Detekt Plugin: Verify Implementation

This is a plugin for detekt, a static code analyzer for Kotlin, which enables verifying whether concrete classes are implemented as specified according to annotations applied to base types.

The following detekt rules are included:

• DataClass: requires extending classes to be data classes or object declarations. This guarantees a predictable default implementation for equals and hashcode implementations, i.e., value equality instead of referential equality.
• Immutable: requires classes or extending classes to be immutable; they may not contain mutable properties (var) or properties of mutable types (types with var properties).

Due to the nature of this plugin, a specific flavor of semantic versioning is used which makes more sense for linters. Any minor update may report more errors than the previous release.

Enabling the Plugin in Gradle

Load the plugin through the detekt Gradle configuration block:

Groovy DSL

detekt {
    dependencies {
        detektPlugins "dk.cachet.detekt.extensions:detekt-verify-implementation:1.2.5"
    }
}

Since this plugin uses type resolution, the rules won't run when using the basic detekt task. Use detektMain or a custom detekt task, as per the detekt documentation.

Configuration

By default, the rules are not activated in the detekt configuration file. To enable a rule, set it to active and specify the fully qualified name of the annotationClass which determines which concrete classes to verify. For example:

verify-implementation:
  DataClass:
    active: true
    annotationClass: "dk.cachet.carp.common.ImplementAsDataClass"
  Immutable:
    active: true
    annotationClass: "dk.cachet.carp.common.Immutable"

In case the annotation class cannot be found and the rule is active, an IllegalStateException will be thrown.

Using assumeNoAnnotations, you can specify a list of fully qualified type names for which it is assumed they don't have the annotation applied to them. This may be useful when the plugin fails to analyze classes which are known not to carry the annotation.

verify-implementation:
  Immutable:
    active: true
    annotationClass: "dk.cachet.carp.common.Immutable"
    assumeNoAnnotations: ['kotlin.Any']

Additional rule-specific configuration options are described next.

Immutable

• assumeImmutable can list fully qualified class names which won't be verified and are assumed to be immutable. This may be useful when the plugin fails to analyze classes which you know to be immutable. Example configuration:

verify-implementation:
  Immutable:
    active: true
    annotationClass: "dk.cachet.carp.common.Immutable"
    includes: ['**/domain/**']
    assumeImmutable: [
      'dk.cachet.carp.common.DateTime',
      'kotlinx.serialization.json.Json'
    ]