cmd/go: go install should warn when installing outside PATH

[pjweinbgo]

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

$ go version
go version go1.13 darwin/amd64

Does this issue reproduce with the latest release?

What operating system and processor architecture are you using (go env)?

go env Output

$ go env

GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/pjw/Library/Caches/go-build"
GOENV="/Users/pjw/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/pjw/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/darwin_amd64"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/pjw/gostuff/src/golang.org/x/tools/gopls/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 -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/72/mj6w6gyj5dn6yp_2_tlbdwym00052r/T/go-build953192293=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

In golang.org/x/tools/gopls, do
go install .
as GOBIN is not set and GOPATH is, the output is put in $GOPATH/bin.

What did you expect to see?

I expected it to warn me that I would not find the new executable in my PATH.

What did you see instead?

silence. I know this is my misconfiguration, but a little help would have been nice.

[dmitshur]

/cc @bcmills @jayconrod

[flavienbwk]

This is still a confusing behaviour in october 2021 with 1.17