Please answer these questions before submitting your issue. Thanks!

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

go version go1.9 darwin/amd64

Does this issue reproduce with the latest release?

Yes

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

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/achilleroussel/dev"
GORACE=""
GOROOT="/usr/local/go"
GOTOOLDIR="/usr/local/go/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/0p/tfjq063j4hdcjnm0_9qb4bww0000gn/T/go-build312584611=/tmp/go-build -gno-record-gcc-switches -fno-common"
CXX="clang++"
CGO_ENABLED="1"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"

What did you do?

go vet gives a false positive when using unsafe.Sizeof on an expression that would copy a sync.Mutex, here's a minimal example:

package main

import (
	"sync"
	"unsafe"
)

func main() {
	mu := sync.Mutex{}
	println(unsafe.Sizeof(mu))
}

$ go vet ./test.go
test.go:10: call of unsafe.Sizeof copies lock value: sync.Mutex
exit status 1

What did you expect to see?

I would expect go vet to not report unsafe.Sizeof as an unsafe operation since it's resolved at compile time and therefore doesn't cause a copy. It should also return 0 in the program given as example.

What did you see instead?

go vet returns 1 to indicate a failure because it misinterpreted the call to unsafe.Sizeof as making a copy of a mutex.