gdb: add an assert to cmd_list_element constructor

The cmd_list_element::doc variable must be non-nullptr, otherwise, in
`help_cmd` (cli/cli-decode.c), we will trigger an assert when we run
one of these lines:

      gdb_puts (c->doc, stream);

or,

      gdb_puts (alias->doc, stream);

as gdb_puts requires that the first argument (the doc string) be
non-nullptr.

Better, I think, to assert when the cmd_list_element is created,
rather than catching an assert later when 'help CMD' is used.

I only ran into this case when messing with the Python API command
creation code, I accidentally created a command with a nullptr doc
string, and only found out when I ran 'help CMD' and got an
assertion.

While I'm adding this assertion, I figure I should also assert that
the command name is not nullptr too.  Looking through cli-decode.c,
there seems to be plenty of places where we assume a non-nullptr name.

Built and tested on x86-64 GNU/Linux with an all-targets build; I
don't see any regressions, so (I hope) there are no commands that
currently violate this assertion.

Approved-By: Simon Marchi <simon.marchi@efficios.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/gdb/cli/cli-decode.h b/gdb/cli/cli-decode.h
index 217afbc..9be446f 100644
--- a/gdb/cli/cli-decode.h
+++ b/gdb/cli/cli-decode.h
@@ -62,6 +62,8 @@ struct cmd_list_element
       type (not_set_cmd),
       doc (doc_)
   {
+    gdb_assert (name != nullptr);
+    gdb_assert (doc != nullptr);
     memset (&function, 0, sizeof (function));
   }