reflect: fix nil array pointer caused panic

Change-Id: I499d3177f219e813e2d88441d04c044feb3081de
GitHub-Last-Rev: 81c4a170d7
GitHub-Pull-Request: golang/go#78928
Reviewed-on: https://go-review.googlesource.com/c/go/+/770302
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Sean Liao <sean@liao.dev>
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Carlos Amedee <carlos@golang.org>
Auto-Submit: Sean Liao <sean@liao.dev>

src/reflect/iter.go

@@ -68,12 +68,12 @@ func (v Value) Seq() iter.Seq[Value] {
 	case Uintptr:
 		return rangeNum[uintptr](v.Uint(), v.Type())
 	case Pointer:
-		if v.Elem().kind() != Array {
+		if v.Type().Elem().Kind() != Array {
 			break
 		}
+		n := v.Type().Elem().Len()
 		return func(yield func(Value) bool) {
-			v = v.Elem()
-			for i := range v.Len() {
+			for i := range n {
 				if !yield(ValueOf(i)) {
 					return
 				}

src/reflect/iter_test.go

@@ -91,6 +91,19 @@ func TestValueSeq(t *testing.T) {
 				t.Fatalf("should loop four times")
 			}
 		}},
+		// Regression: Value.Seq on a nil *[n]int must not panic (Elem of nil ptr is invalid).
+		{"nil *[3]int", ValueOf((*[3]int)(nil)), func(t *testing.T, s iter.Seq[Value]) {
+			i := int64(0)
+			for v := range s {
+				if v.Int() != i {
+					t.Fatalf("got %d, want %d", v.Int(), i)
+				}
+				i++
+			}
+			if i != 3 {
+				t.Fatalf("should loop three times, got %d", i)
+			}
+		}},
 		{"[4]int", ValueOf([4]int{1, 2, 3, 4}), func(t *testing.T, s iter.Seq[Value]) {
 			i := int64(0)
 			for v := range s {