lsp-mode: How to use built-in clangd client?

Question

I'm trying to use lsp-mode (together with company-lsp) for auto completion in C++. According to the docs[0], recent lsp-mode includes clangd support, so I should be all set when I do (require 'lsp-clients). However, lsp-mode can't find any clients to handle c++-mode, and from the documentation I can't find any way of debugging this.

The Main Problem

Here is the (almost) complete init.el file, which I have produced as a minimal example:

(unless (package-installed-p 'lsp-mode)
  (package-install 'lsp-mode))
(unless (package-installed-p 'company-lsp)
  (package-install 'company-lsp))
(unless (package-installed-p 'lsp-ui)
  (package-install 'lsp-ui))

(require 'company-lsp)
(require 'lsp-mode)
(require 'lsp-ui)
(require 'lsp-clients)

(push 'company-lsp company-backends)
(add-hook 'after-init-hook 'global-company-mode)

(add-hook 'lsp-mode-hook 'lsp-ui-mode)

(when (string= (system-name) "i11pcbarth")
    (setq lsp-clients-clangd-executable "/usr/lib/llvm-7/bin/clangd"))

(add-hook 'c++-mode-hook 'lsp)

Now, when I open a C++ file, I get the message

Unable to find client(s) handling c++-mode. Make sure you have required lsp-clients.el or proper extension.

Since I already do (require 'lsp-clients) above, I'm not sure what to do.

Further Weirdness

Looking into lsp-clients.el, I can see that it should define e.g. the variable lsp-clients-clangd-executable. However, the variable seems not to be defined (I can't find it using C-h v). So, I assume that for some reason, the (require 'lsp-clients) from my init.el did not work. Thus, I require the file again (by typing (require 'lsp-clients) into the current buffer and calling eval-last-sexp). Now, C-h v sees the variable lsp-clients-clangd-executable. However, M-x lsp RET (to enable lsp-mode) again only gives me the error message about no client that handles c++-mode.

[0] https://github.com/emacs-lsp/lsp-clangd/blob/master/README.md

Answer 1

EDIT: As of late December 2018, this is no longer required, and lsp-mode does the required setup automatically. It was fixed in this commit as far as I can tell.

You need to call lsp-clients-register-clangd, as per https://github.com/emacs-lsp/lsp-clangd/issues/11. To do this, you can either call it interactively using M-x lsp-clients-register-clangd to enable it in your current emacs session, or call it from your init.el after requiring lsp and lsp-clients. The result should look something like this:

(require 'lsp)
(require 'lsp-clients)
(lsp-clients-register-clangd)
(add-hook 'c++-mode-hook 'lsp)

According to https://github.com/emacs-lsp/lsp-mode/issues/537, this is a temporary issue, and calling lsp-clients-register-clangd should not be necessary in the future.