A few weeks ago, shortly after GO111MODULE=on became the default, I got to watch Rob using it. One problem he had was that when he worked in preexisting GOPATH directories, or just directories newly created for the purpose of testing one bug or another, there was no go.mod, so every go command reresolved "latest" for any imported dependencies. This made things much slower than they are intended to be (that is, much slower than they are when there is a go.mod).

I think we probably need to rethink what we do without any go.mod. There needs to be some place for the go command to write down its decisions from one command to the next. When people say "modules are slow" I wonder if this case is one of the things they mean.

/cc @bcmills @jayconrod @ianthehat