IDE-like Emacs

2017-08-18

Don't let the default bare configuration of Emacs scare you away: It's highly customizable outside (see e.g. better-defaults for what aims to be improvements over default settings), cross-platform, and there are a large number of great packages such as Magit and org-mode. In my opinion, just Magit alone makes your initial investment into learning Emacs worth it. As a plus, when stuck working on a Windows machine, you can still pop open Emacs and make the best of the situation. But Emacs by itself is just a text editor and not a full-blown IDE. But with a little configuration and installing packages, it can be made to act like one.

Initially when I moved the switch to Emacs as my default text editor back in ~2009, I was almost exclusively working with C++. I spent consider about of time setting up the "perfect" configuration for code-completion and jumping to definitions with cedet and semantic combo, which on larger code bases resulted in a pain-stakingly slow code-completion and error- prone jump-to-definition with no support for c++11 standards onward.

These days the three class of languages I frequently use are c++, python, js/nodejs, and the the out-of-the-box code completion with emacs for these languages are minimal or non-existent. But with minimal effort and using existing toolset, you can get a uniform-ish and decent IDE-like behavior in Emacs.

C and C++ : RTags

Any decent code completion for Emacs seems to require a daemon running in the background. By far the best solution I have used for C and C++ is RTags. As a plus, with an initial configuration in place, it will "just work" if the project uses cmake as its build tool.

Installation

I use rtags with company as opposed to auto-complete as the text completion framework. This made the initial build, installation, and setup for getting rtags working was a pretty frustrating experience. Specifically, what I learned was that the code completion for some reason wasn't working if working under /tmp. My final setup documetation was as follows:

Install prerequisites. For this installation I'm using OpenSUSE
```
zypper in gcc-c++ clang clang-devel llvm llvm-devel cmake
```

Build rtags

> git clone --recursive https://github.com/Andersbakken/rtags.git
> cd rtags && mkdir build && cd build
> cmake ..
> cmake -DCMAKE_EXPORT_COMPILE_COMMANDS=1 .
> make -j 4

Copy bin files
```
> cp ./bin/* ~/bin/
```
Install emacs prerequisites from melpa: company, rtags, company-rtags

Update emacs init scripts

;; use and initalize package if haven't already done so
(require 'cl)
(require 'rtags)
(require 'company)

(define-key c-mode-base-map (kbd "M-.")
  (function rtags-find-symbol-at-point))
(define-key c-mode-base-map (kbd "M-,")
  (function rtags-find-references-at-point))
(rtags-enable-standard-keybindings)

(setq rtags-autostart-diagnostics t)
(rtags-diagnostics)
(setq rtags-completions-enabled t)
(push 'company-rtags company-backends)
(global-company-mode)
(define-key c-mode-base-map (kbd "<C-tab>") (function company-complete))

Check if everything's working fine.
```
> rdm &
> cd </path/to/rtags/build/directory>
> rc -J ../
```
If no errors, then pop open a new emacs session, and navigate to /path/to/rtags/src/rdm.cpp and verify that symbol combinations work.

Video of using rtags inside its own codebase:

Troubleshooting

It took me about 3 hours to finally learn that rtags will NOT work for code under /tmp/. Error code:
```
Shouldn't index <FILE_NAME> because of excluded
        filter
```
.
There seem to be issues with rdm, rc, and rp being symbolic links to executables. The error I was seeing "find process for pid".
Including the rtags/build/bin directory to path seems to have issues with code completion. While I know there is a make install command, I ended up manually copying the bin files to my ~/bin/ directory for everything to function.
Having wrappers rtags/bin/ alias gcc/g++ seemed to be causing more issues for code completion.
Must include (require 'cl) in emacs config.

Python

I use jedi and company mode for python. To get started, read the official documentation, or:

Install prerequisites
```
su -c "zypper in python3-virtualenv"
```

Start a project

> mkdir my-project-name
> cd my-project-name
> virtualenv-3.7 env # replace with appropriate virtualenv version

Activate the virtual environment and install jedi

> . ./env/bin/activate
> pip install jedi

Move contents to ~/bin/jedi-env for convenience
Install elpy in emacs. I generally install packages from melpa. Pop open emacs and do M-x package-list-packages and install elpy

Update ~/.emacs.d/ config files

;...
(elpy-enable)
(add-hook 'python-mode '(lambda()
(set (make-local-variable 'company-backends '(elpy-company-backend)))
(company-mode)))

(defun hf/python-mode-hook ()
  (add-to-list 'company-backends 'company-jedi)
  (require 'pyvenv)
  (pyvenv-activate "~/bin/jedi-env/")
  (setq jedi:setup-keys t)
  (setq jedi:complete-on-dot t)
  (setq jedi:use-shortcuts t)
  (jedi:setup)
  )

(add-hook 'python-mode-hook 'hf/python-mode-hook)
;...

If for some reason pyvenv is not enabled, try explicitely enabling jedi virtual environment
```
M-x pyvenv-activate <enter>
```
and direct to parent directory containing the virtual environment.
Everything should work now, e.g.
1. M-. should jump to definition
2. C-M i should force call elpy-company-backend and autocomplete at point
3. C-c ? show docstring of object at given point

Below shows a demo of how it works. Consider playing the video in fullscreen mode and look at messages in the minibuffer especially when there is a small pause.

Javascript and Node.js

Reference

Install tern globally
```
su -c "npm install -g tern"
```
Install company-tern in Emacs

Add following to ~/.emacs.d/init.el

(require 'company-tern)
(eval-after-load 'company
   '(add-to-list 'company-backends 'company-tern))
(add-hook 'js2-mode-hook (lambda () (tern-mode t)))

Create .tern-project in your root project directory with following contents

{
    "plugins": {
        "node": {
    },
        "libs": [
    ]
  }
}

Demo of how it works: