Java w/o IntelliJ would be miserable.
That said, I hate their nonsensical keybindings for (my) most common uses (looking at you function keys). I also wish their plugin API was more stable. A lot of great plugins seem to require a lot of maintenance work release to release.
If you're on macOS, since 2020.3 you can try the macOS System Shortcuts keymap. It should feel much more native, no function keys included.
The text-storage data structure, syntax highlighting and search features are written in Rust, and the UI is written in Swift since we wanted to create a native macOS experience. The Swift and Rust code talk to each other using C FFI, and no, that doesn’t take away the safety features of both languages.
We’re using the Rope data structure for text representation, and the tree-sitter parser for syntax highlighting and some smart features like file outline, local renaming and symbol search. All other language features are powered by LSP servers (rust-analzyer and gopls).
I’d be happy to answer any questions under this comment or anywhere else in this thread.