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[3.9] Fix 'gather' rules in the python parser generator (GH-22021) (GH-22080) 

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.
(cherry picked from commit e55a0e9)

Co-authored-by: Pablo Galindo <Pablogsal@gmail.com>
This commit is contained in:
Pablo Galindo 2020-09-03 16:35:36 +01:00 committed by GitHub
parent be17295280
commit 270e249290
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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