cmd/go: go mod vendor should copy files matched by //go:embed

[jayconrod]

What did you do?

In a package outside the main module (example.com/p), embed some files in a subdirectory sub using a //go:embed directive.

From the main module, import example.com/p.

Run go mod vendor.

What did you expect to see?

The embedded files are present in vendor/example.com/p/sub. Other files from that directory are not vendored.

What did you see instead?

vendor/example.com/p/sub is not present.

cc @bcmills @matloob @rsc

[toothrot]

Any update on this as a Go 1.16 release blocker?

[jayconrod]

This should still be a release blocker.

Ideally, we should report an error if there ends up being conflict or overlap between different vendored packages. There are a few known issues with that (#38571, #38342, #42970), and I don't think it's essential to solve that for 1.17.

[gopherbot]

Change https://golang.org/cl/283641 mentions this issue: cmd/go: have go mod vendor copy embedded files in subdirs