Code completion popup is closing immediately in 2019.2 (ultimate)

Hello, 

Please check this case and follow the troubleshooting steps described inside. 

If it does not help, please report a bug at https://youtrack.jetbrains.com/issues/IDEA with idea.log attached (https://intellij-support.jetbrains.com/hc/articles/207241085) so that we can investigate further. Thank you.

Wow that case is about 4 years old. As it worked in the previous version and the completion engine was changed in the current one I guess there is a regression or something is broken here. So I will file an issue within the bugtracker.

Thank you Stephan. 

Please share the issue link once it is submitted. 

Great, now that I wanted to reproduce and gather the logs for the issue it seems to work. Maybe my PC did not like the Friday and played silly games with me ;)

Back to serious: I have no clue why but it works now somehow.

I stumbled upon a solution that worked for me in RubyMine 2020.2 Mac OSX. The culprit was:

Editor > Code Editiong > Error Highlighting > Autoreparse delay time (milliseconds)

Seems like the reparse is kicking out the popup!

For me this was the solution: I ran it from the console so I could see any errors. Then I saw:

2020-12-16 20:54:30,031 [ 97932] ERROR - stubs.StubProcessingHelperBase - Stub index points to a file without PSI: file type = com.intellij.openapi.fileTypes.UnknownFileType@6619699d, indexed file type = com.intellij.ide.highlighter.JavaClassFileType@426b7237, used scope = KotlinSourceFilterScope(delegate=Module-with-dependencies:lessor-oauth2-client.test compile-only:true include-libraries:true include-other-modules:true include-tests:true src=true libSrc=false cls=true scriptDeps=false scripts=true) 
java.lang.Throwable: Stub index points to a file without PSI: file type = com.intellij.openapi.fileTypes.UnknownFileType@6619699d, indexed file type = com.intellij.ide.highlighter.JavaClassFileType@426b7237, used scope = KotlinSourceFilterScope(delegate=Module-with-dependencies:lessor-oauth2-client.test compile-only:true include-libraries:true include-other-modules:true include-tests:true src=true libSrc=false cls=true scriptDeps=false scripts=true)
at com.intellij.openapi.diagnostic.Logger.error(Logger.java:143)
at com.intellij.psi.stubs.StubProcessingHelperBase.processStubsInFile(StubProcessingHelperBase.java:52)
at com.intellij.psi.stubs.StubIndexImpl.lambda$processElements$2(StubIndexImpl.java:287)
at com.intellij.psi.stubs.StubIndexImpl.processElements(StubIndexImpl.java:317)

A quick google let me to android - Stub index points to a file without PSI: com.intellij.openapi.fileTypes.UnknownFileType@23713b43 - Stack Overflow where the solution is File -> Invalidate Caches/Restart.

That worked for me.

There is *entirely* too much magic in Intellij and the java world.