From ae2b48f5c00b50f1873dc205020288c19bd1c27c Mon Sep 17 00:00:00 2001 From: Akim Demaille Date: Tue, 29 Jan 2013 14:19:40 +0100 Subject: [PATCH] grammar: introduce %empty Provide a means to explicitly denote empty right-hand sides of rules: instead of exp: { ... } allow exp: %empty { ... } Make sure that %empty is properly used. With help from Joel E. Denny and Gabriel Rassoul. http://lists.gnu.org/archive/html/bison-patches/2013-01/msg00142.html * src/reader.h, src/reader.c (grammar_current_rule_empty_set): New. * src/parse-gram.y (%empty): New token. Use it. * src/scan-gram.l (%empty): Scan it. * src/reader.c (grammar_rule_check): Check that %empty is properly used. * tests/actions.at (Invalid uses of %empty, Valid uses of %empty): New. --- THANKS | 1 + src/parse-gram.y | 3 +++ src/reader.c | 17 ++++++++++++ src/reader.h | 2 ++ src/scan-gram.l | 1 + src/symlist.c | 1 + src/symlist.h | 4 +++ tests/actions.at | 69 ++++++++++++++++++++++++++++++++++++++++++++++++ 8 files changed, 98 insertions(+) diff --git a/THANKS b/THANKS index 59e591dc..f30602cb 100644 --- a/THANKS +++ b/THANKS @@ -44,6 +44,7 @@ Fabrice Bauzac noon@cote-dazur.com Florian Krohm florian@edamail.fishkill.ibm.com Frank Heckenbach frank@g-n-u.de Frans Englich frans.englich@telia.com +Gabriel Rassoul gabriel.rassoul@epita.fr Georg Sauthoff gsauthof@TechFak.Uni-Bielefeld.DE George Neuner gneuner2@comcast.net Gilles Espinasse g.esp@free.fr diff --git a/src/parse-gram.y b/src/parse-gram.y index e889eb5e..7ab214ad 100644 --- a/src/parse-gram.y +++ b/src/parse-gram.y @@ -605,6 +605,7 @@ rhses.1: | rhses.1 ";" ; +%token PERCENT_EMPTY "%empty"; rhs: /* Nothing. */ { grammar_current_rule_begin (current_lhs_symbol, current_lhs_location, @@ -615,6 +616,8 @@ rhs: { grammar_current_rule_action_append ($2, @2, $3, false); } | rhs "%?{...}" { grammar_current_rule_action_append ($2, @2, NULL, true); } +| rhs "%empty" + { grammar_current_rule_empty_set (@2); } | rhs "%prec" symbol { grammar_current_rule_prec_set ($3, @3); } | rhs "%dprec" INT diff --git a/src/reader.c b/src/reader.c index 9ef993cc..a83f11c1 100644 --- a/src/reader.c +++ b/src/reader.c @@ -333,6 +333,12 @@ grammar_rule_check (const symbol_list *r) } } + /* Check that %empty => empty rule. */ + if (r->percent_empty_loc.start.file + && r->next && r->next->content.sym) + complain (&r->percent_empty_loc, complaint, + _("%%empty on non-empty rule")); + /* See comments in grammar_current_rule_prec_set for how POSIX mandates this complaint. It's only for identifiers, so skip it for char literals and strings, which are always tokens. */ @@ -434,6 +440,17 @@ grammar_current_rule_prec_set (symbol *precsym, location loc) current_rule->ruleprec = precsym; } +/* Set %empty for the current rule. */ + +void +grammar_current_rule_empty_set (location loc) +{ + if (current_rule->percent_empty_loc.start.file) + complain (&loc, complaint, _("only one %s allowed per rule"), "%empty"); + else + current_rule->percent_empty_loc = loc; +} + /* Attach dynamic precedence DPREC to the current rule. */ void diff --git a/src/reader.h b/src/reader.h index c15544e6..ba6ffe6e 100644 --- a/src/reader.h +++ b/src/reader.h @@ -47,6 +47,8 @@ void grammar_current_rule_begin (symbol *lhs, location loc, named_ref *lhs_named_ref); void grammar_current_rule_end (location loc); void grammar_midrule_action (void); +/* Apply %empty to the current rule. */ +void grammar_current_rule_empty_set (location loc); void grammar_current_rule_prec_set (symbol *precsym, location loc); void grammar_current_rule_dprec_set (int dprec, location loc); void grammar_current_rule_merge_set (uniqstr name, location loc); diff --git a/src/scan-gram.l b/src/scan-gram.l index 2ed6d2fd..7ce3b4b1 100644 --- a/src/scan-gram.l +++ b/src/scan-gram.l @@ -217,6 +217,7 @@ eqopt ([[:space:]]*=)? "%defines" return PERCENT_DEFINES; "%destructor" return PERCENT_DESTRUCTOR; "%dprec" return PERCENT_DPREC; + "%empty" return PERCENT_EMPTY; "%error-verbose" return PERCENT_ERROR_VERBOSE; "%expect" return PERCENT_EXPECT; "%expect-rr" return PERCENT_EXPECT_RR; diff --git a/src/symlist.c b/src/symlist.c index d43591ad..005d808b 100644 --- a/src/symlist.c +++ b/src/symlist.c @@ -44,6 +44,7 @@ symbol_list_sym_new (symbol *sym, location loc) /* Members used for LHS only. */ res->ruleprec = NULL; + res->percent_empty_loc = empty_location; code_props_none_init (&res->action_props); res->dprec = 0; res->merger = 0; diff --git a/src/symlist.h b/src/symlist.h index 657efacd..9b0f1172 100644 --- a/src/symlist.h +++ b/src/symlist.h @@ -78,6 +78,10 @@ typedef struct symbol_list * each RHS are also stored here. */ code_props action_props; + /* The location of the first %empty for this rule, or \a + empty_location. */ + location percent_empty_loc; + int dprec; int merger; location merger_declaration_location; diff --git a/tests/actions.at b/tests/actions.at index 9473f6ef..6dd5a580 100644 --- a/tests/actions.at +++ b/tests/actions.at @@ -64,6 +64,75 @@ AT_PARSER_CHECK([./input], 0, AT_CLEANUP +## ------------------------ ## +## Invalid uses of %empty. ## +## ------------------------ ## + +AT_SETUP([Invalid uses of %empty]) + +AT_DATA_GRAMMAR([[one.y]], +[[%% +exp: + %empty %empty {} +; +]]) + +AT_BISON_CHECK([-fcaret one.y], [1], [], +[[one.y:11.10-15: error: only one %empty allowed per rule + %empty %empty {} + ^^^^^^ +]]) + +AT_DATA_GRAMMAR([[two.y]], +[[%% +exp: + 'a' %empty {} +| %empty 'a' {} +| %empty {} {} +; +]]) + +AT_BISON_CHECK([-fcaret two.y], [1], [], +[[two.y:11.7-12: error: %empty on non-empty rule + 'a' %empty {} + ^^^^^^ +two.y:12.3-8: error: %empty on non-empty rule + | %empty 'a' {} + ^^^^^^ +two.y:13.3-8: error: %empty on non-empty rule + | %empty {} {} + ^^^^^^ +]]) + +AT_CLEANUP + +## ---------------------- ## +## Valid uses of %empty. ## +## ---------------------- ## + +AT_SETUP([Valid uses of %empty]) + +AT_BISON_OPTION_PUSHDEFS +AT_DATA_GRAMMAR([[input.y]], +[[ +%debug +%code +{ +]AT_YYERROR_DECLARE[ +]AT_YYLEX_DECLARE[ +} +%% +exp: %empty {} +%% +]AT_YYERROR_DEFINE[ +]AT_YYLEX_DEFINE[ +]AT_MAIN_DEFINE[ +]]) + +AT_FULL_COMPILE([input]) +AT_PARSER_CHECK([./input]) +AT_BISON_OPTION_POPDEFS +AT_CLEANUP ## ------------------ ## ## Initial location. ## -- 2.45.2