1/*  Part of SWI-Prolog
    2
    3    Author:        Jan Wielemaker
    4    E-mail:        J.Wielemaker@vu.nl
    5    WWW:           http://www.swi-prolog.org
    6    Copyright (c)  2002-2023, University of Amsterdam
    7                              VU University Amsterdam
    8                              CWI, Amsterdam
    9                              SWI-Prolog Solutions b.v.
   10    All rights reserved.
   11
   12    Redistribution and use in source and binary forms, with or without
   13    modification, are permitted provided that the following conditions
   14    are met:
   15
   16    1. Redistributions of source code must retain the above copyright
   17       notice, this list of conditions and the following disclaimer.
   18
   19    2. Redistributions in binary form must reproduce the above copyright
   20       notice, this list of conditions and the following disclaimer in
   21       the documentation and/or other materials provided with the
   22       distribution.
   23
   24    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   25    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   26    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
   27    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
   28    COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
   29    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
   30    BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   31    LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
   32    CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   33    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
   34    ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   35    POSSIBILITY OF SUCH DAMAGE.
   36*/
   37
   38:- module(prolog_debug,
   39          [ debug/3,                    % +Topic, +Format, :Args
   40            debug/1,                    % +Topic
   41            nodebug/1,                  % +Topic
   42            debugging/1,                % ?Topic
   43            debugging/2,                % ?Topic, ?Bool
   44            list_debug_topics/0,
   45            list_debug_topics/1,        % +Options
   46            debug_message_context/1,    % (+|-)What
   47
   48            assertion/1                 % :Goal
   49          ]).   50:- autoload(library(lists),[append/3,delete/3,selectchk/3,member/2]).   51:- autoload(library(prolog_stack),[backtrace/1]).   52:- autoload(library(option), [option/3, option/2]).   53
   54:- set_prolog_flag(generate_debug_info, false).   55:- create_prolog_flag(optimise_debug, default,
   56                      [ keep(true),
   57                        type(oneof([default,false,true]))
   58                      ]).   59
   60:- meta_predicate
   61    assertion(0),
   62    debug(+,+,:).   63
   64:- multifile prolog:assertion_failed/2.   65:- dynamic   prolog:assertion_failed/2.   66
   67/*:- use_module(library(prolog_stack)).*/ % We use the autoloader if needed
   68
   69%:- set_prolog_flag(generate_debug_info, false).
   70
   71:- dynamic
   72    debugging/3.                    % Topic, Enabled, To

?- prolog_ide(debug_monitor).

 debugging(+Topic) is semidet

debugging(-Topic) is nondet

 debugging(?Topic, ?Bool) is nondet

Examine debug topics. The form debugging(+Topic) may be used to perform more complex debugging tasks. A typical usage skeleton is:

      (   debugging(mytopic)
      ->  <perform debugging actions>
      ;   true
      ),
      ...

The other two calls are intended to examine existing and enabled debugging tokens and are typically not used in user programs.

  111debugging(Topic) :-
  112    debugging(Topic, true, _To).
  113
  114debugging(Topic, Bool) :-
  115    debugging(Topic, Bool, _To).

 debug(+Topic) is det

 nodebug(+Topic) is det

Add/remove a topic from being printed. nodebug(_) removes all topics. Gives a warning if the topic is not defined unless it is used from a directive. The latter allows placing debug topics at the start of a (load-)file without warnings.

For debug/1, Topic can be a term Topic > Out, where Out is either a stream or stream-alias or a filename (an atom). This redirects debug information on this topic to the given output. On Linux systems redirection can be used to make the message appear, even if the user_error stream is redefined using

?- debug(Topic > '/proc/self/fd/2').

A platform independent way to get debug messages in the current console (for example, a swipl-win window, or login using ssh to Prolog running an SSH server from the libssh pack) is to use:

?- stream_property(S, alias(user_error)),
   debug(Topic > S).

Do not forget to disable the debugging using nodebug/1 before quitting the console if Prolog must remain running.

  143debug(Topic) :-
  144    with_mutex(prolog_debug, debug(Topic, true)).
  145nodebug(Topic) :-
  146    with_mutex(prolog_debug, debug(Topic, false)).
  147
  148debug(Spec, Val) :-
  149    debug_target(Spec, Topic, Out),
  150    (   (   retract(debugging(Topic, Enabled0, To0))
  151        *-> update_debug(Enabled0, To0, Val, Out, Enabled, To),
  152            assert(debugging(Topic, Enabled, To)),
  153            fail
  154        ;   (   prolog_load_context(file, _)
  155            ->  true
  156            ;   print_message(warning, debug_no_topic(Topic))
  157            ),
  158            update_debug(false, [], Val, Out, Enabled, To),
  159            assert(debugging(Topic, Enabled, To))
  160        )
  161    ->  true
  162    ;   true
  163    ).
  164
  165debug_target(Spec, Topic, To) :-
  166    nonvar(Spec),
  167    Spec = (Topic > To),
  168    !.
  169debug_target(Topic, Topic, -).
  170
  171update_debug(_, To0, true, -, true, To) :-
  172    !,
  173    ensure_output(To0, To).
  174update_debug(true, To0, true, Out, true, Output) :-
  175    !,
  176    (   memberchk(Out, To0)
  177    ->  Output = To0
  178    ;   append(To0, [Out], Output)
  179    ).
  180update_debug(false, _, true, Out, true, [Out]) :- !.
  181update_debug(_, _, false, -, false, []) :- !.
  182update_debug(true, [Out], false, Out, false, []) :- !.
  183update_debug(true, To0, false, Out, true, Output) :-
  184    !,
  185    delete(To0, Out, Output).
  186
  187ensure_output([], [user_error]) :- !.
  188ensure_output(List, List).

 debug_topic(+Topic) is det

Declare a topic for debugging. This can be used to find all topics available for debugging.

  195debug_topic(Topic) :-
  196    (   debugging(Registered, _, _),
  197        Registered =@= Topic
  198    ->  true
  199    ;   assert(debugging(Topic, false, []))
  200    ).

 list_debug_topics is det

 list_debug_topics(+Options) is det

List currently known topics for debug/3 and their setting. Options is either an atom or string, which is a shorthand for [search(String)] or a normal option list. Defined options are:

search(String)

Only show topics that match String. Match is case insensitive on the printed representation of the term.

active(+Boolean)

Only print topics that are active (true) or inactive (false).

output(+To)

Only print topics whose target location matches To. This option implicitly restricts the output to active topics.

  219list_debug_topics :-
  220    list_debug_topics([]).
  221
  222list_debug_topics(Options) :-
  223    (   atom(Options)
  224    ;   string(Options)
  225    ),
  226    !,
  227    list_debug_topics([search(Options)]).
  228list_debug_topics(Options) :-
  229    print_message(information, debug_topics(header)),
  230    option(active(Value), Options, _),
  231    (   debugging(Topic, Value, To),
  232        (   option(output(Stream), Options)
  233        ->  memberchk(Stream, To)
  234        ;   true
  235        ),
  236        numbervars(Topic, 0, _, [singletons(true)]),
  237        term_string(Topic, String, [quoted(true), numbervars(true)]),
  238        (   option(search(Search), Options)
  239        ->  sub_atom_icasechk(String, _, Search)
  240        ;   true
  241        ),
  242        print_message(information, debug_topic(Topic, String, Value, To)),
  243        fail
  244    ;   true
  245    ).
  246
  247:- multifile
  248    prolog_debug_tools:debugging_hook/0.  249
  250prolog_debug_tools:debugging_hook :-
  251    (   debugging(_, true)
  252    ->  list_debug_topics([active(true)])
  253    ).

 debug_message_context(+What) is det

Specify additional context for debug messages.

deprecated

- New code should use the Prolog flag message_context. This predicates adds or deletes topics from this list.

  263debug_message_context(+Topic) :-
  264    current_prolog_flag(message_context, List),
  265    (   memberchk(Topic, List)
  266    ->  true
  267    ;   append(List, [Topic], List2),
  268        set_prolog_flag(message_context, List2)
  269    ).
  270debug_message_context(-Topic) :-
  271    current_prolog_flag(message_context, List),
  272    (   selectchk(Topic, List, Rest)
  273    ->  set_prolog_flag(message_context, Rest)
  274    ;   true
  275    ).

 debug(+Topic, +Format, :Args) is det

Format a message if debug topic is enabled. Similar to format/3 to user_error, but only prints if Topic is activated through debug/1. Args is a meta-argument to deal with goal for the @-command. Output is first handed to the hook prolog:debug_print_hook/3. If this fails, Format+Args is translated to text using the message-translation (see print_message/2) for the term debug(Format, Args) and then printed to every matching destination (controlled by debug/1) using print_message_lines/3.

The message is preceded by '% ' and terminated with a newline.

See also

- format/3.

  293debug(Topic, Format, Args) :-
  294    debugging(Topic, true, To),
  295    !,
  296    print_debug(Topic, To, Format, Args).
  297debug(_, _, _).

 prolog:debug_print_hook(+Topic, +Format, +Args) is semidet

Hook called by debug/3. This hook is used by the graphical frontend that can be activated using prolog_ide/1:

?- prolog_ide(debug_monitor).

  309:- multifile
  310    prolog:debug_print_hook/3.  311
  312print_debug(_Topic, _To, _Format, _Args) :-
  313    nb_current(prolog_debug_printing, true),
  314    !.
  315print_debug(Topic, To, Format, Args) :-
  316    setup_call_cleanup(
  317        nb_setval(prolog_debug_printing, true),
  318        print_debug_guarded(Topic, To, Format, Args),
  319        nb_delete(prolog_debug_printing)).
  320
  321print_debug_guarded(Topic, _To, Format, Args) :-
  322    prolog:debug_print_hook(Topic, Format, Args),
  323    !.
  324print_debug_guarded(_, [], _, _) :- !.
  325print_debug_guarded(Topic, To, Format, Args) :-
  326    phrase('$messages':translate_message(debug(Format, Args)), Lines),
  327    (   member(T, To),
  328        debug_output(T, Stream),
  329        with_output_to(
  330            Stream,
  331            print_message_lines(current_output, kind(debug(Topic)), Lines)),
  332        fail
  333    ;   true
  334    ).
  335
  336
  337debug_output(user, user_error) :- !.
  338debug_output(Stream, Stream) :-
  339    is_stream(Stream),
  340    !.
  341debug_output(File, Stream) :-
  342    open(File, append, Stream,
  343         [ close_on_abort(false),
  344           alias(File),
  345           buffer(line)
  346         ]).
  347
  348
  349                 /*******************************
  350                 *           ASSERTION          *
  351                 *******************************/

 assertion(:Goal) is det

Acts similar to C assert() macro. It has no effect if Goal succeeds. If Goal fails or throws an exception, the following steps are taken:

• call assertion_failed/2. If assertion_failed/2 fails, then:
  • If this is an interactive toplevel thread, print a message, the stack-trace, and finally trap the debugger.
  • Otherwise, throw error(assertion_error(Reason, G),_) where Reason is one of fail or the exception raised.

  367assertion(G) :-
  368    \+ \+ catch(G,
  369                Error,
  370                assertion_failed(Error, G)),
  371
  372    !.
  373assertion(G) :-
  374    assertion_failed(fail, G),
  375    assertion_failed.               % prevent last call optimization.
  376
  377assertion_failed(Reason, G) :-
  378    prolog:assertion_failed(Reason, G),
  379    !.
  380assertion_failed(Reason, _) :-
  381    assertion_rethrow(Reason),
  382    !,
  383    throw(Reason).
  384assertion_failed(Reason, G) :-
  385    print_message(error, assertion_failed(Reason, G)),
  386    backtrace(10),
  387    (   current_prolog_flag(break_level, _) % interactive thread
  388    ->  trace
  389    ;   throw(error(assertion_error(Reason, G), _))
  390    ).
  391
  392assertion_failed.
  393
  394assertion_rethrow(time_limit_exceeded).
  395assertion_rethrow('$aborted').
  396
  397
  398                 /*******************************
  399                 *           EXPANSION          *
  400                 *******************************/
  401
  402%       The optimise_debug flag  defines whether  Prolog  optimizes
  403%       away assertions and  debug/3 statements.  Values are =true=
  404%       (debug is optimized away),  =false= (debug is retained) and
  405%       =default= (debug optimization is dependent on the optimise
  406%       flag).
  407
  408optimise_debug :-
  409    (   current_prolog_flag(optimise_debug, true)
  410    ->  true
  411    ;   current_prolog_flag(optimise_debug, default),
  412        current_prolog_flag(optimise, true)
  413    ->  true
  414    ).
  415
  416:- multifile
  417    system:goal_expansion/2.  418
  419system:goal_expansion(debug(Topic,_,_), true) :-
  420    (   optimise_debug
  421    ->  true
  422    ;   debug_topic(Topic),
  423        fail
  424    ).
  425system:goal_expansion(debugging(Topic), fail) :-
  426    (   optimise_debug
  427    ->  true
  428    ;   debug_topic(Topic),
  429        fail
  430    ).
  431system:goal_expansion(assertion(_), true) :-
  432    optimise_debug.
  433system:goal_expansion(assume(_), true) :-
  434    print_message(informational,
  435                  compatibility(renamed(assume/1, assertion/1))),
  436    optimise_debug.
  437
  438
  439                 /*******************************
  440                 *            MESSAGES          *
  441                 *******************************/
  442
  443:- multifile
  444    prolog:message/3.  445
  446prolog:message(assertion_failed(_, G)) -->
  447    [ 'Assertion failed: ~q'-[G] ].
  448prolog:message(debug(Fmt, Args)) -->
  449    [ Fmt-Args ].
  450prolog:message(debug_no_topic(Topic)) -->
  451    [ '~q: no matching debug topic (yet)'-[Topic] ].
  452prolog:message(debug_topics(header)) -->
  453    [ ansi(bold, '~w~t ~w~35| ~w~n', ['Debug Topic', 'Activated', 'To']),
  454      '~`\u2015t~48|'
  455    ].
  456prolog:message(debug_topic(_, TopicString, true, [user_error])) -->
  457    [ ansi(bold, '~s~t \u2714~35|', [TopicString]) ].
  458prolog:message(debug_topic(_, TopicString, true, To)) -->
  459    [ ansi(bold, '~s~t \u2714~35| ~q', [TopicString, To]) ].
  460prolog:message(debug_topic(_, TopicString, false, _To)) -->
  461    [ '~s~t -~35|'-[TopicString] ].
  462
  463
  464                 /*******************************
  465                 *             HOOKS            *
  466                 *******************************/

 prolog:assertion_failed(+Reason, +Goal) is semidet

This hook is called if the Goal of assertion/1 fails. Reason is unified with either fail if Goal simply failed or an exception call otherwise. If this hook fails, the default behaviour is activated. If the hooks throws an exception it will be propagated into the caller of assertion/1.

  477                 /*******************************
  478                 *            SANDBOX           *
  479                 *******************************/
  480
  481:- multifile sandbox:safe_meta/2.  482
  483sandbox:safe_meta(prolog_debug:assertion(X), [X])