x/tools/go/buildutil: support comma-delimited build tags in buildutil.TagsFlag

[yaaase]

What version of Go are you using (go version)?

$ go version

go version go1.15.6 darwin/amd64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
GO111MODULE="off"

GOARCH="amd64"

GOBIN=""

GOCACHE="/Users/mbillie/Library/Caches/go-build"

GOENV="/Users/mbillie/Library/Application Support/go/env"

GOEXE=""

GOFLAGS="-mod=vendor"

GOHOSTARCH="amd64"

GOHOSTOS="darwin"

GOINSECURE=""

GOMODCACHE="/Users/mbillie/digitalocean/cthulhu/docode/pkg/mod"

GONOPROXY=".internal.digitalocean.com,github.com/digitalocean"

GONOSUMDB=".internal.digitalocean.com,github.com/digitalocean"

GOOS="darwin"

GOPATH="/Users/mbillie/digitalocean/cthulhu/docode:/home/mbillie/digitalocean:/home/mbillie/go"

GOPRIVATE="*.internal.digitalocean.com,github.com/digitalocean"

GOPROXY="https://proxy.golang.org,direct"

GOROOT="/usr/local/Cellar/go/1.15.6/libexec"

GOSUMDB="sum.golang.org"

GOTMPDIR=""

GOTOOLDIR="/usr/local/Cellar/go/1.15.6/libexec/pkg/tool/darwin_amd64"

GCCGO="gccgo"

AR="ar"

CC="clang"

CXX="clang++"

CGO_ENABLED="1"

GOMOD=""

CGO_CFLAGS="-g -O2"

CGO_CPPFLAGS=""

CGO_CXXFLAGS="-g -O2"

CGO_FFLAGS="-g -O2"

CGO_LDFLAGS="-g -O2"

PKG_CONFIG="pkg-config"

GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/w5/jt734dx51w7c9sq8spdrb_6r0000gs/T/go-build425061423=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

I would like to allow tools in the community to support the same format for build tags (e.g. comma delimited) as the go tool supports. Space separate tags have been deprecated in the go tool. This brings parity to tools that rely on golang.org/x/tools/go/build : see https://go-review.googlesource.com/c/tools/+/284214#message-fc9907b03ae75ae24145f421e623330b4b9b9158

[bcmills]

I note, per https://tip.golang.org/cmd/go/#hdr-Compile_packages_and_dependencies:

-tags tag,list
	a comma-separated list of build tags to consider satisfied during the
	build. For more information about build tags, see the description of
	build constraints in the documentation for the go/build package.
	(Earlier versions of Go used a space-separated list, and that form
	is deprecated but still recognized.)

So this seems fine to add to go/buildutil.

CC @stamblerre @alandonovan

[gopherbot]

Change https://golang.org/cl/284214 mentions this issue: Allow buildutil.TagsFlag to handle comma-delimited tag lists

[aykevl]

Any update on this? We'd like to support commas in build tags in TinyGo and it would be really nice if we could keep using buildutil.TagsFlag.

[adonovan]

Seems like https://golang.org/cl/284214 has been languishing. Would you be willing to nudge it across the finish line (in other words, take it over)? It doesn't look very hard.