Regression in docopt package

[dom96]

I pulled and rebootstrapped recently and now my project which uses the docopt package is failing to compile with this error:

/Users/dom/.nimble/pkgs/docopt-0.6.4/docopt.nim(310, 15) template/generic instantiation from here
/Users/dom/projects/nim/lib/system.nim(2217, 6) Error: '==' can have side effects

Steps to reproduce:

nimble install docopt
nim c file.nim

Where file.nim is the example from here.

[dom96]

Works at 4c683e9 in case that helps.

[Araq]

docopt needs to be fixed, the compiler is correct as far as I can tell.

[singularperturbation]

FYI - I ran into this and found that this is fixed by docopt/docopt.nim#27.
A new release (docopt > 0.6.4) containing these changes has not yet been made, but I was able to work around it by installing from HEAD.