go: cmd/go/internal/test: -vet accepts bad input

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

$ go version
go version go1.16.6 linux/amd64

Does this issue reproduce with the latest release?

yes

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

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/user/.cache/go-build"
GOENV="/home/user/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/user/go/pkg/mod"
GOOS="linux"
GOPATH="/home/user/go"
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="go1.16.6"
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-build2105906029=/tmp/go-build -gno-record-gcc-switches"

What did you do?

https://play.golang.org/p/t6Q8DJU3ON6

go test .
go test -vet=all .

What did you expect to see?

ok  	trash/five	(cached) [no tests to run]
deprecated flag provided: -all

What did you see instead?

ok  	trash/five	(cached) [no tests to run]
# trash/five
./main.go:7:8: using r before checking for errors
FAIL	trash/five [build failed]
FAIL

What would you like done?

This came out of development on #45963 [CL 334873]. It was discovered that go test -vet=all, actually works today. This is because unlike what the docs say -vet simply passes the list of “checks”, with - prefixes, to go vet as flag arguments.

-vet list Configure the invocation of “go vet” during “go test” to use the comma-separated list of vet checks. If list is empty, “go test” runs “go vet” with a curated list of checks believed to be always worth addressing. If list is “off”, “go test” does not run “go vet” at all.

This was is an intended feature and seems quite brittle. As such, we should pin -vet to the documented interface, or define what “flags” we accept and update the the documentation. If we are not expanding the definition, we should ignore or error on all the deprecated and non-check name flags: -V, -source, -c, -printfuncs, and -printf.funcs(anything with a dot). (This is very much a blocklist, since we want to allow new checks to be added over time.)