default-args: allow to define default arguments for aliases

Currently, a user can define an alias, but cannot have default
arguments for this alias.

This patch modifies the 'alias' command so that default args can
be provided.
    (gdb) h alias
    Define a new command that is an alias of an existing command.
    Usage: alias [-a] [--] ALIAS = COMMAND [DEFAULT-ARGS...]
    ALIAS is the name of the alias command to create.
    COMMAND is the command being aliased to.

    Options:
      -a
        Specify that ALIAS is an abbreviation of COMMAND.
        Abbreviations are not used in command completion..

    GDB will automatically prepend the provided DEFAULT-ARGS to the list
    of arguments explicitly provided when using ALIAS.
    Use "help aliases" to list all user defined aliases and their default args.

    Examples:
    Make "spe" an alias of "set print elements":
      alias spe set print elements
    Make "elms" an alias of "elements" in the "set print" command:
      alias -a set print elms set print elements
    Make "btf" an alias of "backtrace -full -past-entry -past-main" :
      alias btf = backtrace -full -past-entry -past-main
    Make "wLapPeu" an alias of 2 nested "with":
      alias wLapPeu = with language pascal -- with print elements unlimited --
    (gdb)

The way 'default-args' is implemented makes it trivial to set default
args also for GDB commands (such as "backtrace") and for GDB pre-defined
aliases (such as "bt").  It was however deemed better to not allow to
define default arguments for pre-defined commands and aliases, to avoid
users believing that e.g. default args for "backtrace" would apply to "bt".

If needed, default-args could be allowed for GDB predefined commands
and aliases by adding a command
'set default-args GDB_COMMAND_OR_PREDEFINED_ALIAS [DEFAULT-ARGS...]'.

* 'alias' command now has a completer that helps to complete:
     - ALIAS (if the user defines an alias after a prefix),
     - the aliased COMMAND
     - the possible options for the aliased COMMAND.

* Help and apropos commands show the definitions of the aliases
  that have default arguments, e.g.
        (gdb) help backtrace
        backtrace, btf, where, bt
          alias btf = backtrace -full -past-entry -past-main
        Print backtrace of all stack frames, or innermost COUNT frames.
        Usage: backtrace [OPTION]... [QUALIFIER]... [COUNT | -COUNT]

        Options:
          -entry-values no|only|preferred|if-needed|both|compact|default
            Set printing of function arguments at function entry.
        ...

gdb/ChangeLog
2020-06-22  Philippe Waroquiers  <philippe.waroquiers@skynet.be>

	* cli/cli-cmds.c (lookup_cmd_for_default_args)
	(alias_command_completer)
	(make_alias_options_def_group): New functions.
	(alias_opts, alias_option_defs): New struct and array.
	(alias_usage_error): Update usage.
	(alias_command): Handles optional DEFAULT-ARGS... arguments.
	Use option framework.
	(_initialize_cli_cmds): Update alias command help.
	Update aliases command help.
	(show_user):
	Add NULL for new default_args lookup_cmd argument.
	(valid_command_p): Rename to validate_aliased_command.
	Add NULL for new default_args lookup_cmd argument.  Verify that the
	aliased_command has no default args.
	* cli/cli-decode.c (help_cmd): Show aliases definitions.
	(lookup_cmd_1, lookup_cmd): New argument default_args.
	(add_alias_cmd):
	Add NULL for new default_args lookup_cmd argument.
	(print_help_for_command): Show default args under the layout
	 alias some_alias = some_aliased_cmd some_alias_default_arg.
	* cli/cli-decode.h (struct cmd_list_element): New member default_args.
	xfree default_args in destructor.
	* cli/cli-script.c (process_next_line, do_define_command):
	Add NULL for new default_args lookup_cmd argument.
	* command.h: Declare new default_args argument in lookup_cmd
	and lookup_cmd_1.
	* completer.c (complete_line_internal_1):
	Add NULL for new default_args lookup_cmd or lookup_cmd_1 argument.
	* guile/scm-cmd.c (gdbscm_parse_command_name): Likewise.
	* guile/scm-param.c (add_setshow_generic, pascm_parameter_defined_p):
	Likewise.
	* infcmd.c (_initialize_infcmd): Likewise.
	* python/py-auto-load.c (gdbpy_initialize_auto_load): Likewise.
	* python/py-cmd.c (gdbpy_parse_command_name): Likewise.
	* python/py-param.c (add_setshow_generic): Likewise.
	* remote.c (_initialize_remote): Likewise.
	* top.c (execute_command): Prepend default_args if command has some.
	(set_verbose):
	Add NULL for new default_args lookup_cmd or lookup_cmd_1 argument.
	* tracepoint.c (validate_actionline, encode_actions_1):
	Add NULL for new default_args lookup_cmd or lookup_cmd_1 argument.

1 files changed, 92 insertions, 18 deletions

diff --git a/gdb/cli/cli-decode.c b/gdb/cli/cli-decode.c
index a4ef93c..85f50aa 100644
--- a/gdb/cli/cli-decode.c
+++ b/gdb/cli/cli-decode.c
@@ -337,7 +337,7 @@ add_alias_cmd (const char *name, const char *oldname,
   struct cmd_list_element *old;
 
   tmp = oldname;
-  old = lookup_cmd (&tmp, *list, "", 1, 1);
+  old = lookup_cmd (&tmp, *list, "", NULL, 1, 1);
 
   return add_alias_cmd (name, old, theclass, abbrev_flag, list);
 }
@@ -1040,6 +1040,40 @@ fput_command_name_styled (struct cmd_list_element *c, struct ui_file *stream)
   fprintf_styled (stream, title_style.style (), "%s%s", prefixname, c->name);
 }
 
+/* Print the definition of alias C using title style for alias
+   and aliased command.  */
+
+static void
+fput_alias_definition_styled (struct cmd_list_element *c,
+			      struct ui_file *stream)
+{
+  gdb_assert (c->cmd_pointer != nullptr);
+  fputs_filtered ("  alias ", stream);
+  fput_command_name_styled (c, stream);
+  fprintf_filtered (stream, " = ");
+  fput_command_name_styled (c->cmd_pointer, stream);
+  fprintf_filtered (stream, " %s\n", c->default_args.c_str ());
+}
+
+/* Print the definition of the aliases of CMD that have default args.  */
+
+static void
+fput_aliases_definition_styled (struct cmd_list_element *cmd,
+				struct ui_file *stream)
+{
+  if (cmd->aliases != nullptr)
+    {
+      for (cmd_list_element *iter = cmd->aliases;
+	   iter;
+	   iter = iter->alias_chain)
+	{
+	  if (!iter->default_args.empty ())
+	    fput_alias_definition_styled (iter, stream);
+	}
+    }
+}
+
+
 /* If C has one or more aliases, style print the name of C and
    the name of its aliases, separated by commas.
    If ALWAYS_FPUT_C_NAME, print the name of C even if it has no aliases.
@@ -1081,12 +1115,21 @@ print_doc_of_command (struct cmd_list_element *c, const char *prefix,
   if (verbose)
     fputs_filtered ("\n", stream);
 
-  fput_command_names_styled (c, true, " -- ", stream);
+  fput_command_names_styled (c, true,
+			     verbose ? "" : " -- ", stream);
   if (verbose)
-    fputs_highlighted (c->doc, highlight, stream);
+    {
+      fputs_filtered ("\n", stream);
+      fput_aliases_definition_styled (c, stream);
+      fputs_highlighted (c->doc, highlight, stream);
+      fputs_filtered ("\n", stream);
+    }
   else
-    print_doc_line (stream, c->doc, false);
-  fputs_filtered ("\n", stream);
+    {
+      print_doc_line (stream, c->doc, false);
+      fputs_filtered ("\n", stream);
+      fput_aliases_definition_styled (c, stream);
+    }
 }
 
 /* Recursively walk the commandlist structures, and print out the
@@ -1183,7 +1226,7 @@ help_cmd (const char *command, struct ui_file *stream)
     }
 
   const char *orig_command = command;
-  c = lookup_cmd (&command, cmdlist, "", 0, 0);
+  c = lookup_cmd (&command, cmdlist, "", NULL, 0, 0);
 
   if (c == 0)
     return;
@@ -1205,6 +1248,7 @@ help_cmd (const char *command, struct ui_file *stream)
   /* If the user asked 'help somecommand' and there is no alias,
      the false indicates to not output the (single) command name.  */
   fput_command_names_styled (c, false, "\n", stream);
+  fput_aliases_definition_styled (c, stream);
   fputs_filtered (c->doc, stream);
   fputs_filtered ("\n", stream);
 
@@ -1341,7 +1385,7 @@ help_all (struct ui_file *stream)
 	      fprintf_filtered (stream, "\nUnclassified commands\n\n");
 	      seen_unclassified = 1;
 	    }
-	  print_help_for_command (c, 1, stream);
+	  print_help_for_command (c, true, stream);
 	}
     }
 
@@ -1399,6 +1443,9 @@ print_help_for_command (struct cmd_list_element *c,
   fput_command_names_styled (c, true, " -- ", stream);
   print_doc_line (stream, c->doc, false);
   fputs_filtered ("\n", stream);
+  if (!c->default_args.empty ())
+    fput_alias_definition_styled (c, stream);
+  fput_aliases_definition_styled (c, stream);
 
   if (recurse
       && c->prefixlist != 0
@@ -1582,8 +1629,12 @@ valid_user_defined_cmd_name_p (const char *name)
    the list in which there are ambiguous choices (and *TEXT will be set to
    the ambiguous text string).
 
+   if DEFAULT_ARGS is not null, *DEFAULT_ARGS is set to the found command
+   default args (possibly empty).
+
    If the located command was an abbreviation, this routine returns the base
-   command of the abbreviation.
+   command of the abbreviation.  Note that *DEFAULT_ARGS will contain the
+   default args defined for the alias.
 
    It does no error reporting whatsoever; control will always return
    to the superior routine.
@@ -1610,11 +1661,13 @@ valid_user_defined_cmd_name_p (const char *name)
 
 struct cmd_list_element *
 lookup_cmd_1 (const char **text, struct cmd_list_element *clist,
-	      struct cmd_list_element **result_list, int ignore_help_classes)
+	      struct cmd_list_element **result_list, std::string *default_args,
+	      int ignore_help_classes)
 {
   char *command;
   int len, nfound;
   struct cmd_list_element *found, *c;
+  bool found_alias = false;
   const char *line = *text;
 
   while (**text == ' ' || **text == '\t')
@@ -1646,10 +1699,12 @@ lookup_cmd_1 (const char **text, struct cmd_list_element *clist,
 
   if (nfound > 1)
     {
-      if (result_list != NULL)
+      if (result_list != nullptr)
 	/* Will be modified in calling routine
 	   if we know what the prefix command is.  */
 	*result_list = 0;
+      if (default_args != nullptr)
+	*default_args = std::string ();
       return CMD_LIST_AMBIGUOUS;	/* Ambiguous.  */
     }
 
@@ -1665,22 +1720,30 @@ lookup_cmd_1 (const char **text, struct cmd_list_element *clist,
        are warning about the alias, we may also warn about the command
        itself and we will adjust the appropriate DEPRECATED_WARN_USER
        flags.  */
-      
+
       if (found->deprecated_warn_user)
 	deprecated_cmd_warning (line);
+
+      /* Return the default_args of the alias, not the default_args
+	 of the command it is pointing to.  */
+      if (default_args != nullptr)
+	*default_args = found->default_args;
       found = found->cmd_pointer;
+      found_alias = true;
     }
   /* If we found a prefix command, keep looking.  */
 
   if (found->prefixlist)
     {
       c = lookup_cmd_1 (text, *found->prefixlist, result_list,
-			ignore_help_classes);
+			default_args, ignore_help_classes);
       if (!c)
 	{
 	  /* Didn't find anything; this is as far as we got.  */
-	  if (result_list != NULL)
+	  if (result_list != nullptr)
 	    *result_list = clist;
+	  if (!found_alias && default_args != nullptr)
+	    *default_args = found->default_args;
 	  return found;
 	}
       else if (c == CMD_LIST_AMBIGUOUS)
@@ -1688,13 +1751,16 @@ lookup_cmd_1 (const char **text, struct cmd_list_element *clist,
 	  /* We've gotten this far properly, but the next step is
 	     ambiguous.  We need to set the result list to the best
 	     we've found (if an inferior hasn't already set it).  */
-	  if (result_list != NULL)
+	  if (result_list != nullptr)
 	    if (!*result_list)
 	      /* This used to say *result_list = *found->prefixlist.
 	         If that was correct, need to modify the documentation
 	         at the top of this function to clarify what is
 	         supposed to be going on.  */
 	      *result_list = found;
+	  /* For ambiguous commands, do not return any default_args args.  */
+	  if (default_args != nullptr)
+	    *default_args = std::string ();
 	  return c;
 	}
       else
@@ -1705,8 +1771,10 @@ lookup_cmd_1 (const char **text, struct cmd_list_element *clist,
     }
   else
     {
-      if (result_list != NULL)
+      if (result_list != nullptr)
 	*result_list = clist;
+      if (!found_alias && default_args != nullptr)
+	*default_args = found->default_args;
       return found;
     }
 }
@@ -1726,8 +1794,13 @@ undef_cmd_error (const char *cmdtype, const char *q)
 
 /* Look up the contents of *LINE as a command in the command list LIST.
    LIST is a chain of struct cmd_list_element's.
-   If it is found, return the struct cmd_list_element for that command
-   and update *LINE to point after the command name, at the first argument.
+   If it is found, return the struct cmd_list_element for that command,
+   update *LINE to point after the command name, at the first argument
+   and update *DEFAULT_ARGS (if DEFAULT_ARGS is not null) to the default
+   args to prepend to the user provided args when running the command.
+   Note that if the found cmd_list_element is found via an alias,
+   the default args of the alias are returned.
+
    If not found, call error if ALLOW_UNKNOWN is zero
    otherwise (or if error returns) return zero.
    Call error if specified command is ambiguous,
@@ -1741,6 +1814,7 @@ undef_cmd_error (const char *cmdtype, const char *q)
 struct cmd_list_element *
 lookup_cmd (const char **line, struct cmd_list_element *list,
 	    const char *cmdtype,
+	    std::string *default_args,
 	    int allow_unknown, int ignore_help_classes)
 {
   struct cmd_list_element *last_list = 0;
@@ -1752,7 +1826,7 @@ lookup_cmd (const char **line, struct cmd_list_element *list,
   if (!*line)
     error (_("Lack of needed %scommand"), cmdtype);
 
-  c = lookup_cmd_1 (line, list, &last_list, ignore_help_classes);
+  c = lookup_cmd_1 (line, list, &last_list, default_args, ignore_help_classes);
 
   if (!c)
     {