cmd/go: build tags do not work quite as expected using devel version of Go

[rogpeppe]

Go version

go version devel go1.23-2ab9218c86 Mon Mar 11 22:10:38 2024 +0000 linux/amd64

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='amd64'
GOBIN=''
GOCACHE='/home/rogpeppe/.cache/go-build'
GOENV='/home/rogpeppe/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/home/rogpeppe/src/go/pkg/mod'
GONOPROXY='github.com/cue-unity'
GONOSUMDB='github.com/cue-unity'
GOOS='linux'
GOPATH='/home/rogpeppe/src/go'
GOPRIVATE='github.com/cue-unity'
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/home/rogpeppe/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/home/rogpeppe/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='devel go1.23-1653833811 Fri Jan 19 19:23:40 2024 +0000'
GCCGO='gccgo'
GOAMD64='v1'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD='/home/rogpeppe/go/src/go.mod'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build3220629220=/tmp/go-build -gno-record-gcc-switches'
 /tmp/go1.23-2ab9218c86 env
GO111MODULE=''
GOARCH='amd64'
GOBIN=''
GOCACHE='/home/rogpeppe/.cache/go-build'
GOENV='/home/rogpeppe/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/home/rogpeppe/src/go/pkg/mod'
GONOPROXY='github.com/cue-unity'
GONOSUMDB='github.com/cue-unity'
GOOS='linux'
GOPATH='/home/rogpeppe/src/go'
GOPRIVATE='github.com/cue-unity'
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/home/rogpeppe/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/home/rogpeppe/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='devel go1.23-2ab9218c86 Mon Mar 11 22:10:38 2024 +0000'
GODEBUG=''
GCCGO='gccgo'
GOAMD64='v1'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD='/home/rogpeppe/go/src/go.mod'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build1992602758=/tmp/go-build -gno-record-gcc-switches'

What did you do?

I ran the following testscript script:

exec go build
-- go.mod --
module test

go 1.20
-- x.go --
package x
-- x_iter.go --
//go:build go1.23 || goexperiment.rangefunc

package x

func f() {
	for _ = range func(func(int) bool) {} {}
}

What did you see happen?

> exec go build
[stderr]
# test
./x_iter.go:6:16: cannot range over func(func(int) bool) {} (value of type func(func(int) bool))
[exit status 1]
FAIL: /tmp/testscript4277131041/x.txtar/script.txtar:1: unexpected command failure

What did you expect to see?

A passing test. It seems that something about the devel version causes the build logic to ignore the usual build tag conventions that suppress the error even though the go version declared in go.mod is less than the guarded version in the x_iter.go file.

If I build go from a tagged version such as go1.22.1, the test passes fine.

I verified that a commit very shortly after go1.22.1 was tagged (1653833) fails in the same way.

[rogpeppe]

Ooops, I just realised the problem is obvious: iteration over functions is not (yet) enabled in Go tip! Sorry for the noise.