x/tools/gopls: support multiple local values in the local prefix setting

[bravoecho]

The goimports tool allows to specify the -local option multiple times. gopls imports has a local option to reproduce that, but it only seems to work for a single prefix (gopls docs)

Everything works as expected when only one prefix is specified.

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

$ go version
go version go1.15.7 darwin/amd64
$ gopls version
golang.org/x/tools/gopls v0.6.4
    golang.org/x/tools/gopls@v0.6.4 h1:PO8rURGmi+QEKZ3pk+ZXJh51EFTVTSXqxzoRzrGSTJM=

Does this issue reproduce with the latest release?

✅

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

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/luca.belmondo/Library/Caches/go-build"
GOENV="/Users/luca.belmondo/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/luca.belmondo/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/luca.belmondo/go"
GOPRIVATE=""
GOPROXY="athens.glintpay.com"
GOROOT="/usr/local/Cellar/go/1.15.7_1/libexec"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/Cellar/go/1.15.7_1/libexec/pkg/tool/darwin_amd64"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/luca.belmondo/projects/svc/adjust-events/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/7l/jq5b64g946n0lxq82d8x32tryf6wnc/T/go-build147895208=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

In Vim, using the vim-go plugin, and setting the following options:

let g:go_fmt_command = 'gopls'
let g:go_imports_mode = 'gopls'
let g:go_gopls_gofumpt = v:true
let g:go_imports_autosave = 1
let g:go_gopls_local = 'acme.com,foobar.org'

What did you expect to see?

After saving any .go file:

import (
  "net"

  "google.golang.org/grpc"

  "acme.com/lib1"
  "acme.com/lib2"
  "foobar.org/lib1"
  "foobar.org/lib2"
)

What did you see instead?

import (
  "net"

  "acme.com/lib1"
  "acme.com/lib2"
  "foobar.org/lib1"
  "foobar.org/lib2"
  "google.golang.org/grpc"
)

[heschi]

goimports may allow you to specify the -local flag, but as far as I know, later values override, not add to, earlier values. The value of the flag is a comma separated list in both goimports and gopls. The gopls documentation should be updated.

[ArtAndreev]

It works with comma-separated module names, I checked.