proposal: cmd/go: allow 'go get -u' to upgrade the targets of replacements

[dfang]

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

$ go version
go version go1.12.5 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
go env
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/mj/Library/Caches/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/mj/go"
GOPROXY=""
GORACE=""
GOROOT="/usr/local/Cellar/go/1.12.5/libexec"
GOTMPDIR=""
GOTOOLDIR="/usr/local/Cellar/go/1.12.5/libexec/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
CXX="clang++"
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 -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/xb/dsd0_2b92x7bsl92xlzj6fbm0000gn/T/go-build803671561=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

go get -u github.com/dfang/auth

What did you expect to see?

replace github.com/qor/auth => github.com/dfang/auth v0.0.0-20190621054412-96c274f7c597 

just update/replace the hash with updated one in go.mod

What did you see instead?

the hash didn't change, but add one dependency on

require(
    ....
   github.com/dfang/auth v-0.0.0-<hash>
   .....
)

for now i have to copy hash in require, delete the line, update the hash in replace

[bcmills]

What did you do?

go get -u github.com/dfang/auth

That's not enough information for us to reproduce this error, let alone to verify a fix for it. Please provide complete steps to reproduce the problem.

[dfang]

@bcmills ok, simple files

main.go

package main

import (
	"fmt"
	"test/faker"
)

func main() {
	fmt.Println(faker.App().Version())
}

faker/app.go

package faker

type FakeApp interface {
	Version() string // => "2.6.0"
}

type fakeApp struct{}

func App() FakeApp {
	return fakeApp{}
}

func (a fakeApp) Version() string {
	return "0.1"
}

go.mod

module github.com/user/test

go 1.12

replace github.com/user/test/faker => syreclabs.com/go/faker v1.0.0

just create these files, then run go mod tidy, now it's ready.

if syreclabs.com/go/faker updates, i want to keep up, i will run go get -u syreclabs.com/go/faker@v1.1.0

now go.mod became

module github.com/user/test

go 1.12

replace github.com/user/test/faker => syreclabs.com/go/faker v1.0.0

require syreclabs.com/go/faker v1.1.0 // indirect

what i expected is

go.mod

module github.com/user/test

go 1.12

replace github.com/user/test/faker => syreclabs.com/go/faker v1.1.0

let me know if there is anything unclear ....

thanks

[bcmills]

This seems closely related to #28176, in that both want to track updates in replacements.

But note that the argument to go get -u is in general a package import path, and the target of a replace directive is not importable (see #26904). The replace directive today replaces source code, not import paths.

If/when we go support path replacements (as in #26904) instead of source code replacements, then you could do something like:

module github.com/user/test

go 1.14

replace github.com/user/test/faker => syreclabs.com/go/faker

require (
	github.com/user/test/faker v0.0.0-00000101000000-000000000000
	syrelabs.com/go/faker v1.0.0
)

And then go get -u would do, I suspect, exactly what you want.

[dfang]

This is a feature request or proposal, i'll change the title first ...

[rsc]

I think it would be a mistake to do this.
Replace is the developer's all-purpose override mechanism, opting out of all the usual logic.
It should remain so.
If we make "go get -u" apply to replace right-hand-sides, then we will need "go get -u -no-replace" as well.