cmd/link: -pluginpath seems to no longer work with go1.13

[e-nikolov]

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

$ go version
go version go1.13 linux/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=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/enikolov/.cache/go-build"
GOENV="/home/enikolov/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GONOPROXY="bitbucket.org/unchain/*"
GONOSUMDB="bitbucket.org/unchain/*"
GOOS="linux"
GOPATH="/home/enikolov/go"
GOPRIVATE="bitbucket.org/unchain/*"
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/home/enikolov/.gvm/gos/go1.13"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/home/enikolov/.gvm/gos/go1.13/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
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-build411225951=/tmp/go-build -gno-record-gcc-switches"

What did you do?

go build -ldflags "-pluginpath=custom/path" -buildmode=plugin ./path/to/plugin

With go1.13 this seems to no longer map the packages to the custom path.

What did you expect to see?

I have the variable Version in my main package

With go 1.12 after running the strings utility on the produced binary, I would see this somewhere in the output:

custom/path.Version

What did you see instead?

With go1.13 I now see this instead:

path/to/plugin.Version

Could this be related to go modules?