[PATCH 2/4] gdb: add assert in cmd_list_element::set_context

[Simon Marchi <simon.marchi@polymtl.ca>]

If something tries to set a context pointer on a cmd_list_element and
m_context is no nullptr, it's likely that two parts of the code are
trying to set different contexts, and one will overwrite the other.
This is almost guaranteed to lead to bad behavior or a crash, as one of
the spots will not be using the data it expects.  This happened to me
during development, so I think having this assert would be useful to
catch this problem earlier.

gdb/ChangeLog:

	* cli/cli-decode.h (struct cmd_list_element) <set_context>: Add
	assert.

Change-Id: I1f2e9fda1bf2bec1b732c9b90e7d7910a97f2ac6
---
 gdb/cli/cli-decode.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/gdb/cli/cli-decode.h b/gdb/cli/cli-decode.h
index 1692a6e28352..241535ae5b50 100644
--- a/gdb/cli/cli-decode.h
+++ b/gdb/cli/cli-decode.h
@@ -94,7 +94,10 @@ struct cmd_list_element
   { return this->func == nullptr; }
 
   void set_context (void *context)
-  { m_context = context; }
+  {
+    gdb_assert (m_context == nullptr);
+    m_context = context;
+  }
 
   void *context () const
   { return m_context; }
-- 
2.32.0