Allow to document user-defined aliases.

Compared to the previous version, this version fixes the comments reported by
Tom Tromey and ensures that the 'help some-user-documented-alias'
shows the alias definition to ensure the user understands this is an
alias even if specifically documented.

When using 'help ALIASNAME', GDB shows the help of the aliased command.
This is a good default behaviour.

However, GDB alias command allows to define aliases with arguments
possibly changing or tuning significantly the behaviour of
the aliased command.  In such a case, showing the help of the aliased
command might not be ideal.

This is particularly true when defining an alias as a set of
nested 'with' followed by a last command to launch, such as:
  (gdb) alias pp10 = with print pretty -- with print elements 10 -- print
Asking 'help pp10' shows the help of the 'with' command, which is
not particularly useful:
  (gdb) help pp10
  with, pp10, w
    alias pp10 = with print pretty -- with print elements 10 -- print
  Temporarily set SETTING to VALUE, run COMMAND, and restore SETTING.
  Usage: with SETTING [VALUE] [-- COMMAND]
  ....

Such an alias can now be documented by the user:
  (gdb) document pp10
  >Pretty printing an expressiong, printing 10 elements.
  >Usage: pp10 [PRINT-COMMAND-OPTIONS] EXP
  >See 'help print' for more information.
  >end
  (gdb) help pp10
    alias pp10 = with print pretty -- with print elements 10 -- print
  Pretty printing an expressiong, printing 10 elements.
  Usage: pp10 [PRINT-COMMAND-OPTIONS] EXP
  See 'help print' for more information.
  (gdb)

When a user-defined alias is documented specifically, help and apropos
use the provided alias documentation instead of the documentation of
the aliased command.

Such a documented alias is also not shown anymore in the help of the
aliased command, and the alias is not listed anymore in the help
of the aliased command.  In particular for cases such as pp10 example above,
indicating that pp10 is an alias of the 'with' command is confusing.

2 files changed, 69 insertions, 31 deletions

diff --git a/gdb/cli/cli-decode.c b/gdb/cli/cli-decode.c
index fde554c..7c98029 100644
--- a/gdb/cli/cli-decode.c
+++ b/gdb/cli/cli-decode.c
@@ -1349,6 +1349,18 @@ fput_command_name_styled (const cmd_list_element &c, struct ui_file *stream)
 		  prefixname.c_str (), c.name);
 }
 
+/* True if ALIAS has a user-defined documentation.  */
+
+static bool
+user_documented_alias (const cmd_list_element &alias)
+{
+  gdb_assert (alias.is_alias ());
+  /* Alias is user documented if it has an allocated documentation
+     that differs from the aliased command.  */
+  return (alias.doc_allocated
+	  && strcmp (alias.doc, alias.alias_target->doc) != 0);
+}
+
 /* Print the definition of alias C using title style for alias
    and aliased command.  */
 
@@ -1364,20 +1376,22 @@ fput_alias_definition_styled (const cmd_list_element &c,
   gdb_printf (stream, " %s\n", c.default_args.c_str ());
 }
 
-/* Print the definition of the aliases of CMD that have default args.  */
+/* Print the definition of CMD aliases not deprecated and having default args
+   and not specifically documented by the user.  */
 
 static void
 fput_aliases_definition_styled (const cmd_list_element &cmd,
 				struct ui_file *stream)
 {
   for (const cmd_list_element &alias : cmd.aliases)
-    if (!alias.cmd_deprecated && !alias.default_args.empty ())
+    if (!alias.cmd_deprecated
+	&& !user_documented_alias (alias)
+	&& !alias.default_args.empty ())
       fput_alias_definition_styled (alias, stream);
 }
 
-
-/* If C has one or more aliases, style print the name of C and
-   the name of its aliases, separated by commas.
+/* If C has one or more aliases, style print the name of C and the name of its
+   aliases not documented specifically by the user, separated by commas.
    If ALWAYS_FPUT_C_NAME, print the name of C even if it has no aliases.
    If one or more names are printed, POSTFIX is printed after the last name.
 */
@@ -1389,11 +1403,11 @@ fput_command_names_styled (const cmd_list_element &c,
 {
   /* First, check if we are going to print something.  That is, either if
      ALWAYS_FPUT_C_NAME is true or if there exists at least one non-deprecated
-     alias.  */
+     alias not documented specifically by the user.  */
 
   auto print_alias = [] (const cmd_list_element &alias)
     {
-      return !alias.cmd_deprecated;
+      return !alias.cmd_deprecated && !user_documented_alias (alias);
     };
 
   bool print_something = always_fput_c_name;
@@ -1474,11 +1488,11 @@ apropos_cmd (struct ui_file *stream,
   /* Walk through the commands.  */
   for (c=commandlist;c;c=c->next)
     {
-      if (c->is_alias ())
+      if (c->is_alias () && !user_documented_alias (*c))
 	{
-	  /* Command aliases/abbreviations are skipped to ensure we print the
-	     doc of a command only once, when encountering the aliased
-	     command.  */
+	  /* Command aliases/abbreviations not specifically documented by the
+	     user are skipped to ensure we print the doc of a command only once,
+	     when encountering the aliased command.  */
 	  continue;
 	}
 
@@ -1571,11 +1585,24 @@ help_cmd (const char *command, struct ui_file *stream)
      number of this class so that the commands in the class will be
      listed.  */
 
-  /* 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);
-  gdb_puts (c->doc, stream);
+  if (alias == nullptr || !user_documented_alias (*alias))
+    {
+      /* Case of a normal command, or an alias not explictly
+	 documented by the user.  */
+      /* 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);
+      gdb_puts (c->doc, stream);
+    }
+  else
+    {
+      /* Case of an alias explictly documented by the user.
+	 Only output the alias definition and its explicit documentation.  */
+      fput_alias_definition_styled (*alias, stream);
+      fput_command_names_styled (*alias, false, "\n", stream);
+      gdb_puts (alias->doc, stream);
+    }
   gdb_puts ("\n", stream);
 
   if (!c->is_prefix () && !c->is_command_class_help ())
diff --git a/gdb/cli/cli-script.c b/gdb/cli/cli-script.c
index 5f81db4..6c67b60 100644
--- a/gdb/cli/cli-script.c
+++ b/gdb/cli/cli-script.c
@@ -1500,39 +1500,49 @@ define_command (const char *comname, int from_tty)
   do_define_command (comname, from_tty, nullptr);
 }
 
-/* Document a user-defined command.  If COMMANDS is NULL, then this is a
-   top-level call and the document will be read using read_command_lines.
-   Otherwise, it is a "document" command in an existing command and the
-   commands are provided.  */
+/* Document a user-defined command or user defined alias.  If COMMANDS is NULL,
+   then this is a top-level call and the document will be read using
+   read_command_lines.  Otherwise, it is a "document" command in an existing
+   command and the commands are provided.  */
 static void
 do_document_command (const char *comname, int from_tty,
                      const counted_command_line *commands)
 {
-  struct cmd_list_element *c, **list;
-  const char *tem;
+  struct cmd_list_element *alias, *prefix_cmd, *c;
   const char *comfull;
 
   comfull = comname;
-  list = validate_comname (&comname);
+  validate_comname (&comname);
 
-  tem = comname;
-  c = lookup_cmd (&tem, *list, "", NULL, 0, 1);
+  lookup_cmd_composition (comfull, &alias, &prefix_cmd, &c);
 
-  if (c->theclass != class_user)
-    error (_("Command \"%s\" is built-in."), comfull);
+  if (c->theclass != class_user
+      && (alias == nullptr || alias->theclass != class_alias))
+    {
+      if (alias == nullptr)
+	error (_("Command \"%s\" is built-in."), comfull);
+      else
+	error (_("Alias \"%s\" is built-in."), comfull);
+    }
+
+  /* If we found an alias of class_alias, the user is documenting this
+     user-defined alias.  */
+  if (alias != nullptr)
+    c = alias;
 
   counted_command_line doclines;
 
   if (commands == nullptr)
     {
-      std::string prompt 
+      std::string prompt
         = string_printf ("Type documentation for \"%s\".", comfull);
       doclines = read_command_lines (prompt.c_str (), from_tty, 0, 0);
     }
   else
     doclines = *commands;
 
-  xfree ((char *) c->doc);
+  if (c->doc_allocated)
+    xfree ((char *) c->doc);
 
   {
     struct command_line *cl1;
@@ -1553,6 +1563,7 @@ do_document_command (const char *comname, int from_tty,
       }
 
     c->doc = doc;
+    c->doc_allocated = 1;
   }
 }
 
@@ -1681,8 +1692,8 @@ _initialize_cli_script ()
      its prefixes.  */
   document_cmd_element = add_com ("document", class_support, document_command,
                                   _("\
-Document a user-defined command.\n\
-Give command name as argument.  Give documentation on following lines.\n\
+Document a user-defined command or user-defined alias.\n\
+Give command or alias name as argument.  Give documentation on following lines.\n\
 End with a line of just \"end\"."));
   set_cmd_completer (document_cmd_element, command_completer);
   define_cmd_element = add_com ("define", class_support, define_command, _("\