lsp-sourcekit is a client for SourceKit-lsp, a Swift/C/C++/Objective-C language server created by Apple.

Uses lsp-mode, but it's also open to be extended with additions outside of the LSP protocol, like semantic highlighting, if the server supports that.

The SourceKit-LSP language server is included by default in Xcode 11.4+, so the simplest way to get started is the following:

• Download and install Xcode 11.4+ from the Mac App Store or from the Apple developer portal.
• In Emacs, install lsp-sourcekit: M-x package-install lsp-sourcekit RET.
• Then you need to configure the package to point to the sourcekit-lsp executable:

If you use use-package:

(use-package lsp-sourcekit
  :after lsp-mode
  :config
  (setq lsp-sourcekit-executable "/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/sourcekit-lsp"))

If you don't use use-package:

(eval-after-load 'lsp-mode
  (progn
    (require 'lsp-sourcekit)
    (setq lsp-sourcekit-executable
          "/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/sourcekit-lsp")))

On macOS, you can get the path to the SourceKit-LSP executable by running xcrun --find sourcekit-lsp in Terminal. This also works to populate the path, if your emacs shell is configured correctly:

(setq lsp-sourcekit-executable (string-trim (shell-command-to-string "xcrun --find sourcekit-lsp")))

• Finally, if you want to enable lsp automatically whenever you visit a .swift file:

(use-package swift-mode
  :hook (swift-mode . (lambda () (lsp))))

If you don't use use-package:

(add-hook 'swift-mode-hook (lambda () (lsp)))

If you are using a custom Swift toolchain, a toolchain you compiled from source, or simply want to run SourceKit-LSP on a platform different from macOS, the above steps are almost the same, but you may need to set a different value for lsp-sourcekit-executable, or set a special environment variable to search for the corresponding toolchain. You can get further details in the SourceKit-LSP repository.