Do we need to add this environment into go help environment ?

I think that's fine, as long as it's made clear that it's for enabling experimental features that aren't supported or guaranteed to work and may change incompatibly or go away entirely in future releases.

I'd also recommend not listing available experiments. If necessary, point users towards cmd/internal/objabi.

Change https://golang.org/cl/304350 mentions this issue: cmd/go/internal/envcmd: add GOEXPERIMENT environment in env cmd

Change https://golang.org/cl/328751 mentions this issue: cmd/go: add GOEXPERIMENT to go env output

I don't know why this got moved off the Go 1.17 milestone. I think it's important for user reports that go env indicate whether they've tampered with experiments.

@mdempsky @bcmills Anything else to do before merging this change? The RC date is soon.

@toothrot I have a change for it, I just need to rebase it on top of the fix that was merged for #46815 for Go 1.17.

I plan to do that after mailing out CLs for #46742. I expect to have CLs for both of these out by EOD.

Okay, CLs 331109, 329654, and 328751 are mailed out for this issue.

@bcmills already approved the third only before rebasing. It's substantially unmodified by the rebase, so I think that CR+2 is still valid. I think just the first 2 need review.