Switch check_strings plugin to using the lexer

Had to monkey patch the lexer a bit to differentiate between single quoted
and double quoted strings, so we might have issues here down the track
supporting multiple versions of Puppet (although hopefully the lexer doesn't
change that much).

Closes #22
Closes #24

lib/puppet-lint/plugins/check_strings.rb

@@ -25,21 +25,26 @@ def test(data)
       token = tokens[token_idx]
 
       if token.first == :STRING
-        contents = token.last[:value]
-        line_no = token.last[:line]
-        variable_found = false
-
-        contents.scan(/.\$./) do |w|
-          if w.start_with? '\\'
-            next
-          elsif w.end_with? '{'
-            variable_found = true
-          else
-            warn "variable not enclosed in {} on line #{line_no}"
+        warn "double quoted string containing no variables on line #{token.last[:line]}"
+      end
+
+      if token.first == :DQPRE and token.last[:value] == ""
+        if tokens[token_idx + 1].first == :VARIABLE
+          if tokens[token_idx + 2].first == :DQPOST and tokens[token_idx + 2].last[:value] == ""
+            warn "string containing only a variable on line #{tokens[token_idx + 1].last[:line]}"
           end
         end
-        unless variable_found
-          warn "double quoted string containing no variables on line #{line_no}"
+      end
+
+      if token.first == :DQPRE
+        end_of_string_idx = tokens[token_idx..-1].index { |r| r.first == :DQPOST }
+        tokens[token_idx..end_of_string_idx].each do |t|
+          if t.first == :VARIABLE
+            line = data.split("\n")[t.last[:line] - 1]
+            if line.is_a? String and line.include? "$#{t.last[:value]}"
+              warn "variable not enclosed in {} on line #{t.last[:line]}"
+            end
+          end
         end
       end
 
@@ -48,7 +53,7 @@ def test(data)
         line_no = token.last[:line]
 
         if contents.include? '${'
-          error "single quoted string containing a variable found on line #{line_no}"
+          error "single quoted string containing a variable found on line #{token.last[:line]}"
         end
       end
     end

spec/puppet-lint/check_strings_spec.rb

@@ -27,4 +27,25 @@
     its(:warnings) { should include "string containing only a variable on line 1" }
     its(:errors) { should be_empty }
   end
+
+  describe 'variable not enclosed in {}' do
+    let(:code) { '" $gronk"' }
+
+    its(:warnings) { should include "variable not enclosed in {} on line 1" }
+    its(:errors) { should be_empty }
+  end
+
+  describe 'double quoted string nested in a single quoted string' do
+    let(:code) { "'grep \"status=sent\" /var/log/mail.log'" }
+
+    its(:warnings) { should be_empty }
+    its(:errors) { should be_empty }
+  end
+
+  describe 'double quoted string after a comment' do
+    let(:code) { "service { 'foo': } # \"bar\"" }
+
+    its(:warnings) { should be_empty }
+    its(:errors) { should be_empty }
+  end
 end