cmd/go: add -reuse flag [freeze exception]

[rsc]

We have been working on a -reuse flag for use by module proxies to reduce redundant 'git fetch' / 'git clone' traffic. The code paths only trigger when the new flag is used, so the chance of incidental problems should be quite low. There is some more provenance information in the .info files too, which may make people happy. We want to get it into Go 1.19 so that proxy.golang.org can start using it once Go 1.19 is out in August, rather than having to wait for Feb 2023 (Go 1.20).

Filing for freeze exception.

CL 411397 and CL 411398.

/cc @bcmills

[gopherbot]

Change https://go.dev/cl/411397 mentions this issue: cmd/go: record origin metadata during module download

[gopherbot]

Change https://go.dev/cl/415678 mentions this issue: cmd/go: make module@nonexistentversion failures reusable

[gopherbot]

Change https://go.dev/cl/411398 mentions this issue: cmd/go: add -reuse flag to make proxy invocations more efficient

[rsc]

Bryan agrees with this request (personal communication and also a thumbs-up above) but is now on a brief vacation. I'm not sure what else needs to happen for formal approval, but I'm going to submit the CLs once I get the TryBots happy so as not to miss the Go 1.19 release candidate later this week.

[mvdan]

Does this address #44577? If so, we may want to unlock that thread and post a brief update when proxy.golang.org starts using -reuse.

[dmitshur]

Thanks for letting us know.

I'm not sure what else needs to happen for formal approval

It's documented at https://go.dev/s/release#freeze-exceptions. I've retitled to fit the format (so this freeze exception is findable if we want to count them per release, etc.) and added CC @golang/release here.

We want to get it into Go 1.19 so that proxy.golang.org can start using it once Go 1.19 is out in August, rather than having to wait for Feb 2023 (Go 1.20).

I think that rationale is reasonable, it's done, and it's fine to consider it approved.