Ability to have a single mock implement multiple interfaces

[jpopadak]

For some Go code, a single struct might implement multiple interfaces.

For example:

type IType1 interface {
   Method1() error
}

type IType2 interface {
   Method2() string
}

func DoWork(input IType1) error {
   if err := input.Method1(); err != nil {
      return err
   }
   if i2, ok := input.(IType2); !ok {
      return error.New("does not implement IType2")
   }

   fmt.Println(i2.Method2())
   return nil
}

This helps with plug and play code, where you are accepting outside objects to execute logic on more than one interface.

Suggested generate command can be: pegomock generate github.com/path/to/pkg IType1 github.com/path/to/other/pkg IType2

[petergtz]

Hey @jpopadak, very interesting use case. Have you worked around it so far by defining a interface along the lines of

type IType12 interface {
  IType1
  IType2
}

And generating the mock based on that or how did you work around it?

From the top of my head I don't remember if the command you suggested is unambiguous, specifically because in the past you could generate multiple mocks by specifying multiple interfaces. Have you checked?

[jpopadak]

I have not tried doing that, although that could work too.

In my case, there were only 2 methods, one for each interface, so I created a stub struct with the implemented methods as needed.

[petergtz]

@jpopadak So I've checked the CLI: in theory it's possible to implement the command you suggested. However, I'm not convinced yet, that we should really add it: it will make the generate command quite a bit more complex. Not only implementation-wise, but also its usage, because you can now provide multiple space-separated interfaces + prefix each one with a package path, also space-separated. I think there is real potential for a user to get this wrong without understanding what is actually wrong. Compared to that, adding a compound interface to your test package as I suggested above seems like the lesser evil. What do you think?

[jpopadak]

I honestly think the best route forward is the one you suggested here: https://github.com/petergtz/pegomock/issues/81#issuecomment-478749658

Might be useful in your documentation, but it's an obvious solution I didn't think about. 🙄

[petergtz]

Agree, that could be part of the documentation. Let's leave this issue open and I'll see where it fits in best. (Will probably take a little longer this time as I'm a bit busy...)