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Allow no whitespace after lambda body in certain cases #939

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Merged
zsol merged 9 commits into from
Jun 7, 2023
Merged

Allow no whitespace after lambda body in certain cases #939

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110109a
Allow walrus in slices
zsol May 27, 2023
a5958d1
Fix parsing of nested f-string specifiers
zsol May 27, 2023
b230302
Fix tokenizing `0else`
zsol May 27, 2023
744d6fd
Allow no whitespace between lambda keyword and params in certain cases
zsol May 27, 2023
f45ba63
Allow any expression in comprehensions' evaluated expression
zsol May 28, 2023
aa51671
Allow no space around an ifexp in certain cases
zsol May 28, 2023
4ce3660
Allow no spaces after `as` in a contextmanager in certain cases
zsol May 28, 2023
862b702
Allow no spaces around walrus in certain cases
zsol May 28, 2023
ea4ea34
Allow no whitespace after lambda body in certain cases
zsol May 28, 2023
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Allow no whitespace between lambda keyword and params in certain cases 
Python accepts code where `lambda` follows a `*`, so this PR relaxes validation rules for Lambdas.

Raised in #930.
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@zsol
zsol committed May 27, 2023
commit 744d6fd3cd72ca1edbc1f9ba43a4a86a317643aa
20 changes: 20 additions & 0 deletions libcst/_nodes/expression.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1983,6 +1983,25 @@ def _visit_and_replace_children(self, visitor: CSTVisitorT) -> "Parameters":
star_kwarg=visit_optional(self, "star_kwarg", self.star_kwarg, visitor),
)

def _safe_to_join_with_lambda(self) -> bool:
"""
Determine if Parameters need a space after the `lambda` keyword. Returns True
iff it's safe to omit the space between `lambda` and these Parameters.

See also `BaseExpression._safe_to_use_with_word_operator`.

For example: `lambda*_: pass`
"""
if len(self.posonly_params) != 0:
return False

# posonly_ind can't appear if above condition is false

if len(self.params) > 0 and self.params[0].star not in {"*", "**"}:
return False

return True

def _codegen_impl(self, state: CodegenState) -> None: # noqa: C901
# Compute the star existence first so we can ask about whether
# each element is the last in the list or not.
Expand Down Expand Up @@ -2115,6 +2134,7 @@ def _validate(self) -> None:
if (
isinstance(whitespace_after_lambda, BaseParenthesizableWhitespace)
and whitespace_after_lambda.empty
and not self.params._safe_to_join_with_lambda()
):
raise CSTValidationError(
"Must have at least one space after lambda when specifying params"
Expand Down
56 changes: 32 additions & 24 deletions libcst/_nodes/tests/test_lambda.py
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Expand Up @@ -303,30 +303,6 @@ def test_valid(
),
"at least one space after lambda",
),
(
lambda: cst.Lambda(
cst.Parameters(star_arg=cst.Param(cst.Name("arg"))),
cst.Integer("5"),
whitespace_after_lambda=cst.SimpleWhitespace(""),
),
"at least one space after lambda",
),
(
lambda: cst.Lambda(
cst.Parameters(kwonly_params=(cst.Param(cst.Name("arg")),)),
cst.Integer("5"),
whitespace_after_lambda=cst.SimpleWhitespace(""),
),
"at least one space after lambda",
),
(
lambda: cst.Lambda(
cst.Parameters(star_kwarg=cst.Param(cst.Name("arg"))),
cst.Integer("5"),
whitespace_after_lambda=cst.SimpleWhitespace(""),
),
"at least one space after lambda",
),
(
lambda: cst.Lambda(
cst.Parameters(
Expand Down Expand Up @@ -944,6 +920,38 @@ class LambdaParserTest(CSTNodeTest):
),
"( lambda : 5 )",
),
# No space between lambda and params
(
cst.Lambda(
cst.Parameters(star_arg=cst.Param(cst.Name("args"), star="*")),
cst.Integer("5"),
whitespace_after_lambda=cst.SimpleWhitespace(""),
),
"lambda*args: 5",
),
(
cst.Lambda(
cst.Parameters(star_kwarg=cst.Param(cst.Name("kwargs"), star="**")),
cst.Integer("5"),
whitespace_after_lambda=cst.SimpleWhitespace(""),
),
"lambda**kwargs: 5",
),
(
cst.Lambda(
cst.Parameters(
star_arg=cst.ParamStar(
comma=cst.Comma(
cst.SimpleWhitespace(""), cst.SimpleWhitespace("")
)
),
kwonly_params=[cst.Param(cst.Name("args"), star="")],
),
cst.Integer("5"),
whitespace_after_lambda=cst.SimpleWhitespace(""),
),
"lambda*,args: 5",
),
)
)
def test_valid(
Expand Down