cmd/link: -X not applied if target is the result of a function call

[daenney]

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

$ go version
1.11.4

Does this issue reproduce with the latest release?

Yes

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

go env

GOARCH="amd64"
GOBIN=""
GOCACHE="/home/daenney/.cache/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/daenney/Development/go"
GOPROXY=""
GORACE=""
GOROOT="/home/daenney/.asdf/installs/golang/1.11.4/go"
GOTMPDIR=""
GOTOOLDIR="/home/daenney/.asdf/installs/golang/1.11.4/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
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 -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build378681064=/tmp/go-build -gno-record-gcc-switches"

What did you do?

package main

import (
        "fmt"
        "time"
)

var (
        Version string = "1"
        Time string = time.Unix(0, 0).String()
)

func main() {
        fmt.Println(Version)
        fmt.Println(Time)
}

go build -o main -ldflags "-X main.Version=2 -X main.Time=3" main.go
./main

What did you expect to see?

2
3

What did you see instead?

2
1970-01-01 01:00:00 +0100 CET

[daenney]

I'm not sure if this is a bug or a lack of documentation but I couldn't find anything in go help build that would explain this.

If I change Time to be Time string = "0" the -ldflags applies as expected and I end up with 2 3 being printed.

[FiloSottile]

/cc @ianlancetaylor

[ianlancetaylor]

The docs (https://golang.org/cmd/link) say "This is only effective if the variable is declared in the source code either uninitialized or initialized to a constant string expression. -X will not work if the initializer makes a function call or refers to other variables." So while this is unfortunate it's a known and documented limitation.

[daenney]

Ah, it had not occurred to me to check cmd/link instead. Thanks for the pointer!