reflect: handle String kind in Value.{Pointer,UnsafePointer}

Updates #61308

Change-Id: I92d459383c520d137787ce5c8f135d205af74e5d
Reviewed-on: https://go-review.googlesource.com/c/go/+/516596
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Auto-Submit: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>

src/reflect/all_test.go

@@ -8512,3 +8512,39 @@ func TestClear(t *testing.T) {
 		})
 	}
 }
+
+func TestValuePointerAndUnsafePointer(t *testing.T) {
+	ptr := new(int)
+	ch := make(chan int)
+	m := make(map[int]int)
+	unsafePtr := unsafe.Pointer(ptr)
+	slice := make([]int, 1)
+	fn := func() {}
+	s := "foo"
+
+	tests := []struct {
+		name              string
+		val               Value
+		wantUnsafePointer unsafe.Pointer
+	}{
+		{"pointer", ValueOf(ptr), unsafe.Pointer(ptr)},
+		{"channel", ValueOf(ch), *(*unsafe.Pointer)(unsafe.Pointer(&ch))},
+		{"map", ValueOf(m), *(*unsafe.Pointer)(unsafe.Pointer(&m))},
+		{"unsafe.Pointer", ValueOf(unsafePtr), unsafePtr},
+		{"function", ValueOf(fn), **(**unsafe.Pointer)(unsafe.Pointer(&fn))},
+		{"slice", ValueOf(slice), unsafe.Pointer(unsafe.SliceData(slice))},
+		{"string", ValueOf(s), unsafe.Pointer(unsafe.StringData(s))},
+	}
+
+	for _, tc := range tests {
+		tc := tc
+		t.Run(tc.name, func(t *testing.T) {
+			if got := tc.val.Pointer(); got != uintptr(tc.wantUnsafePointer) {
+				t.Errorf("unexpected uintptr result, got %#x, want %#x", got, uintptr(tc.wantUnsafePointer))
+			}
+			if got := tc.val.UnsafePointer(); got != tc.wantUnsafePointer {
+				t.Errorf("unexpected unsafe.Pointer result, got %#x, want %#x", got, tc.wantUnsafePointer)
+			}
+		})
+	}
+}