x/tools/gopls: do not include replace directive in release versions

[myitcv]

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

$ go version
go version devel +7307e86afd Sun Nov 8 12:19:55 2020 +0000 linux/amd64
$ go list -m golang.org/x/tools
golang.org/x/tools v0.0.0-20201102212025-f46e4245211d
$ go list -m golang.org/x/tools/gopls
golang.org/x/tools/gopls v0.0.0-20201102212025-f46e4245211d

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="/home/myitcv/.cache/go-build"
GOENV="/home/myitcv/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/myitcv/gostuff/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/myitcv/gostuff"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/home/myitcv/gos"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/home/myitcv/gos/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/home/myitcv/.vim/plugged/govim/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-build946386886=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Putting together a Play with Go guide on how to use the new go install $pkg@$version in Go 1.16 with @mvdan (https://play-with-go.dev/installing-go-programs-directly_go116_en/), we had hoped to be able to use gopls as our canonical example of a Go program. However:

$ go install golang.org/x/tools/gopls@v0.5.3
go install golang.org/x/tools/gopls@v0.5.3: golang.org/x/tools/gopls@v0.5.3
    The go.mod file for the module providing named packages contains one or
    more replace directives. It must not contain directives that would cause
    it to be interpreted differently than if it were the main module.

This is as a result of:

https://github.com/golang/tools/blob/ae6603bdc3c4d025cb6c000c3b8dd778b1355266/gopls/go.mod#L14

What did you expect to see?

gopls install successfully.

What did you see instead?

As above.

The current guidance is that release versions of modules should not include replace directives:

https://go.googlesource.com/proposal/+/refs/changes/77/243077/15/design/40276-go-install.md#why-can_t-directory-directives-be-used

Also referencing #26640 for context.

@stamblerre

cc @jayconrod

[mvdan]

100% agree - gopls is probably the first module most newcomers to Go have to install, so it's unfortunate that it doesn't follow our own best practices and go install [...]@latest does not work.

Thinking outloud, and as an extension to this issue, it would also be unfortunate for @latest to work, but @master to fail, if we simply remove the replace directives from tagged releases. Though I don't think we can make go install [...]@master work today easily, as that would require a feature like #26640.

[gopherbot]

Change https://golang.org/cl/272688 mentions this issue: [gopls-release-branch.0.5] gopls: remove replace from release branch