Starting with Emacs lsp-mode for Java development

First the Rant

In ancient times (the 1980s) I learned programming mostly using Emacs and some key bindings got chiseled into my brain forever. When I started Java programming in Emacs, support for coding actions based on compiler output, like quick fixes suggestions, was not available, sadly. So I switched to Eclipse for Java programming. But my first action was to enable Emacs key bindings as far as available.

Only recently, around 2019, I switched mostly to Intellij, because around that time, Eclipse got weirder by the day. For example on my Linux with XFCE4, menus tended to be non-functional. And I had hated the workspace concept of Eclipse from day one. Again Emacs key bindings were applied as good as possible, several manual rebindings included.

Around the same time I also started using vscode for Typescript programming and again enabled Emacs key bindings, including manual fixes as far as I felt the need for.

Then, recently, I started into a sabbatical and thought, hey, nobody forces you to use Eclipse/Intellij/vscode. How's the support for Java in Emacs these days. Could I go back?

But why should I? Well, I never stopped using Emacs for other editing and all three IDEs have some lacking when it comes to some slickness I got used to in my programmer "infancy":

• Incremental Search (CTRL-s). Yes, all IDEs have some support for it, but for me they all feel weird. Take Intellij: the left, right, up, down keys either edit the search string or move between search results. Weird. In Emacs they all leave incremental search and I start editing. Hey, this is incremental search, why would I want the left, right key edit the search term. Backspace is all I need. And CTRL-s, CTRL-r to jump to next or previous is enough, no need to override the up and down keys.
• Transpose adjacent entitites CTRL-t, Meta-t. For single characters, this is available in Intelli and Vscode at least, don't remember Eclipse, but does any of those have it for words. I often in particular missed the latter.
• Switch Buffer CTRL-x b switches between what others call editors, mostly the files that are open. I tweaked all three IDEs a lot to get the same super-simple and effective switching, but all were weird with modal menu popups showing buffers in weird order or even files no longer open and additional possible actions I didn't ask for. Not my thing.
• Undo CTRL-x u. Well, this just does not work in most IDEs as it does in Emacs. It is this little trick of Emacs to record the Undo action itself in the chain of commands which allow you to undo the Undo action itself. I remember that I was not only slightly confused back then when I used it the first time, but once you get the idea, it is just great. But I was told by another long term Emacs user that he doesn't like that particular Emacs approach at all. So take your pick.
• Keyboard Macros CTRL-x (in those IDEs are not worth talking about, really. I tried one or the other plugin or use what is available, but basically they work only half of the time. Drop in a command from a menu and shit happens. Not so in Emacs. I never came across any action that would freak out either recording or replaying a keyboard macro. Where other's use repeated search&replace I often use a keyboard macro with embedded search to some anchor point, then editing, then the next anchor point, some other editing, jump to a defined place, like the start of the next line, stop recording. Play!
• Registers are a way to store the current cursor position in a "register" with a single character name and later jump back to the place. The IDEs have bookmarks, but I found them cumbersome to use. I have bound F6 to store the cursor position in one fixed register and Meta-F6 to go back there, so basically just one bookmark. This covers 99% of all the cases for me, because who could remember more than one bookmark to jump to anyway?

So lets see if I can make friend with lsp-java which uses the incremental compiler from eclipse to stay informed about the code structure.

As somewhat expected, though, getting started is a bit tough, despite the seemingly good documentation.

Starting with lsp-java

Git the .emacs.d

Reading the Quick Start it is obvious that big things will happen with my to my hand crafted, dry aged emacs configuration files. So I decided to preserve the current state and be able to see all the changes by checking my ~/.emacs.d into a local git repository.

In particular I renamed ~/.emacs to ~/.emacs.d/init.el which, according to the manual are equivalent, so that no tricks were needed to include the initialization file into git.

Follow the installation instructions

Next I basically did what I was told:

1. install the package
2. add the magic spells (on the same page as the above link)

Try it and ... ughhh? ... aaaah!

Then I opened up the first Java file of a small project of mine. It looked good, as I noticed that the jdt server was downloaded an started a the syntax highlighting was working.

Next I deleted an import some.Stuff line from the code and nicely, the first use of Stuff was highlighted with an error.

But now comes the point I had somewhat expected where Emacs shows that it does not easily make friends with every odd dev coming along. A bit of peristence is required at the start. Even for long-term users like me. How can I tell it to just fix the missing import?

Even if you don't know the keyboard shortcut of some function do-stuff, in Emacs you can always invoke it by typing Meta-x and then enter the function name, do-stuff, in what is called the "minibuffer". Intellij has this as find action typically invoked by hitting SHIFT twice quickly. So I thought it should suffice to find the right function name and invoke it.

Somehow I got astray on the lsp-ui page and invoked lsp-ui-sideline-apply-code-actions, which sounded right, but it insisted to tell me: there are no code actions on this line. Even the error message seemed to tell me I had the right function, but, hey, there is nothing to offer. If this was to be true, the whole thing would be completely useless. Quickly fixing a missing import is a must.

Next I tried CTRL-x m to describe the Emacs editing "mode" for the current file. This usually comes with long lists of key bindings available. Sadly not for the lsp stuff. Hmm.

Of course I tried more commands, somewhat randomly picked, to see what happens. For one, Emacs told me "you could run command ... also with s-l T a. The "s" is for the Super key. So I tried this and since I was somewhat slow after the s-l, a list of alternatives valid after it appeared at the bottom of the screen, thanks to which-key mode that was installed and activated as part of the whole thing. Somehow I had never come across this minor-mode before, likely because I have used Emacs only for simple text editing in the last years.

But now I am in business because the possibilities are all listed nicely and it is a matter of exploration to find things that I like to use. It will surely also enable me to find more documentation as I'll see the keywords to search for.

Fixing the wrong import, or other mistakes I entered on purpose, was now as simple as s-l a a which invokes lsp-execute-code-action, listed first on the lsp-java page. Stupid me.

To be continued.

...June 2024 addition: use Eglot, not lsp-mode. Though I actually also tried Eglot, but I am back to Intellj. Emacs is still very, very far from what can be done with IDEs such as Intellij or Eclipse. Sorry to say this.