[pdonis]

> "go mod download && go run ."

No: "go mod download" if I want to update dependencies; then look to see what got updated and how it will affect what I'm doing. Then "go run".

> What's the point in making `go run` error out when it already knows what dependencies to get and how to get them.

Because I don't care what "go run" knows. I care what code is going to run when I say "go run". I want that code to be the code I already know is there and understand. I don't want it to be some new code that "go run" downloads because it sees that an update to a dependency is available. Downloading that update and understanding what effects it has is something that I want to do before "go run", not as part of it.

[cpuguy83]

That is the purpose of go.mod/go.sum. `go mod download` never updates anything unless you change go.mod.