Add regex support to Lua lexer (#1403)

The Lua lexer does not currently provide any support for tokenising
regular expressions. This commit adds support for regular expressions
using code based on the regular expression rules in the JavaScript
lexer.

lib/rouge/lexers/lua.rb

@@ -72,7 +72,10 @@ def builtins
 
         rule %r([A-Za-z_][A-Za-z0-9_]*(\.[A-Za-z_][A-Za-z0-9_]*)?) do |m|
           name = m[0]
-          if self.builtins.include?(name)
+          if name == "gsub"
+            token Name::Builtin
+            push :gsub
+          elsif self.builtins.include?(name)
             token Name::Builtin
           elsif name =~ /\./
             a, b = name.split('.', 2)
@@ -98,6 +101,41 @@ def builtins
         rule %r(\(), Punctuation, :pop!
       end
 
+      state :gsub do
+        rule %r/\)/, Punctuation, :pop!
+        rule %r/[(,]/, Punctuation
+        rule %r/\s+/, Text
+        rule %r/"/, Str::Regex, :regex
+      end
+
+      state :regex do
+        rule %r(") do
+          token Str::Regex
+          goto :regex_end
+        end
+
+        rule %r/\[\^?/, Str::Escape, :regex_group
+        rule %r/\\./, Str::Escape
+        rule %r{[(][?][:=<!]}, Str::Escape
+        rule %r/[{][\d,]+[}]/, Str::Escape
+        rule %r/[()?]/, Str::Escape
+        rule %r/./, Str::Regex
+      end
+
+      state :regex_end do
+        rule %r/[$]+/, Str::Regex, :pop!
+        rule(//) { pop! }
+      end
+
+      state :regex_group do
+        rule %r(/), Str::Escape
+        rule %r/\]/, Str::Escape, :pop!
+        rule %r/(\\)(.)/ do |m|
+          groups Str::Escape, Str::Regex
+        end
+        rule %r/./, Str::Regex
+      end
+
       state :escape_sqs do
         mixin :string_escape
         mixin :sqs

spec/visual/samples/lua

@@ -258,3 +258,6 @@ end
 acc = Account.create(1000)
 acc:withdraw(100)
 
+if
+   url = url:gsub("^['\"]", ""):gsub("['\"]$", "")
+end