Adding back R/Rebol heuristics

lib/linguist/heuristics.rb

@@ -350,5 +350,13 @@ module Linguist
         Language["xBase"]
       end
     end
+
+    disambiguate ".r", ".R" do |data|
+      if /\bRebol\b/i.match(data)
+        Language["Rebol"]
+      elsif data.include?("<-")
+        Language["R"]
+      end
+    end
   end
 end

test/test_heuristics.rb

@@ -179,4 +179,11 @@ class TestHeuristcs < Minitest::Test
       "xBase" => all_fixtures("xBase", ".ch")
     })
   end
+
+  def test_r_by_heuristics
+    assert_heuristics({
+      "R" => all_fixtures("R", "*.r") + all_fixtures("R", "*.R"),
+      "Rebol" => all_fixtures("Rebol", "*.r")
+    })
+  end
 end