Use pretty printers for struct member stubs

PR29079 shows that pretty printers can be used for an incomplete
type (stub), but only when printing it directly, not if it's
part of another struct:
```
(gdb) p s
$1 = {pp m_i = 5}
(gdb) p s2
$2 = {m_s = <incomplete type>, m_l = 20}
```

The reason is simply that in common_val_print the check for stubs
is before any pretty printer is tried.
It works if the pretty printer is tried before the stub check:
```
(gdb) p s
$1 = {pp m_i = 5}
(gdb) p s2
$2 = {m_s = {pp m_i = 10}, m_l = 20}
```

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29079
Approved-By: Tom Tromey <tom@tromey.com>

1 files changed, 36 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.python/py-prettyprint-stub.cc b/gdb/testsuite/gdb.python/py-prettyprint-stub.cc
new file mode 100644
index 0000000..9b0aef3
--- /dev/null
+++ b/gdb/testsuite/gdb.python/py-prettyprint-stub.cc
@@ -0,0 +1,36 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2023 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include "py-prettyprint-stub.h"
+
+struct S2
+{
+  S2 (int i, long l) : m_s (i), m_l (l)
+  {
+  }
+
+  S m_s;
+  long m_l;
+};
+
+int main ()
+{
+  S s (5);
+  S2 s2 (10, 20);
+
+  return 0; /* Break here.  */
+}