cmd/go: error out in 'go mod tidy' if the result uses a module for multiple paths

[budougumi0617]

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

$ go version
go version go1.13.1 darwin/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="/Users/budougumi0617/Library/Caches/go-build"
GOENV="/Users/budougumi0617/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/budougumi0617/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/opt/go/libexec"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/opt/go/libexec/pkg/tool/darwin_amd64"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/budougumi0617/go/src/github.com/budougumi0617/til/go/tui/promptui/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 -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/sy/ls4cfp216x774g54brzl67yw0000gn/T/go-build596997761=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

https://play.golang.org/p/LTTwK6ldWiB

I put below files in current directory.

main.go

package main

import (
        "fmt"

        "github.com/manifoldco/promptui"
)

func main() {
        fmt.Println(promptui.FGRed)
}

go.mod

module github.com/budougumi0617/til/go/tui/promptui

go 1.13

require (
        github.com/BurntSushi/toml v0.3.1 // indirect
        github.com/alecthomas/units v0.0.0-20190910110746-680d30ca3117 // indirect
        github.com/manifoldco/promptui v0.3.2
        github.com/nicksnyder/go-i18n v1.10.1 // indirect
        gopkg.in/alecthomas/kingpin.v3-unstable v3.0.0-20180810215634-df19058c872c // indirect
)

replace github.com/nicksnyder/go-i18n v1.10.1 => github.com/nicksnyder/go-i18n/v2 v2.0.2

go build command is success.

$ go clean --modcache
$ rm go.sum
$ go build . // build ok

And, I did go mod tidy command for format go.mod. As a result, go mod tidy changed go.modfile.

$ cp go.mod go.mod.before // keep original go.mod file
$ go mod tidy
$ diff go.mod.before go.mod
--- go.mod.before       2019-10-01 16:25:03.000000000 +0900
+++ go.mod      2019-10-01 16:25:11.000000000 +0900
@@ -7,6 +7,7 @@
        github.com/alecthomas/units v0.0.0-20190910110746-680d30ca3117 // indirect
        github.com/manifoldco/promptui v0.3.2
        github.com/nicksnyder/go-i18n v1.10.1 // indirect
+       github.com/nicksnyder/go-i18n/v2 v2.0.2 // indirect
        gopkg.in/alecthomas/kingpin.v3-unstable v3.0.0-20180810215634-df19058c872c // indirect
 )

But, go build now failed.

$ go build .
go: github.com/nicksnyder/go-i18n/v2@v2.0.2 used for two different module paths (github.com/nicksnyder/go-i18n and github.com/nicksnyder/go-i18n/v2)

What did you expect to see?

I expect the result of go mod tidy is able to buld, or go mod tidy failed if go.mod file is invalid.

What did you see instead?

I tried same procedures, on docker. Unfortunately, I get same result.

$ docker container run -it --name my_golang -v $(pwd):/go/src/ golang:latest

go env Output ( on container)

$ root@734e4aabfb61:/go/src# 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="/go/src/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-build324591870=/tmp/go-build -gno-record-gcc-switches"

[andybons]

@bcmills @jayconrod

[bcmills]

replace directives replace source code, not import paths, so attempting to use a replace directive in this way would break internal import statements within the module in question and is therefore not supported.

(Redirecting imports paths is #26904, which I am still hoping to address for 1.14.)

However, I agree that go mod tidy should have reported this error instead of deferring it until go build.

[gopherbot]

Change https://golang.org/cl/199598 mentions this issue: cmd/go/internal/modcmd: error out if one module with two different paths