gnu: Add ruby-railties.

* gnu/packages/rails.scm (ruby-railties): New variable.

gnu/packages/rails.scm

@@ -333,3 +333,30 @@ applications.")
 pattern.  Including support for multipart email and attachments.")
    (home-page "https://rubyonrails.org/")
    (license license:expat)))
+
+(define-public ruby-railties
+  (package
+   (name "ruby-railties")
+   (version "5.2.2")
+   (source
+    (origin
+     (method url-fetch)
+     (uri (rubygems-uri "railties" version))
+     (sha256
+      (base32
+       "00pnylmbz4c46mxw5lhxi8h39lndfg6fs1hpd0qd6swnjhkqsr1l"))))
+   (build-system ruby-build-system)
+   (arguments
+    '(;; No included tests
+      #:tests? #f))
+   (propagated-inputs
+    `(("ruby-actionpack" ,ruby-actionpack)
+      ("ruby-activesupport" ,ruby-activesupport)
+      ("ruby-method-source" ,ruby-method-source)
+      ("ruby-thor" ,ruby-thor)))
+   (synopsis "Rails internals, including application bootup and generators")
+   (description
+    "@code{railties} provides the core Rails internals including handling
+application bootup, plugins, generators, and Rake tasks.")
+   (home-page "https://rubyonrails.org/")
+   (license license:expat)))