cmd/vet: fix copylocks false positive on unsafe.Sizeof(mutex)

Fixes #21800

Change-Id: I6c61d3543f28e9951b2a219b3c7298077b38f29e
Reviewed-on: https://go-review.googlesource.com/66210
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

src/cmd/vet/copylock.go

@@ -93,9 +93,16 @@ func checkCopyLocksReturnStmt(f *File, rs *ast.ReturnStmt) {
 
 // checkCopyLocksCallExpr detects lock copy in the arguments to a function call
 func checkCopyLocksCallExpr(f *File, ce *ast.CallExpr) {
-	if id, ok := ce.Fun.(*ast.Ident); ok && f.pkg.types[id].IsBuiltin() {
-		switch id.Name {
-		case "new", "len", "cap":
+	var id *ast.Ident
+	switch fun := ce.Fun.(type) {
+	case *ast.Ident:
+		id = fun
+	case *ast.SelectorExpr:
+		id = fun.Sel
+	}
+	if fun, ok := f.pkg.uses[id].(*types.Builtin); ok {
+		switch fun.Name() {
+		case "new", "len", "cap", "Sizeof":
 			return
 		}
 	}

src/cmd/vet/testdata/copylock.go

@@ -3,6 +3,9 @@ package testdata
 import (
 	"sync"
 	"sync/atomic"
+	"unsafe"
+	. "unsafe"
+	unsafe1 "unsafe"
 )
 
 func OkFunc() {
@@ -102,6 +105,17 @@ func LenAndCapOnLockArrays() {
 	cap(a) // ERROR "call of cap copies lock value: sync.Mutex"
 }
 
+func SizeofMutex() {
+	var mu sync.Mutex
+	unsafe.Sizeof(mu)  // OK
+	unsafe1.Sizeof(mu) // OK
+	Sizeof(mu)         // OK
+	unsafe := struct{ Sizeof func(interface{}) }{}
+	unsafe.Sizeof(mu) // ERROR "call of unsafe.Sizeof copies lock value: sync.Mutex"
+	Sizeof := func(interface{}) {}
+	Sizeof(mu) // ERROR "call of Sizeof copies lock value: sync.Mutex"
+}
+
 // SyncTypesCheck checks copying of sync.* types except sync.Mutex
 func SyncTypesCheck() {
 	// sync.RWMutex copying