Gradle Checkstyle plugin is incompatible with Google Checks by default

Question

Please note: I created this GitHub project to help you exactly produce the issue.

---

Java 8 and Gradle 4.6 here. If you create a new Java Gradle project via gradle init --type java-library and then the Gradle Checkstyle plugin to it, and configure that plugin to use Google's Checkstyle XML it will fail right out of the box:

plugins {
    id 'java-library'
}

apply plugin: 'checkstyle'

dependencies {
    testCompile(
        'junit:junit:4.12'
    )
}

repositories {
    jcenter()
    mavenCentral()
}

checkstyle {
    // Go to the Google Checks link above and paste its
    // contents into checkstyle.xml
    config = rootProject.resources.text.fromFile('buildConfig/checkstyle/checkstyle.xml')
}

With that config, running ./gradle clean build produces:

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':checkstyleMain'.
> Unable to create a Checker: configLocation {/Users/myuser/workspace/test-gradle-checkstyle/buildConfig/checkstyle/checkstyle.xml}, classpath {/Users/myuser/workspace/test-gradle-checkstyle/build/classes/java/main:/Users/myuser/workspace/test-gradle-checkstyle/build/resources/main}.

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

* Get more help at https://help.gradle.org

BUILD FAILED in 1s
4 actionable tasks: 4 executed
$ pwd
/Users/myuser/workspace/test-gradle-checkstyle
$ git init
Initialized empty Git repository in /Users/myuser/workspace/test-gradle-checkstyle/.git/

I'm wondering why?!

---

Edit (for future Googlers):

Using --stacktrace, the actual error is

cannot initialize module TreeWalker - Token "METHOD_REF" was not found in Acceptable tokens list in check com.puppycrawl.tools.checkstyle.checks.whitespace.SeparatorWrapCheck

Answer 1

Apparently Gradle uses an old version of CheckStyle - but there is a way to solve this!

First, I'd suggest that when you encounter issues in your build, use the --stacktrace or -S to see the actual failure, by using it you'll see exactly what is failing:

cannot initialize module TreeWalker - Token "METHOD_REF" was not found in Acceptable tokens list in check com.puppycrawl.tools.checkstyle.checks.whitespace.SeparatorWrapCheck

This is because Gradle 4.6 uses CheckStyle 6.19, which is quite old by now (latest is 8.11) Upgrading the configuration to use latest solves this issue:

checkstyle {
    config = rootProject.resources.text.fromFile('buildConfig/checkstyle/checkstyle.xml')
    toolVersion '8.11'
}

The result is:

> Task :checkstyleMain
[ant:checkstyle] [WARN] /.../test-gradle-checkstyle/src/main/java/Library.java:5: 'method def modifier' has incorrect indentation level 4, expected level should be 2. [Indentation]
[ant:checkstyle] [WARN] /.../test-gradle-checkstyle/src/main/java/Library.java:6: 'method def' child has incorrect indentation level 8, expected level should be 4. [Indentation]
[ant:checkstyle] [WARN] /.../test-gradle-checkstyle/src/main/java/Library.java:7: 'method def rcurly' has incorrect indentation level 4, expected level should be 2. [Indentation]

> Task :checkstyleTest
[ant:checkstyle] [WARN] /.../test-gradle-checkstyle/src/test/java/LibraryTest.java:5: 'import' should be separated from previous statement. [EmptyLineSeparator]
[ant:checkstyle] [WARN] /.../test-gradle-checkstyle/src/test/java/LibraryTest.java:5: Import statement for 'org.junit.Assert.*' is in the wrong order. Should be in the 'STATIC' group, expecting not assigned imports on this line. [CustomImportOrder]
[ant:checkstyle] [WARN] /.../test-gradle-checkstyle/src/test/java/LibraryTest.java:5: Using the '.*' form of import should be avoided - org.junit.Assert.*. [AvoidStarImport]
[ant:checkstyle] [WARN] /.../test-gradle-checkstyle/src/test/java/LibraryTest.java:8: 'method def modifier' has incorrect indentation level 4, expected level should be 2. [Indentation]
[ant:checkstyle] [WARN] /.../test-gradle-checkstyle/src/test/java/LibraryTest.java:9: 'method def' child has incorrect indentation level 8, expected level should be 4. [Indentation]
[ant:checkstyle] [WARN] /.../test-gradle-checkstyle/src/test/java/LibraryTest.java:10: 'method def' child has incorrect indentation level 8, expected level should be 4. [Indentation]
[ant:checkstyle] [WARN] /.../test-gradle-checkstyle/src/test/java/LibraryTest.java:11: 'method def rcurly' has incorrect indentation level 4, expected level should be 2. [Indentation]


BUILD SUCCESSFUL in 9s
7 actionable tasks: 7 executed

There are several bugs open on this issue both in the Gradle project and the CheckStyle project