reflect: panic on recv channel close

It is possible to call reflect.ValueOf(ch).Close() on a recv-only channel,
 while close(ch) is a compile-time error. Following the same reflect
semantics as send and recv this should result in a panic.

Fixes #61445

Change-Id: I2a9ee8f45963593a37bd6df4643dd64fb322f9f9
GitHub-Last-Rev: fe2d5e09f5
GitHub-Pull-Request: golang/go#61453
Reviewed-on: https://go-review.googlesource.com/c/go/+/511295
Auto-Submit: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>

src/reflect/all_test.go

@@ -1706,6 +1706,12 @@ func TestChan(t *testing.T) {
 		if i, ok := cv.Recv(); i.Int() != 0 || ok {
 			t.Errorf("after close Recv %d, %t", i.Int(), ok)
 		}
+		// Closing a read-only channel
+		shouldPanic("", func() {
+			c := make(<-chan int, 1)
+			cv := ValueOf(c)
+			cv.Close()
+		})
 	}
 
 	// check creation of unbuffered channel

src/reflect/value.go

@@ -1187,10 +1187,16 @@ func (v Value) capNonSlice() int {
 }
 
 // Close closes the channel v.
-// It panics if v's Kind is not Chan.
+// It panics if v's Kind is not Chan or
+// v is a receive-only channel.
 func (v Value) Close() {
 	v.mustBe(Chan)
 	v.mustBeExported()
+	tt := (*chanType)(unsafe.Pointer(v.typ()))
+	if ChanDir(tt.Dir)&SendDir == 0 {
+		panic("reflect: close of receive-only channel")
+	}
+
 	chanclose(v.pointer())
 }