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

$ go version
go version go1.14.2 linux/amd64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/dominic/.cache/go-build"
GOENV="/home/dominic/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GONOPROXY="github.com/segment*"
GONOSUMDB="github.com/segment*"
GOOS="linux"
GOPATH="/home/dominic/dev"
GOPRIVATE="github.com/segment*"
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/lib/go-1.14"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/lib/go-1.14/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/home/dominic/Desktop/go-modules-bug/go.mod"
CGO_CFLAGS="-I/home/dominic/src/db2/clidriver/include"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-L/home/dominic/src/db2/clidriver/lib"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build523802799=/tmp/go-build -gno-record-gcc-switches"

What did you do?

My project is using a dependency (bitbucket.org/phiggins/db2cli) that has a test package with another dependency ("odbc") which has recently moved from Google Code to Github.

main.go

package main

import _ "bitbucket.org/phiggins/db2cli"

func main() {}

go.mod

module bug-report

go 1.14

Since this dependency isn't a direct one, I'm still able to run many commands (eg: go mod vendor, go test) without any trouble. However, upon trying to run go mod tidy, I get the following error:

go: finding module for package code.google.com/p/odbc
bug-report imports
	bitbucket.org/phiggins/db2cli tested by
	bitbucket.org/phiggins/db2cli.test imports
	code.google.com/p/odbc: cannot find module providing package code.google.com/p/odbc: unrecognized import path "code.google.com/p/odbc": parse https://code.google.com/p/odbc?go-get=1: no go-import meta tags ()

Once I realized this was a moved dependency, I addressed this with the following replace directive in my go.mod:

replace code.google.com/p/odbc => github.com/alexbrainman/odbc latest

Unfortunately, go mod tidy still does not work fully, though as far as I understand the replace directive is what should be used to resolve such an issue.

What did you expect to see?

I would expect the replace directive to allow go mod tidy to continue working, notably to prune unused dependencies.

What did you see instead?

Running go mod tidy prints this error just before exiting with error code 1:

go: github.com/alexbrainman/odbc@v0.0.0-20200426075526-f0492dfa1575 used for two different module paths (code.google.com/p/odbc and github.com/alexbrainman/odbc)

Consequently, go mod tidy no longer prunes unused dependencies. On a related note, the command go mod why prints this same error and also fails to work as designed.