Linux Debugging has some Emacs-specific debugging tips.
Ninja users get in-line highlighting of syntax errors usingflymake.el on each buffer-save:
(load-file "src/tools/emacs/flymake-chromium.el")
emacs-ycmd in combination with flycheck provides:
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:
~/dev/ycmdcd~/dev/ycmd git submodule update--init--recursive python3 install.py--clang-completer
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.ycmdcompany-ycmdflycheck-ycmdAssuming your checkout of Chromium is in~/dev/blink, i.e. this is the directory in which you find thesrcfolder, create a symbolic link as follows:
cd~/dev/blinkln-s src/tools/vim/chromium.ycm_extra_conf.py.ycm_extra_conf.py
Add something like the following to yourinit.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-delay0.15);; 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-statusnil)
*ycmd-server* buffer for errors. See the next bullet point for how to handle “OS Error: No such file or directory”ycmd does not find ninja. In that case, you can use a package likeexec-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))
There's a builtin function calledff-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 variablecc-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
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
<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")
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 canrequire the feature. (See emacs documentation onNamed Features.)
(add-to-list'load-path"/<path/to/chromium>/src/tools/emacs/")(require'mojom-mode)
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-columnnil)(set-face-attribute'whitespace-linenil:background"purple":foreground"white":weight'bold)(global-whitespace-mode1)
Note: You might need to grab the latest version ofwhitespace.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#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\\)" eolt)(if(or(string-prefix-p"#if"(match-string0))(string-prefix-p"#else"(match-string0)))(push(current-line-text) directives-stack)(if(string-prefix-p"#endif"(match-string0))(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, calledFind Things Fast. It contains ido completion overgit ls-files (or the svn find equivalent) andgrepsource that only git greps files with extensions we care about (or the equivalent thefind | 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-valuenil))ad-do-it))(ad-activate'vc-registered))
We're collecting Chrome-specific tools undertools/emacs. See the files there for details.
trybot.el: import Windows trybot output into acompilation-mode buffer.SeeErcIrc.
It's usually useful to first find the top directory with locate-dominating-file, and runM-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 ")))))