x/tools/gopls coc.nvim wrong highlight for undeclared and unused vars

[qumusabel]

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

$ go version
go version go1.17.1 linux/amd64

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=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/qumu/.cache/go-build"
GOENV="/home/qumu/.config/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/qumu/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/qumu/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/lib/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/lib/go/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="go1.17.1"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/dev/null"
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-build1213733929=/tmp/go-build -gno-record-gcc-switches"

What did you do?

gopls with coc.nvim uses wrong highlight for unused and undeclared variables

What did you expect to see?

Underlined undeclared names, greyed out unused names

What did you see instead?

(below is pyright)

[findleyr]

Thanks for the report!

I haven't had time to repro, but it looks like our undeclared name analysis suggests a fix which uses a command, rather than edits. This logic is then incorrect:
https://cs.opensource.google/go/x/tools/+/master:internal/lsp/cache/errors.go;l=234;drc=a55d5155d907b5d1114e99daae56070cc0253114

We need to check that we have non-zero textual edits, not that we have non-zero fixes...

[gopherbot]

Change https://golang.org/cl/355769 mentions this issue: internal/lsp/cache: fix incorrect detection of useless code

[qumusabel]

Thanks! Undeclared variables are showed correctly for me now.
Unused vars are still underlined though, but if I understand it right, they are indeed errors and this is correct behavior. (Still I would have preferred them to be greyed out...)

[findleyr]

Unused vars are still underlined though, but if I understand it right, they are indeed errors and this is correct behavior.

The current logic to detect 'unnecessary' code in gopls looks for suggested edits that are pure deletions. We don't have such a suggested fix for unused vars. (note that while we could apply the 'Unnecessary' label without a suggested fix, doing either is approximately the same amount of work).

Filed #48975 for the suggested fix.