x/tools/gopls: document how to run the daemon in docker

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

go1.12.17 darwin/amd64

Does this issue reproduce with the latest release?

YES recent version of gopls 0.4.4

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

GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/ninja/Library/Caches/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/ninja/go"
GOPROXY=""
GORACE=""
GOROOT="/usr/local/go"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/ninja/Documents/<name>/<project>/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 -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/65/7_p4zdgn2llfqf6fvn1zymjw0000gn/T/go-build716194075=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

I am trying to setup gopls for neovim with the builtin lsp. But I have a dependency on linux to build the source I cannot build it on mac. So I tried setting up docker gopls server to listen at 7050.

Dockerfile

FROM golang:1.12.16-stretch
RUN apt-get update && apt-get install -y libudev-dev

ARG GOPATH
ENV GOPATH $GOPATH

ARG MY_PWD
ENV MY_PWD ${MY_PWD}

RUN mkdir -p $GOPATH
RUN mkdir -p $MY_PWD

ENV PATH="/usr/local/go/bin:$GOPATH/bin:${PATH}"
RUN GOPROXY=https://proxy.golang.org GO111MODULE=on go get golang.org/x/tools/gopls@latest
WORKDIR $MY_PWD

CMD /go/bin/gopls  -listen=":7050"

I opened nvim and it throws the same build error as the one I got on mac.

Neovim config

:lua << EOF
require'nvim_lsp'.gopls.setup{
cmd = {"gopls","-remote","localhost:7050"};
}
EOF

I initially tried this docker setup for a simple hello world example and that worked. But now I am not sure whether it actually compiled inside docker and communicated the results outside or it just compiled in mac itself. Gopls listen inside docker doesn't give any logs other than connected and exited (atleast when I run docker logs ).

PS: I execed into docker and built the source and it worked as expected.

What did you expect to see?

I expect gopls -remote to build the source inside docker and give back the results to the client.

What did you see instead?

I see the same build error which I got on mac, which might mean gopls is not forwarding the commands to the remote and doing it locally.