The document discusses code conventions and tooling for code quality. It introduces the Gandalf Gradle plugin, which provides a standardized way to integrate linting tools like Ktlint and Detekt into Gradle builds. The plugin applies the tools incrementally, supports custom rules, and caches results for faster builds. Tests validate the plugin works as expected on sample projects. The plugin reduces duplication and maintenance overhead compared to integrating tools directly in build scripts.

1. Gandalf: Bad code shall not
pass
Ilya Ghirici

2. Agenda
● Code formatting
● Coding Conventions
● Writing Gradle build scripts
● Gandalf Gradle Plugin

3. Who deals with your code?
● Computer
● Your colleagues

4. What is “bad” code?
fun Fibonacci( n:Int){
var a=0; var b = 1;
(1.. n ) .forEach { val temp =b
b += a; a= temp; }
}

5. Code Conventions
Do.
val v = ""
println(v)
Don't.
val v="";
println(v);

6. Tools
● Java:
○ Checkstyle
● Kotlin:
○ Ktlint
○ Detekt

7. Tools integration
● Java:
○ Checkstyle - Gradle Plugin
● Kotlin:
○ Ktlint - Java application
○ Detekt - Java application

8. Ktlint integration
configurations {
ktlint
}
dependencies {
ktlint "com.github.shyiko:ktlint:0.31.0"
}
task ktlint(type: JavaExec, group: "verification") {
description = "Check Kotlin code style."
main = "com.github.shyiko.ktlint.Main"
classpath = configurations.ktlint
args "src/**/*.kt"
}
check.dependsOn ktlint

9. Ktlint task
task ktlint(type: JavaExec, group: "verification") {
description = "Check Kotlin code style."
main = "com.github.shyiko.ktlint.Main"
classpath = configurations.ktlint
args = "src/**/*.kt"
}
check.dependsOn ktlint

10. Evolution of code verification tools at Ellation
● Our team joining Ellation - no style on projects
● Defining code convention
● Project Clean up
● Checkstyle integration
● Kotlin integration
● Ktlint & Detekt integration

11. Cons of using build script integration
● Code duplication
● Not scalable
● Hard to maintain

12. Arrival of Gandalf Plugin
● Code style tools integration
● Single source of configs and custom rules
● Report generation

13. Gandalf’s heart
class GandalfPlugin implements Plugin<Project> {
@Override
void apply(Project project) {
...
def configuration = project.configurations.create("ktlint")
project.dependencies.add(configuration, com.github.shyiko:ktlint:0.30.0")
project.tasks.create(name, JavaExec) {
main "com.github.shyiko.ktlint.Main"
group "verification"
description "Runs Ktlint"
classpath configuration
args "src/**/*.kt"
}
}
}

14. Incremental tasks
./gradlew ktlint
BUILD SUCCESSFUL in 36s
1 actionable task: 1 executed
./gradlew ktlint
BUILD SUCCESSFUL in 1s
1 actionable task: 1 up-to-date

15. Incremental tasks
class KtlintPlugin implements Plugin<Project> {
@Override
void apply(Project project) {
def configuration = project.configurations.create("ktlint")
project.dependencies.add(configuration, "com.github.shyiko:ktlint:0.30.0")
project.tasks.create(name, JavaExec) {
main "com.github.shyiko.ktlint.Main"
group "verification"
description "Runs Ktlint"
classpath configuration
args "src/**/*.kt"
outputs.file reportPath
inputs.files files
}
}
}

16. Gradle remote build cache
class KtlintPlugin implements Plugin<Project> {
@Override
void apply(Project project) {
def configuration = project.configurations.create("ktlint")
project.dependencies.add(configuration,
"com.github.shyiko:ktlint:0.30.0")
project.tasks.create(name, JavaExec) {
main "com.github.shyiko.ktlint.Main"
group "verification"
description "Runs Ktlint"
classpath configuration
args "src/**/*.kt"
outputs.file reportPath
inputs.files files
outputs.cacheIf { true }
}
}
}

17. Gradle plugin = Java application
def copyConfigFileToProject(Project project) {
def inputStream = getClass()
.getClassLoader()
.getResourceAsStream("detekt-config.yml")
FileUtil.copyFileToRootProject(project, inputStream, "detekt-config.yml")
}

18. Custom rules
● NoKtFilesInJavaDirectoryRule
● TodoFormatRule

19. class NoKtFilesInJavaDirectoryRule : Rule(Config.empty) {
override fun visitKtFile(file: KtFile) {
super.visitKtFile(file)
if (file.virtualFile.path.contains("java/")) {
report(
CodeSmell(
issue,
Entity.from(file),
message = "The $file should be in the kotlin dir."
)
)
}
}
}

21. Gandalf integration tests
@Test
void 'runs with failure gandalf task on Android Kotlin Project'() {
androidTestBuildFile += """
apply plugin: 'com.ellation.gandalf'
"""
runCommand(command: "gandalf", fixtureName: "failing_project", shouldSucceed: false)
}

22. Challenges we faced
● Groovy
● Learning curve
● Debugging

23. ● Reduced the overhead of maintaining similar logic
● Increased degree of modularization
● Made developers a bit happier
What we achieved by using Gandalf

24. About me
● https://github.com/Ilya-Gh
● ilya.ghiric@gmail.com