go/types: don't allow f()... if f() is multi-valued

Also: Better position for error messages related to wrong use of ... .

Fixes #9473.

Change-Id: I90565f51a42897b7292f651a84a23611a5d8f359
Reviewed-on: https://go-review.googlesource.com/2390
Reviewed-by: Alan Donovan <adonovan@google.com>

go/types/builtins.go

@@ -48,7 +48,6 @@ func (check *Checker) builtin(x *operand, call *ast.CallExpr, id builtinId) (_ b
 		// make argument getter
 		arg, nargs, _ = unpack(func(x *operand, i int) { check.expr(x, call.Args[i]) }, nargs, false)
 		if arg == nil {
-			x.mode = invalid
 			return
 		}
 		// evaluate first argument, if present

go/types/call.go

@@ -179,14 +179,18 @@ func unpack(get getter, n int, allowCommaOk bool) (getter, int, bool) {
 // arguments checks argument passing for the call with the given signature.
 // The arg function provides the operand for the i'th argument.
 func (check *Checker) arguments(x *operand, call *ast.CallExpr, sig *Signature, arg getter, n int) {
-	passSlice := false
 	if call.Ellipsis.IsValid() {
 		// last argument is of the form x...
-		if sig.variadic {
+		if len(call.Args) == 1 && n > 1 {
-			passSlice = true
+			// f()... is not permitted if f() is multi-valued
-		} else {
+			check.errorf(call.Ellipsis, "cannot use ... with %d-valued expression %s", n, call.Args[0])
+			check.useGetter(arg, n)
+			return
+		}
+		if !sig.variadic {
 			check.errorf(call.Ellipsis, "cannot use ... in call to non-variadic %s", call.Fun)
-			// ok to continue
+			check.useGetter(arg, n)
+			return
 		}
 	}
 
@@ -194,7 +198,11 @@ func (check *Checker) arguments(x *operand, call *ast.CallExpr, sig *Signature,
 	for i := 0; i < n; i++ {
 		arg(x, i)
 		if x.mode != invalid {
-			check.argument(sig, i, x, passSlice && i == n-1)
+			var ellipsis token.Pos
+			if i == n-1 && call.Ellipsis.IsValid() {
+				ellipsis = call.Ellipsis
+			}
+			check.argument(sig, i, x, ellipsis)
 		}
 	}
 
@@ -211,8 +219,8 @@ func (check *Checker) arguments(x *operand, call *ast.CallExpr, sig *Signature,
 }
 
 // argument checks passing of argument x to the i'th parameter of the given signature.
-// If passSlice is set, the argument is followed by ... in the call.
+// If ellipsis is valid, the argument is followed by ... at that position in the call.
-func (check *Checker) argument(sig *Signature, i int, x *operand, passSlice bool) {
+func (check *Checker) argument(sig *Signature, i int, x *operand, ellipsis token.Pos) {
 	n := sig.params.Len()
 
 	// determine parameter type
@@ -232,13 +240,19 @@ func (check *Checker) argument(sig *Signature, i int, x *operand, passSlice bool
 		return
 	}
 
-	if passSlice {
+	if ellipsis.IsValid() {
 		// argument is of the form x...
 		if i != n-1 {
-			check.errorf(x.pos(), "can only use ... with matching parameter")
+			check.errorf(ellipsis, "can only use ... with matching parameter")
 			return
 		}
-		if _, ok := x.typ.Underlying().(*Slice); !ok {
+		switch t := x.typ.Underlying().(type) {
+		case *Slice:
+			// ok
+		case *Tuple:
+			check.errorf(ellipsis, "cannot use ... with %d-valued expression %s", t.Len(), x)
+			return
+		default:
 			check.errorf(x.pos(), "cannot use %s as parameter of type %s", x, typ)
 			return
 		}

go/types/initorder.go

@@ -137,7 +137,7 @@ func (check *Checker) reportCycle(cycle []*objNode, i int) {
 	obj := cycle[i].obj
 	check.errorf(obj.Pos(), "initialization cycle for %s", obj.Name())
 	// print cycle
-	for _ = range cycle {
+	for range cycle {
 		check.errorf(obj.Pos(), "\t%s refers to", obj.Name()) // secondary error, \t indented
 		i++
 		if i >= len(cycle) {

go/types/testdata/builtins.src

@@ -24,11 +24,11 @@ func append1() {
 	_ = append(s, b)
 	_ = append(s, x /* ERROR cannot pass argument x */ )
 	_ = append(s, s /* ERROR cannot pass argument s */ )
-	_ = append(s /* ERROR can only use ... with matching parameter */ ...)
+	_ = append(s... /* ERROR can only use ... with matching parameter */ )
-	_ = append(s, b, s /* ERROR can only use ... with matching parameter */ ...)
+	_ = append(s, b, s... /* ERROR can only use ... with matching parameter */ )
 	_ = append(s, 1, 2, 3)
 	_ = append(s, 1, 2, 3, x /* ERROR cannot pass argument x */ , 5, 6, 6)
-	_ = append(s, 1, 2, s /* ERROR can only use ... with matching parameter */ ...)
+	_ = append(s, 1, 2, s... /* ERROR can only use ... with matching parameter */ )
 	_ = append([]interface{}(nil), 1, 2, "foo", x, 3.1425, false)
 
 	type S []byte

go/types/testdata/expr3.src

@@ -439,7 +439,7 @@ func _calls() {
 	fv(s /* ERROR "cannot pass" */ )
 	fv(s...)
 	fv(x /* ERROR "cannot use" */ ...)
-	fv(1, s /* ERROR "can only use ... with matching parameter" */ ...)
+	fv(1, s... /* ERROR "can only use ... with matching parameter" */ )
 	fv(gs /* ERROR "cannot pass" */ ())
 	fv(gs /* ERROR "cannot pass" */ ()...)
 
@@ -448,7 +448,7 @@ func _calls() {
 	t.fm(1, 2.0, x)
 	t.fm(s /* ERROR "cannot pass" */ )
 	t.fm(g1())
-	t.fm(1, s /* ERROR "can only use ... with matching parameter" */ ...)
+	t.fm(1, s... /* ERROR "can only use ... with matching parameter" */ )
 	t.fm(gs /* ERROR "cannot pass" */ ())
 	t.fm(gs /* ERROR "cannot pass" */ ()...)
 
@@ -456,7 +456,7 @@ func _calls() {
 	T.fm(t, 1, 2.0, x)
 	T.fm(t, s /* ERROR "cannot pass" */ )
 	T.fm(t, g1())
-	T.fm(t, 1, s /* ERROR "can only use ... with matching parameter" */ ...)
+	T.fm(t, 1, s... /* ERROR "can only use ... with matching parameter" */ )
 	T.fm(t, gs /* ERROR "cannot pass" */ ())
 	T.fm(t, gs /* ERROR "cannot pass" */ ()...)
 
@@ -465,7 +465,7 @@ func _calls() {
 	i.fm(1, 2.0, x)
 	i.fm(s /* ERROR "cannot pass" */ )
 	i.fm(g1())
-	i.fm(1, s /* ERROR "can only use ... with matching parameter" */ ...)
+	i.fm(1, s... /* ERROR "can only use ... with matching parameter" */ )
 	i.fm(gs /* ERROR "cannot pass" */ ())
 	i.fm(gs /* ERROR "cannot pass" */ ()...)
 

go/types/testdata/issues.src

@@ -41,3 +41,33 @@ func issue9182() {
 	// no error for composite literal based on unknown type
 	_ = Point{x: 1, y: 2}
 }
+
+func f0() (a []int)         { return }
+func f1() (a []int, b int)  { return }
+func f2() (a, b []int)      { return }
+
+func append_([]int, ...int) {}
+
+func issue9473(a []int, b ...int) {
+	// variadic builtin function
+	_ = append(f0())
+	_ = append(f0(), f0()...)
+	_ = append(f1())
+	_ = append(f2 /* ERROR cannot pass argument */ ())
+	_ = append(f2()... /* ERROR cannot use ... */ )
+	_ = append(f0(), f1 /* ERROR 2-valued expression */ ())
+	_ = append(f0(), f2 /* ERROR 2-valued expression */ ())
+	_ = append(f0(), f1()... /* ERROR cannot use ... */ )
+	_ = append(f0(), f2()... /* ERROR cannot use ... */ )
+
+	// variadic user-defined function
+	append_(f0())
+	append_(f0(), f0()...)
+	append_(f1())
+	append_(f2 /* ERROR cannot pass argument */ ())
+	append_(f2()... /* ERROR cannot use ... */ )
+	append_(f0(), f1 /* ERROR 2-valued expression */ ())
+	append_(f0(), f2 /* ERROR 2-valued expression */ ())
+	append_(f0(), f1()... /* ERROR cannot use */ )
+	append_(f0(), f2()... /* ERROR cannot use */ )
+}