What if you first do
go install domain
And then invoke go generate on impl directory?

You wrote domain/domain.go but your impl/impl.go imports test/domain. Can you confirm that your impl.go is importing the domain package that contains domain/domain.go?

@ianlancetaylor Yes. I wrote the code above as an example, but did a bad job of making it clear. I originally encountered the issue in this code (you need to checkout that specific branch if you want to see for yourself).

To @minux's point, yes, running go install github.com/obeattie/sase/domain first does fix this. Is this, in fact, expected behaviour?

It seems a lot of tools expect you to have installed all dependent
packages, so in that sense, it's expected behavior, as of today.

However, that is certainly not ideal, given that source code is
available, it probably should fallback to source code if the installed
package is not available or stale.

I will leave the judgement to the x/tools developers.

/cc @alandonovan and @griesemer

Used directly, the type checker satisfies direct import dependencies by loading export data for installed packages. This assumes that the packages have been built and installed more recently than their source code was edited.

Because this is assumption is often false, the golang.org/x/tools/go/loader package provides a means of loading all dependencies from source code as needed. I recommend that you use that.

The stringer tool doesn't use go/loader; perhaps it should.

Expected behavior as explained above.