issue #298 - go 1.23 go/types alias change

[xanderflood]

From the go 1.23 changelog:

By default, go/types now produces Alias type nodes for type aliases. This behavior can be controlled by the GODEBUG gotypesalias flag. Its default has changed from 0 in Go 1.22 to 1 in Go 1.23.

Previously, the AST node for an alias-typed value would point directly at the underlying type, and counterfeiter would consequently see the underlying type and load the correct package(s) for that type.

In go 1.23 or newer, when processing such a node, we get the unrecognized *types.Alias type, and fall through to the default case, which prints an error and moves on. Then, when it comes time to render that type in (for instance) a method signature, it is rendered as a simple name, since the package alias was never added to the Imports struct.

This change ensures that we load the appropriate package for each alias type. This resolves a bug introduced by go 1.23, and also slightly changes the behavior from previous versions of counterfeiter, which implicitly resolved alias types and replaced them with the RHS (right-hand side) of the alias assignment. If we wanted to preserve that behavior, I believe we could instead use:

case *types.Alias:
    f.addImportsFor(t.Rhs())

However, I think using the actual alias (mimicking the interface being mocked) is preferable to resolving the alias.

[joefitzgerald]

Thanks for the contribution! I will take a look tonight.

[joefitzgerald]

The change looks good to me. I added an integration test to prevent any regression. This is released in v6.10.0.