Support an "unlimited" number of user-defined arguments

New in v2:

  - A few adjustments / simplifications were possible now that we
    require C++11:

    . Use std::unique_ptr to make the user_args_stack std::vector own
      its elements:

       static std::vector<std::unique_ptr<user_args>> user_args_stack;

    . use vector::emplace_back to construct elements directly in the
      corresponding vectors.

    . use std::to_string instead of adding a gdb::to_string
      replacement.

  - Now includes a test.

Docs/NEWS are unchanged from v1 and have already been approved.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

I recently wrote a user-defined command that could benefit from
supporting an unlimited number of arguments:

 http://palves.net/list-active-signal-handlers-with-gdb/

E.g., 'info signal-dispositions 1 2 3 4 5 6 7 8 9 10 11'

However, we currently only support up to 10 arguments passed to
user-defined commands ($arg0..$arg9).

I can't find a good reason for that, other than "old code with hard
coded limits".  This patch removes that limit and modernizes the code
along the way:

  - Makes the user_args struct a real C++ class that uses std::vector
    for storage.

  - Removes the "next" pointer from within user_args and uses a
    std::vector to maintain a stack instead.

  - Adds a new RAII-based scoped_user_args_level class to help
    push/pop user args in the stack instead of using a cleanup.

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

	* NEWS: Mention that user commands now accept an unlimited number
	of arguments.
	* cli/cli-script.c: Include <vector>.
	(struct string_view): New type.
	(MAXUSERARGS): Delete.
	(struct user_args): Now a C++ class.
	(user_args_stack): New.
	(struct scoped_user_args_level): New type.
	(execute_user_command): Use scoped_user_args_level.
	(arg_cleanup): Delete.
	(setup_user_args): Deleted, and refactored as ...
	(user_args::user_args): ... this new constructor.  Limit of number
	of arguments removed.
	(insert_user_defined_cmd_args): Defer to user_args_stack.
	(user_args::insert_args): New, bits based on old
	insert_user_defined_cmd_args with limit of number of arguments
	eliminated.

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

	* gdb.texinfo (User-defined Commands): Limit on number of
	arguments passed to user-defined commands removed; update.

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

	* gdb.base/commands.exp (user_defined_command_manyargs_test): New
	procedure.
	(top level): Call it.

1 files changed, 100 insertions, 81 deletions

diff --git a/gdb/cli/cli-script.c b/gdb/cli/cli-script.c
index 15947a9..b19e550 100644
--- a/gdb/cli/cli-script.c
+++ b/gdb/cli/cli-script.c
@@ -33,6 +33,8 @@
 #include "interps.h"
 #include "compile/compile.h"
 
+#include <vector>
+
 /* Prototypes for local functions.  */
 
 static enum command_control_type
@@ -41,8 +43,6 @@ recurse_read_control_structure (char * (*read_next_line_func) (void),
 				void (*validator)(char *, void *),
 				void *closure);
 
-static struct cleanup * setup_user_args (char *p);
-
 static char *read_next_line (void);
 
 /* Level of control structure when reading.  */
@@ -54,24 +54,68 @@ static int command_nest_depth = 1;
 /* This is to prevent certain commands being printed twice.  */
 static int suppress_next_print_command_trace = 0;
 
+/* A non-owning slice of a string.  */
+
+struct string_view
+{
+  string_view (const char *str_, size_t len_)
+    : str (str_), len (len_)
+  {}
+
+  const char *str;
+  size_t len;
+};
+
 /* Structure for arguments to user defined functions.  */
-#define MAXUSERARGS 10
-struct user_args
+
+class user_args
+{
+public:
+  /* Save the command line and store the locations of arguments passed
+     to the user defined function.  */
+  explicit user_args (const char *line);
+
+  /* Insert the stored user defined arguments into the $arg arguments
+     found in LINE.  */
+  std::string insert_args (const char *line) const;
+
+private:
+  /* Disable copy/assignment.  (Since the elements of A point inside
+     COMMAND, copying would need to reconstruct the A vector in the
+     new copy.)  */
+  user_args (const user_args &) =delete;
+  user_args &operator= (const user_args &) =delete;
+
+  /* It is necessary to store a copy of the command line to ensure
+     that the arguments are not overwritten before they are used.  */
+  std::string m_command_line;
+
+  /* The arguments.  Each element points inside M_COMMAND_LINE.  */
+  std::vector<string_view> m_args;
+};
+
+/* The stack of arguments passed to user defined functions.  We need a
+   stack because user-defined functions can call other user-defined
+   functions.  */
+static std::vector<std::unique_ptr<user_args>> user_args_stack;
+
+/* An RAII-base class used to push/pop args on the user args
+   stack.  */
+struct scoped_user_args_level
+{
+  /* Parse the command line and push the arguments in the user args
+     stack.  */
+  explicit scoped_user_args_level (const char *line)
   {
-    struct user_args *next;
-    /* It is necessary to store a malloced copy of the command line to
-       ensure that the arguments are not overwritten before they are
-       used.  */
-    char *command;
-    struct
-      {
-	char *arg;
-	int len;
-      }
-    a[MAXUSERARGS];
-    int count;
+    user_args_stack.emplace_back (new user_args (line));
   }
- *user_args;
+
+  /* Pop the current user arguments from the stack.  */
+  ~scoped_user_args_level ()
+  {
+    user_args_stack.pop_back ();
+  }
+};
 
 
 /* Return non-zero if TYPE is a multi-line command (i.e., is terminated
@@ -362,12 +406,12 @@ execute_user_command (struct cmd_list_element *c, char *args)
     /* Null command */
     return;
 
-  old_chain = setup_user_args (args);
+  scoped_user_args_level push_user_args (args);
 
   if (++user_call_depth > max_user_call_depth)
     error (_("Max user call depth exceeded -- command aborted."));
 
-  make_cleanup (do_restore_user_call_depth, &user_call_depth);
+  old_chain = make_cleanup (do_restore_user_call_depth, &user_call_depth);
 
   /* Set the instream to 0, indicating execution of a
      user-defined function.  */
@@ -668,62 +712,32 @@ if_command (char *arg, int from_tty)
   free_command_lines (&command);
 }
 
-/* Cleanup */
-static void
-arg_cleanup (void *ignore)
-{
-  struct user_args *oargs = user_args;
-
-  if (!user_args)
-    internal_error (__FILE__, __LINE__,
-		    _("arg_cleanup called with no user args.\n"));
-
-  user_args = user_args->next;
-  xfree (oargs->command);
-  xfree (oargs);
-}
-
-/* Bind the incomming arguments for a user defined command to
-   $arg0, $arg1 ... $argMAXUSERARGS.  */
+/* Bind the incoming arguments for a user defined command to $arg0,
+   $arg1 ... $argN.  */
 
-static struct cleanup *
-setup_user_args (char *p)
+user_args::user_args (const char *command_line)
 {
-  struct user_args *args;
-  struct cleanup *old_chain;
-  unsigned int arg_count = 0;
-
-  args = XNEW (struct user_args);
-  memset (args, 0, sizeof (struct user_args));
-
-  args->next = user_args;
-  user_args = args;
-
-  old_chain = make_cleanup (arg_cleanup, 0/*ignored*/);
+  const char *p;
 
-  if (p == NULL)
-    return old_chain;
+  if (command_line == NULL)
+    return;
 
-  user_args->command = p = xstrdup (p);
+  m_command_line = command_line;
+  p = m_command_line.c_str ();
 
   while (*p)
     {
-      char *start_arg;
+      const char *start_arg;
       int squote = 0;
       int dquote = 0;
       int bsquote = 0;
 
-      if (arg_count >= MAXUSERARGS)
-	error (_("user defined function may only have %d arguments."),
-	       MAXUSERARGS);
-
       /* Strip whitespace.  */
       while (*p == ' ' || *p == '\t')
 	p++;
 
       /* P now points to an argument.  */
       start_arg = p;
-      user_args->a[arg_count].arg = p;
 
       /* Get to the end of this argument.  */
       while (*p)
@@ -757,11 +771,8 @@ setup_user_args (char *p)
 	    }
 	}
 
-      user_args->a[arg_count].len = p - start_arg;
-      arg_count++;
-      user_args->count++;
+      m_args.emplace_back (start_arg, p - start_arg);
     }
-  return old_chain;
 }
 
 /* Given character string P, return a point to the first argument
@@ -787,40 +798,48 @@ insert_user_defined_cmd_args (const char *line)
 {
   /* If we are not in a user-defined command, treat $argc, $arg0, et
      cetera as normal convenience variables.  */
-  if (user_args == NULL)
+  if (user_args_stack.empty ())
     return line;
 
+  const std::unique_ptr<user_args> &args = user_args_stack.back ();
+  return args->insert_args (line);
+}
+
+/* Insert the user defined arguments stored in user_args into the $arg
+   arguments found in line.  */
+
+std::string
+user_args::insert_args (const char *line) const
+{
   std::string new_line;
   const char *p;
 
   while ((p = locate_arg (line)))
     {
-      int i, len;
-
       new_line.append (line, p - line);
 
       if (p[4] == 'c')
 	{
-	  gdb_assert (user_args->count >= 0 && user_args->count <= 10);
-	  if (user_args->count == 10)
-	    {
-	      new_line += '1';
-	      new_line += '0';
-	    }
-	  else
-	    new_line += user_args->count + '0';
+	  new_line += std::to_string (m_args.size ());
+	  line = p + 5;
 	}
       else
 	{
-	  i = p[4] - '0';
-	  if (i >= user_args->count)
-	    error (_("Missing argument %d in user function."), i);
-
-	  len = user_args->a[i].len;
-	  if (len > 0)
-	    new_line.append (user_args->a[i].arg, len);
+	  char *tmp;
+	  unsigned long i;
+
+	  errno = 0;
+	  i = strtoul (p + 4, &tmp, 10);
+	  if ((i == 0 && tmp == p + 4) || errno != 0)
+	    line = p + 4;
+	  else if (i >= m_args.size ())
+	    error (_("Missing argument %ld in user function."), i);
+	  else
+	    {
+	      new_line.append (m_args[i].str, m_args[i].len);
+	      line = tmp;
+	    }
 	}
-      line = p + 5;
     }
   /* Don't forget the tail.  */
   new_line.append (line);