How to attach gradle-api sources in IntelliJ

I'm working on a custom Gradle plugin. For some reason IntelliJ is unable to find the sources of the gradle-api artifact and only shows the decompiled .class file. I am already using the -all distribution of the Gradle Wrapper (which includes some sources, but apparently not the ones I need right here). Clicking Download... results in an error:

Sources not found: Sources for 'gradle-api-6.5.1.jar' not found

How do I correctly attach/choose sources for gradle-api in IntelliJ?

EDIT:

I have a minimal Gradle plugin with code like that (taken from the official samples):

plugins {
    id 'java-gradle-plugin'
}

repositories {
    jcenter()
}

dependencies {
    testImplementation 'junit:junit:4.13'
}

gradlePlugin {
    // ...
}

According to this excellent manual you should add gradleApi() as a runtimeOnly dependency:

dependencies {
   //...
   runtimeOnly(gradleApi())

I guess that, the default Intellij config use gradle from gradle-wrapper.properties file will use /gradle/wrapper/gradle-wrapper.jar, but it doesn't contain source code. what you need is a jar like gradle-wrapper-all.jar. But I don't know how to let Gradle redownload that. Just setting Wrapper.DistributionType.ALL is not working.

Solution

1. set Wrapper.DistributionType.ALL

wrapper {
    jarFile = file(System.getProperty("user.dir") + '/gradle/wrapper/gradle-wrapper.jar')
    gradleVersion = '6.7.1'
    distributionType = Wrapper.DistributionType.ALL
}

2. I download Gradle, and use it. Set two things here and refresh it.

Here is the source code, the version is right and with all in the name (gradle-6.7.1-all):

1. delete gradle dir
2. run "gradle wrapper"
3. check the suffix "-all" in the file gradle/wrapper/gradle-wrapper.properties
   sample:
   distributionUrl=https://services.gradle.org/distributions/gradle-7.5-all.zip