go: x/tools/gopls: error when using vendoring with 1.14

What did you do?

I was using gopls as usual with VS Code.

My environment uses vendoring (implicitly) with the new 1.14 automatic vendor detection.

What did you expect to see?

No errors.

What did you see instead?

An error pop up:

Your workspace is misconfigured: go [-m -json all]: exit status 1: go list -m: can't compute 'all' using the vendor directory (Use -mod=mod or -mod=readonly to bypass.)

It seems some command used by gopls is causing issues when -mod=vendor is set implicitly by the go tool.

Build info

golang.org/x/tools/gopls v0.3.3
    golang.org/x/tools/gopls@v0.3.3 h1:mTFqRDJQmpSsgDDWvbtGnSva1z9uX2XcDszSWa6DhBQ=
    github.com/BurntSushi/toml@v0.3.1 h1:WXkYYl6Yr3qBf1K79EBnL4mak0OimBfB0XUf9Vl28OQ=
    github.com/sergi/go-diff@v1.0.0 h1:Kpca3qRNrduNnOQeazBd0ysaKrUJiIuISHxogkT9RPQ=
    golang.org/x/mod@v0.1.1-0.20191105210325-c90efee705ee h1:WG0RUwxtNT4qqaXX3DPA8zHFNm/D9xaBpxzHt1WcA/E=
    golang.org/x/sync@v0.0.0-20190423024810-112230192c58 h1:8gQV6CLnAEikrhgkHFbMAEhagSSnXWGV915qUMm9mrU=
    golang.org/x/tools@v0.0.0-20200227200655-6862ededa516 h1:OX66ZzpltgCOuBSGdaeT77hS2z3ub2AB+EuGxvGRBLE=
    golang.org/x/xerrors@v0.0.0-20191011141410-1b5146add898 h1:/atklqdjdhuosWIl6AIbOeHJjicWYPqR9bpxqxYG2pA=
    honnef.co/go/tools@v0.0.1-2020.1.3 h1:sXmLre5bzIR6ypkjXCDI3jHPssRhc8KD/Ome589sc3U=
    mvdan.cc/xurls/v2@v2.1.0 h1:KaMb5GLhlcSX+e+qhbRJODnUUBvlw01jt4yrjFIHAuA=

Go info

go version go1.14 linux/amd64

GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/<redacted>/.cache/go-build"
GOENV="/home/<redacted>/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GONOPROXY="<redacted>"
GONOSUMDB="<redacted>"
GOOS="linux"
GOPATH="/home/<redacted>/go"
GOPRIVATE="<redacted>"
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/lib/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/lib/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
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-build121565687=/tmp/go-build -gno-record-gcc-switches"