x/tools/gopls: no diagnostics where go vet reports an error

[myitcv]

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

$ go version
go version devel +869e2957b9 Mon Nov 16 22:24:14 2020 +0000 linux/amd64
$ go list -m golang.org/x/tools
golang.org/x/tools v0.0.0-20201118030313-598b068a9102
$ go list -m golang.org/x/tools/gopls
golang.org/x/tools/gopls v0.0.0-20201118030313-598b068a9102

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/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"
GOVCS=""
GOVERSION="devel +869e2957b9 Mon Nov 16 22:24:14 2020 +0000"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/home/myitcv/.vim/plugged/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-build720948317=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Consider:

-- go.mod --
module mod.com

go 1.16

require github.com/rogpeppe/go-internal v1.6.2
-- main.go --
package main

import "github.com/rogpeppe/go-internal/testscript"

func main() {
	var ts *testscript.TestScript
	ts.Fatalf("this is a test %s")
}

• Open main.go with a gopls connected editor
• Notice there are no diagnostics
• Run go vet from the command line
• Notice you get:

# mod.com
./main.go:7:2: Fatalf format %s reads arg #1, but call has 0 args

What did you expect to see?

A diagnostic in gopls

What did you see instead?

As above

Log file: bad.log

---

cc @stamblerre

FYI @leitzler

[stamblerre]

This is caused by the fact that we type-check dependencies in "exported" mode, so the facts from the testscript package are not produced.

[stamblerre]

Duplicate of #38278