cmd/go: confusing error message when flags come before package paths

[josharian]

-- go.mod --
module m

go 1.19
-- x/t_test.go --
package x

// some test code that has a -foo flag

(Warning: hand-written, untested txtar.)

$ go test ./x -foo
<OK>
$ go test -foo ./x
no Go files in /current/pwd

This is a confusing error message. I think(?) the Go tool has interpreted -foo as a package path, but the error message doesn't reflect that. It's true that there are no Go files in the root, but that's not the problem.

Maybe the Go command could make these two equivalent. But even if it can't, a more useful error message would be welcome.

[dr2chase]

@bcmills @rsc
I am not sure what the best approach here might be, it seems like it might involve some pattern-matching in the error path.

[bcmills]

I think(?) the Go tool has interpreted -foo as a package path, but the error message doesn't reflect that.

Nope: it has interpreted -foo ./x as the flag -foo with argument ./x, leaving an implicit package path of “.”.

I agree that the diagnostic could perhaps be improved, though.

[josharian]

Oof.

Why should cmd/go assume that -foo takes an arg, as opposed to being a bool flag?

[bcmills]

It doesn't know, so it has to make a conservative guess. (FWIW, the situation was even worse before https://go.dev/cl/211358 and https://go.dev/cl/248618. 😅)