Robe

Robe is a code assistance tool that uses a Ruby REPL subprocess with your application or gem code loaded, to provide information about loaded classes and modules, and where each method is defined.

Generally, you'll want to start with M-x inf-ruby-console-auto or with M-x robe-start (which will offer to call the former function as well if there is no Ruby console running). Some interactive commands provided by Robe will also offer to launch it first.

The exceptions are code completion and eldoc, which only work if the server is already running. To launch it, type M-x robe-start.

As you change the code in your project, you'll want to update the running process. To load the current file, type C-c C-l (ruby-load-file), see inf-ruby for more commands. When you're working on a Rails project, you can type C-c C-k instead to reload the whole environment at once.

Features

• Jump to method definition
• Jump to super or a constructor called at point
• Jump to a module/class/constant definition
• Display method documentation
• Display information about method called at point using ElDoc
• Method and constant name completion
• Jumping and completion for instance and local variable names, using simple regexp search in the current file

To see the available commands, type M-x describe-package RET robe RET.

Details

When performing one of the commands defined here, we either need to narrow the method name at point down to a specific method in a specific module, or enumerate the possible method names or constants allowed at point (for code completion).

To do that, we look at the contents of the buffer, and the context at point: in which method it is, of which class, and if it's in singleton class context. Then we look at the method call at point.

If the method call target is implicit (there's no target or the method is super), or the call target is obvious (Foo.new, self.foo), then we first try to look for the definition in the inheritance hierarchy of the target class. Otherwise, or if the initial search yields no result, scan all defined classes and modules.

Depending on the command, if the result is ambiguous, you're either prompted to resolve the ambiguity manually, or the results are merged together.

Install

Set up MELPA if you haven't already, then type M-x package-install RET robe RET.

In the init file:

(add-hook 'ruby-mode-hook 'robe-mode)
(add-hook 'ruby-ts-mode-hook 'robe-mode)

or

(global-robe-mode)

Dependencies

• pry >= 0.10
• pry-doc >= 0.6.0 (for stdlib docs on MRI; optional)
• Ruby must be compiled with Readline support (how to check).
• With Ruby 3.3, the gem readline-ext is also needed.

The alternative to the last two items is to configure the app not to use the Pry shell (at least when inside Emacs) while still keeping pry available for loading.

Note that if your project is using Bundler, all dependencies have to be in the Gemfile.

Completion

company-mode (screenshot):

(eval-after-load 'company
  '(push 'company-robe company-backends))

Built-in completion (triggered with C-M-i) is also supported, no extra setup required.

Both of the above work only when the connection to the Ruby subprocess has been established. To do that, either use one of the core Robe commands, or type M-x robe-start.

Integration with rvm.el

rvm.el may not have activated the correct project Ruby before robe-start runs.

Either manually run M-x rvm-activate-corresponding-ruby before starting Robe, or advise inf-ruby-console-auto to activate rvm automatically.

(advice-add 'inf-ruby-console-auto :before #'rvm-activate-corresponding-ruby)

Compatibility

• Tested in Emacs 27.1+, with Ruby 2.3-3.3, on GNU/Linux.
• But see the section Dependencies above.
• Essential features work with JRuby, though the startup is longer.
• Mostly works on MS Windows, with minor glitches.
• Built-in ruby-mode or ruby-ts-mode (Emacs 29+) work best, enh-ruby-mode is not recommended (it breaks the detection of the current context, see #47 and enhanced-ruby-mode#96).

Notes

• We can't jump to methods defined in C (such as most of the core classes). To read their docs, install pry-doc or add it to your Gemfile.
• We can't jump to lazily defined methods, such as model.column or find_by_ ActiveRecord methods, before they've been called. This is treatable, but low priority.
• Jumping to methods defined with Module#delegate just brings us to the place where delegate is called, which is accurate, but often less than useful.
• To work on several projects in the same Emacs session, you'll have to create the Ruby console for each project after the first one manually with M-x inf-ruby-console-auto. Otherwise, the first one will be used for all Ruby files, with suboptimal results.
• We may get the context wrong for code inside a block if the method it's passed to uses instance_eval or instance_exec.

TODO

• Handle delegate and send, Class.new.method and self.class.method.
• For methods defined through macros, optionally jump to where the macro was called, instead of its definition?
• Apropos search for classes and methods.
• Better type inference.

Copying

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with GNU Emacs; see the file COPYING. If not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.