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Fix unsafe defaulted_state reductions and align with Bison defaulted_state reduction behavior #314

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Fix unsafe defaulted_state reductions and align with Bison defaulted_state reduction behavior #314

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21d4541
Update yacc.py to fix a deadlock issue caused by defaulted_state redu…
justincui Aug 7, 2025
51956ad
Update yacc_error5.py to remove the invalid error handling rule.
justincui Aug 7, 2025
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14 changes: 11 additions & 3 deletions src/ply/yacc.py
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Original file line number Diff line number Diff line change
Expand Up @@ -255,9 +255,17 @@ def restart(self):
def set_defaulted_states(self):
self.defaulted_states = {}
for state, actions in self.action.items():
if not actions:
continue
rules = list(actions.values())
if len(rules) == 1 and rules[0] < 0:
self.defaulted_states[state] = rules[0]
first_rule = rules[0]
if first_rule < 0:
if len(rules) == 1:
self.defaulted_states[state] = first_rule
else:
all_rules = set(rules)
if len(all_rules) == 1:
self.defaulted_states[state] = first_rule

def disable_defaulted_states(self):
self.defaulted_states = {}
Expand Down Expand Up @@ -324,7 +332,7 @@ def parse(self, input=None, lexer=None, debug=False, tracking=False):
if debug:
debug.debug('State : %s', state)

if state not in defaulted_states:
if state not in defaulted_states or errorcount>0:
if not lookahead:
if not lookaheadstack:
lookahead = get_token() # Get the next token
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6 changes: 0 additions & 6 deletions tests/yacc_error5.py
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Expand Up @@ -21,12 +21,6 @@ def p_statement_assign(t):
'statement : NAME EQUALS expression'
names[t[1]] = t[3]

def p_statement_assign_error(t):
'statement : NAME EQUALS error'
line_start, line_end = t.linespan(3)
pos_start, pos_end = t.lexspan(3)
print("Assignment Error at %d:%d to %d:%d" % (line_start,pos_start,line_end,pos_end))

def p_statement_expr(t):
'statement : expression'
print(t[1])
Expand Down