Here are some examples:
- Extract class / method / function (takes a piece of code and converts it to a class/method/free-floating function, while detecting all context dependencies and turning them to parameters or fields; also generates the proper constructors to populate those fields; and calls the right constructors/methods passing those parameters from context)
- Extract parameter / field (takes a local variable and makes it a parameter/field, and identifies all callers to propagate a value)
- Versions of the previous extractions that can go through a deeper call stack, automatically propagating along all functions along the way; essentially identical to using the same thing repeatedly, but in a single step
- Data flow to/from here (takes a variable and tells you something like 'the value here is coming from this parameter, which was populated from that field, which is assigned to in these two places; in the first place, it is assigned from this IO function; in the second place it is set to the value of this parameter which is populated from this constant; for "from", it is doing the same, but for all downstream uses of this value)
LSP itself certainly doesn't support this, though they can probably be built on top of it with some effort. For that matter, I also don't think VSCode supports them, though I have used Emacs far far more than that.
Of course Emacs has none of it. Through a combination of various extensions and plugins of wildly varying quality, and through increasingly arcane config files you can have some semblance of what an IDE offers, but definitely not even close to "all of it".
> through ... various extensions and plugins of wildly varying quality
Most Emacs plugins that I've seen are higher quality than most professional codebases I've seen.
> through increasingly arcane config files
Things are getting better not worse, so they are _decreasingly_ arcane config files. And Doom Emacs or Spacemacs make this dead simple to setup. This is no longer a valid issue.
I ended up moving to IntelliJ after being a long term Eclipse user and then using Emacs for about a year. I miss the keyboard-driven environment in Emacs and the more parsimonious keybindings, but IntelliJ is better as an IDE. Still use Magit though.
You don’t have to master Elisp at all to use Emacs, I have written very little Elisp. However I did use a distribution (Prelude, then Doom Emacs) which did a lot of the heavy lifting in setting up my initial environment - YMMV if you go in with vanilla Emacs and then edit your init.el until you find a working configuration for your needs.