I develop new PlantUML IntelliJ Plugin with an editor function that also supports PlantUML syntax,so I introduced it features!

https://plugins.jetbrains.com/plugin/14821-plantuml-studio

It has been released as a paid plug-in, and I plan to continue active development in the future,
so I would be very grateful if you could give us feedback.

Features

Editor

Syntax Highlighting

All major UML diagram's syntax are supported, including class diagrams.
Other diagrams that cannot be supported will be supported in the future.

Auto Completion

It provides the completion of keywords optimized for each notation of each diagram and the completion of simple Identifiers.
Like the below image, It focuses reducing the things to remember and improving visibility, I think which lead to more comfortable writing.

Auto completion sample on the sequence diagram

Refactoring

It provides the rename feature of identifiers.

Code formatting

It provides the auto indenting when entering block token(ex: {})

It also supports batch conversion using "Code" > "Reformat Code" in the menu.

Auto inserting a closing tag

For smooth writing the block syntax, It provides automatic input a closing tag.

File Viewer

I put PlantUML codes in a project, and I wanted a feature to view a list of PlantUML files, so I made a simple one.

I think PlantUML is a powerful tool for drawing nice diagrams with simple code,
I also think that it can be a more powerful tool when combined with a good editor.

Once again, I'm waiting for your feedback!