x/exp/cmd/gorelease: avoid using -mod=mod and support lazy module loading

Details:

- Replaces `go list -mod=mod` with `go list -mod=readonly`.
- Switches to `go get -d` to download dependencies rather than relying on `go
  list` doing so.
- Missing go.sum/go.mod data is now an error.

This CL will be followed by a CL that ensures the filepath.Walk stops at
submodules, and a test asserting that. I figured it'd be good to do separately
since this CL is getting to be hefty. Give a shout if you prefer otherwise!

Updates golang/go#41456

Change-Id: I66f12fe0325e4fed432d8b10c1fe977068e4a030
Reviewed-on: https://go-review.googlesource.com/c/exp/+/263178
Run-TryBot: Jean de Klerk <deklerk@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>
Trust: Jean de Klerk <deklerk@google.com>
8 files changed
tree: 2a7ee4d2e201006b88781b6c8b8c6a7aeb5e0a2c
  1. apidiff/
  2. cmd/
  3. ebnf/
  4. ebnflint/
  5. errors/
  6. fsnotify/
  7. inotify/
  8. io/
  9. mmap/
  10. rand/
  11. shiny/
  12. shootout/
  13. sumdb/
  14. utf8string/
  15. winfsnotify/
  16. .gitattributes
  17. .gitignore
  18. AUTHORS
  19. codereview.cfg
  20. CONTRIBUTING.md
  21. CONTRIBUTORS
  22. go.mod
  23. go.sum
  24. LICENSE
  25. PATENTS
  26. README.md
README.md

exp

PkgGoDev

This subrepository holds experimental and deprecated (in the old directory) packages.

The idea for this subrepository originated as the pkg/exp directory of the main repository, but its presence there made it unavailable to users of the binary downloads of the Go installation. The subrepository has therefore been created to make it possible to go get these packages.

Warning: Packages here are experimental and unreliable. Some may one day be promoted to the main repository or other subrepository, or they may be modified arbitrarily or even disappear altogether.

In short, code in this subrepository is not subject to the Go 1 compatibility promise. (No subrepo is, but the promise is even more likely to be violated by go.exp than the others.)

Caveat emptor.