Support go modules

[joefitzgerald]

This PR is intended to support go modules and set the stage for future changes (namely, to permit a variety of different fake types to be generated).

In effect, it's a total rewrite.

• We have switched from go/ast to text/template to generate the output from counterfeiter. This means that in the future, people will be able to write their own templates and supply them to counterfeiter.
• We have switched from go/parser to go/packages to load types. go/packages is module aware.
  • The go team officially supports N-1 (at the time of this PR, go 1.11 is out, and the go team support go 1.10 and go 1.11. This means that counterfeiter is only tested to work with go 1.10 or go 1.11 at the time of this PR (although we expect to support future versions.
• counterfeiter is now a go module

We would very much appreciate it if you can try out this branch and validate that your tests continue to function after using it.

Outstanding items:

• Support "package mode" (generate an interface and fake for an entire package)
• Ensure Windows CI succeeds
• Remove unused code
• Enhance test coverage; we've used an integration / acceptance test approach for the rewrite, and now we need to lock things in so we can refactor
• Ensure integration tests work in go 1.11 module mode

Fixes #90

[vito]

Looking forward to this! Just tried the branch out on Concourse, and noticed that the templates should be using text/template rather than html/template, otherwise the fakes end up with <-chan foo instead of <-chan foo. 🙂 Aside from that everything worked!

[joefitzgerald]

Nice catch on the html/template error @vito, thanks! I think it may have happened as I extracted the templates into their own files.

Have quite a bit more progress to push up tomorrow.

[maxbrunsfeld]

Awesome work on this @joefitzgerald and @zmb3!

[joefitzgerald]

golang/go#24661

[glyn]

Thanks so much for this PR. It provided an escape route when moving some code to a go modules repo and found that mockery was broken.