Intellij editor won't see the gradle api

This class belongs to gradle-core.

Sorry, but I don't understand.

Vast majority of guides about writing your own gradle plugin says, that I must add

plugins {
   id 'java-gradle-plugin' 
}

or

apply plugin: 'java'
dependencies {
   compile gradleApi()
}

And nothing about "gradle core"

Ok, I tried to add it manually:

dependencies {
  compile "org.gradle:gradle-core:3.5"
}

But no changes, intellij still can't resolve any symbol that I need to write simple gradle plugin.

May be I am missing something important. Help me, pls, just save my soul.

Not sure what's the problem, I've tried the sample from Gradle distribution and it works fine:

Please try File | Invalidate Caches | Invalidate and Restart.

Serge, seems I found what's the problem.

Preferences -> Editor -> File Types -> Ignore files and folders. In my case root "gradle" (not ".gradle") folder was added there (because I never used it, like a .git folder). And this caused broken suggestions and completions for the gradle api.

It's a bit strange behaviour, because I use gradle api via plugin (and not via buildSrc folder, which automatically adds gradle-api to the intellij module dependencis from that "gradle" folder) and it's not working

plugins {
   id 'java-gradle-plugin'
}

Is it a bug?

It's not a bug, libraries are loaded from .gradle directory (http://i.imgur.com/EQG9QAB.png). If it's ignored, IDE will not see or index any of the libraries. "gradle" directory also contains files that are needed for proper integration work. Please don't exclude these folders.