add interfaces flag with unit test

[kliukovkin]

This is a proposal for -interfaces flag using source mode. Using this flag it is possible to list only required interfaces to be mocked in source mode. Currently, source mode mocks all interfaces which -source file contains.

Thanks @KastenMike for raising this!

Fixes golang/mock#660

[CLAassistant]

All committers have signed the CLA.

[kliukovkin]

Hey @JacobOaks , can you please take a look?

[JacobOaks]

Hey @kliukovkin! Thanks for the PR!

I am in favor of having this feature, just two questions/comments:

• Instead of using an -interfaces flag, what do you think about having source mode read positional arguments (i.e., mockgen -source <path/to/file.go> InterfaceOne,InterfaceTwo) to align it with how reflect mode works? (If there are no positional arguments specified, we would parse all interfaces to keep backwards compatibility)
• Instead of parsing and then dropping interfaces that aren't specified, can we simply not parse ones that aren't requested? This is similar to how the exclusion flag already works and would avoid some wasted computation.

[kliukovkin]

Hey @kliukovkin! Thanks for the PR!

I am in favor of having this feature, just two questions/comments:

• Instead of using an -interfaces flag, what do you think about having source mode read positional arguments (i.e., mockgen -source <path/to/file.go> InterfaceOne,InterfaceTwo) to align it with how reflect mode works? (If there are no positional arguments specified, we would parse all interfaces to keep backwards compatibility)

• Instead of parsing and then dropping interfaces that aren't specified, can we simply not parse ones that aren't requested? This is similar to how the exclusion flag already works and would avoid some wasted computation.

Hey @JacobOaks ! Done, can you please review and let me know if that looks good?