cmd/go: unable to install sub-module with buildmode=shared with go modules but $GOPATH works

[affanshahid]

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

$ go version
go version go1.13.7 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="/root/.cache/go-build"
GOENV="/root/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/home/project/go.mod"
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-build808455707=/tmp/go-build -gno-record-gcc-switches"

What did you do?

I am trying to compile a project with -buildmode=shared. My project has the following file structure:

go.mod
main.go
util
   /util.go

My go.mod file:

module example.com/affan/project

go 1.13

and my main.go simply imports example.com/affan/project/util and runs some code. Now following this stackoverflow link I am trying to compile my project in a way such that my main binary links to an .so of example.com/affan/project/util.

What did you expect to see?

I expected it to compile a binary and link to an so file of my sub-package

What did you see instead?

When I run go install -buildmode=shared -linkshared example.com/affan/project/util, I get the following:

panic: runtime error: slice bounds out of range [:-2]

goroutine 1 [running]:
cmd/go/internal/load.(*Package).load(0xc000096900, 0xc0001359f0, 0xc000045180, 0x0, 0x0)
        /usr/local/go/src/cmd/go/internal/load/pkg.go:1491 +0x36db
cmd/go/internal/load.loadImport(0xc000280200, 0x7fff3c03febc, 0x1e, 0xc000024024, 0xd, 0x0, 0xc0001359f0, 0x0, 0x0, 0x0, ...)
        /usr/local/go/src/cmd/go/internal/load/pkg.go:511 +0xdf2
cmd/go/internal/load.PackagesAndErrors(0xc000020090, 0x1, 0x1, 0x0, 0x0, 0x0)
        /usr/local/go/src/cmd/go/internal/load/pkg.go:1982 +0x398
cmd/go/internal/load.PackagesForBuild(0xc000020090, 0x1, 0x1, 0x9b9a00, 0x0, 0x0)
        /usr/local/go/src/cmd/go/internal/load/pkg.go:2028 +0x5d
cmd/go/internal/work.runInstall(0xea4340, 0xc000020090, 0x1, 0x1)
        /usr/local/go/src/cmd/go/internal/work/build.go:483 +0x44
main.main()
        /usr/local/go/src/cmd/go/main.go:189 +0x57f

I thought maybe I'm not specifying the path correctly so I tried. ./util as the final argument as well, but it had the same result.

It works with $GOPATH

I removed go.mod and copied everything to under $GOPATH/src with the correct paths. After that running the commands from the above link works perfectly, I get a binary linked to an .so of my util package just as I expect. So this is definitely something to do with go-modules (or maybe me doing something wrong?)

[odeke-em]

Thank you for this report @affanshahid and welcome to the Go project!

Interesting bug report and crash! Kindly paging @jayconrod @bcmills
In the meantime @affanshahid, could you please try with Go1.14 beta as per https://golang.org/dl/#unstable and see if the problem persists?

[bcmills]

Duplicate of #35759

[odeke-em]

@bcmills thanks for the follow-up! Shall we then recommend that the user expect it the fix in Go1.14?