go: x/tools/gopls: doesn't work on unsaved buffers in module mode

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

$ go version
go version go1.12.4 darwin/amd64

Does this issue reproduce with the latest release?

yes

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

$ go env
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/pendragon/Library/Caches/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/pendragon/workstation"
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=""
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/ct/5f1j4fl91mz_sdsl_3ksr5ph0000gp/T/go-build198016486=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

I am a vimer and gopher. Since gocode removed the autobuild feature, I switched to lsp and coc.nvim. At first I used go-langserver, which worked fine, but it was slow and high CPU usage. I tried the functions of bingo and gopls, bingo and gopls are problematic. The problem is always there and I didn’t see it being fixed. problem with gopls problem 1 GOPATH Project： this file in $GOPATH/src/test/main.go,I can’t get any completion information when i input these。

package main
import "net/http"
func main(){
       http.
}

save the file and reopen file gopls works。

problem 2 Go mod Project: When I introduce a third party package, I can’t get any completion information.

What did you expect to see?

Completion of normal work

What did you see instead?

go -langserver. but its performance is terrible