proposal: cmd/go: support bracketed expressions for build constraints

[bronze1man]

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

$ go version
go version go1.13.1 darwin/amd64

Does this issue reproduce with the latest release?

do not know

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

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/a/Library/Caches/go-build"
GOENV="/Users/a/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/a/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/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/m9/qtbxkp6s3p96fk54rln7qhj80000gp/T/go-build303619785=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

write a build contstraint that is not to // +build linux,!cgo darwin,!cgo

What did you expect to write?

add bracket simple// +build !(linux,!cgo darwin,!cgo)
or
using golang syntax // +build !((linux && (!cgo)) || (darwin && (!cgo)))
or
the boolean formula in https://golang.org/pkg/go/build/#hdr-Build_Constraints // +build (NOT ((linux AND (NOT cgo)) OR (darwin AND (NOT cgo))))

What did you write instead?

// +build !linux cgo
// +build !darwin cgo

I have read the document of https://golang.org/pkg/go/build/#hdr-Build_Constraints
Then I do some boolean algebra from https://en.wikipedia.org/wiki/Boolean_algebra#Laws
Then I get the working code.
I think the golang should support bracket in this place.

[smasher164]

Note that the above build constraint can be further simplified to

// +build !linux,!darwin cgo

which gives you the one-liner you were looking for at the beginning.

[josharian]

Dup of #25348?

[smasher164]

@josharian Thanks for spotting it. I'll reopen that issue since it appears there wasn't a consensus.