cmd/vet: allow lock types inside built-in new()

Updates #14839
Fixes #14994

Change-Id: I9bb51bad19105a17c80d690c5486e5dd007ac84a
Reviewed-on: https://go-review.googlesource.com/21222
Run-TryBot: Rob Pike <r@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>

src/cmd/vet/copylock.go

@@ -91,8 +91,12 @@ func checkCopyLocksReturnStmt(f *File, rs *ast.ReturnStmt) {
 	}
 }
 
-// checkCopyLocksCallExpr detects lock copy in function call
+// 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 && id.Name == "new" && f.pkg.types[id].IsBuiltin() {
+		// Skip 'new(Type)' for built-in 'new'
+		return
+	}
 	for _, x := range ce.Args {
 		if path := lockPathRhs(f, x); path != nil {
 			f.Badf(x.Pos(), "function call copies lock value: %v", path)

src/cmd/vet/testdata/copylock.go

@@ -17,11 +17,17 @@ func OkFunc() {
 	}
 
 	yy := []Tlock{
-		sync.Tlock{},
-		sync.Tlock{
+		Tlock{},
+		Tlock{
 			once: sync.Once{},
 		},
 	}
+
+	nl := new(sync.Mutex)
+	mx := make([]sync.Mutex, 10)
+	xx := struct{ L *sync.Mutex }{
+		L: new(sync.Mutex),
+	}
 }
 
 type Tlock struct {
@@ -55,4 +61,8 @@ func BadFunc() {
 		t,   // ERROR "literal copies lock value from t: testdata.Tlock contains sync.Once contains sync.Mutex"
 		*tp, // ERROR "literal copies lock value from \*tp: testdata.Tlock contains sync.Once contains sync.Mutex"
 	}
+
+	// override 'new' keyword
+	new := func(interface{}) {}
+	new(t) // ERROR "function call copies lock value: testdata.Tlock contains sync.Once contains sync.Mutex"
 }