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gh-90994: Improve error messages upon call arguments syntax errors #96893

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Nov 20, 2022
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gh-90994: Improve error messages upon call arguments syntax errors #96893

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gh-90994: Improve error messages upon call arguments syntax errors
lysnikolaou Sep 17, 2022
b2286f0
📜🤖 Added by blurb_it.
blurb-it[bot] Sep 17, 2022
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7 changes: 7 additions & 0 deletions Grammar/python.gram
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Original file line number Diff line number Diff line change
Expand Up @@ -957,6 +957,7 @@ kwargs[asdl_seq*]:
| ','.kwarg_or_double_starred+

starred_expression[expr_ty]:
| invalid_starred_expression
| '*' a=expression { _PyAST_Starred(a, Load, EXTRA) }

kwarg_or_starred[KeywordOrStarred*]:
Expand Down Expand Up @@ -1083,6 +1084,8 @@ invalid_arguments:
RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, _PyPegen_get_last_comprehension_item(PyPegen_last_item(b, comprehension_ty)), "Generator expression must be parenthesized") }
| a=NAME b='=' expression for_if_clauses {
RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, b, "invalid syntax. Maybe you meant '==' or ':=' instead of '='?")}
| (args ',')? a=NAME b='=' &(',' | ')') {
RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, b, "expected argument value expression")}
| a=args b=for_if_clauses { _PyPegen_nonparen_genexp_in_call(p, a, b) }
| args ',' a=expression b=for_if_clauses {
RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, _PyPegen_get_last_comprehension_item(PyPegen_last_item(b, comprehension_ty)), "Generator expression must be parenthesized") }
Expand All @@ -1095,6 +1098,8 @@ invalid_kwarg:
| !(NAME '=') a=expression b='=' {
RAISE_SYNTAX_ERROR_KNOWN_RANGE(
a, b, "expression cannot contain assignment, perhaps you meant \"==\"?") }
| a='**' expression '=' b=expression {
RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, b, "cannot assign to keyword argument unpacking") }

# IMPORTANT: Note that the "_without_invalid" suffix causes the rule to not call invalid rules under it
expression_without_invalid[expr_ty]:
Expand Down Expand Up @@ -1328,3 +1333,5 @@ invalid_kvpair:
RAISE_ERROR_KNOWN_LOCATION(p, PyExc_SyntaxError, a->lineno, a->end_col_offset - 1, a->end_lineno, -1, "':' expected after dictionary key") }
| expression ':' a='*' bitwise_or { RAISE_SYNTAX_ERROR_STARTING_FROM(a, "cannot use a starred expression in a dictionary value") }
| expression a=':' &('}'|',') {RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "expression expected after dictionary key and ':'") }
invalid_starred_expression:
| a='*' expression '=' b=expression { RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, b, "cannot assign to iterable argument unpacking") }
21 changes: 21 additions & 0 deletions Lib/test/test_syntax.py
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Expand Up @@ -756,6 +756,27 @@
>>> __debug__: int
Traceback (most recent call last):
SyntaxError: cannot assign to __debug__
>>> f(a=)
Traceback (most recent call last):
SyntaxError: expected argument value expression
>>> f(a, b, c=)
Traceback (most recent call last):
SyntaxError: expected argument value expression
>>> f(a, b, c=, d)
Traceback (most recent call last):
SyntaxError: expected argument value expression
>>> f(*args=[0])
Traceback (most recent call last):
SyntaxError: cannot assign to iterable argument unpacking
>>> f(a, b, *args=[0])
Traceback (most recent call last):
SyntaxError: cannot assign to iterable argument unpacking
>>> f(**kwargs={'a': 1})
Traceback (most recent call last):
SyntaxError: cannot assign to keyword argument unpacking
>>> f(a, b, *args, **kwargs={'a': 1})
Traceback (most recent call last):
SyntaxError: cannot assign to keyword argument unpacking


More set_context():
Expand Down
4 changes: 4 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2022-09-17-17-08-01.gh-issue-90994.f0H2Yd.rst
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@@ -0,0 +1,4 @@
Improve error messages when there's a syntax error with call arguments. The following three cases are covered:
- No value is assigned to a named argument, eg ``foo(a=)``.
- A value is assigned to a star argument, eg ``foo(*args=[0])``.
- A value is assigned to a double-star keyword argument, eg ``foo(**kwarg={'a': 0})``.
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