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b34b12c4f9
This change allows one to document (and check) which rules participate
in shift/reduce and reduce/reduce conflicts. This is particularly
important GLR parsers, where conflicts are a normal occurrence. For
example,
%glr-parser
%expect 1
%%
...
argument_list:
arguments %expect 1
| arguments ','
| %empty
;
arguments:
expression
| argument_list ',' expression
;
...
Looking at the output from -v, one can see that the shift-reduce
conflict here is due to the fact that the parser does not know whether
to reduce arguments to argument_list until it sees the token AFTER the
following ','. By marking the rule with %expect 1 (because there is a
conflict in one state), we document the source of the 1 overall shift-
reduce conflict.
In GLR parsers, we can use %expect-rr in a rule for reduce/reduce
conflicts. In this case, we mark each of the conflicting rules. For
example,
%glr-parser
%expect-rr 1
%%
stmt:
target_list '=' expr ';'
| expr_list ';'
;
target_list:
target
| target ',' target_list
;
target:
ID %expect-rr 1
;
expr_list:
expr
| expr ',' expr_list
;
expr:
ID %expect-rr 1
| ...
;
In a statement such as
x, y = 3, 4;
the parser must reduce x to a target or an expr, but does not know
which until it sees the '='. So we notate the two possible reductions
to indicate that each conflicts in one rule.
See https://lists.gnu.org/archive/html/bison-patches/2013-02/msg00105.html.
* doc/bison.texi (Suppressing Conflict Warnings): Document %expect,
%expect-rr in grammar rules.
* src/conflicts.c (count_state_rr_conflicts): Adjust comment.
(rule_has_state_sr_conflicts): New static function.
(count_rule_sr_conflicts): New static function.
(rule_nast_state_rr_conflicts): New static function.
(count_rule_rr_conflicts): New static function.
(rule_conflicts_print): New static function.
(conflicts_print): Also use rule_conflicts_print to report on individual
rules.
* src/gram.h (struct rule): Add new fields expected_sr_conflicts,
expected_rr_conflicts.
* src/reader.c (grammar_midrule_action): Transfer expected_sr_conflicts,
expected_rr_conflicts to new rule, and turn off in current_rule.
(grammar_current_rule_expect_sr): New function.
(grammar_current_rule_expect_rr): New function.
(packgram): Transfer expected_sr_conflicts, expected_rr_conflicts
to new rule.
* src/reader.h (grammar_current_rule_expect_sr): New function.
(grammar_current_rule_expect_rr): New function.
* src/symlist.c (symbol_list_sym_new): Initialize expected_sr_conflicts,
expected_rr_conflicts.
* src/symlist.h (struct symbol_list): Add new fields expected_sr_conflicts,
expected_rr_conflicts.
* tests/conflicts.at: Add tests "%expect in grammar rule not enough",
"%expect in grammar rule right.", "%expect in grammar rule too much."
79 lines
2.6 KiB
C
79 lines
2.6 KiB
C
/* Input parser for Bison
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Copyright (C) 2000-2003, 2005-2007, 2009-2015, 2018 Free Software
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Foundation, Inc.
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This file is part of Bison, the GNU Compiler Compiler.
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>. */
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#ifndef READER_H_
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# define READER_H_
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# include "location.h"
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# include "symlist.h"
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# include "named-ref.h"
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# include "parse-gram.h"
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typedef struct merger_list
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{
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struct merger_list* next;
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uniqstr name;
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uniqstr type;
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location type_declaration_location;
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} merger_list;
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/* From the parser. */
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extern int gram_debug;
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int gram_parse (void);
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char const *token_name (int type);
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/* From reader.c. */
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void grammar_start_symbol_set (symbol *sym, location loc);
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void grammar_current_rule_begin (symbol *lhs, location loc,
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named_ref *lhs_named_ref);
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void grammar_current_rule_end (location loc);
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void grammar_midrule_action (void);
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/* Apply %empty to the current rule. */
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void grammar_current_rule_empty_set (location loc);
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void grammar_current_rule_prec_set (symbol *precsym, location loc);
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void grammar_current_rule_dprec_set (int dprec, location loc);
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void grammar_current_rule_merge_set (uniqstr name, location loc);
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void grammar_current_rule_expect_sr (int count, location loc);
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void grammar_current_rule_expect_rr (int count, location loc);
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void grammar_current_rule_symbol_append (symbol *sym, location loc,
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named_ref *nref);
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/* Attach an ACTION to the current rule. */
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void grammar_current_rule_action_append (const char *action, location loc,
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named_ref *nref, uniqstr tag);
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/* Attach a PREDICATE to the current rule. */
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void grammar_current_rule_predicate_append (const char *predicate, location loc);
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void reader (void);
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void free_merger_functions (void);
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extern merger_list *merge_functions;
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/* Was %union seen? */
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extern bool union_seen;
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/* Was a tag seen? */
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extern bool tag_seen;
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/* Should rules have a default precedence? */
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extern bool default_prec;
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#endif /* !READER_H_ */
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