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bpo-41667: Fix 'gather' rules in the python parser generator #22021

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Merged
pablogsal merged 1 commit into from
Sep 3, 2020
Merged

bpo-41667: Fix 'gather' rules in the python parser generator #22021

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Fix 'gather' rules in the python parser generator 
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.
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@pablogsal
pablogsal committed Aug 30, 2020
commit f5f7b54e5ead8aba2fe9a1a494856d494b14a84a
16 changes: 15 additions & 1 deletion Lib/test/test_peg_generator/test_pegen.py
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Original file line number Diff line number Diff line change
Expand Up @@ -74,7 +74,7 @@ def test_typed_rules(self) -> None:
"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
Expand All @@ -85,6 +85,20 @@ def test_repeat_with_separator_rules(self) -> None:
"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 = """
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3 changes: 3 additions & 0 deletions Tools/peg_generator/pegen/python_generator.py
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Original file line number Diff line number Diff line change
Expand Up @@ -217,6 +217,9 @@ def visit_Alt(self, node: Alt, is_loop: bool, is_gather: bool) -> None:
else:
self.print("and")
self.visit(item)
if is_gather:
self.print("is not None")

self.print("):")
with self.indent():
action = node.action
Expand Down