False positive from UnusedImports on org.gradle.kotlin.dsl.provideDelegate

[alphaho]

Hi,

I've found that when I'm writing the gradle buildSrc using kotlin dsl, and use the kotlin delegation, I would need to import org.gradle.kotlin.dsl.provideDelegate. But Detekt would give me an UnusedImports error in this case.

For example, with the following code, detekt task would fail:

import org.gradle.api.Plugin
import org.gradle.api.Project
import org.gradle.api.tasks.WriteProperties
import org.gradle.kotlin.dsl.getValue
import org.gradle.kotlin.dsl.provideDelegate  // got UnusedImports from this line
import org.gradle.kotlin.dsl.registering

class DumpVersionProperties : Plugin<Project> {
    override fun apply(target: Project) {
        with(target) {
            val dumpVersionProperties by tasks.registering(WriteProperties::class) {
                setProperties(mapOf("version" to "1.2.3"))
                outputFile = rootDir.resolve("version.properties")
            }

        }
    }
}

Expected Behavior

It should not report UnusedImports if I do use it for delegation.

Observed Behavior

Detekt task fails and report there's an UnusedImports error.

Your Environment

• Version of detekt used: 1.0.0-RC14
• Version of Gradle used (if applicable): 5.4
• Operating System and version: Windows 10

[3flex]

This is interesting, because provideDelegate is not used in the file, but still has to be imported otherwise build fails. I feel that detekt's behaviour is correct and it's only flagging this because of an issue either in Gradle Kotlin DSL or Kotlin itself, because I don't know expect this implementation detail to be exposed here.

See KT-22101 and gradle/kotlin-dsl-samples#564

Not sure what best thing to do is, since trying to whitelist this case in detekt doesn't seem the right approach.

[alphaho]

Hmm, that makes sense to me.

But looking at the delegated properties doc, this imported function seems to be an overloaded operator. So when we use the delegated property in scope, it should be considered as being in used theoretically.
But not sure whether we can tell that difference or not from Detekt's perspective.

[3flex]

Sorry, haven't had time to look at this more closely.

Can you see what ktlint does here? It has a similar rule.

[3flex]

Couldn't help myself - there's a whitelist of all the operators in the rule in detekt, just need to add provideDelegate to it. I'll submit a PR shortly unless someone beats me to it!

[alphaho]

Sounds good to me

[alphaho]

have tried running ktlint, it would also report provideDelegate as Unused import