In the language specification: https://github.com/puppetlabs/puppet-specifications/blob/master/language/expressions.md#function-calls
under the "statement style" subhead, there's a list like:
Where "error" is wrong and don't exist. There are also several similar functions that aren't listed. cf. http://docs.puppetlabs.com/references/latest/configuration.html#loglevel
We should allow the 'err' function to be called as a statement. The remaining logging functions are almost never used and should continue to require parentheses.
risk: medium (qa manual validate only for now)
severity: low (work arounds exist)
test layer: acceptance (unit test only confirms parser transform)