Implement the check

As both the datatype definition as the parameter default can contain
comma's we cannot rely on the `:COMMA` token to find the boundaries but
have to count parenthesis instead. This is done using a simple state
machine.

Code inspired by some of checks built in to `puppet-lint` and
`puppet-lint-param-docs`.

lib/puppet-lint/plugins/check_parameter_types.rb

@@ -0,0 +1,53 @@
+PuppetLint.new_check(:parameter_types) do
+  def check
+    (class_indexes + defined_type_indexes).each do |idx|
+      next if idx[:param_tokens].nil?
+      # https://github.com/puppetlabs/puppet-specifications/blob/master/language/catalog_expressions.md
+      # Each individual parameter in the parameter list must start with
+      # either a datatype or a variable name, so testing whether the parameter is typed
+      # is easy.
+      state = :ST_BEGIN
+      paren_stack = []
+      data_stack = []
+      idx[:param_tokens].each do |token|
+        next if [ :NEWLINE, :WHITESPACE, :INDENT, :COMMENT, :MLCOMMENT, :SLASH_COMMENT].include?(token.type)
+
+        case state
+        when :ST_BEGIN
+          paren_stack = []
+          data_stack = []
+          if (token.type == :TYPE) or (token.value =~ /^[A-Z]/)
+            state = :ST_SKIP_TYPE
+          elsif token.type == :VARIABLE
+            notify :warning, {
+              :message => "missing datatype for parameter #{idx[:name_token].value}::#{token.value}",
+              :line    => token.line,
+              :column  => token.column
+            }
+            state = :ST_SKIP
+          end
+        # skip over the parameter default which can contain complex data types with variable references
+        # so a simple comma check isn't enough, brackets must be counted.
+        when :ST_SKIP
+          if token.type == :LPAREN
+            paren_stack.push(true)
+          elsif token.type == :RPAREN
+            paren_stack.pop
+          elsif token.type == :LBRACE || token.type == :LBRACK
+            data_stack.push(true)
+          elsif token.type == :RBRACE || token.type == :RBRACK
+            data_stack.pop
+          elsif token.type == :COMMA && data_stack.empty? && paren_stack.empty?
+            state = :ST_BEGIN
+        end
+        # Datatypes cannot have variables so when a variable is found it must be
+        # end of the data type
+        when :ST_SKIP_TYPE
+          if token.type == :VARIABLE
+            state = :ST_SKIP
+          end
+        end
+      end
+    end
+  end
+end