[PATCH 2/3] gdb/record: add an assert in cmd_record_start

[Andrew Burgess <aburgess@redhat.com>]

The 'record' command is both a prefix command AND an alias for 'target
record-full'.  As it is a prefix command, if a user types:

  (gdb) record blah

Then GDB will look for, and try to invoke the 'blah' sub-command.
This will either succeed (if blah is found) or throw an error (if blah
is not found).

As such, the only way to invoke the 'record' command is like:

  (gdb) record

It is impossible to pass arguments to the 'record' command.  As we
know this is true then we can assert this in cmd_record_start.

I added this assert because initially I was going to try forwarding
ARGS from cmd_record_start to the 'target record-full' command, but
then I realised passing arguments to 'record' was impossible.

There should be no user visible changes after this commit.
---
 gdb/record.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/gdb/record.c b/gdb/record.c
index 25a4c1e71b6..5b1093dd12e 100644
--- a/gdb/record.c
+++ b/gdb/record.c
@@ -260,11 +260,16 @@ show_record_debug (struct ui_file *file, int from_tty,
 	      value);
 }
 
-/* Alias for "target record".  */
+/* Alias for "target record-full".  */
 
 static void
 cmd_record_start (const char *args, int from_tty)
 {
+  /* As 'record' is a prefix command then if the user types 'record blah'
+     GDB will search for the 'blah' sub-command and either run that instead
+     of calling this function, or throw an error if 'blah' doesn't exist.
+     As a result, we only get here if no args are given.  */
+  gdb_assert (args == nullptr);
   execute_command ("target record-full", from_tty);
 }
 
-- 
2.25.4