env GO111MODULE=on

go build -o a1.exe .
exec ./a1.exe
stdout 'Don''t communicate by sharing memory'

# Modules can be replaced by local packages.
go mod edit -replace=rsc.io/quote/v3=./local/rsc.io/quote/v3
go build -o a2.exe .
exec ./a2.exe
stdout 'Concurrency is not parallelism.'

# The module path of the replacement doesn't need to match.
# (For example, it could be a long-running fork with its own import path.)
go mod edit -replace=rsc.io/quote/v3=./local/not-rsc.io/quote/v3
go build -o a3.exe .
exec ./a3.exe
stdout 'Clear is better than clever.'

# However, the same module can't be used as two different paths.
go mod edit -dropreplace=rsc.io/quote/v3 -replace=not-rsc.io/quote/v3@v3.0.0=rsc.io/quote/v3@v3.0.0 -require=not-rsc.io/quote/v3@v3.0.0
! go build -o a4.exe .
stderr 'rsc.io/quote/v3@v3.0.0 used for two different module paths \(not-rsc.io/quote/v3 and rsc.io/quote/v3\)'

-- go.mod --
module quoter

require rsc.io/quote/v3 v3.0.0

-- main.go --
package main

import (
	"fmt"
	"rsc.io/quote/v3"
)

func main() {
	fmt.Println(quote.GoV3())
}

-- local/rsc.io/quote/v3/go.mod --
module rsc.io/quote/v3

require rsc.io/sampler v1.3.0

-- local/rsc.io/quote/v3/quote.go --
// Copyright 2018 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Package quote collects pithy sayings.
package quote

import "rsc.io/sampler"

// Hello returns a greeting.
func HelloV3() string {
	return sampler.Hello()
}

// Glass returns a useful phrase for world travelers.
func GlassV3() string {
	// See http://www.oocities.org/nodotus/hbglass.html.
	return "I can eat glass and it doesn't hurt me."
}

// Go returns a REPLACED Go proverb.
func GoV3() string {
	return "Concurrency is not parallelism."
}

// Opt returns a optimization truth.
func OptV3() string {
	// Wisdom from ken.
	return "If a program is too slow, it must have a loop."
}

-- local/not-rsc.io/quote/v3/go.mod --
module not-rsc.io/quote/v3

-- local/not-rsc.io/quote/v3/quote.go --
package quote

func GoV3() string {
	return "Clear is better than clever."
}