Setup Intellij IDEA for plugin development - cannot find symbol PathInfo

Question

Followed the instructions in setting_up_environment 'IntelliJ Platform SDK DevGuide' and checkout_and_build_community:

• Installed the IDE
• Installed JDK 8
• Checked out the SDK source code from GIT
• Followed the other instructions in these two pages

All the above was done twice, on an Ubuntu 15 and Windows 8.1 vm. When I try to build the project, I get numerous warnings about deprecated classes and two errors:

C:\IdeaProjects\community\plugins\cvs\cvs-core\src\com\intellij\cvsSupport2\config\ProxySettings.java
    Warning:Warning:line (19)java: com.intellij.openapi.util.DefaultJDOMExternalizer in com.intellij.openapi.util has been deprecated
    Warning:Warning:line (21)java: com.intellij.openapi.util.JDOMExternalizable in com.intellij.openapi.util has been deprecated
    Warning:Warning:line (25)java: com.intellij.openapi.util.JDOMExternalizable in com.intellij.openapi.util has been deprecated
    Warning:Warning:line (72)java: com.intellij.openapi.util.DefaultJDOMExternalizer in com.intellij.openapi.util has been deprecated
    Warning:Warning:line (77)java: com.intellij.openapi.util.DefaultJDOMExternalizer in com.intellij.openapi.util has been deprecated
C:\IdeaProjects\community\plugins\cvs\cvs-core\src\com\intellij\cvsSupport2\config\ExtConfiguration.java
    Warning:Warning:line (20)java: com.intellij.openapi.util.DefaultJDOMExternalizer in com.intellij.openapi.util has been deprecated
    Warning:Warning:line (22)java: com.intellij.openapi.util.JDOMExternalizable in com.intellij.openapi.util has been deprecated
    Warning:Warning:line (29)java: com.intellij.openapi.util.JDOMExternalizable in com.intellij.openapi.util has been deprecated
    Warning:Warning:line (39)java: com.intellij.openapi.util.DefaultJDOMExternalizer in com.intellij.openapi.util has been deprecated
    Warning:Warning:line (44)java: com.intellij.openapi.util.DefaultJDOMExternalizer in com.intellij.openapi.util has been deprecated
C:\IdeaProjects\community\platform\built-in-server-api\src\org\jetbrains\builtInWebServer\WebServerRootsProvider.java
    Error:Error:line (13)java: cannot find symbol
  symbol:   class PathInfo
  location: class org.jetbrains.builtInWebServer.WebServerRootsProvider
    Error:Error:line (16)java: cannot find symbol
  symbol:   class PathInfo
  location: class org.jetbrains.builtInWebServer.WebServerRootsProvider

I have googled, but failed to find anything relevant regarding PathInfo, builtInWebServer or WebServerRootsProvider. Probably because google automatically assumes I mean 'path info' and silently mixes these results in.

I suspect it's probably something I didn't download with IDEA, such as J2EE or some Apache library, but after several hours, I'm ready to throw the towel and ask.

A few comments in response to answers:

1. Java is installed and configured in the project. It probably would not complain of deprecation if Java were completely missing
2. The SDK is defined as 'IDEA jdk' so it will work automatically, as per the instructions

Answer 1

The IDEA SDK is written partly in Kotlin, a statically-typed programming language that runs on the Java Virtual Machine.

The missing PathInfo class is defined in PathInfo.kt, a Kotlin file.

Select File | Settings | Plugin and click 'Install JetBrains Plugin'. Select the Kotlin plugin and the error will go away.