From df179eba43b7e93e5ace1e4d54194adc709cd07b Mon Sep 17 00:00:00 2001
From: "Sven M. Hallberg" <pesco@khjk.org>
Date: Fri, 25 Sep 2015 01:28:52 +0200
Subject: [PATCH] fix conflict resolution with charset productions
---
src/backends/lalr.c | 63 +++++++++++++++++++++++++++++----------------
src/t_regression.c | 21 +++++++++++----
2 files changed, 57 insertions(+), 27 deletions(-)
diff --git a/src/backends/lalr.c b/src/backends/lalr.c
index 1e629422..b82ef71c 100644
--- a/src/backends/lalr.c
+++ b/src/backends/lalr.c
@@ -208,6 +208,46 @@ static bool match_production(HLREnhGrammar *eg, HCFChoice **p,
&& state == endstate);
}
+// variant of match_production where the production lhs is a charset
+// [..x..] -> x
+static bool match_charset_production(const HLRTable *table, HLREnhGrammar *eg,
+ const HCFChoice *lhs, HCFChoice *rhs,
+ size_t endstate)
+{
+ assert(lhs->type == HCF_CHARSET);
+ assert(rhs->type == HCF_CHAR);
+
+ if(!charset_isset(lhs->charset, rhs->chr))
+ return false;
+
+ // determine the enhanced-grammar right-hand side and check end state
+ HLRTransition *t = h_hashtable_get(eg->smap, lhs);
+ assert(t != NULL);
+ return (follow_transition(table, t->from, rhs) == endstate);
+}
+
+// check wether any production for sym (enhanced-grammar) matches the given
+// (original-grammar) rhs and terminates in the given end state.
+static bool match_any_production(const HLRTable *table, HLREnhGrammar *eg,
+ const HCFChoice *sym, HCFChoice **rhs,
+ size_t endstate)
+{
+ assert(sym->type == HCF_CHOICE || sym->type == HCF_CHARSET);
+
+ if(sym->type == HCF_CHOICE) {
+ for(HCFSequence **p=sym->seq; *p; p++) {
+ if(match_production(eg, (*p)->items, rhs, endstate))
+ return true;
+ }
+ } else { // HCF_CHARSET
+ assert(rhs[0] != NULL);
+ assert(rhs[1] == NULL);
+ return match_charset_production(table, eg, sym, rhs[0], endstate);
+ }
+
+ return false;
+}
+
// desugar parser with a fresh start symbol
// this guarantees that the start symbol will not occur in any productions
HCFChoice *h_desugar_augmented(HAllocator *mm__, HParser *parser)
@@ -286,28 +326,7 @@ int h_lalr_compile(HAllocator* mm__, HParser* parser, const void* params)
HHashSet *lhss = h_hashtable_get(eg->corr, item->lhs);
assert(lhss != NULL);
H_FOREACH_KEY(lhss, HCFChoice *lhs)
- assert(lhs->type == HCF_CHOICE || lhs->type == HCF_CHARSET);
-
- bool match = false;
- if(lhs->type == HCF_CHOICE) {
- for(HCFSequence **p=lhs->seq; *p; p++) {
- HCFChoice **rhs = (*p)->items;
- if(match_production(eg, rhs, item->rhs, state)) {
- match = true;
- break;
- }
- }
- } else { // HCF_CHARSET
- assert(item->rhs[0] != NULL);
- assert(item->rhs[1] == NULL);
- assert(item->rhs[0]->type == HCF_CHAR);
- HLRTransition *t = h_hashtable_get(eg->smap, lhs);
- assert(t != NULL);
- match = (t->to == state
- && charset_isset(lhs->charset, item->rhs[0]->chr));
- }
-
- if(match) {
+ if(match_any_production(table, eg, lhs, item->rhs, state)) {
// the left-hand symbol's follow set is this production's
// contribution to the lookahead
const HStringMap *fs = h_follow(1, eg->grammar, lhs);
diff --git a/src/t_regression.c b/src/t_regression.c
index 4097fb6c..faa953c8 100644
--- a/src/t_regression.c
+++ b/src/t_regression.c
@@ -121,13 +121,24 @@ static void test_llk_zero_end(void) {
static void test_lalr_charset_lhs(void) {
HParserBackend be = PB_LALR;
- HParser *p = h_choice(h_ch('A'), h_uint8(), NULL);
+ HParser *p = h_many(h_choice(h_sequence(h_ch('A'), h_ch('B'), NULL),
+ h_in((uint8_t*)"AB",2), NULL));
- // the above would fail to compile because of an unhandled case in trying
- // to resolve a conflict where an item's left-hand-side was an HCF_CHARSET.
+ // the above would abort because of an unhandled case in trying to resolve
+ // a conflict where an item's left-hand-side was an HCF_CHARSET.
+ // however, the compile should fail - the conflict cannot be resolved.
- g_check_parse_match(p, be, "A",1, "u0x41");
- g_check_parse_match(p, be, "B",1, "u0x42");
+ if(h_compile(p, be, NULL) == 0) {
+ g_test_message("LALR compile didn't detect ambiguous grammar");
+
+ // it says it compiled it - well, then it should parse it!
+ // (this helps us see what it thinks it should be doing.)
+ g_check_parse_match(p, be, "AA",2, "(u0x41 u0x41)");
+ g_check_parse_match(p, be, "AB",2, "((u0x41 u0x42))");
+
+ g_test_fail();
+ return;
+ }
}
static void test_cfg_many_seq(void) {
--
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