text/template: error on range over send channel

template range require channel contains RecvDir
if recv on send only channel will raise an panic.

Fixes #43065

Change-Id: Ie0ea70ce60e074bf8c9f2378e07ef1d4c41dc38f
Reviewed-on: https://go-review.googlesource.com/c/go/+/276532
Trust: Meng Zhuo <mzh@golangcn.org>
Run-TryBot: Meng Zhuo <mzh@golangcn.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Jonathan Amsterdam <jba@google.com>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>

src/text/template/exec.go

@@ -373,6 +373,10 @@ func (s *state) walkRange(dot reflect.Value, r *parse.RangeNode) {
 		if val.IsNil() {
 			break
 		}
+		if val.Type().ChanDir() == reflect.SendDir {
+			s.errorf("range over send-only channel %v", val)
+			break
+		}
 		i := 0
 		for ; ; i++ {
 			elem, ok := val.Recv()

src/text/template/exec_test.go

@@ -1697,3 +1697,16 @@ func TestIssue31810(t *testing.T) {
 		t.Errorf("%s got %q, expected %q", textCall, b.String(), "result")
 	}
 }
+
+// Issue 43065, range over send only channel
+func TestIssue43065(t *testing.T) {
+	var b bytes.Buffer
+	tmp := Must(New("").Parse(`{{range .}}{{end}}`))
+	ch := make(chan<- int)
+	err := tmp.Execute(&b, ch)
+	if err == nil {
+		t.Error("expected err got nil")
+	} else if !strings.Contains(err.Error(), "range over send-only channel") {
+		t.Errorf("%s", err)
+	}
+}