafix.conf:
rules = [
  "github:zio/zio/Zio2Upgrade?sha=series/2.x"
]

And then just run mvn scalafix:scalafix.

This is equivalent to sbt "scalafixEnable; scalafixAll github:zio/zio/Zio2Upgrade?sha=series/2.x".

  1. To use a third-party rule, you may need to add its dependencies if the compiler complains about missing classes or methods. For example, scala-rewrites requires scalafix-core and typelevel-scalafix:
<plugin>
    <groupId>io.github.evis</groupId>
    <artifactId>scalafix-maven-plugin_${scala.version.short}</artifactId>
    <version>0.1.9_${scalafix.version}</version>
    <dependencies>
        <dependency>
            <groupId>ch.epfl.scala</groupId>
            <artifactId>scalafix-core_${scala.version.short}</artifactId>
            <version>${scalafix.version}</version>
        </dependency>
        <dependency>
            <groupId>org.scala-lang</groupId>
            <artifactId>scala-rewrites_${scala.version.short}</artifactId>
            <version>0.1.3</version>
        </dependency>
        <dependency>
            <groupId>org.typelevel</groupId>
            <artifactId>typelevel-scalafix_${scala.version.short}</artifactId>
            <version>0.1.4</version>
        </dependency>
    </dependencies>
</plugin>

Contributing

Pull requests are welcome. For major changes, please open an issue first to discuss what you would like to change. If you need some help with your PR at any time, please feel free to mention @evis.

Support

The best way to get help is to open an issue. You can do it for things like asking questions about the project or requesting technical help.

License

BSD-3-Clause