Semantic Mode
Table of Contents
| Author | Lee Hinman (leehinman@fastmail.com) |
| Date | 2017-02-22 09:08:35 |
1 Introduction
Semantic is part of CEDET, which stands for "Collection of Emacs Development Environment Tools". There are other tools in CEDET other than semantic, but today that's all we're going to talk about.
CEDET comes with Emacs, which means that Semantic is included in Emacs. However, the stand-alone version of CEDET includes some semantic features not yet bundled with Emacs itself.
1.1 What is Semantic?
Semantic is all of the pieces and parts needed for doing parsed text analysis in Emacs. It includes
- Lexer
- Parser and Incremental Parser1
- Parser-Generator
- Database used for storing parsed information
- Idle services and tools
It allows Emacs to parse source code for semantic information, and use that information in a variety of ways.
1.2 Supported languages
Out of the box, it supports:
- Emacs Lisp
- C/C++
- C#
- Java
- Python
- Erlang
- awk
- Makefile
- Scheme
- HTML
- Texinfo
- Javascript
- dot (graphviz)
2 How to install Semantic
Check what version of Semantic you have bundled with Emacs by doing M-x
cedet-version, you should see something like this table:
CEDET Version: 2.0
Requested File Loaded
Package Version Version Version
------------------------------------------------------------
cedet: 2.0 ok ok
eieio: 1.4 nil ok
semantic: 2.2 ok ok
srecode: 1.2 ok ok
ede: 1.2 2.0 2.0
cogre: 1.2 ok ok
cedet-contrib: 1.2 nil Not Loaded
You have have to execute (require 'cedet) if cedet-version doesn't
immediately work.
Personally, I find it the easiest to run CEDET from source, because I use some
of the features that don't come with the bundled version, in order to do that, I
clone the repository and set up a early in my init.el configuration
(replace ~/src/elisp/cedet with whatever path you want)
git clone http://git.code.sf.net/p/cedet/git ~/src/elisp/cedet
cd ~/src/elisp/cedet
make
And then early4 in your init.el file:
;; Load a custom version of cedet, if available (when (file-exists-p "~/src/elisp/cedet/cedet-devel-load.el") (load "~/src/elisp/cedet/cedet-devel-load.el"))
Unfortunately there is no MELPA or ELPA package for this, though work is underway to merge CEDET into Emacs itself entirely, so that it can be a native feature instead of half-missing.
Once you've set up CEDET as above, check out cedet-version again and see if
it's the same (or different, as long as its installed you should be good to go).
3 How to set up Semantic in your Emacs configuration
Semantic has a lot of different minor modes that can be toggled on and off as needed, they follow the form of
global-semantic-*-mode
These can be used individually, but the best way to configure these is to set
the semantic-default-submodes variable to be a list of the modes you want to
enable, the default value for this variable is
'(global-semantic-idle-scheduler-mode global-semanticdb-minor-mode)
Which is fine, but you may want to add modes to it
(setq semantic-default-submodes '(;; Perform semantic actions during idle time global-semantic-idle-scheduler-mode ;; Use a database of parsed tags global-semanticdb-minor-mode ;; Decorate buffers with additional semantic information global-semantic-decoration-mode ;; Highlight the name of the function you're currently in global-semantic-highlight-func-mode ;; show the name of the function at the top in a sticky global-semantic-stickyfunc-mode ;; Generate a summary of the current tag when idle global-semantic-idle-summary-mode ;; Show a breadcrumb of location during idle time global-semantic-idle-breadcrumbs-mode ;; Switch to recently changed tags with `semantic-mrub-switch-tags', ;; or `C-x B' global-semantic-mru-bookmark-mode))
Then it's as simple as adding in your configuration
(add-hook 'emacs-lisp-mode-hook 'semantic-mode) (add-hook 'python-mode-hook 'semantic-mode) (add-hook 'java-mode-hook 'semantic-mode) (add-hook 'c-mode-hook 'semantic-mode) ;; etc etc (add-hook 'prog-mode-hook 'semantic-mode)
4 How to use Semantic
Most semantic keybindings are behind the prefix
C-c ,
| Command | What it does | Bound to |
|---|---|---|
semantic-mrub-switch-tags |
show the most recently edited tags | C-x B |
semantic-ia-show-doc |
show documentation for the symbol at point | |
semantic-ia-show-summary |
show summary for the symbol at point | |
semantic-ia-describe-class |
describe the prompted class | |
semantic-ia-fast-jump |
jump to the location of a tag | |
semantic-symref |
find references to the symbol at point | C-c , G |
semantic-complete-jump |
jump to the location of a tag | C-c , J |
semantic-complete-jump-local |
jump to the location of a local tag | C-c , j |
semantic-complete-analyze-inline |
completion based on semantic information | C-c , SPC |
semantic-analyze-possible-completions |
completion possibilities | C-c , l |
semantic-force-refresh |
force semantic to reparse buffers | =C-c , ,= |
To see what sort of information semantic can parse from a buffer, try M-x bovinate.
5 Demo(s)
5.1 Java (my use)
public class Person { private int favoriteNumber; private String name; Person(String name, int favoriteNumber) { this.favoriteNumber = favoriteNumber; this.name = name; } public String getName() { return this.name; } public int getFavoriteNumber() { return this.favoriteNumber; } public void sayHi() { Person p = new Person("Lee", 42); System.out.println("Hi my name is " + this.name + " and my favorite number is " + this.favoriteNumber); } }