Fix PR 20559 - "eval" command and $arg0...$arg9/$argc substitution

It'd be handy to be able to iterate over command arguments in
user-defined commands, in order to support optional arguments
($arg0..$argN).

I thought I could make it work with "eval", but alas, it doesn't work
currently.  E.g., with:

 define test
   set $i = 0
   while $i < $argc
     eval "print $arg%d", $i
     set $i = $i + 1
   end
 end

we get:

 (gdb) test 1
 $1 = void
 (gdb) test 1 2 3
 $2 = void
 $3 = void
 $4 = void
 (gdb)

The problem is that "eval" doesn't do user-defined command arguments
substitution after expanding its own argument.  This patch fixes that,
which makes the example above work:

 (gdb) test 1
 $1 = 1
 (gdb) test 1 2 3
 $2 = 1
 $3 = 2
 $4 = 3
 (gdb)

New test included, similar the above, but also exercises expanding
$argc.

I think this is likely to simplify many scripts out there, so I'm
adding an example to the manual and mentioning it in NEWS as well.

gdb/ChangeLog:
2016-12-02  Pedro Alves  <palves@redhat.com>

	PR cli/20559
	* NEWS: Mention "eval" expands user-defined command arguments.
	* cli/cli-script.c (execute_control_command): Adjust to rename.
	(insert_args): Rename to ...
	(insert_user_defined_cmd_args): ... this, and make extern.
	* cli/cli-script.h (insert_user_defined_cmd_args): New
	declaration.
	* printcmd.c: Include "cli/cli-script.h".
	(eval_command): Call insert_user_defined_cmd_args.

gdb/doc/ChangeLog:
2016-12-02  Pedro Alves  <palves@redhat.com>

	PR cli/20559
	* gdb.texinfo (Define): Add example of using "eval" to process a
	variable number of arguments.
	(Output) <eval>: Add anchor.

gdb/testsuite/ChangeLog:
2016-12-02  Pedro Alves  <palves@redhat.com>

	PR cli/20559
	* gdb.base/commands.exp (user_defined_command_args_eval): New
	procedure.
	(top level): Call it.

1 files changed, 12 insertions, 0 deletions

diff --git a/gdb/NEWS b/gdb/NEWS
index a597405..4089124 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -32,6 +32,18 @@
 
 * Support for Java programs compiled with gcj has been removed.
 
+* The "eval" command now expands user-defined command arguments.
+
+  This makes it easier to process a variable number of arguments:
+
+   define mycommand
+     set $i = 0
+     while $i < $argc
+       eval "print $arg%d", $i
+       set $i = $i + 1
+     end
+   end
+
 * New targets
 
 Synopsys ARC			arc*-*-elf32