cmd/go: doc: inconsistent handling of build tags, cgo, goexperiment #76829
Description
Go version
go version go1.26-devel_f2d96272cb 2025-12-08 10:58:21 -0800 linux/amd64
Output of go env in your module/workspace:
-g'
CGO_LDFLAGS='-O2 -g'
CXX='g++'
GCCGO='gccgo'
GO111MODULE=''
GOAMD64='v3'
GOARCH='amd64'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/home/user/.cache/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/home/user/.config/go/env'
GOEXE=''
GOEXPERIMENT='jsonv2'
GOFIPS140='off'
GOFLAGS='-trimpath "-ldflags=-s -w" -vet=all'
GOGCCFLAGS='-fPIC -m64 -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build1893534021=/tmp/go-build -gno-record-gcc-switches'
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMOD='/home/user/tmp/testrepo1348/go.mod'
GOMODCACHE='/home/user/.data/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/user/.data/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/home/user/sdk/gotip'
GOSUMDB='sum.golang.org'
GOTELEMETRY='on'
GOTELEMETRYDIR='/home/user/.config/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='path'
GOTOOLDIR='/home/user/sdk/gotip/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.26-devel_f2d96272cb 2025-12-08 10:58:21 -0800'
GOWORK=''
PKG_CONFIG='pkg-config'What did you do?
Run go doc:
-- c.go --
//go:build cgo
package xxx
// C is cgo
func C() {}
-- exp.go --
//go:build goexperiment.jsonv2
package xxx
// E is goexperiment
func E() {}
-- notc.go --
//go:build !cgo
package xxx
// C is !cgo
func C() {}
-- notexp.go --
//go:build !goexperiment.jsonv2
package xxx
// E is !goexperiment
func E() {}
-- nott.go --
//go:build !mytag
package xxx
// T is !mytag
func T() {}
-- t.go --
//go:build mytag
package xxx
// T is mytag
func T() {}What did you see happen?
$ go doc -all
package xxx // import "go.seankhliao.com/testrepo1348"
FUNCTIONS
func C()
C is cgo
func E()
E is !goexperiment
func T()
T is !mytaggo doc by default uses cgo, no goexperiment, no extra tags.
It ignores CGO_ENABLED and GOEXPERIMENT set in the GOENV config file, but it does use those settings if they are set as environment variables.
Custom build tags are always ignored (including if set via GOFLAGS=-tags=...).
go doc -http ignores all optional tags.
What did you expect to see?
A -tags flag for go doc.
Handling of environment / tags consistent with other go commands like go build.
cc @golang/command-line