Forked from #31467.
This is only applicable to modules, as it works fine in $GOPATH mode.

To reproduce, create a directory foo outside of your $GOPATH.
Open foo in VSCode (using gopls), then create file foo.go, but do not save it.
Add some code like

package foo

import (
	"fmt"
)

func _() {
	fmt.Println()
}

gopls will not provide autocompletion for this file because go/packages will not return a valid package. The reason for this is that there are no rootDirs in this case: https://github.com/golang/tools/blob/c5a2fd39b72a2403dae32d544b008ff4973c8b29/go/packages/golist_overlay.go#L78, so the pkgPath will never be set.

/cc @matloob