Add allowed-expressions flag

[3timeslazy]

Hi @leighmcculloch,

First of all, thank you for your work!

I noticed that a lot of people asking for exceptions for different frequently used expressions, such as strings.Replace or template.Must. I myself would be happy if the linter could ignore certain expressions rather than putting nolint tag each time or disabling the linter entirely. But I think manually adding exceptions is not scalable, so I made this PR as a proposal of a new allowed-expressions flag.

The format of the flag is a comma separated list of allowed expressions. Each expression has a format of name.Selector. An example: --allowed-expressions=regexp.MustCompile,template.Must.

If the given list is invalid, it is ignored.

Please, let me know what you think.

Thanks!

[leighmcculloch]

Hi @3timeslazy! Thanks for opening the change. I think the direction this linter should go in is to focus on preventing the mutation of package level variables as documented in the linked issue below. While allowed expressions would get a long way there, if we did the below, no configuration would be required.

• Proposal: Change linter to allow globals and disallow mutation of global variables #41