cmd/go: continue conversion to bug-resistant //go:build constraints

[rsc]

In June I posted a draft design for moving from // +build lines with ad-hoc syntax to //go:build lines with standard Boolean expressions; that doc also has links to a video overview and a prototype implementation.

I propose that we adopt this design, with N = 17 in the Transition section, meaning that the prep work would happen in Go 1.16, the main change would land in Go 1.17, and the transition would be finalized in Go 1.18.

[rsc]

Based on the emoji above and the lack of any objections (along with the overwhelmingly positive Reddit thread), this seems like a likely accept.

[cristaloleg]

Post on Reddit: https://www.reddit.com/r/golang/comments/hitexe/qa_gobuild_draft_design/

[rsc]

No change in consensus, so accepted.

[rsc]

Please note that accepting this means that //go:build lines will start working in Go 1.17, not Go 1.16.
Don't everyone rush to put them in.