cmd/go: go help packages should document that in module mode import paths must be fully qualified

[perillo]

go help packages, for go1.13.6, also available at
https://golang.org/pkg/cmd/go/#hdr-Package_lists_and_patterns,
in an example about a unique prefix that belongs to you, says:

For example, paths used internally at Google all begin with 'google'

I don't know if Google is still using 'google' and GOPATH mode. However I think the documentation should say (here or somewhere else) that in module mode non fully qualified import path like 'google' are rejected by the go tool.

[toothrot]

The linked documentation does recommend reading go help importpath, which covers this in some detail.

Relative import paths are also supported: https://golang.org/cmd/go/#hdr-Relative_import_paths

[perillo]

Just to clarify, I'm referring to the error message emitted by go build:

cannot load google/xxx: malformed module path "google/xxx": missing dot in first path element

However, I noted that go mod init google/xxx does not report problems.
Also if in a source file inside google/xxx I import google/xxx/a, go build does not complain.

So an importpath without a dot in the first path element is allowed if it belongs to the current module, but disallowed if it belongs to an external required module. In this case the example in the documentation is valid, probably.