Modules and vendoring
When using modules, the go command completely ignores vendor directories.
By default, the go command satisfies dependencies by downloading modules
from their sources and using those downloaded copies (after verification,
as described in the previous section). To allow interoperation with older
versions of Go, or to ensure that all files used for a build are stored
together in a single file tree, 'go mod -vendor' creates a directory named
vendor in the root directory of the main module and stores there all the
packages from dependency modules that are needed to support builds and
tests of packages in the main module.
To build using the main module's top-level vendor directory to satisfy
dependencies (disabling use of the usual network sources and local
caches), use 'go build -getmode=vendor'. Note that only the main module's
top-level vendor directory is used; vendor directories in other locations
are still ignored.
So far, I get a feeling that vendoring will be a second-class citizen in the world of modules. Unfortunately, I will not be surprised if the team considers removing the support entirely in a future release. I just hope that a viable alternative will be proposed.
