go/types: print, println accept 0 or more arguments

R=adonovan
CC=golang-dev
https://golang.org/cl/7304089

src/pkg/go/types/builtins.go

@@ -41,7 +41,7 @@ func (check *checker) builtin(x *operand, call *ast.CallExpr, bin *builtin, iota
 	if n > 0 {
 		arg0 = args[0]
 		switch id {
-		case _Make, _New, _Trace:
+		case _Make, _New, _Print, _Println, _Trace:
 			// respective cases below do the work
 		default:
 			// argument must be an expression
@@ -301,9 +301,15 @@ func (check *checker) builtin(x *operand, call *ast.CallExpr, bin *builtin, iota
 		x.mode = variable
 		x.typ = &Pointer{Base: resultTyp}
 
-	case _Panic, _Print, _Println:
-		for _, arg := range args[1:] {
+	case _Panic:
+		x.mode = novalue
+
+	case _Print, _Println:
+		for _, arg := range args {
 			check.expr(x, arg, nil, -1)
+			if x.mode == invalid {
+				goto Error
+			}
 		}
 		x.mode = novalue
 

src/pkg/go/types/testdata/builtins.src

@@ -214,6 +214,32 @@ func _new() {
 	new /* ERROR "not used" */ (int)
 }
 
+func _panic() {
+	panic /* ERROR "arguments" */ ()
+	panic /* ERROR "arguments" */ (1, 2)
+	panic(0)
+	panic("foo")
+	panic(false)
+}
+
+func _print() {
+	print()
+	print(1)
+	print(1, 2)
+	print("foo")
+	print(2.718281828)
+	print(false)
+}
+
+func _println() {
+	println()
+	println(1)
+	println(1, 2)
+	println("foo")
+	println(2.718281828)
+	println(false)
+}
+
 func _real() {
 	var f32 float32
 	var f64 float64

src/pkg/go/types/universe.go

@@ -73,8 +73,8 @@ var predeclaredFunctions = [...]*builtin{
 	{_Make, "make", 1, true, false},
 	{_New, "new", 1, false, false},
 	{_Panic, "panic", 1, false, true},
-	{_Print, "print", 1, true, true},
-	{_Println, "println", 1, true, true},
+	{_Print, "print", 0, true, true},
+	{_Println, "println", 0, true, true},
 	{_Real, "real", 1, false, false},
 	{_Recover, "recover", 0, false, true},