Merge pull request #59412 from gottesmm/pr-42c3a6f19df445d0ceab9eecc10e1d84a8d8f7f4

[docs] Add a small howto on setting up LSP/Emacs as a C++ IDE for working on the compiler code base.

Author: swift-ci

docs/HowToGuides/SettingUpLSPEmacs.md

@@ -0,0 +1,76 @@
+# How to setup LSP + Emacs as a C++ IDE for Swift
+
+This document describes how to setup a new emacs installation to use LSP and
+other modes to create a C++ IDE for working on the compiler code base. It
+enables autocompletion, lookup API at point, as well as formatting, renaming,
+and syntax highlighting.
+
+## Setting up Package.el for MELPA
+
+Before we do anything, we need to setup package.el so we can grab packages from
+[https://melpa.org/](MELPA) and GNU. This can be done by
+including the below in your elisp startup file. Make sure it is run before any
+other code is run.
+
+```
+(require 'package)
+(add-to-list 'package-archives '("melpa" . "https://melpa.org/packages/") t)
+(add-to-list 'package-archives '("gnu" . "http://elpa.gnu.org/packages/") t)
+(package-initialize)
+```
+
+## Download packages
+
+The packages needed as of this document being written (Jun 2022) are:
+
+* use-package
+* company
+* lsp-mode
+* lsp-ui
+* helm-lsp
+* lsp-treemacs
+
+One can install these by running the command `package-install` inside emacs.
+
+## Configuring LSP
+
+Finally, now we need to configure out installation so everything is setup
+correctly. This can be done by including the following in ones .emacs:
+
+```
+(use-package company
+  :ensure t
+  :config
+  ;; Enable completion-as-you-type behavior.
+  ;; don't add any dely before trying to complete thing being typed
+  ;; the call/response to gopls is asynchronous so this should have little
+  ;; to no affect on edit latency
+  (setq company-idle-delay 0.1)
+  ;; start completing after a single character instead of 3
+  (setq company-minimum-prefix-length 1)
+  ;; align fields in completions
+  (setq company-tooltip-align-annotations t)
+  )
+(use-package lsp-mode
+  :ensure t
+  :commands (lsp lsp-deferred)
+  :hook (c-mode-common . lsp)
+  :custom
+  ;; Prevent lsp from inserting header decorators.
+  (lsp-clients-clangd-args '("--header-insertion-decorators=0" "--header-insertion=never"))
+  :init
+  ;; Enable easy local renaming using LSP
+  (bind-key "C-x l" 'lsp-rename)
+  :config
+  ;; The CAPF back-end provides a bridge to the standard
+  ;; completion-at-point-functions facility, and thus works with any major mode
+  ;; that defines a proper completion function.
+  (setq lsp-completion-provider :capf)
+  (add-hook 'go-mode-hook #'lsp-go-install-save-hooks))
+
+(use-package lsp-ui :commands lsp-ui-mode)
+(use-package helm-lsp :commands helm-lsp-workspace-symbol
+  :config
+  (define-key lsp-mode-map [remap xref-find-apropos] #'helm-lsp-workspace-symbol))
+(use-package lsp-treemacs :commands lsp-treemacs-errors-list)
+```