x/tools/gopls: no diagnostics received for initially empty files (sometimes)

[myitcv]

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

$ go version
go version devel +d286e61b67 Mon Jun 15 23:29:23 2020 +0000 linux/amd64
$ go list -m golang.org/x/tools
golang.org/x/tools v0.0.0-20200617042924-7f3f4b10a808
$ go list -m golang.org/x/tools/gopls
golang.org/x/tools/gopls v0.0.0-20200617042924-7f3f4b10a808

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=""
GOMODCACHE="/home/myitcv/gostuff/pkg/mod"
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-build538522998=/tmp/go-build -gno-record-gcc-switches"

What did you do?

govim has a test that verifies we receive expected diagnostics in the case where files are initially empty on disk, but subsequently get populated with content in the editor.

https://github.com/govim/govim/blob/e2a1802131f331832d667736aa27f023636f0c3a/cmd/govim/testdata/scenario_default/quickfix_empty_files.txt

Recently (apologies, I can't be any more specific than saying "in the last 2-3 weeks) we have started to see, and continue to see, a small number of flakes in this test.

In a normal run of this test we expect a set of diagnostics; when we see these flakes, we don't see any diagnostics.

Here is a gopls log file from a passing test run. Notice the DidChange notifications, as well as the PublishDiagnostics notifications: gopls.log

And here is the gopls log from a failing test run. Notice the DidChange notifications, but no PublishDiagnostics notifications: gopls.log

What did you expect to see?

A consistently passing test.

What did you see instead?

Flakes as described above.

---

cc @stamblerre @findleyr

FYI @leitzler

[myitcv]

FYI we're still seeing ~1 failure per day (in a build matrix of 12 entries) in the govim gopls@master build runs.

[stamblerre]

Thanks for the report! I am going to convert this into a gopls regression test and see if I can reproduce the issue.

[gopherbot]

Change https://golang.org/cl/240063 mentions this issue: internal/lsp: add a new regtest to reproduce golang/go#39646

[stamblerre]

I tried to reproduce the test as carefully as possible in my CL, but I haven't been able to trigger the failure. The issue is that the new files are getting treated like command-line-arguments packages, which should only happen when they are empty. I wonder if we will see similar flakes on the builders.

In the logs, I see command-line-arguments in the packages.Load at snapshot 3, which is the point at which p/p.go should be in a good state. I don't see any packages.Load results for snapshot 1, which is when you might expect a command-line-arguments result. One more thing to try would be adding an analogous go/packages test.

[gopherbot]

Change https://golang.org/cl/240098 mentions this issue: internal/lsp: reproduce and fix golang/go#39646