We can implement some custom lint for Kotlin code.
So, I put an example the custom lint.

Some helpful links.

• http://tools.android.com/tips/lint-custom-rules
• http://tools.android.com/tips/lint/writing-a-lint-check

You can also find examples in the GitHub repositories. Let’s try to implement custom lint and reduce easy mistake from your projects.

Gradle

dependencies {
    compileOnly "com.android.tools.lint:lint-api:26.0.1"
    compileOnly "com.android.tools.lint:lint-checks:26.0.1"
}

sourceCompatibility = "1.8"
targetCompatibility = "1.8"

jar {
    manifest {
        attributes("Lint-Registry-v2": "your.custom.lint.package.LintClassName")
    }
}

Detector

class yourCustomLintDetector : Detector(), UastScanner {
    companion object {
        private val issueId = "yourCustomLint"
        private val issueDescription = "Description for yourCustomLint"
        private val issueExplanation = "Some more concrete explanation for yourCustomLint"
        // https://android.googlesource.com/platform/tools/base/+/master/lint/libs/lint-api/src/main/java/com/android/tools/lint/detector/api/Category.java#122
        private val issueCategory = Category.CORRECTNESS
        private val issuePriority = 10
        private val issueSeverity = Severity.FATAL
        private val implementation = Implementation(yourCustomLintDetector::class.java, Scope.JAVA_FILE_SCOPE)

        internal val issue = Issue.create(issueId, issueDescription, issueExplanation, issueCategory, issuePriority, issueSeverity, implementation)
    }

    override fun applicableSuperClasses() = listOf("some.super.class.of.yourCustomLint")

    // If a target, class which inherits "some.super.class.of.yourCustomLint", has no "yourCustomLintName" method, then the following lines report it user.
    override fun visitClass(context: JavaContext, declaration: UClass) {
        val isOverridden = declaration.methods
                .firstOrNull { method -> method.isOverride && method.name.contains("yourCustomLintName") } != null

        if (!isOverridden) {
            declaration.uastAnchor?.let {
                context.report(issue, context.getLocation(it), "$issueDescription \n $issueExplanation")
            }
        }
    }
}

Registry

import your.custom.lint.package

class LintClassName : IssueRegistry() {
    override fun getIssues() = listOf(yourCustomLintDetector.issue)
}

check

Add the lines on your gradle dependencies.

dependencies {
  lintChecks project(':your-lint-project')
}

Test

You can implement tests for the custom rule.

https://android.googlesource.com/platform/tools/base/+/studio-master-dev/lint/libs/lint-tests/src/main/java/com/android/tools/lint/checks/infrastructure/LintDetectorTest.java

import com.android.tools.lint.checks.infrastructure.LintDetectorTest

class yourCustomLintDetectorNotOverrideTest : LintDetectorTest() {
    fun testBasic() {
        lint().files(
                LintDetectorTest.java("" +
                        "package test.pkg;\n" +
                        "import some.super.class.of.yourCustomLint;\n" +
                        "public class TestClass1 extends yourCustomLint {\n" +
                        "    @Override public void yourCustomLintName() {}\n" +
                        "}")) // an example
                .allowCompilationErrors()
                .run()
                .expect("Error message the lint should raise.....\n"
                        "1 errors, 0 warnings") // an example
    }

    override fun getDetector() = yourCustomLintDetector()

    override fun getIssues() = listOf(yourCustomLintDetector.issue)
}

import com.android.tools.lint.checks.infrastructure.LintDetectorTest

class yourCustomLintDetectorOverrideTest : LintDetectorTest() {
    fun testBasic() {
        lint().files(
                LintDetectorTest.java("" +
                        "package test.pkg;\n" +
                        "import some.super.class.of.yourCustomLint;\n" +
                        "public class TestClass1 extends yourCustomLint {\n" +
                        "    @Override public void yourCustomLintName() {}\n" +
                        "}")) // an example
                .allowCompilationErrors()
                .run()
                .expectClean()
    }

    override fun getDetector() = yourCustomLintDetector()

    override fun getIssues() = listOf(yourCustomLintDetector.issue)
}

Conclusion

I described an example to implement Custom Lint for Gradle plugin. I believe custom lint help your projects and if you work with some guys, the feature should help you more powerful.

Have a good testing 🙂