anchor.diff:      optionalString
       ;
   
  -  args = filterAttrs (name: _: name != "extraSrcs") args';
  -
     removeReferences = [
       go
     ];
  
positive.code:     if [ -z "$allowVendoredSources" ]; then
        find go/src/$goPackagePath -type d \( -name vendor -or -name Godeps \) -prune -exec rm -r {} \;
      fi
    '' + flip concatMapStrings extraSrcs ({ src, goPackagePath }: ''
      mkdir extraSrc
      (cd extraSrc; unpackFile "${src}")
      mkdir -p "go/src/$(dirname "${goPackagePath}")"
  
negative.code: # IE: programs coupled with the compiler
  , allowGoReference ? false
  
  , meta ? {}, ... } @ args:
  
  if disabled
    then throw "${name} not supported for go ${go.meta.branch}"
  