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, 16 insertions, 0 deletions

diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 6ad2754..f4dfac2 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -24096,6 +24096,21 @@ define adder
 end
 @end smallexample
 
+Combining with the @code{eval} command (@pxref{eval}) makes it easier
+to process a variable number of arguments:
+
+@smallexample
+define adder
+  set $i = 0
+  set $sum = 0
+  while $i < $argc
+    eval "set $sum = $sum + $arg%d", $i
+    set $i = $i + 1
+  end
+  print $sum
+end
+@end smallexample
+
 @table @code
 
 @kindex define
@@ -24526,6 +24541,7 @@ Here's an example of printing DFP types using the above conversion letters:
 printf "D32: %Hf - D64: %Df - D128: %DDf\n",1.2345df,1.2E10dd,1.2E1dl
 @end smallexample
 
+@anchor{eval}
 @kindex eval
 @item eval @var{template}, @var{expressions}@dots{}
 Convert the values of one or more @var{expressions} under the control of