[TOC]
Linux Debugging has some Emacs-specific debugging tips.
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:
- Your build system is set up for building with clang or wrapper+clang
- 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
- 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. - Install the following packages to emacs, for example from melpa:
ycmd
company-ycmd
flycheck-ycmd
- More info on configuring emacs-ycmd
-
Assuming your checkout of Chromium is in
~/dev/blink
, i.e. this is the directory in which you find thesrc
folder, create a symbolic link as follows:cd ~/dev/blink ln -s src/tools/vim/chromium.ycm_extra_conf.py .ycm_extra_conf.py
-
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)
- 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 yourinit.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.
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! - [email protected]
We have an emacs module, google-c-style.el, which adds c-mode formatting. Then add to your .emacs:
(load "/<path/to/chromium>/src/buildtools/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
<Tab>
key to format the current line (even a long line) or region.
BUILD.gn and gni files are supported by the official gn-mode which can be enabled with:
(load-file "src/tools/emacs/gn.el")
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.
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 #if
s and
#else
s 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"))))))
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.)
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)
)
We're collecting Chrome-specific tools under tools/emacs
. See the files there
for details.
trybot.el
: import Windows trybot output into acompilation-mode
buffer.
See ErcIrc.
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 ")))))