x/tools/gopls: add ability to set deep completion Budget via LSP Configuration

[myitcv]

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

$ go version
go version devel +da4d58587e Sat Dec 7 15:57:30 2019 +0000 linux/amd64
$ go list -m golang.org/x/tools
golang.org/x/tools v0.0.0-20191213221258-04c2e8eff935
$ go list -m golang.org/x/tools/gopls
golang.org/x/tools/gopls v0.1.8-0.20191213221258-04c2e8eff935

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"
GOINSECURE=""
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-build191688178=/tmp/go-build -gno-record-gcc-switches"

What did you do?

See below for background. We very quickly established this is related to the deep completion Budget being exceeded. Hence #36142 (comment) and the updated title.

Background

In govim test complete_deep_fuzzy we verify that deep fuzzy completions work.

The test is as simple as ensuring that the input file:

package main

func main() {
	var a struct {
		b struct {
			crikey int
		}
		d int
	}
	var x int
	x = a.ck
}

when completed after a.ck results in:

package main

func main() {
	var a struct {
		b struct {
			crikey int
		}
		d int
	}
	var x int
	x = a.b.crikey
}

However, over 50% of the time we're seeing this test fail because no completion items are returned.

Here are the gopls logs from a failing and passing run:

• fail.log
• pass.log

Much like #35638 this is a timing/race related issue and hard to reproduce standalone. Generally I find this fails when my machine is under high stress.

The test can be run on a machine that uses Docker via:

go test -exec="dockexec govim/govim:go1.13.4_vim_v8.1.2253_v1 -t -e VIM_FLAVOR=vim" -count=1 -v -run "TestScripts/scenario_default/complete_deep_fuzzy" ./cmd/govim

(download of Docker image may initially take some time)

What did you expect to see?

A consistently passing test.

What did you see instead?

Intermittent failures.

---

cc @stamblerre @muirdm

[muirdm]

It might be the completion budget. If it runs out of the (default) 100ms budget, it will give up on deep completions. You can try disabling the "Budget" completion option by setting it to 0, but it isn't currently exposed over LSP.

[myitcv]

The log files attached to the initial comment were incorrect: now fixed.

Also worth noting is that if the initial go.mod is "tidy" then I've currently been unable to reproduce this.

More explicitly, if the initial go.mod is:

module mod.com

Then the test fails as reported above.

However if it is:

module mod.com

go 1.13

it has not yet failed.

[myitcv]

You can try disabling the "Budget" completion option by setting it to 0

Thanks @muirdm - hadn't thought about that. Will try now.

[myitcv]

@muirdm - brilliant observation, thank you. Setting the Budget to 0 has indeed "fixed" the test failures. Hence for integration tests we will need the ability to do this.

I'll change the title of this description to instead be a request to expose gopls configuration to set this value.

[gopherbot]

Change https://golang.org/cl/211584 mentions this issue: internal/lsp: expose option to disable timeouts for completion

[stamblerre]

@myitcv: does the above CL work for you?

[myitcv]

Re-opening until https://go-review.googlesource.com/c/tools/+/211759 lands

[myitcv]

All fixes for this have now landed.