cmd/go, runtime/cgo: go module didn't download cgo soft links of dynamic library

[lihaic]

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

$ go version
go version go1.12 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
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/lhc/.cache/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/lhc/go"
GOPROXY=""
GORACE=""
GOROOT="/usr/local/go"
GOTMPDIR=""
GOTOOLDIR="/usr/local/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-build969375030=/tmp/go-build -gno-record-gcc-switches"

What did you do?

I am trying to switch my golang project from gopath to gomodule. One of the package my project imported is using cgo to call ffmpeg, the package have several dynamic ffmpeg libraries, for example:libavcodec.so ,libavcodec.so.57 ,libavcodec.so.57.107.100 , the fisrt two file is soft link file The problem is when i go build my golang project, go module only download libavcodec.so.57.107.100, it didn't download the other two soft link file

What did you expect to see?

I expect go module download all c dynamic libraries files including soft link files

What did you see instead?

i didn't get the soft link files

ps:1. When i use go get to get the package, i got all the dynamic libraries successfully, including all the soft link files
ps:2. Here is all the dynamic libraries i want and i get.

ls ~/go/src/plugins/ffmpeg Output

$ ls ~/go/src/plugins/ffmpeg
libavcodec.so             libavdevice.so            libavfilter.so            libavformat.so            libavutil.so            libswresample.so          libswscale.so
libavcodec.so.57          libavdevice.so.57         libavfilter.so.6          libavformat.so.57         libavutil.so.55         libswresample.so.2        libswscale.so.4
libavcodec.so.57.107.100  libavdevice.so.57.10.100  libavfilter.so.6.107.100  libavformat.so.57.83.100  libavutil.so.55.78.100  libswresample.so.2.9.100  libswscale.so.4.8.100

ls ~/go/pkg/mod/gitlab.com/plugins/ffmpeg Output

$ ls ~/go/pkg/mod/gitlab.com/plugins/ffmpeg
libavcodec.so.57.107.100  libavdevice.so.57.10.100  libavfilter.so.6.107.100  libavformat.so.57.83.100  libavutil.so.55.78.100  libswresample.so.2.9.100  libswscale.so.4.8.100

[andybons]

@bcmills @jayconrod @ianlancetaylor

[bcmills]

This behavior is intentional. See #24057 (comment) (via #27093).