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.

[gopherbot]

Change https://golang.org/cl/240600 mentions this issue: go/build: reject //go:build without // +build

[gopherbot]

Change https://golang.org/cl/240553 mentions this issue: cmd/go: add IgnoredOtherFiles to go list; pass IgnoredFiles to vet

[gopherbot]

Change https://golang.org/cl/240601 mentions this issue: cmd/compile: reject misplaced go:build comments

[gopherbot]

Change https://golang.org/cl/240602 mentions this issue: cmd/asm: reject misplaced go:build comments

[gopherbot]

Change https://golang.org/cl/240554 mentions this issue: cmd/vet: look at ignored files in buildtag check

[gopherbot]

Change https://golang.org/cl/261958 mentions this issue: cmd: go get golang.org/x/tools@d88ec18 && go mod vendor

[rsc]

All the Go 1.16 prep work for //go:build lines is now landed. I've retitled and remilestoned the issue to track the Go 1.17 work.

[gopherbot]

Change https://golang.org/cl/240604 mentions this issue: go/build/constraint: add parser for build tag constraint expressions

[gopherbot]

Change https://golang.org/cl/240609 mentions this issue: cmd/vet: update buildtag check for //go:build lines

[gopherbot]

Change https://golang.org/cl/240608 mentions this issue: go/printer: canonicalize //go:build and // +build lines while formatting

[gopherbot]

Change https://golang.org/cl/240607 mentions this issue: go/build: prefer //go:build over // +build lines

[gopherbot]

Change https://golang.org/cl/287412 mentions this issue: api/go1.16: add build/constraint APIs

[gopherbot]

Change https://golang.org/cl/287472 mentions this issue: doc/go1.16: document go/build/constraint package

[gopherbot]

Change https://golang.org/cl/240611 mentions this issue: cmd/fix: add buildtag fix

[gopherbot]

Change https://golang.org/cl/294430 mentions this issue: all: go fmt std cmd (but revert vendor)

[zephyr]

How will this effect the Go1.4-bootstrap once the transition will be finalized in Go 1.18?

I just took master@d4b2638234 and crudely removed all //+build lines:

$ find . -name '*.go' -exec sed -i '/\/\/ +build /d' {} \;

After that, i could no longer bootstrap master with go1.4:

dennis@inara:/opt/golang$ update-golang.py dennis
Building Go cmd/dist using /opt/golang1.4. (go1.4-bootstrap-20170531 linux/amd64)
# _/opt/golang/src/cmd/dist
cmd/dist/util_gccgo.go:9: useVFPv1 redeclared in this block
    previous declaration at cmd/dist/util_gc.go:11
cmd/dist/util_gccgo.go:11: useVFPv3 redeclared in this block
    previous declaration at cmd/dist/util_gc.go:15
cmd/dist/util_gccgo.go:13: useARMv6K redeclared in this block
    previous declaration at cmd/dist/util_gc.go:20
Error: /opt/golang/src/make.bash returned

So should go/build/constraint be backported to Go1.4?

[rsc]

The compiler has to be kept building with Go 1.4 for now. That means it has to keep its // +build comments. I do plan to propose bumping the bootstrap version to Go 1.17, though, for a variety of reasons, and after we've done that, we'd be able to remove the // +build comments.

[rsc]

All the Go 1.17 prep work for //go:build lines is now landed. I've remilestoned the issue to track the Go 1.18 work (submitting golang.org/cl/240611).

[gopherbot]

Change https://golang.org/cl/296889 mentions this issue: unix: add //go:build lines when generating files

[gopherbot]

Change https://golang.org/cl/319389 mentions this issue: all: add //go:build lines to assembly files

[gopherbot]

Change https://golang.org/cl/319410 mentions this issue: cmd/vendor: update golang.org/x/sys to latest

[gopherbot]

Change https://golang.org/cl/319469 mentions this issue: all: add //go:build lines to assembly files

[gopherbot]

Change https://golang.org/cl/320312 mentions this issue: all: update golang.org/x/sys to latest

[gopherbot]

Change https://golang.org/cl/323750 mentions this issue: runtime/internal/sys: generate //go:build lines in gengoos.go

[gopherbot]

Change https://golang.org/cl/341009 mentions this issue: all: gofmt more (but vendor, testdata, and top-level test directories)

[cagedmantis]

This issue is currently labeled as early-in-cycle for Go 1.18. That time is now, so this is a friendly ping so the issue is looked at again.

[toothrot]

Reminder that this is an early-in-cycle release-blocker for Go 1.18 and should be addressed soon.

[gopherbot]

Change https://golang.org/cl/344955 mentions this issue: all: go fix -fix=buildtag std (except for bootstrap deps)

[heschi]

ping @rsc -- to me this seems like something we would like to get in well before the freeze?

[dmitshur]

For quick reference, the outstanding CLs for this issue that I'm aware of and their status as of this posting:

• CL 240611 - includes "For #​41184", has +2, outstanding TryBot failures, one trivial code review comment, needs rebasing
• CL 344955 - includes "Fixes #​41184", unreviewed, outstanding TryBot failures, needs rebasing

[gopherbot]

Change https://golang.org/cl/359314 mentions this issue: cmd/dist: implement //go:build parsing

[gopherbot]

Change https://golang.org/cl/359315 mentions this issue: go/build: update for //go:build lines

[gopherbot]

Change https://golang.org/cl/359355 mentions this issue: cmd/go: update for //go:build lines

[gopherbot]

Change https://golang.org/cl/359476 mentions this issue: all: manual fixups for //go:build vs // +build

[gopherbot]

Change https://golang.org/cl/359404 mentions this issue: cmd/go: update for //go:build lines

[gopherbot]

Change https://golang.org/cl/359484 mentions this issue: net/http: restore generated // +build comment

[gopherbot]

Change https://golang.org/cl/361480 mentions this issue: all: remove more leftover // +build lines

[gopherbot]

Change https://golang.org/cl/362577 mentions this issue: all: add missing //go:build comments

[gopherbot]

Change https://golang.org/cl/366894 mentions this issue: cmd/dist: add buildtag parsing test

[gopherbot]

Change https://go.dev/cl/386774 mentions this issue: doc/go1.18: document Go 1.17 bootstrap and //go:build fix