A custom lint check for verifying any classes using the `@Json` annotation must also use the `@JsonClass` annotation.

MissingJsonClassAnnotationDetector.kt

package // ...

import com.android.tools.lint.client.api.UElementHandler
import com.android.tools.lint.detector.api.Category
import com.android.tools.lint.detector.api.Detector
import com.android.tools.lint.detector.api.Implementation
import com.android.tools.lint.detector.api.Issue
import com.android.tools.lint.detector.api.JavaContext
import com.android.tools.lint.detector.api.Scope
import com.android.tools.lint.detector.api.Severity
import com.android.tools.lint.detector.api.TextFormat
import org.jetbrains.uast.UClass
import org.jetbrains.uast.UElement
import org.jetbrains.uast.kotlin.KotlinUClass

@Suppress("UnstableApiUsage")
class MissingJsonClassAnnotationDetector : Detector(), Detector.UastScanner {

    override fun getApplicableUastTypes(): List<Class<out UElement>> {
        return listOf(UClass::class.java)
    }

    override fun createUastHandler(context: JavaContext): UElementHandler {
        return JsonClassElementHandler(context)
    }

    private class JsonClassElementHandler(private val context: JavaContext) : UElementHandler() {

        override fun visitClass(node: UClass) {
            if (node is KotlinUClass) {
                val hasJsonFields = doesClassHaveJsonFieldAnnotation(node)

                if (hasJsonFields) {
                    val hasJsonClassAnnotation =
                        node.findAnnotation("com.squareup.moshi.JsonClass") != null

                    if (!hasJsonClassAnnotation) {
                        context.report(
                            issue = ISSUE_MISSING_JSON_CLASS_ANNOTATION,
                            location = context.getLocation(node.javaPsi),
                            message = ISSUE_MISSING_JSON_CLASS_ANNOTATION.getExplanation(TextFormat.TEXT),
                        )
                    }
                }
            }
        }

        private fun doesClassHaveJsonFieldAnnotation(kotlinUClass: KotlinUClass): Boolean {
            return kotlinUClass
                .fields
                .any { field ->
                    field.findAnnotation("com.squareup.moshi.Json") != null
                }
        }
    }

    companion object {
        internal val ISSUE_MISSING_JSON_CLASS_ANNOTATION = Issue.create(
            id = "MissingJsonClassAnnotation",
            briefDescription = "Classes that use Moshi parsing should have the JsonClass annotation.",
            explanation = "The JsonClass annotation is required to use Moshi Code-Gen.",
            category = Category.CORRECTNESS,
            severity = Severity.ERROR,
            implementation = Implementation(
                MissingJsonClassAnnotationDetector::class.java,
                Scope.JAVA_FILE_SCOPE,
            ),
            priority = 10
        )
    }
}