proposal: go.mod's replace in .go import section, not in go.mod

[VertexToEdge]

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

$ go version
go version go1.13.6 linux/amd64

Does this issue reproduce with the latest release?

FeatureRequest

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

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/vertex/.cache/go-build"
GOENV="/home/vertex/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/vertex/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=""
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-build816677868=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Go module is a very simple and explicit way to manage dependency and package.
but I want to FeatureRequest about "replace in import section" because of enhancing source readability and convenience of coding.

I usually use replace feature when import local modules.

let me give you an example about importing local module and read the code.

there is example source tree

/example
    ㄴ/foo
        ㄴfoo.go
        ㄴgo.mod
        ㄴgo.sum
    ㄴmain.go
    ㄴgo.mod
    ㄴgo.sum

case 1: Importing local module

When I want to import local module foo
i will do edit two file. /example/main.go and /example/go.mod

/example/main.go:

package main

import (
    "fmt"
    "github.com/VertexToEdge/example/foo"  // <----- 1.import foo
)

func main() {
    fmt.Println("Hello World")
    foo.Foo()                              //  <----- 2. use foo
}

and also edit /example/go.mod for replace github.com/VertexToEdge/example/foo
to import module in local path.

/example/go.mod

module github.com/VertexToEdge/example

go 1.13

 // 3. replace to import local module
replace github.com/VertexToEdge/example/foo => ./foo 

case 2: Read the code

a third party got this code.

/example/main.go:

package main

import (
    "fmt"
    "github.com/VertexToEdge/example/foo"  // <----- 2. what is foo?
)

func main() {
    fmt.Println("Hello World")
    foo.Foo()                              //  <----- 1. what is this? foo?
}

In order to assure what exactly github.com/VertexToEdge/example/foo do,
he will have to open /example/go.mod.

/example/go.mod

module github.com/VertexToEdge/example

go 1.13

 // 3. ah ha! this is local module!
replace github.com/VertexToEdge/example/foo => ./foo  

What did you expect to see?

when replace module.

just replace in import section, not in go.mod
/example/main.go:

package main

import (
    "fmt"
    "github.com/VertexToEdge/example/foo" => ./foo
)

func main() {
    fmt.Println("Hello World")
    foo.Foo()
}

them, code writer and reader need not to open to read other file(go.mod)