x/tools/cmd/gopls: hover returns error when over non-identifier

[myitcv]

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

$ go version
go version devel +9a00e64633 Fri Jul 5 12:11:36 2019 +0000 linux/amd64
$ go list -m golang.org/x/tools
golang.org/x/tools v0.0.0-20190706070813-72ffa07ba3db
$ go list -m golang.org/x/tools/gopls
golang.org/x/tools/gopls v0.1.2-0.20190706070813-72ffa07ba3db

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="on"
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/myitcv/.cache/go-build"
GOENV="/home/myitcv/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
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/gostuff/src/github.com/myitcv/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-build249835069=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Take the following simple example:

package main

import "fmt"

func main() {
	fmt.Println()
}

In Vim using govim, if we hover over the () of main() then we get the following response from gopls:

[Trace - 10:02:06 AM] Sending request 'textDocument/hover - (6)'.
Params: {"textDocument":{"uri":"file:///home/myitcv/gostuff/src/github.com/myitcv/playground/main.go"},"position":{"line":4,"character":10}}


[Error - 10:02:06 AM] send textDocument/hover#6 no identifier found

For the client to know this is an error that can be ignored would require it to know the structure of the document, which defeats the point of the LSP.

What did you expect to see?

In this instance I think gopls should simply report there is nothing to display, i.e. return empty string with no error.

What did you see instead?

As above.

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cc @stamblerre @ianthehat

[stamblerre]

Duplicate of #32967