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clojure-lsp Development#

There are several ways of finding and fixing a bug or implementing a new feature:

  • The Clojure Way
  • Create a test for your bug/feature, then implement the code following the test (TDD).
  • Build clojure-lsp[.bat] using bb debug-cli each time you have made changes, and test it manually in your client. This is the slowest option.

Whichever development path you choose: For final testing, it is good to rebuild the binary with bb debug-cli.

There are two custom LSP methods clojure/serverInfo/log and clojure/cursorInfo/log. They can assist in debugging.

The Clojure Way#

With a clojure-lsp + nREPL powered Clojure editor you can modify your editor session's clojure-lsp server using the Clojure REPL.

Here's demo video:

These are the steps:

  1. bb debug-cli - to build a clojure-lsp[.bat] executable that includes cider-nrepl in the jar. This executable will be saved at the root of the project.
  2. Configure your editor to use this clojure-lsp[.bat] executable
  3. Have your editor restart its clojure-lsp server
  4. Issue the clojure-lsp serverInfo command
  5. Find the port entry in the output
  6. Connect your editors nREPL client to this port
  7. Hack away!

Seeing is believing. An easy way to convince yourself that you can actually change clojure-lsp mid-flight is to:

  1. Modify the server-info function in src/clojure_lsp/handlers.clj
    • Say, you add a :foo :bar entry to the map returned
  2. Evaluate the new server-info function definition
  3. Issue the clojure-lsp serverInfo command
  4. Find :foo :bar in the output

You have just modified the LSP server powering your editor while it was running! This is the Clojure way. No recompiling and restarting and reloading. That is some other, non-Clojure, way.

The details in how to perform these steps can vary a bit between the various Clojure editors/plugins.

Visual Studio Code with Calva#

  • This project comes with Calva configuration to use the clojure-lsp[.bat] executable built in step 1 above. You can skip step 2, unless are running on MS-Widnows, in which case you should update the setting in .vscode/settings.json to add the .bat extension, i.e. "calva.clojureLspPath": "./clojure-lsp.bat".

  • To restart the clojure-lsp server, use the VS Code command Developer: Reload Window

  • The Hack away! step needs to start with you issuing the command Calva: Load Current File and Dependencies.

Emacs with CIDER#

  • To configure Emacs to use the nREPL-enabled executable, run (setq lsp-clojure-custom-server-command '("~/path/to/clojure-lsp/clojure-lsp")), adjusting the path as necessary. If you add this to your Emacs config, you can skip this step in the future.
  • To restart the clojure-lsp server, execute the Emacs command lsp-workspace-restart.
  • To find the server info, execute lsp-clojure-server-info.
  • To connect the nREPL client, run cider-connect-clj, with "localhost" and the port.

If you re-connect regulary, you may want to add this Emacs shortcut:

(defun lsp-clojure-nrepl-connect ()
  "Connect to the running nrepl debug server of clojure-lsp."
  (let ((info (lsp-clojure-server-info-raw)))
      (when-let (port (and (string-match "\"port\":\\([0-9]+\\)" info)
                           (match-string 1 info)))
        (cider-connect-clj `(:host "localhost"
                             :port ,port))))))

Vim with coc.nvim and Fireplace#

  • Change coc-settings.json (:CocConfig) clojure-lsp: {command: "~/path/to/clojure-lsp/clojure-lsp"}, adjusting the past as necessary.
  • To restart the clojure-lsp server use :CocRestart
  • To find the server info, :echo CocRequest('clojure-lsp', 'clojure/serverInfo/raw')['port']
  • To find the server log, :echo CocRequest('clojure-lsp', 'clojure/serverInfo/raw')['log-path']
  • To connect the nREPL client, run :Connect <port>

If you re-connect regulary, you may want to add something like this to your vimrc:

" Copies the log-path to your clipboard
nnoremap <silent> crsl :call setreg('*', CocRequest('clojure-lsp', 'clojure/serverInfo/raw')['log-path'])<CR>
" Connects to nrepl
nnoremap <silent> crsp :execute 'Connect' CocRequest('clojure-lsp', 'clojure/serverInfo/raw')['port']<CR>

Your Favorite Editor#

TBD. PR welcome.

Debugging & Profiling#

The nREPL includes tools for debugging and profiling clojure-lsp. See cli/dev/clojure_lsp/debug.clj.

If you're interested in using the profiling tools in that file, you'll need to be familiar with criterium and clj-async-profiler.

Note that the performance of clojure-lsp is highly dependent on the size of its db. If you load a repl with -A:build, you'll have access to the debugging tools, but the db will be nearly empty. Follow the [steps][#the-clojure-way] above to connect to an nREPL which has a populated db.


Run bb tasks for a list of available dev tasks.

The codebase consists of the lib/ library and the cli/ program which depends on it.

  1. bb test-lib,
  2. bb test-cli, and
  3. bb test (for both of the above).

cli/ produces a standalone .jar file that can be converted to a self contained clojure-lsp[.bat] script or a clojure-lsp[.exe] binary executable file.

  1. bb prod-jar -> cli\ standalone jar,
  2. bb prod-cli -> executable script with embedded cli/ jar,
  3. bb debug-cli -> same as prod-cli but includes support for cider-nrepl and clj-async-profile, and
  4. bb native-cli -> binary executable produced with graalvm.

There are also cli/ integration tests. They require ./clojure[.bat|.exe] to have already been built with one of the above cli tasks (__NOTE:__always ensure that you rebuild the cli/ executable every time you make changes to lib/ or cli/ source code so tha the integration tests use an up to date executable).

  1. bb integration-tests

The same development version can be used to lint all of the source code.

  1. bb lint

Writing tests#

A test should be able to run on all JDK versions in scope starting with 1.8 and across GNU/Linux, macos and MS-Windows operating systems.

The test author should be aware of the following important differences between nix and windows: 1. Line endings 1. On nix: the single Line Feed (LF) char, i.e. \n. 1. On windows: the Carriage Return (CR) followed by the LF char (CRLF), i.e. \r\n. 1. Paths 1. On *nix: Use / as the path separator, absolute paths start with /. 1. On windows: use \ as the path separator, absolute paths start either with a drive letter followed by :\, i.e. [A-Za-Z]:\ (e.g. c:\temp and D:\src) or with a double \\ indicating a network path (e.g. \\computer39\temp).

Below are a few hints to assist with writing test that work accross the different platforms. 1. Line Endings 1. When comparing strings, Use clojure-lsp.test-helper/string= with \n in your expected result. 1. e.g. use (is (h/strings= "one\n" result) instead of (is (= "one\r\n" result)) or (is (= "one\n" result)). 1. Use h/str-includes? with \n in the string to search for instead of clojure.string/includes?. 1. e.g. (is (h/str-includes? (slurp "path") "something\n")) instead of (is (str/includes? (slurp "path") "something\n")) or (is (str/includes? (slurp "path") "something\r\n")). 2. Paths 1. Always use babashka.fs/canonicalize when converting a relative path to an absolute path. Avoiding using any of java File/Path absolute or canonical equivalent fns. This ensures that the drive letter on windows is always in capitals (e.g. D:\ instead of d:\). This is also the convention used throughout the codebase and it works as well with both existing and non-existing files. 1. Use clojure-lsp.test-helper/file-path, clojure-lsp.test-helper/file->uri with *nix paths. They are converted to the format expected by the OS. 1. e.g. (load-code (h/file-path "/aaa.clj") "(ns aaa)") instead of (load-code "/aaa.clj" "(ns aaa)") or (load-code "c:\\aaa.clj" "(ns aaa)")

Last update: September 25, 2022