Chromium Docs - Emacs (original) (raw)

Debugging

Linux Debugging has some Emacs-specific debugging tips.

Syntax-error Highlighting

Ninja users get in-line highlighting of syntax errors using flymake.el on each buffer-save:

(load-file "src/tools/emacs/flymake-chromium.el")

ycmd (YouCompleteMe) + flycheck

emacs-ycmd in combination with flycheck provides:

• advanced code completion
• syntax checking
• navigation to declarations and definitions (using ycmd-goto) based on on-the-fly processing using clang. A quick demo video showing code completion and flycheck highlighting a missing semicolon syntax error:

Requirements

• Your build system is set up for building with clang or wrapper+clang

Setup

1. Clone, update external git repositories and build.sh ycmd from https://github.com/ycm-core/YouCompleteMe into a directory, e.g. ~/dev/ycmd
   • The ycmd packaging changed, the server is in a different location. To build it, run:
     cd ~/dev/ycmd
     git submodule update --init --recursive
     python3 install.py --clang-completer
2. Test ycmd by running ~/dev/ycmd$ python third_party/ycmd/__main__.py --options_file /tmp/test.json. The options file can be created with e.g. echo '{"hmac_secret": "1234567812345678"}' > /tmp/test.json. The server should start normally.
3. Install the following packages to emacs, for example from melpa:
   • ycmd
   • company-ycmd
   • flycheck-ycmd
4. More info on configuring emacs-ycmd
   1. Assuming your checkout of Chromium is in ~/dev/blink, i.e. this is the directory in which you find the srcfolder, create a symbolic link as follows:
      cd ~/dev/blink
      ln -s src/tools/vim/chromium.ycm_extra_conf.py .ycm_extra_conf.py
   2. Add something like the following to your init.el

;; ycmd

;;; Googlers can replace a lot of this with (require 'google-ycmd).

(require 'ycmd) (require 'company-ycmd) (require 'flycheck-ycmd)

(company-ycmd-setup) (flycheck-ycmd-setup)

;; Show completions after 0.15 seconds (setq company-idle-delay 0.15)

;; Activate for editing C++ files (add-hook 'c++-mode-hook 'ycmd-mode) (add-hook 'c++-mode-hook 'company-mode) (add-hook 'c++-mode-hook 'flycheck-mode)

;; Replace the directory information with where you downloaded ycmd to (set-variable 'ycmd-server-command (list "python3" (substitute-in-file-name "$HOME/dev/ycmd/third_party/ycmd/ycmd/main.py")))

;; Edit according to where you have your Chromium/Blink checkout (add-to-list 'ycmd-extra-conf-whitelist (substitute-in-file-name "$HOME/dev/blink/.ycm_extra_conf.py"))

;; Show flycheck errors in idle-mode as well (setq ycmd-parse-conditions '(save new-line mode-enabled idle-change))

;; Makes emacs-ycmd less verbose (setq url-show-status nil)

Troubleshooting

• If no completions show up or emacs reports errors, you can check the *ycmd-server* buffer for errors. See the next bullet point for how to handle “OS Error: No such file or directory”
• Launching emacs from an OS menu might result in a different environment so that ycmd does not find ninja. In that case, you can use a package like exec-path from shell and add the following to your init.el:

(require 'exec-path-from-shell) (when (memq window-system '(mac ns x)) (exec-path-from-shell-initialize))

• ycmd depends on the installed version of python. For googlers running gLinux, a system update may have changed the python version. In this case, you need to recompile ycmd first.

ff-get-other-file

There's a builtin function called ff-get-other-file which will get the “other file” based on file extension. I have this bound to C-o in c-mode ((local-set-key "\C-o" 'ff-get-other-file)). While “other file” is per-mode defined, in c-like languages it means jumping between the header and the source file. So I switch back and forth between the header and the source with C-o. If we had separate include/ and src/ directories, this would be a pain to setup, but this might just work out of the box for you. See the documentation for the variable cc-other-file-alist for more information.

One drawback of ff-get-other-file is that it will always switch to a matching buffer, even if the other file is in a different directory, so if you have A.cc,A.h,A.cc(2) then ff-get-other-file will switch to A.h from A.cc(2) rather than load A.h(2) from the appropriate directory. If you prefer something (C specific) that always finds, try this:

(defun cc-other-file() "Toggles source/header file" (interactive) (let ((buf (current-buffer)) (name (file-name-sans-extension (buffer-file-name))) (other-extens (cadr (assoc (concat "\." (file-name-extension (buffer-file-name)) "\'") cc-other-file-alist)))) (dolist (e other-extens) (if (let ((f (concat name e))) (and (file-exists-p f) (find-file f))) (return))) ) )

Note: if you know an easy way to change the ff-get-other-file behavior, please replace this hack with that solution! - stevenjb@chromium.org

Use Google's C++ style!

We have an emacs module, google-c-style.el, which adds c-mode formatting. Then add to your .emacs:

(load "/<path/to/chromium>/src/third_party/clang-format/script/clang-format.el") (add-hook 'c-mode-common-hook (function (lambda () (local-set-key (kbd "TAB") 'clang-format-region))))

Now, you can use the

key to format the current line (even a long line) or region.

BUILD.gn and .gni files

BUILD.gn and gni files are supported by the official gn-mode which can be enabled with:

(load-file "src/tools/emacs/gn.el")

Mojom IDL (.mojom files)

Mojom files are supported by mojom-mode, which can be enabled with:

(load-file "/<path/to/chromium>/src/tools/emacs/mojom-mode.el")

Alternatively, you can require the feature. (See emacs documentation on Named Features.)

(add-to-list 'load-path "/<path/to/chromium>/src/tools/emacs/") (require 'mojom-mode)

Highlight long lines

One nice way to highlight long lines and other style issues:

(require 'whitespace) (setq whitespace-style '(face indentation trailing empty lines-tail)) (setq whitespace-line-column nil) (set-face-attribute 'whitespace-line nil :background "purple" :foreground "white" :weight 'bold) (global-whitespace-mode 1)

Note: You might need to grab the latest version of whitespace.el.

deep nesting

A couple of helpers that show a summary of where you are; the first by tracing the indentation hierarchy upwards, the second by only showing #ifs and #elses that are relevant to the current line:

(defun ami-summarize-indentation-at-point () "Echo a summary of how one gets from the left-most column to POINT in terms of indentation changes." (interactive) (save-excursion (let ((cur-indent most-positive-fixnum) (trace '())) (while (not (bobp)) (let ((current-line (buffer-substring (line-beginning-position) (line-end-position)))) (when (and (not (string-match "^\s-$" current-line)) (< (current-indentation) cur-indent)) (setq cur-indent (current-indentation)) (setq trace (cons current-line trace)) (if (or (string-match "^\s-}" current-line) (string-match "^\s-*else " current-line) (string-match "^\s-*elif " current-line)) (setq cur-indent (1+ cur-indent))))) (forward-line -1)) (message "%s" (mapconcat 'identity trace "\n")))))

(require 'cl) (defun ami-summarize-preprocessor-branches-at-point () "Summarize the C preprocessor branches needed to get to point." (interactive) (flet ((current-line-text () (buffer-substring (line-beginning-position) (line-end-position)))) (save-excursion (let ((eol (or (end-of-line) (point))) deactivate-mark directives-stack) (goto-char (point-min)) (while (re-search-forward "^#\(if\|else\|endif\)" eol t) (if (or (string-prefix-p "#if" (match-string 0)) (string-prefix-p "#else" (match-string 0))) (push (current-line-text) directives-stack) (if (string-prefix-p "#endif" (match-string 0)) (while (string-prefix-p "#else" (pop directives-stack)) t)))) (message "%s" (mapconcat 'identity (reverse directives-stack) "\n"))))))

find-things-fast

erg wrote a suite of tools that do common operations from the root of your repository, called Find Things Fast. It contains ido completion over git ls-files (or the svn find equivalent) and grepsource that only git greps files with extensions we care about (or the equivalent the find | xargs grep statement in non-git repos.)

vc-mode and find-file performance

When you first open a file under git control, vc mode kicks in and does a high level stat of your git repo. For huge repos, especially WebKit and Chromium, this makes opening a file take literally seconds. This snippet disables VC git for chrome directories:

; Turn off VC git for chrome (when (locate-library "vc") (defadvice vc-registered (around nochrome-vc-registered (file)) (message (format "nochrome-vc-registered %s" file)) (if (string-match ".chrome/src." file) (progn (message (format "Skipping VC mode for %s" % file)) (setq ad-return-value nil) ) ad-do-it) ) (ad-activate 'vc-registered) )

git tools

We're collecting Chrome-specific tools under tools/emacs. See the files there for details.

• trybot.el: import Windows trybot output into a compilation-mode buffer.

ERC for IRC

See ErcIrc.

Compilation with M-x compile

It's usually useful to first find the top directory with locate-dominating-file, and run M-x compile

(defun chromium-compile () "Run compile for chromium." (interactive) (let ((chrome-dir (locate-dominating-file "." "chrome/BUILD.gn"))) (when chrome-dir (let* ((default-directory chrome-dir)) (compile "ninja -C out/Debug chrome chrome_sandbox ")))))