x/tools/gopls: 30s delay before completion menu popups

[netjune]

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

go version go1.14.2 darwin/amd64

Does this issue reproduce with the latest release?

Yes, with 0.3.4 and 0.4.0.

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

go env Output

GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/jun/Library/Caches/go-build"
GOENV="/Users/jun/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/jun/Projects/go"
GOPRIVATE=""
GOPROXY="https://goproxy.io,direct"
GOROOT="/usr/local/Cellar/go/1.14.2_1/libexec"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/Cellar/go/1.14.2_1/libexec/pkg/tool/darwin_amd64"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/jun/Projects/go/src/golang.org/x/tools/gopls/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/yl/0xyrgw396fj89vd1n2vk649c0000gn/T/go-build696214569=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

1. open the example package of go-qt (https://github.com/therecipe/examples/tree/master/basic/qml)
2. open main.go, and type "core." at line 18 and then wait for the completion
3. after about 30s, the completion menu popups

What did you expect to see?

the delay is less than 1s

What did you see instead?

the delay is about 30s

[gopherbot]

Thank you for filing a gopls issue! Please take a look at the Troubleshooting guide, and make sure that you have provided all of the relevant information here.

[stamblerre]

Thanks for the report! I am able to reproduce the issue. We'll try to figure out what's going on here.

[heschi]

I reproduced this. Profile shows heavy usage in PathEnclosingInterval, which I think is a known problem.

[heschi]

Specifically, duplicate of #37450.