DeriveCompletionContributor.kt

package org.rust.ide

import com.intellij.codeInsight.completion.*
import com.intellij.codeInsight.lookup.LookupElementBuilder
import com.intellij.patterns.PlatformPatterns
import com.intellij.util.ProcessingContext
import org.rust.lang.RustLanguage
import org.rust.lang.core.psi.RustOuterAttrElement

class DeriveCompletionContributor : CompletionContributor() {
    init {
        extend(CompletionType.BASIC, PlatformPatterns.psiElement(RustOuterAttrElement::class.java).withLanguage(RustLanguage), object : CompletionProvider<CompletionParameters>() {

            override fun addCompletions(parameters: CompletionParameters, context: ProcessingContext?, result: CompletionResultSet) {
                result.addElement(LookupElementBuilder.create("Clone"));
                result.addElement(LookupElementBuilder.create("Copy"));
            }
        })
    }
}

To preface: I'm new both to Kotlin and IntelliJ plugin development, so please excuse any naivety!

I'm following the example here for creating a CompletionContributor. I'm having trouble getting this simple completion to trigger, presumably because I'm not passing the correct parameters to PlatformPatterns.psiElement().

Ultimately, we'll want completion to trigger when the following conditions are met:

1. It's an attribute element
2. It's a derive attribute, specifically
3. The carat is within the parens, eg: #[derive(C<carat>)]

Right now, I'm just trying to accomplish step one, which is to correctly identify the element.

FWIW, I've gotten this completion to trigger on RustLiteral.Text elements, simply to rule out any issues with getting the completion contributor registered.