cmd/go: plugin versions do not match when built within vs. outside a module

[zimnx]

What did you do?

I have simple application that loads Go plugins and allows them to communicate with app via exported interface.

Simplified version can be found here.
Shared interface is stored under ext directory, real implementation is located underplugin directory.
Application passes pointer to real implementation to dynamically loaded plugin which expects interface.

Example plugin code can be found here.

Unfortunately combination of Go Modules and Go Plugins doesn't work unless go.mod of plugins module has replace entry with local relative path for shared interface path.
When I use remote location in plugins module, application crashes because of wrong version of packages.

Build app:

~/tmp/go-plugin-bug/central on  master ⌚ 16:12:19
$ go clean -modcache 

~/tmp/go-plugin-bug/central on  master ⌚ 16:12:21
$ git checkout v1.0.0
Note: checking out 'v1.0.0'.

~/tmp/go-plugin-bug/central on  f1d7e9f ⌚ 16:12:22
$ go install -a

Then build plugin

~/tmp/go-plugin-bug/central on  f1d7e9f ⌚ 16:12:27
$ cd ../plugins 

~/tmp/go-plugin-bug/plugins on  master ⌚ 16:12:28
$ cat go.mod 
module github.com/zimnx/plugins

go 1.12

require github.com/zimnx/central v1.0.0


~/tmp/go-plugin-bug/plugins on  master ⌚ 16:12:30
$ go build -buildmode=plugin -o plugin.so
go: finding github.com/zimnx/central v1.0.0
go: downloading github.com/zimnx/central v1.0.0
go: extracting github.com/zimnx/central v1.0.0

~/tmp/go-plugin-bug/plugins on  master ⌚ 16:12:39
$ central plugin.so 
2019/04/08 16:12:42 cant open plugin: plugin.Open("plugin"): plugin was built with a different version of package github.com/zimnx/central/ext

When I change plugins go mod to use local path instead of remote one everything works.

~/tmp/go-plugin-bug/plugins on  master ⌚ 16:12:42
$ cat go.mod                             
module github.com/zimnx/plugins

go 1.12

require github.com/zimnx/central v1.0.0

replace github.com/zimnx/central => ../central

~/tmp/go-plugin-bug/plugins on  master! ⌚ 16:14:30
$ go build -buildmode=plugin -o plugin.so

~/tmp/go-plugin-bug/plugins on  master! ⌚ 16:14:33
$ central plugin.so 
hello = world

What did you expect to see?

Go Modules and plugins working fine when remote path is used.

What did you see instead?

Error about different package versions.

Does this issue reproduce with the latest release (go1.12.3)?

Yes.

System details

go version go1.12.3 linux/amd64
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/maciej/.cache/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/maciej/work"
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="/home/maciej/tmp/go-plugin-bug/plugins/go.mod"
GOROOT/bin/go version: go version go1.12.3 linux/amd64
GOROOT/bin/go tool compile -V: compile version go1.12.3
uname -sr: Linux 4.14.13-041413-generic
Distributor ID:	Ubuntu
Description:	Ubuntu 17.10
Release:	17.10
Codename:	artful
/lib/x86_64-linux-gnu/libc.so.6: GNU C Library (Ubuntu GLIBC 2.26-0ubuntu2.1) stable release version 2.26, by Roland McGrath et al.
gdb --version: GNU gdb (Ubuntu 8.0.1-0ubuntu1) 8.0.1

[zimnx]

Bump. Any plans to fix this? Seems that algorithm which verifies package version integrity needs alignment.

[bcmills]

This is the same underlying problem as #29814.

The workaround should be to build both the plugin and the main binary from outside of their respective repositories, or (as you note) to use a replace directive when building locally.

[bcmills]

CC @jayconrod