ScalaFix SudokuFX

I released a new version of SudokuFX, this time a maintenance release. I some warnings I got from compiling.

To make this a little bit more interesting, I used scalafix and autofix. What are those things?

Scalafix is a compiler plugin on top of Scalameta which helps rewriting source code. It provides a framework which can be used for creating own code rewriting rules as well. Autofix is an example for that - it encodes migration rules specifically for ScalaTest.

After a little bit of maven pom fiddling, autofix is configured for my project. All I needed to do was to add a compiler plugin and an additional plugin in my pluginsection of my root pom.xml:

        <pluginManagement>
            <plugins>
                <plugin>
                    <groupId>net.alchim31.maven</groupId>
                    <artifactId>scala-maven-plugin</artifactId>
                    <version>4.3.1</version>
                    <executions>
                        <execution>
                            <goals>
                                <goal>compile</goal>
                                <goal>testCompile</goal>
                            </goals>
                        </execution>
                    </executions>
                    <configuration>
                        <scalaVersion>${scala.major.version}</scalaVersion>
                        <args>
                        ...
                        </args>
                        <compilerPlugins>
                            <compilerPlugin>
                                <groupId>org.scalameta</groupId>
                                <artifactId>semanticdb-scalac_${scala.full.version}</artifactId>
                                <version>4.3.9</version>
                            </compilerPlugin>
                        </compilerPlugins>
                    </configuration>
                </plugin>
                <plugin>
                    <groupId>io.github.evis</groupId>
                    <artifactId>scalafix-maven-plugin</artifactId>
                    <version>0.1.2_0.9.5</version>
                    <dependencies>
                        <dependency>
                            <groupId>org.scalatest</groupId>
                            <artifactId>autofix_2.12</artifactId>
                            <version>3.1.0.0</version>
                        </dependency>
                    </dependencies>
                </plugin>
            </plugins>
        </pluginManagement>

Thats it ... more or less.

What is still missing is a configuration for scalafix, which is placed in a file called .scalafix.conf. (Note the '.' at the beginning of the file name). This file should be placed next to the main pom file.

Here is the file how I configured it:

rules = [
  RemoveUnused,RewriteDeprecatedNames,ProcedureSyntax,NoValInForComprehension,LeakingImplicitClassVal,NoAutoTupling
]

The inverted rule name is an autofix rule, which comes with the additional dependency for scalafix-maven-plugin. 

After configuring this, you have to call maven like that:

mvn clean compile test-compile scalafix:scalafix

After that, have a look at your git status, you'll see that many files have changed, and the plugin did what was promised: it rewrote source code, applied trivial but useful transformations. For example, it can remove unused imports out of the box, or rewrite code written in procedural style and many other things.

Scalafix can be extended with own plugins, that means in theory you could implement your own rules, specific to your needs. This enables then automatic rewrites which are not only syntactic (which could also be achieved by clever scripting) but semantic: rewrite rules know about the structure of the code. This helps for automating tasks which otherwise would bind valuable developer time ...

I removed other warnings as well, albeit manually, from the source. By doing that, I got new 'unused imports', which swiftly went away by calling just beforementioned mvn command again while I gazed with amazement to my editor watching the computer doing the work for me.

Here is a list of available scalafix rules - or at least the closest to such a list I could find.


Hope I raised your interest in this amazing tooling, check out how to configure ScalaFix for maven (and try to solve some Sudokus and let me know if it worked ;-))