feat: Java support with Nix

config.org

@@ -992,7 +992,7 @@ emacs-lisp
 ;;hy
 idris
 ;;json
-;;(java +lsp)
+(java +lsp +tree-sitter)
 ;;javascript
 ;;julia
 ;;kotlin
@@ -3928,6 +3928,34 @@ Operators being in italics looks ugly in this mode too, but unfortunately due to
     `(idris-semantic-postulate-face :foreground ,(doom-color 'yellow))))
 #+end_src
 
+** Java
+
+The =lsp-java= package provides LSP support using the standard language server, the Eclipse-based ~jdtls~. Unfortunately, this package isn't designed for Nix, so it fails to find the server script in our Nix store. We need to do a bit of legwork to patch in this support, as well as some extra considerations, such as per-project config directories.
+
+#+begin_src emacs-lisp
+(defun +lsp-java-server-store-path ()
+  "Return the Nix store derivation path to the Java language server."
+  (string-remove-suffix
+   (concat "/bin/" lsp-java-jdt-ls-command)
+   (or
+    (executable-find lsp-java-jdt-ls-command)
+    (user-error "Could not find Java language server"))))
+
+(after! java-mode
+  (setq lsp-java-jdt-ls-prefer-native-command t))
+(add-hook! java-mode
+  (setq-local lsp-java-server-install-dir
+              (concat (+lsp-java-server-store-path) "/share/java/jdtls/")))
+
+(defadvice! ~/lsp-java-ls-command ()
+  "Configure `lsp-java' to work with Nix."
+  :override #'lsp-java--ls-command
+  (let ((root (or (doom-project-root) (f-join (getenv "XDG_DATA_HOME") "jdtls"))))
+    (list lsp-java-jdt-ls-command
+          "-configuration" (f-join root "config-linux")
+          "-data" (f-join root "java-workspace"))))
+#+end_src
+
 ** Yuck
 
 #+call: confpkg("Mode: Yuck")