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    1/*  Part of SWI-Prolog
    2
    3    Author:        Jan Wielemaker and Anjo Anjewierden
    4    E-mail:        J.Wielemaker@vu.nl
    5    WWW:           http://www.swi-prolog.org/
    6    Copyright (c)  2011-2018, University of Amsterdam
    7                              VU University Amsterdam
    8                              CWI, Amsterdam
    9    All rights reserved.
   10
   11    Redistribution and use in source and binary forms, with or without
   12    modification, are permitted provided that the following conditions
   13    are met:
   14
   15    1. Redistributions of source code must retain the above copyright
   16       notice, this list of conditions and the following disclaimer.
   17
   18    2. Redistributions in binary form must reproduce the above copyright
   19       notice, this list of conditions and the following disclaimer in
   20       the documentation and/or other materials provided with the
   21       distribution.
   22
   23    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   24    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   25    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
   26    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
   27    COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
   28    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
   29    BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   30    LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
   31    CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   32    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
   33    ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   34    POSSIBILITY OF SUCH DAMAGE.
   35*/
   36
   37:- module(prolog_breakpoints,
   38          [ set_breakpoint/4,           % +File, +Line, +CharPos, -Id
   39            set_breakpoint/5,           % +Owner, +File, +Line, +CharPos, -Id
   40            delete_breakpoint/1,        % +Id
   41            breakpoint_property/2       % ?Id, ?Property
   42          ]).   43:- autoload(library(debug), [debug/3]).   44:- autoload(library(error), [existence_error/2]).   45:- autoload(library(lists), [nth1/3, member/2]).   46:- autoload(library(prolog_clause), [clause_info/4, clause_name/2]).

Manage Prolog break-points

This module provides an interface for development tools to set and delete break-points, giving a location in the source. Development tools that want to track changes to breakpoints must use user:message_hook/3 to intercept these message terms:

Note that the hook must fail after creating its side-effects to give other hooks the opportunity to react. */

 set_breakpoint(+File, +Line, +Char, -Id) is det
 set_breakpoint(+Owner, +File, +Line, +Char, -Id) is det
Put a breakpoint at the indicated source-location. File is a current sourcefile (as reported by source_file/1). Line is the 1-based line in which Char is. Char is the position of the break.

First, '$clause_from_source'/4 uses the SWI-Prolog clause-source information to find the last clause starting before Line. '$break_pc' generated (on backtracking), a list of possible break-points.

Note that in addition to setting the break-point, the system must be in debug mode for the breakpoint to take effect. With threading enabled, there are various different ways this may be done. See debug/0, tdebug/0 and tdebug/1. Therefore, this predicate does not enable debug mode.

Arguments:
Owner- denotes the file that owns the clause. set_breakpoint/5 is used to set breakpoints in an included file in the context of the Owner main file. See source_file_property/2.
   85set_breakpoint(File, Line, Char, Id) :-
   86    set_breakpoint(File, File, Line, Char, Id).
   87set_breakpoint(Owner, File, Line, Char, Id) :-
   88    debug(break, 'break_at(~q, ~d, ~d).', [File, Line, Char]),
   89    '$clause_from_source'(Owner, File, Line, ClauseRefs),
   90    member(ClauseRef, ClauseRefs),
   91    clause_info(ClauseRef, InfoFile, TermPos, _NameOffset),
   92    (   InfoFile == File
   93    ->  '$break_pc'(ClauseRef, PC, NextPC),
   94        debug(break, 'Clause ~p, PC=~p NextPC=~p', [ClauseRef, PC, NextPC]),
   95        '$clause_term_position'(ClauseRef, NextPC, List),
   96        debug(break, 'Location = ~w', [List]),
   97        range(List, TermPos, A, Z),
   98        debug(break, 'Term from ~w-~w', [A, Z]),
   99        Z >= Char, !,
  100        Len is Z - A,
  101        b_setval('$breakpoint', file_location(File, Line, A, Len))
  102    ;   print_message(warning, breakpoint(no_source(ClauseRef, File, Line))),
  103        '$break_pc'(ClauseRef, PC, _), !,
  104        nb_delete('$breakpoint')
  105    ),
  106    debug(break, 'Break at clause ~w, PC=~w', [ClauseRef, PC]),
  107    '$break_at'(ClauseRef, PC, true),
  108    nb_delete('$breakpoint'),
  109    known_breakpoint(ClauseRef, PC, _Location, Id).
  110
  111range(_,  Pos, _, _) :-
  112    var(Pos), !, fail.
  113range([], Pos, A, Z) :-
  114    arg(1, Pos, A),
  115    arg(2, Pos, Z).
  116range([H|T], term_position(_, _, _, _, PosL), A, Z) :-
  117    nth1(H, PosL, Pos),
  118    range(T, Pos, A, Z).
  119
  120:- dynamic
  121    known_breakpoint/4,             % ClauseRef, PC, Location, Id
  122    break_id/1.  123
  124next_break_id(Id) :-
  125    retract(break_id(Id0)),
  126    !,
  127    Id is Id0+1,
  128    asserta(break_id(Id)).
  129next_break_id(1) :-
  130    asserta(break_id(1)).
 delete_breakpoint(+Id) is det
Delete breakpoint with given Id. If successful, print_message(breakpoint(delete, Id)) is called. Message hooks working on this message may still call breakpoint_property/2.
Errors
- existence_error(breakpoint, Id).
  140delete_breakpoint(Id) :-
  141    integer(Id),
  142    known_breakpoint(ClauseRef, PC, _Location, Id),
  143    !,
  144    '$break_at'(ClauseRef, PC, false).
  145delete_breakpoint(Id) :-
  146    existence_error(breakpoint, Id).
 breakpoint_property(?Id, ?Property) is nondet
True when Property is a property of the breakpoint Id. Defined properties are:
file(File)
Provided if the breakpoint is in a clause associated to a file. May not be known.
line_count(Line)
Line of the breakpoint. May not be known.
character_range(Start, Len)
One-based character offset of the break-point. May not be known.
clause(Reference)
Reference of the clause in which the breakpoint resides.
  164breakpoint_property(Id, file(File)) :-
  165    known_breakpoint(ClauseRef,_,_,Id),
  166    clause_property(ClauseRef, file(File)).
  167breakpoint_property(Id, line_count(Line)) :-
  168    known_breakpoint(_,_,Location,Id),
  169    location_line(Location, Line).
  170breakpoint_property(Id, character_range(Start, Len)) :-
  171    known_breakpoint(ClauseRef,PC,Location,Id),
  172    (   Location = file_location(_File, _Line, Start, Len)
  173    ->  true
  174    ;   break_location(ClauseRef, PC, _File, Start-End),
  175        Len is End+1-Start
  176    ).
  177breakpoint_property(Id, clause(Reference)) :-
  178    known_breakpoint(Reference,_,_,Id).
  179
  180location_line(file_location(_File, Line, _Start, _Len), Line).
  181location_line(file_character_range(File, Start, _Len), Line) :-
  182    file_line(File, Start, Line).
  183location_line(file_line(_File, Line), Line).
 file_line(+File, +StartIndex, -Line) is det
True when Line is the 1-based line offset in which we find character StartIndex.
  191file_line(File, Start, Line) :-
  192    setup_call_cleanup(
  193        prolog_clause:try_open_source(File, In),
  194        stream_line(In, Start, 1, Line),
  195        close(In)).
  196
  197stream_line(In, _, Line0, Line) :-
  198    at_end_of_stream(In),
  199    !,
  200    Line = Line0.
  201stream_line(In, Index, Line0, Line) :-
  202    skip(In, 0'\n),
  203    character_count(In, At),
  204    (   At > Index
  205    ->  Line = Line0
  206    ;   Line1 is Line0+1,
  207        stream_line(In, Index, Line1, Line)
  208    ).
  209
  210
  211                 /*******************************
  212                 *            FEEDBACK          *
  213                 *******************************/
  214
  215:- initialization
  216    prolog_unlisten(break, onbreak),
  217    prolog_listen(break, onbreak).  218
  219onbreak(exist, ClauseRef, PC) :-
  220    known_breakpoint(ClauseRef, PC, _Location, Id),
  221    !,
  222    break_message(breakpoint(exist, Id)).
  223onbreak(true, ClauseRef, PC) :-
  224    !,
  225    debug(break, 'Trap in Clause ~p, PC ~d', [ClauseRef, PC]),
  226    with_mutex('$break', next_break_id(Id)),
  227    (   nb_current('$breakpoint', Location)
  228    ->  true
  229    ;   break_location(ClauseRef, PC, File, A-Z)
  230    ->  Len is Z+1-A,
  231        Location = file_character_range(File, A, Len)
  232    ;   clause_property(ClauseRef, file(File)),
  233        clause_property(ClauseRef, line_count(Line))
  234    ->  Location = file_line(File, Line)
  235    ;   Location = unknown
  236    ),
  237    asserta(known_breakpoint(ClauseRef, PC, Location, Id)),
  238    break_message(breakpoint(set, Id)).
  239onbreak(false, ClauseRef, PC) :-
  240    debug(break, 'Remove breakpoint from ~p, PC ~d', [ClauseRef, PC]),
  241    clause(known_breakpoint(ClauseRef, PC, _Location, Id), true, Ref),
  242    call_cleanup(break_message(breakpoint(delete, Id)), erase(Ref)).
  243onbreak(gc, ClauseRef, PC) :-
  244    debug(break, 'Remove breakpoint from ~p, PC ~d (due to CGC)',
  245          [ClauseRef, PC]),
  246    retractall(known_breakpoint(ClauseRef, PC, _Location, _Id)).
  247
  248break_message(Message) :-
  249    print_message(informational, Message).
 break_location(+ClauseRef, +PC, -File, -AZ) is det
True when File and AZ represent the location of the goal called at PC in ClauseRef.
Arguments:
AZ- is a term A-Z, where A and Z are character positions in File.
  259break_location(ClauseRef, PC, File, A-Z) :-
  260    clause_info(ClauseRef, File, TermPos, _NameOffset),
  261    '$fetch_vm'(ClauseRef, PC, NPC, _VMI),
  262    '$clause_term_position'(ClauseRef, NPC, List),
  263    debug(break, 'ClausePos = ~w', [List]),
  264    range(List, TermPos, A, Z),
  265    debug(break, 'Range: ~d .. ~d', [A, Z]).
  266
  267
  268                 /*******************************
  269                 *            MESSAGES          *
  270                 *******************************/
  271
  272:- multifile
  273    prolog:message/3.  274
  275prolog:message(breakpoint(no_source(ClauseRef, _File, Line))) -->
  276    [ 'Failed to find line ~d in body of clause ~p.  Breaking at start of body.'-
  277      [Line, ClauseRef]
  278    ].
  279prolog:message(breakpoint(SetClear, Id)) -->
  280    setclear(SetClear),
  281    breakpoint(Id).
  282
  283setclear(set) -->
  284    ['Breakpoint '].
  285setclear(exist) -->
  286    ['Existing breakpoint '].
  287setclear(delete) -->
  288    ['Deleted breakpoint '].
  289
  290breakpoint(Id) -->
  291    breakpoint_name(Id),
  292    (   { breakpoint_property(Id, file(File)),
  293          breakpoint_property(Id, line_count(Line))
  294        }
  295    ->  [ ' at ', url(File:Line) ]
  296    ;   []
  297    ).
  298
  299breakpoint_name(Id) -->
  300    { breakpoint_property(Id, clause(ClauseRef)) },
  301    (   { clause_property(ClauseRef, erased) }
  302    ->  ['~w'-[Id]]
  303    ;   { clause_name(ClauseRef, Name) },
  304        ['~w in ~w'-[Id, Name]]
  305    )