Introduce generic command options framework

This commit adds a generic command options framework, that makes it
easy enough to add '-'-style options to commands in a uniform way,
instead of each command implementing option parsing in its own way.

Options are defined in arrays of option_def objects (for option
definition), and the same options definitions are used for supporting
TAB completion, and also for generating the relevant help fragment of
the "help" command.  See the gdb::options::build_help function, which
returns a string with the result of replacing %OPTIONS% in a template
string with an auto-generated "help" string fragment for all the
passed-in options.

Since most options in GDB are in the form of "-OPT", with a single
dash, this is the format that the framework supports.

I like to think of gdb's "-OPT" as the equivalent to getopt's long
options format ("--OPT"), and gdb's "/" as the equivalent to getopt's
short options format.  getopt's short options format allows mixing
several one-character options, like "ls -als", kind of similar to
gdb's "x /FMT" and "disassemble /MOD", etc.  While with gdb's "-"
options, the option is expected to have a full name, and to be
abbreviatable.  E.g., "watch -location", "break -function main", etc.

This patch only deals with "-" options.  The above comment serves more
to disclose why I don't think we should support mixing several
unrelated options in a single "-" option invocation, like "thread
apply -qcs" instead of "thread apply -q -c -s".

The following patches will add uses of the infrastructure to several
key commands.  Most notably, "print", "compile print", "backtrace",
"frame apply" and "thread apply".  I tried to add options to several
commands in order to make sure the framework didn't leave that many
open holes open.

Options use the same type as set commands -- enum var_types.  So
boolean options are var_boolean, enum options are var_enum, etc.  The
idea is to share code between settings commands and command options.
The "print" options will be based on the "set print" commands, and
their names will be the same.  Actually, their definitions will be the
same too.  There is a function to create "set/show" commands from an
array for option definitions:

 /* Install set/show commands for options defined in OPTIONS.  DATA is
    a pointer to the structure that holds the data associated with the
    OPTIONS array.  */
 extern void add_setshow_cmds_for_options (command_class cmd_class, void *data,
					   gdb::array_view<const option_def> options,
					   struct cmd_list_element **set_list,
					   struct cmd_list_element **show_list);

That will be used by several following patches.

Other features:

 - You can use the "--" delimiter to explicitly indicate end of
   options.  Several existing commands use this token sequence for
   this effect already, so this just standardizes it.

 - You can shorten option names, as long as unambiguous.  Currently,
   some commands allow this (e.g., break -function), while others do
   not (thread apply all -ascending).  As GDB allows abbreviating
   command names and other things, it feels more GDB-ish to allow
   abbreviating option names too, to me.

 - For boolean options, 0/1 stands for off/on, just like with boolean
   "set" commands.

 - For boolean options, "true" is implied, just like with boolean "set
   commands.

These are the option types supported, with a few examples:

 - boolean options (var_boolean).  The option's argument is optional.

   (gdb) print -pretty on -- *obj
   (gdb) print -pretty off -- *obj
   (gdb) print -p -- *obj
   (gdb) print -p 0 -- *obj

 - flag options (like var_boolean, but no option argument (on/off))

   (gdb) thread apply all -s COMMAND

 - enum options  (var_enum)

   (gdb) bt -entry-values compact
   (gdb) bt -e c

 - uinteger options (var_uinteger)

   (gdb) print -elements 100 -- *obj
   (gdb) print -e 100 -- *obj
   (gdb) print -elements unlimited -- *obj
   (gdb) print -e u -- *obj

 - zuinteger-unlimited options (var_zuinteger_unlimited)

   (gdb) print -max-depth 100 -- obj
   (gdb) print -max-depth -1 -- obj
   (gdb) print -max-depth unlimited -- obj

Other var_types could be supported, of course.  These were just the
types that I needed for the commands that I ported over, in the
following patches.

It was interesting (and unfortunate) to find that we need at least 3
different modes to cover the existing commands:

- Commands that require ending options with "--" if you specify any
  option: "print" and "compile print".

- Commands that do not want to require "--", and want to error out if
  you specify an unknown option (i.e., an unknown argument that starts
  with '-'): "compile code" / "compile file".

- Commands that do not want to require "--", and want to process
  unknown options themselves: "bt", because of "bt -COUNT",
  "thread/frame apply", because "-" is a valid command.

The different behavior is encoded in the process_options_mode enum,
passed to process_options/complete_options.

For testing, this patch adds one representative maintenance command
for each of the process_options_mode values, that are used by the
testsuite to exercise the options framework:

 (gdb) maint test-options require-delimiter
 (gdb) maint test-options unknown-is-error
 (gdb) maint test-options unknown-is-operand

and adds another command to help with TAB-completion testing:

 (gdb) maint show test-options-completion-result

See their description at the top of the maint-test-options.c file.

Docs/NEWS are in a patch later in the series.

gdb/ChangeLog:
2019-06-13  Pedro Alves  <palves@redhat.com>

	* Makefile.in (SUBDIR_CLI_SRCS): Add cli/cli-option.c.
	(COMMON_SFILES): Add maint-test-settings.c.
	* cli/cli-decode.c (boolean_enums): New global, factored out from
	...
	(add_setshow_boolean_cmd): ... here.
	* cli/cli-decode.h (boolean_enums): Declare.
	* cli/cli-option.c: New file.
	* cli/cli-option.h: New file.
	* cli/cli-setshow.c (parse_cli_boolean_value(const char **)): New,
	factored out from ...
	(parse_cli_boolean_value(const char *)): ... this.
	(is_unlimited_literal): Change parameter type to pointer to
	pointer.  Adjust and advance ARG pointer.
	(parse_cli_var_uinteger, parse_cli_var_zuinteger_unlimited)
	(parse_cli_var_enum): New, factored out from ...
	(do_set_command): ... this.  Adjust.
	* cli/cli-setshow.h (parse_cli_boolean_value)
	(parse_cli_var_uinteger, parse_cli_var_zuinteger_unlimited)
	(parse_cli_var_enum): Declare.
	* cli/cli-utils.c: Include "cli/cli-option.h".
	(get_ulongest): New.
	* cli/cli-utils.h (get_ulongest): Declare.
	(check_for_argument): New overloads.
	* maint-test-options.c: New file.

gdb/testsuite/ChangeLog:
2019-06-13  Pedro Alves  <palves@redhat.com>

	* gdb.base/options.c: New file.
	* gdb.base/options.exp: New file.

1 files changed, 335 insertions, 0 deletions

diff --git a/gdb/cli/cli-option.h b/gdb/cli/cli-option.h
new file mode 100644
index 0000000..1bfbfce
--- /dev/null
+++ b/gdb/cli/cli-option.h
@@ -0,0 +1,335 @@
+/* CLI options framework, for GDB.
+
+   Copyright (C) 2017-2019 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#ifndef CLI_OPTION_H
+#define CLI_OPTION_H 1
+
+#include "common/gdb_optional.h"
+#include "common/array-view.h"
+#include "completer.h"
+#include <string>
+#include "command.h"
+
+namespace gdb {
+namespace option {
+
+/* A type-erased option definition.  The actual type of the option is
+   stored in the TYPE field.  Client code cannot define objects of
+   this type directly (the ctor is protected).  Instead, one of the
+   wrapper types below that extends this (boolean_option_def,
+   flag_option_def, uinteger_option_def, etc.) should be defined.  */
+struct option_def
+{
+  /* The ctor is protected because you're supposed to construct using
+     one of bool_option_def, etc. below.  */
+protected:
+  typedef void *(erased_get_var_address_ftype) ();
+
+  /* Construct an option.  NAME_ is the option's name.  VAR_TYPE_
+     defines the option's type.  ERASED_GET_VAR_ADDRESS_ is a pointer
+     to a function that returns the option's control variable.
+     SHOW_CMD_CB_ is a pointer to callback for the "show" command that
+     is installed for this option.  SET_DOC_, SHOW_DOC_, HELP_DOC_ are
+     used to create the option's "set/show" commands.  */
+  constexpr option_def (const char *name_,
+			var_types var_type_,
+			erased_get_var_address_ftype *erased_get_var_address_,
+			show_value_ftype *show_cmd_cb_,
+			const char *set_doc_,
+			const char *show_doc_,
+			const char *help_doc_)
+    : name (name_), type (var_type_),
+      erased_get_var_address (erased_get_var_address_),
+      var_address {},
+      show_cmd_cb (show_cmd_cb_),
+      set_doc (set_doc_), show_doc (show_doc_), help_doc (help_doc_)
+  {}
+
+public:
+  /* The option's name.  */
+  const char *name;
+
+  /* The option's type.  */
+  var_types type;
+
+  /* A function that gets the controlling variable's address, type
+     erased.  */
+  erased_get_var_address_ftype *erased_get_var_address;
+
+  /* Get the controlling variable's address.  Each type of variable
+     uses a different union member.  We do this instead of having a
+     single hook that return a "void *", for better type safety.  This
+     way, actual instances of concrete option_def types
+     (boolean_option_def, etc.) fail to compile if you pass in a
+     function with incorrect return type.  CTX here is the aggregate
+     object that groups the option variables from which the callback
+     returns the address of some member.  */
+  union
+    {
+      int *(*boolean) (const option_def &, void *ctx);
+      unsigned int *(*uinteger) (const option_def &, void *ctx);
+      int *(*integer) (const option_def &, void *ctx);
+      const char **(*enumeration) (const option_def &, void *ctx);
+    }
+  var_address;
+
+  /* Pointer to null terminated list of enumerated values (like argv).
+     Only used by var_enum options.  */
+  const char *const *enums = nullptr;
+
+  /* True if the option takes an argument.  */
+  bool have_argument = true;
+
+  /* The "show" callback to use in the associated "show" command.
+     E.g., "show print elements".  */
+  show_value_ftype *show_cmd_cb;
+
+  /* The set/show/help strings.  These are shown in both the help of
+     commands that use the option group this option belongs to (e.g.,
+     "help print"), and in the associated commands (e.g., "set/show
+     print elements", "help set print elements").  */
+  const char *set_doc;
+  const char *show_doc;
+  const char *help_doc;
+
+  /* Convenience method that returns THIS as an option_def.  Useful
+     when you're putting an option_def subclass in an option_def
+     array_view.  */
+  const option_def &def () const
+  {
+    return *this;
+  }
+};
+
+namespace detail
+{
+
+/* Get the address of the option's value, cast to the right type.
+   RetType is the restored type of the variable, and Context is the
+   restored type of the context pointer.  */
+template<typename RetType, typename Context>
+static inline RetType *
+get_var_address (const option_def &option, void *ctx)
+{
+  using unerased_ftype = RetType *(Context *);
+  unerased_ftype *fun = (unerased_ftype *) option.erased_get_var_address;
+  return fun ((Context *) ctx);
+}
+
+/* Convenience identity helper that just returns SELF.  */
+
+template<typename T>
+static T *
+return_self (T *self)
+{
+  return self;
+}
+
+} /* namespace detail */
+
+/* Follows the definitions of the option types that client code should
+   define.  Note that objects of these types are placed in option_def
+   arrays, by design, so they must not have data fields of their
+   own.  */
+
+/* A var_boolean command line option.  */
+
+template<typename Context>
+struct boolean_option_def : option_def
+{
+  boolean_option_def (const char *long_option_,
+		      int *(*get_var_address_cb_) (Context *),
+		      show_value_ftype *show_cmd_cb_,
+		      const char *set_doc_,
+		      const char *show_doc_ = nullptr,
+		      const char *help_doc_ = nullptr)
+    : option_def (long_option_, var_boolean,
+		  (erased_get_var_address_ftype *) get_var_address_cb_,
+		  show_cmd_cb_,
+		  set_doc_, show_doc_, help_doc_)
+  {
+    var_address.boolean = detail::get_var_address<int, Context>;
+  }
+};
+
+/* A flag command line option.  This is a var_boolean option under the
+   hood, but unlike boolean options, flag options don't take an on/off
+   argument.  */
+
+template<typename Context = int>
+struct flag_option_def : boolean_option_def<Context>
+{
+  flag_option_def (const char *long_option_,
+		     int *(*var_address_cb_) (Context *),
+		     const char *set_doc_,
+		     const char *help_doc_ = nullptr)
+    : boolean_option_def<Context> (long_option_,
+				   var_address_cb_,
+				   NULL,
+				   set_doc_, NULL, help_doc_)
+  {
+    this->have_argument = false;
+  }
+
+  flag_option_def (const char *long_option_,
+		     const char *set_doc_,
+		     const char *help_doc_ = nullptr)
+    : boolean_option_def<Context> (long_option_,
+				   gdb::option::detail::return_self,
+				   NULL,
+				   set_doc_, nullptr, help_doc_)
+  {
+    this->have_argument = false;
+  }
+};
+
+/* A var_uinteger command line option.  */
+
+template<typename Context>
+struct uinteger_option_def : option_def
+{
+  uinteger_option_def (const char *long_option_,
+		       unsigned int *(*get_var_address_cb_) (Context *),
+		       show_value_ftype *show_cmd_cb_,
+		       const char *set_doc_,
+		       const char *show_doc_ = nullptr,
+		       const char *help_doc_ = nullptr)
+    : option_def (long_option_, var_uinteger,
+		  (erased_get_var_address_ftype *) get_var_address_cb_,
+		  show_cmd_cb_,
+		  set_doc_, show_doc_, help_doc_)
+  {
+    var_address.uinteger = detail::get_var_address<unsigned int, Context>;
+  }
+};
+
+/* A var_zuinteger_unlimited command line option.  */
+
+template<typename Context>
+struct zuinteger_unlimited_option_def : option_def
+{
+  zuinteger_unlimited_option_def (const char *long_option_,
+				  int *(*get_var_address_cb_) (Context *),
+				  show_value_ftype *show_cmd_cb_,
+				  const char *set_doc_,
+				  const char *show_doc_ = nullptr,
+				  const char *help_doc_ = nullptr)
+    : option_def (long_option_, var_zuinteger_unlimited,
+		  (erased_get_var_address_ftype *) get_var_address_cb_,
+		  show_cmd_cb_,
+		  set_doc_, show_doc_, help_doc_)
+  {
+    var_address.integer = detail::get_var_address<int, Context>;
+  }
+};
+
+/* An var_enum command line option.  */
+
+template<typename Context>
+struct enum_option_def : option_def
+{
+  enum_option_def (const char *long_option_,
+		   const char *const *enumlist,
+		   const char **(*get_var_address_cb_) (Context *),
+		   show_value_ftype *show_cmd_cb_,
+		   const char *set_doc_,
+		   const char *show_doc_ = nullptr,
+		   const char *help_doc_ = nullptr)
+    : option_def (long_option_, var_enum,
+		  (erased_get_var_address_ftype *) get_var_address_cb_,
+		  show_cmd_cb_,
+		  set_doc_, show_doc_, help_doc_)
+  {
+    var_address.enumeration = detail::get_var_address<const char *, Context>;
+    this->enums = enumlist;
+  }
+};
+
+/* A group of options that all share the same context pointer to pass
+   to the options' get-current-value callbacks.  */
+struct option_def_group
+{
+  /* The list of options.  */
+  gdb::array_view<const option_def> options;
+
+  /* The context pointer to pass to the options' get-current-value
+     callbacks.  */
+  void *ctx;
+};
+
+/* Modes of operation for process_options.  */
+enum process_options_mode
+{
+  /* In this mode, options are only processed if we find a "--"
+     delimiter.  Throws an error if unknown options are found.  */
+  PROCESS_OPTIONS_REQUIRE_DELIMITER,
+
+  /* In this mode, a "--" delimiter is not required.  Throws an error
+     if unknown options are found, regardless of whether a delimiter
+     is present.  */
+  PROCESS_OPTIONS_UNKNOWN_IS_ERROR,
+
+  /* In this mode, a "--" delimiter is not required.  If an unknown
+     option is found, assume it is the command's argument/operand.  */
+  PROCESS_OPTIONS_UNKNOWN_IS_OPERAND,
+};
+
+/* Process ARGS, using OPTIONS_GROUP as valid options.  Returns true
+   if the string has been fully parsed and there are no operands to
+   handle by the caller.  Return false if options were parsed, and
+   *ARGS now points at the first operand.  */
+extern bool process_options
+  (const char **args,
+   process_options_mode mode,
+   gdb::array_view<const option_def_group> options_group);
+
+/* Complete ARGS on options listed by OPTIONS_GROUP.  Returns true if
+   the string has been fully parsed and there are no operands to
+   handle by the caller.  Return false if options were parsed, and
+   *ARGS now points at the first operand.  */
+extern bool complete_options
+  (completion_tracker &tracker,
+   const char **args,
+   process_options_mode mode,
+   gdb::array_view<const option_def_group> options_group);
+
+/* Complete on all options listed by OPTIONS_GROUP.  */
+extern void
+  complete_on_all_options (completion_tracker &tracker,
+			   gdb::array_view<const option_def_group> options_group);
+
+/* Return a string with the result of replacing %OPTIONS% in HELP_TMLP
+   with an auto-generated "help" string fragment for all the options
+   in OPTIONS_GROUP.  */
+extern std::string build_help
+  (const char *help_tmpl,
+   gdb::array_view<const option_def_group> options_group);
+
+/* Install set/show commands for options defined in OPTIONS.  DATA is
+   a pointer to the structure that holds the data associated with the
+   OPTIONS array.  */
+extern void add_setshow_cmds_for_options (command_class cmd_class, void *data,
+					  gdb::array_view<const option_def> options,
+					  struct cmd_list_element **set_list,
+					  struct cmd_list_element **show_list);
+
+} /* namespace option */
+} /* namespace gdb */
+
+#endif /* CLI_OPTION_H */