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.

2 files changed, 14 insertions, 11 deletions

diff --git a/gdb/cli/cli-script.c b/gdb/cli/cli-script.c
index ce4d8cb..15947a9 100644
--- a/gdb/cli/cli-script.c
+++ b/gdb/cli/cli-script.c
@@ -41,8 +41,6 @@ recurse_read_control_structure (char * (*read_next_line_func) (void),
 				void (*validator)(char *, void *),
 				void *closure);
 
-static std::string insert_args (const char *line);
-
 static struct cleanup * setup_user_args (char *p);
 
 static char *read_next_line (void);
@@ -455,7 +453,7 @@ execute_control_command (struct command_line *cmd)
     case simple_control:
       {
 	/* A simple command, execute it and return.  */
-	std::string new_line = insert_args (cmd->line);
+	std::string new_line = insert_user_defined_cmd_args (cmd->line);
 	execute_command (&new_line[0], 0);
 	ret = cmd->control_type;
 	break;
@@ -486,7 +484,7 @@ execute_control_command (struct command_line *cmd)
 	print_command_trace (buffer);
 
 	/* Parse the loop control expression for the while statement.  */
-	std::string new_line = insert_args (cmd->line);
+	std::string new_line = insert_user_defined_cmd_args (cmd->line);
 	expression_up expr = parse_expression (new_line.c_str ());
 
 	ret = simple_control;
@@ -551,7 +549,7 @@ execute_control_command (struct command_line *cmd)
 	print_command_trace (buffer);
 
 	/* Parse the conditional for the if statement.  */
-	std::string new_line = insert_args (cmd->line);
+	std::string new_line = insert_user_defined_cmd_args (cmd->line);
 	expression_up expr = parse_expression (new_line.c_str ());
 
 	current = NULL;
@@ -591,7 +589,7 @@ execute_control_command (struct command_line *cmd)
       {
 	/* Breakpoint commands list, record the commands in the
 	   breakpoint's command list and return.  */
-	std::string new_line = insert_args (cmd->line);
+	std::string new_line = insert_user_defined_cmd_args (cmd->line);
 	ret = commands_from_control_command (new_line.c_str (), cmd);
 	break;
       }
@@ -782,13 +780,12 @@ locate_arg (const char *p)
   return NULL;
 }
 
-/* Insert the user defined arguments stored in user_arg into the $arg
-   arguments found in line.  */
+/* See cli-script.h.  */
 
-static std::string
-insert_args (const char *line)
+std::string
+insert_user_defined_cmd_args (const char *line)
 {
-  /* If we are not in a user-defined function, treat $argc, $arg0, et
+  /* If we are not in a user-defined command, treat $argc, $arg0, et
      cetera as normal convenience variables.  */
   if (user_args == NULL)
     return line;
diff --git a/gdb/cli/cli-script.h b/gdb/cli/cli-script.h
index 7db6e82..8920d44 100644
--- a/gdb/cli/cli-script.h
+++ b/gdb/cli/cli-script.h
@@ -53,6 +53,12 @@ extern struct cleanup *
 
 extern void execute_user_command (struct cmd_list_element *c, char *args);
 
+/* If we're in a user-defined command, replace any $argc/$argN
+   reference found in LINE with the arguments that were passed to the
+   command.  Otherwise, treat $argc/$argN as normal convenience
+   variables.  */
+extern std::string insert_user_defined_cmd_args (const char *line);
+
 /* Exported to top.c */
 
 extern void print_command_trace (const char *cmd);