cmd/go: confusing error "missing dot in first path element" when importing missing package

[a8m]

This issue was created as a follow-up to my comment in #34769 and CL 203118.

When running go build on a module foo, that imports a local module bar without a package (no Go files), the returned error is:

build foo: cannot load bar: malformed module path "bar": missing dot in first path 
element

CL 203118 changes the module importer to print more friendly error as:

main.go:3:8: module bar@ found (v0.0.0-00010101000000-000000000000, replaced by ../bar), 
but does not contain package

Full example exists here: https://github.com/a8m/go-issue-34769

---

If you ask yourself why creating a module without any Go files (the bar module), well, we tried to build a few Docker images and accidentally forgot to copy some of the Go files to the image. It took us hours to figure out what the "missing dot in first path element" means in this case.

[gopherbot]

Change https://golang.org/cl/203118 mentions this issue: cmd/go/internal/modload: fail if no package was found in local module

[aayushrathore]

for me the issue was resolved after changing the GOROOT environment variable from "/usr/loca/go/bin" to "/usr/local/go"

OS : Linux centos

[gopherbot]

Change https://golang.org/cl/205878 mentions this issue: cmd/go/internal/modload: improve error when a missing package has a replaced-but-unfetchable module as a prefix

[Peakchen]

at windows，how to solve？