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Fix 'gather' rules in the python parser generator (GH-22021)

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Currently, empty sequences in gather rules make the conditional for
gather rules fail as empty sequences evaluate as "False". We need to
explicitly check for "None" (the failure condition) to avoid false
negatives.
This commit is contained in:
Pablo Galindo 2020-09-03 15:29:55 +01:00 • committed by GitHub
parent 315a61f7a9
commit e55a0e971b
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2 changed files with 18 additions and 1 deletions
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16
Lib/test/test_peg_generator/test_pegen.py
View file

@ -74,7 +74,7 @@ class TestPegen(unittest.TestCase):
"Rule('term', 'int', Rhs([Alt([NamedItem(None, NameLeaf('NUMBER'))])]))"
)
def test_repeat_with_separator_rules(self) -> None:
def test_gather(self) -> None:
grammar = """
start: ','.thing+ NEWLINE
thing: NUMBER
@ -85,6 +85,20 @@ class TestPegen(unittest.TestCase):
"Rule('start', None, Rhs([Alt([NamedItem(None, Gather(StringLeaf(\"','\"), NameLeaf('thing'"
))
self.assertEqual(str(rules["thing"]), "thing: NUMBER")
parser_class = make_parser(grammar)
node = parse_string("42\n", parser_class)
assert node == [
[[TokenInfo(NUMBER, string="42", start=(1, 0), end=(1, 2), line="42\n")]],
TokenInfo(NEWLINE, string="\n", start=(1, 2), end=(1, 3), line="42\n"),
]
node = parse_string("1, 2\n", parser_class)
assert node == [
[
[TokenInfo(NUMBER, string="1", start=(1, 0), end=(1, 1), line="1, 2\n")],
[TokenInfo(NUMBER, string="2", start=(1, 3), end=(1, 4), line="1, 2\n")],
],
TokenInfo(NEWLINE, string="\n", start=(1, 4), end=(1, 5), line="1, 2\n"),
]
def test_expr_grammar(self) -> None:
grammar = """

3
Tools/peg_generator/pegen/python_generator.py
View file

@ -217,6 +217,9 @@ class PythonParserGenerator(ParserGenerator, GrammarVisitor):
else:
self.print("and")
self.visit(item)
if is_gather:
self.print("is not None")
self.print("):")
with self.indent():
action = node.action