ruby: improve chruby configuration

Look for a .ruby-version file, if it does not exist then use the
currently activated ruby.

Update documentation.

layers/+lang/ruby/README.org

@@ -60,15 +60,17 @@ specific documentation for details and caveats):
 #+END_SRC
 
 ** Ruby version management
-This layer supports the use of [[https://rvm.io/][RVM]], [[https://github.com/sstephenson/rbenv][Rbenv]], and [[https://github.com/postmodern/chruby][Chruby]].
-To enable it, set the =ruby-version-manager= var in your =~/.spacemacs=:
+This layer supports [[https://rvm.io/][RVM]], [[https://github.com/sstephenson/rbenv][Rbenv]], and [[https://github.com/postmodern/chruby][Chruby]]. You can choose the default version
+manager by setting the variable =ruby-version-manager= in your dotfile, for
+example:
 
 #+BEGIN_SRC emacs-lisp
   (defun dotspacemacs-configuration-layers ()
-     '((ruby :variables ruby-version-manager 'rbenv)))
+     '((ruby :variables ruby-version-manager 'rvm)))
 #+END_SRC
 
-Possible values are =rbenv=, =rvm= and =chruby=.
+=Tip:= You can enable different version manager for different projects by using
+directory local variables.
 
 ** Test runner
 This layer supports both =RSpec= and =ruby-test= test runners (frameworks).

layers/+lang/ruby/config.el

@@ -19,7 +19,8 @@
   "If non-nil, use `enh-ruby-mode' package instead of the built-in Ruby Mode.")
 
 (defvar ruby-version-manager nil
-  "If non nil, defines the Ruby version manager (i.e. rbenv, rvm)")
+  "If non nil, defines the Ruby version manager.
+Possible values are `rbenv', `rvm' or `chruby'.)")
 
 (defvar ruby-use-ruby-test nil
   "If non-nil, use `ruby-test-mode' package instead of `rspec-mode'.")
@@ -27,9 +28,6 @@
 (defvar ruby-test-runner 'ruby-test
   "Test runner to use. Possible values are `ruby-test' or `rspec'.")
 
-(defvar chruby-ruby-version nil
-  "If non-nil, sets chruby ruby version, see https://github.com/plexus/chruby.el for more information.")
-
 ;; Command prefixes
 
 (spacemacs/declare-prefix-for-mode 'ruby-mode "mt" "ruby/test")

layers/+lang/ruby/packages.el

@@ -13,6 +13,7 @@
 (setq ruby-packages
       '(
         bundler
+        chruby
         company
         evil-matchit
         flycheck
@@ -30,14 +31,25 @@
 (when ruby-version-manager
   (add-to-list 'ruby-packages ruby-version-manager))
 
-(defun ruby/init-chruby()
-  "Initialize Chruby mode"
+(defun ruby/init-chruby ()
   (use-package chruby
     :defer t
-    :init (dolist (hook '(ruby-mode-hook enh-ruby-mode-hook)))
-                  (add-hook hook
-                    (lambda () (chruby (if chruby-ruby-version 'chruby-ruby-version
-                                         (message "chruby version not set!!")))))))
+    :init
+    (progn
+      (defun spacemacs//enable-chruby ()
+        "Enable chruby, use .ruby-version if exists."
+        (when (equal 'chruby 'ruby-version-manager)
+          (let ((version-file-path (chruby--locate-file ".ruby-version")))
+            (require 'chruby)
+            ;; try to use the ruby defined in .ruby-version
+            (if version-file-path
+                (progn
+                  (chruby-use (chruby--read-version-from-file
+                               version-file-path))
+                  (message "Using ruby version from .ruby-version file."))
+              (message "Using the currently activated ruby.")))))
+      (spacemacs/add-to-hooks 'spacemacs//enable-chruby
+                              '(ruby-mode-hook enh-ruby-mode-hook)))))
 
 (defun ruby/init-rbenv ()
   "Initialize RBENV mode"