x/tools/gopls: renaming test file package declaration `package_test `-> `package` falsely claims import cycle

[soypat]

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

$ go version
go version go1.16.2 linux/amd64
$ gopls version
golang.org/x/tools/gopls v0.6.9
    golang.org/x/tools/gopls@v0.6.9 h1:LBBcE2y3Tb4bp79JVLWCQBbvYCFEs5ADGWsQDoSLk1Q=

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

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN="/home/pato/go/bin"
GOCACHE="/home/pato/.cache/go-build"
GOENV="/home/pato/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/pato/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/pato/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="go1.16.2"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="0"
GOMOD="/home/pato/src/godesim/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 -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build1047604572=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Renamed a *_test.go file package declaration from package godesim_test to package godesim

What did you expect to see?

All good, package renamed. No biggie.

What did you see instead?

Gopls insisted there was an import cycle, even after removing the import ( "godesim" ) statement. After restarting gopls this did not persist. I've been able to reproduce it on several packages.

[soypat]

The problem seems to happen when there are other files with package_test package declaration who import the base package.

[findleyr]

I believe this is now fixed, along with #52500, but it warrants confirmation.

[findleyr]

I've confirmed that this is now resolved.