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Git Code Format Maven Plugin

A maven plugin that automatically deploys code formatters as pre-commit git hook. On commit, the hook will automatically format staged files.

Breaking changes between 4.x and 5.x

If the plugin runs without any formatter dependency, it will fail. This is done to prevent silent misconfiguration from happening.

Breaking changes between 3.x and 4.x

Google Java Format is not enabled by default anymore. com.cosium.code:google-java-format must be added as a dependency to the plugin to keep using it.
Google Java Format options declaration structure has changed. You will need to migrate any eventual existing declaration to the new structure described by the google-java-format-options chapter .

Breaking changes between 2.x and 3.x

#64 google-java-format 1.8 dropped support for java 8. The minimum supported runtime version for the plugin is JDK 11. i.e. Maven must run on JDK 11+ while the target project can still be built and run using JDK 8.

Breaking changes between 1.x and 2.x

#37 To prevent conflicts with other plugins all keys are now prefixed with gcf. e.g. -DglobPattern=**/* becomes -Dgcf.globPattern=**/*
#38 To avoid infringement to Apache Maven Trademark, the plugin was renamed to git-code-format-maven-plugin. Its new coordinates are com.cosium.code:git-code-format-maven-plugin.

1.x documentation can be found here

Automatic code format and validation activation

Add this to your maven project root pom.xml :

<build>
  <plugins>
    <plugin>
      <groupId>com.cosium.code</groupId>
      <artifactId>git-code-format-maven-plugin</artifactId>
      <version>${git-code-format-maven-plugin.version}</version>
      <executions>
        <!-- On commit, format the modified files -->
        <execution>
          <id>install-formatter-hook</id>
          <goals>
            <goal>install-hooks</goal>
          </goals>
        </execution>
        <!-- On Maven verify phase, fail if any file
        (including unmodified) is badly formatted -->
        <execution>
          <id>validate-code-format</id>
          <goals>
            <goal>validate-code-format</goal>
          </goals>
        </execution>
      </executions>
      <dependencies>
        <!-- Enable https://github.com/google/google-java-format -->
        <dependency>
          <groupId>com.cosium.code</groupId>
          <artifactId>google-java-format</artifactId>
          <version>${git-code-format-maven-plugin.version}</version>
        </dependency>
      </dependencies>
    </plugin>
  </plugins>
</build>

Manual code formatting

mvn git-code-format:format-code -Dgcf.globPattern=**/*

Manual code format validation

mvn git-code-format:validate-code-format -Dgcf.globPattern=**/*

Google Java Format

Google Java Format options

The plugin allows you to tweak Google Java Format options :

<build>
  <plugins>
    <plugin>
      <groupId>com.cosium.code</groupId>
      <artifactId>git-code-format-maven-plugin</artifactId>
      <version>${git-code-format-maven-plugin.version}</version>
      <executions>
        <!-- ... -->
      </executions>
      <dependencies>
        <!-- ... -->
      </dependencies>        
      <configuration>
        <formatterOptions>
          <!-- Use AOSP style instead of Google Style (4-space indentation). -->
          <googleJavaFormat.aosp>false</googleJavaFormat.aosp>
          <!-- Format the javadoc -->
          <googleJavaFormat.formatJavadoc>true</googleJavaFormat.formatJavadoc>
          <!-- Fix import order and remove any unused imports, but do no other formatting. -->
          <googleJavaFormat.fixImportsOnly>false</googleJavaFormat.fixImportsOnly>
          <!-- Do not fix the import order. Unused imports will still be removed. -->
          <googleJavaFormat.skipSortingImports>false</googleJavaFormat.skipSortingImports>
          <!-- Do not remove unused imports. Imports will still be sorted. -->
          <googleJavaFormat.skipRemovingUnusedImports>false</googleJavaFormat.skipRemovingUnusedImports>
        </formatterOptions>
      </configuration>
    </plugin>
  </plugins>
</build>

JDK 16+ peculiarities

Since google-java-format uses JDK internal apis, if you need to run the plugin with JDK 16+, you must pass some additional arguments to the JVM. Those are described at https://github.com/google/google-java-format/releases/tag/v1.10.0.

Thanks to https://maven.apache.org/configure.html#mvn-jvm-config-file, you should be able to pass them to .mvn/jvm.config as follow:

--add-exports jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED --add-exports jdk.compiler/com.sun.tools.javac.file=ALL-UNNAMED --add-exports jdk.compiler/com.sun.tools.javac.parser=ALL-UNNAMED --add-exports jdk.compiler/com.sun.tools.javac.tree=ALL-UNNAMED --add-exports jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED

Custom code formatter

Thanks to its code formatter SPI, this plugin can execute any code formatter.

How to

Note that you can take inspiration from the google-java-format module of this project.

Implement com.cosium.code.format_spi.CodeFormatterFactory. This interface is provided by com.cosium.code:git-code-format-maven-plugin-spi.
Add your com.cosium.code.format_spi.CodeFormatterFactory implementation canonical name in META-INF/services/com.cosium.code.format_spi.CodeFormatterFactory.
Pack this in a jar that you declare as a dependency in this plugin declaration.

Example of usage

Suppose:

the chosen configurationId (declared by com.cosium.code.format_spi.CodeFormatterFactory#configurationId()) is aqme
the formatter dependency is com.aqme.formatter:formatter:1.0

A plugin declaration making use of this custom code formatter would look like this:

<build>
  <plugins>
    <plugin>
      <groupId>com.cosium.code</groupId>
      <artifactId>git-code-format-maven-plugin</artifactId>
      <version>${git-code-format-maven-plugin.version}</version>
      <executions>
        <!-- ... -->
      </executions>
      <dependencies>
        <dependency>
          <groupId>com.aqme.formatter</groupId>
          <artifactId>formatter</artifactId>
          <version>1.0</version>
        </dependency>
      </dependencies>
      <configuration>
        <formatterOptions>
          <aqme.option1>false</aqme.option1>
          <aqme.option2>foo</aqme.option2>
        </formatterOptions>
      </configuration>
    </plugin>
  </plugins>
</build>

Frequently asked questions

If I have a multi-module project, do I need to install anything in the sub-projects?

You only need to put the plugin in your root project pom.xml. By default all submodules will be handled.

Do I need to run mvn initialize or is that a stage that happens automatically when I run mvn compile or mvn test?

initialize is the first phase of the Maven lifecycle. Any goal that you perform (e.g. compile or test) will automatically trigger initialize and thus trigger the git pre-commit hook installation.

I'm not noticing anything happening.

If after setting up the plugin in your pom, you just executed a maven goal, the only expected output is a pre-commit hook installed in your .git/hooks directory. To trigger the automatic formatting, you have to perform a commit of a modified file. You can also manually format or validate any file.

I'd like to skip code formatting in a child project

I inherit an enterprise parent pom, which I cannot modify, with formatting plugin specified, and I need to turn off formatting for my group's project. Either use add a <skip>true</skip> configuration in the inheriting project or set the gcf.skip property to true.

How the hook works

On the initialize maven phase, git-code-format:install-hooks installs a git pre-commit hook that looks like this :

#!/bin/bash
"./.git/hooks/${project.artifactId}.git-code-format.pre-commit.sh"

and .git/hooks/${project.artifactId}.git-code-format.pre-commit.sh has the following content:

#!/bin/bash
set -e
"${env.M2_HOME}/bin/mvn" -f "${project.basedir}/pom.xml" git-code-format:on-pre-commit

On pre-commit git phase, the hook triggers the git-code-format:on-pre-commit which formats the code of the modified files.

Advanced pre-commit pipeline hook

If you wish to modify the output of the pre-commit hook, you can set the preCommitHookPipeline configuration.

To completely ignore the hook output, you could use the following configuration:

      <configuration>
        <preCommitHookPipeline>&gt;/dev/null</preCommitHookPipeline>
      </configuration>

To display error lines from the maven output and fail build with any errors, you could use the following configuration:

      <configuration>
        <preCommitHookPipeline>| grep -F '[ERROR]' || exit 0 &amp;&amp; exit 1</preCommitHookPipeline>
      </configuration>