Issues building IDEA

Alright, I must be doing something stupid.

I'm using Arch with Open JDK 1.8.

I have followed both of the following instructions perfectly (minus JDK 1.6 -- see below):

https://github.com/JetBrains/intellij-community/blob/master/README.md

https://github.com/JetBrains/intellij-community/tree/143#building-and-running-from-the-ide

Basically:

• Checked out master at https://github.com/JetBrains/intellij-community
• Ran getPlugins.sh
• Opened the project with IDEA community 19.1.3
• Setup the "1.8" and "IDEA jdk" SDKs with tools.jar in Project Structure per the instructions *using JDK 1.8 for 'IDEA jdk' as the README.md file says that is OK*
• The 'Maven 2 Integration', 'Groovy' and 'UI Designer' plugins are all installed and enabled.
• Build

At first I get errors like the following:

Error:(7, 28) java: package com.sun.javafx.embed does not exist
Error:(8, 25) java: package com.sun.javafx.tk does not exist
Error:(9, 26) java: package javafx.application does not exist

I then added Settings -> Appearance and Behavior -> Path Variables -> MAVEN_REPOSITORY ... </my/home>/.m2/repository

Then trying to rebuild I see errors like:

Warning:Kotlin: Classpath entry points to a non-existent location: $MAVEN_REPOSITORY$/org/jetbrains/kotlin/kotlin-stdlib-jdk8/1.3.31/kotlin-stdlib-jdk8-1.3.31.jar

...
Error:(23, 23) Kotlin: Cannot access built-in declaration 'kotlin.Double'. Ensure that you have a dependency on the Kotlin standard library
Error:(25, 26) Kotlin: Unresolved reference: Pair
Error:(25, 31) Kotlin: Cannot access built-in declaration 'kotlin.String'. Ensure that you have a dependency on the Kotlin standard library
Error:(25, 39) Kotlin: Cannot access built-in declaration 'kotlin.String'. Ensure that you have a dependency on the Kotlin standard library
...

I've tried removing the MAVEN_REPOSITORY entry but it always comes back after restarting IDEA.

Inside my ~/.IdeaIC2019.1/config/options/path.macros.xml file I see two entries:

<macro name="KOTLIN_BUNDLED" value="/home/mkd/.IdeaIC2019.1/config/plugins/Kotlin/kotlinc" />
<macro name="MAVEN_REPOSITORY" value="/home/mkd/.m2/repository" />

If I remove the MAVEN_REPOSITORY entry and re-launch IDEA and go back to Settings -> Appearance and Behavior -> Path Variables, MAVEN_REPOSITORY is back (in the Settings UI)! At this point reading path.macros.xml again only shows KOTLIN_BUNDLED, but after hitting "OK" in Settings MAVEN_REPOSITORY is back in path.macros.xml too!

Also note that I do see a number of things in my ~/.m2/repositories directory, including things at org/jetbrains, and things at com/sun/ but nothing, for example, in com/sun/javafx