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[3.9] bpo-40334: Produce better error messages on invalid targets (GH-20106) #20973

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Jun 19, 2020
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[3.9] bpo-40334: Produce better error messages on invalid targets (GH-20106) #20973

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cc9106b
bpo-40334: Produce better error messages on invalid targets (GH-20106)
lysnikolaou Jun 18, 2020
53afe79
Remove a test from test_syntax that fails with the old parser
lysnikolaou Jun 18, 2020
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77 changes: 52 additions & 25 deletions Grammar/python.gram
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Original file line number Diff line number Diff line change
Expand Up @@ -94,7 +94,7 @@ assignment[stmt_ty]:
CHECK_VERSION(6, "Variable annotations syntax is", _Py_AnnAssign(a, b, c, 0, EXTRA)) }
| a=(z=star_targets '=' { z })+ b=(yield_expr | star_expressions) !'=' tc=[TYPE_COMMENT] {
_Py_Assign(a, b, NEW_TYPE_COMMENT(p, tc), EXTRA) }
| a=single_target b=augassign c=(yield_expr | star_expressions) {
| a=single_target b=augassign ~ c=(yield_expr | star_expressions) {
_Py_AugAssign(a, b->kind, c, EXTRA) }
| invalid_assignment

Expand Down Expand Up @@ -122,7 +122,9 @@ yield_stmt[stmt_ty]: y=yield_expr { _Py_Expr(y, EXTRA) }

assert_stmt[stmt_ty]: 'assert' a=expression b=[',' z=expression { z }] { _Py_Assert(a, b, EXTRA) }

del_stmt[stmt_ty]: 'del' a=del_targets { _Py_Delete(a, EXTRA) }
del_stmt[stmt_ty]:
| 'del' a=del_targets &(';' | NEWLINE) { _Py_Delete(a, EXTRA) }
| invalid_del_stmt

import_stmt[stmt_ty]: import_name | import_from
import_name[stmt_ty]: 'import' a=dotted_as_names { _Py_Import(a, EXTRA) }
Expand Down Expand Up @@ -165,10 +167,11 @@ while_stmt[stmt_ty]:
| 'while' a=named_expression ':' b=block c=[else_block] { _Py_While(a, b, c, EXTRA) }

for_stmt[stmt_ty]:
| 'for' t=star_targets 'in' ex=star_expressions ':' tc=[TYPE_COMMENT] b=block el=[else_block] {
| 'for' t=star_targets 'in' ~ ex=star_expressions ':' tc=[TYPE_COMMENT] b=block el=[else_block] {
_Py_For(t, ex, b, el, NEW_TYPE_COMMENT(p, tc), EXTRA) }
| ASYNC 'for' t=star_targets 'in' ex=star_expressions ':' tc=[TYPE_COMMENT] b=block el=[else_block] {
| ASYNC 'for' t=star_targets 'in' ~ ex=star_expressions ':' tc=[TYPE_COMMENT] b=block el=[else_block] {
CHECK_VERSION(5, "Async for loops are", _Py_AsyncFor(t, ex, b, el, NEW_TYPE_COMMENT(p, tc), EXTRA)) }
| invalid_for_target

with_stmt[stmt_ty]:
| 'with' '(' a=','.with_item+ ','? ')' ':' b=block {
Expand All @@ -180,7 +183,9 @@ with_stmt[stmt_ty]:
| ASYNC 'with' a=','.with_item+ ':' tc=[TYPE_COMMENT] b=block {
CHECK_VERSION(5, "Async with statements are", _Py_AsyncWith(a, b, NEW_TYPE_COMMENT(p, tc), EXTRA)) }
with_item[withitem_ty]:
| e=expression o=['as' t=target { t }] { _Py_withitem(e, o, p->arena) }
| e=expression 'as' t=target &(',' | ')' | ':') { _Py_withitem(e, t, p->arena) }
| invalid_with_item
| e=expression { _Py_withitem(e, NULL, p->arena) }

try_stmt[stmt_ty]:
| 'try' ':' b=block f=finally_block { _Py_Try(b, NULL, NULL, f, EXTRA) }
Expand Down Expand Up @@ -312,7 +317,7 @@ star_named_expression[expr_ty]:
| '*' a=bitwise_or { _Py_Starred(a, Load, EXTRA) }
| named_expression
named_expression[expr_ty]:
| a=NAME ':=' b=expression { _Py_NamedExpr(CHECK(_PyPegen_set_expr_context(p, a, Store)), b, EXTRA) }
| a=NAME ':=' ~ b=expression { _Py_NamedExpr(CHECK(_PyPegen_set_expr_context(p, a, Store)), b, EXTRA) }
| expression !':='
| invalid_named_expression

Expand Down Expand Up @@ -489,18 +494,20 @@ strings[expr_ty] (memo): a=STRING+ { _PyPegen_concatenate_strings(p, a) }
list[expr_ty]:
| '[' a=[star_named_expressions] ']' { _Py_List(a, Load, EXTRA) }
listcomp[expr_ty]:
| '[' a=named_expression b=for_if_clauses ']' { _Py_ListComp(a, b, EXTRA) }
| '[' a=named_expression ~ b=for_if_clauses ']' { _Py_ListComp(a, b, EXTRA) }
| invalid_comprehension
tuple[expr_ty]:
| '(' a=[y=star_named_expression ',' z=[star_named_expressions] { _PyPegen_seq_insert_in_front(p, y, z) } ] ')' {
_Py_Tuple(a, Load, EXTRA) }
group[expr_ty]: '(' a=(yield_expr | named_expression) ')' { a }
group[expr_ty]:
| '(' a=(yield_expr | named_expression) ')' { a }
| invalid_group
genexp[expr_ty]:
| '(' a=expression b=for_if_clauses ')' { _Py_GeneratorExp(a, b, EXTRA) }
| '(' a=expression ~ b=for_if_clauses ')' { _Py_GeneratorExp(a, b, EXTRA) }
| invalid_comprehension
set[expr_ty]: '{' a=expressions_list '}' { _Py_Set(a, EXTRA) }
setcomp[expr_ty]:
| '{' a=expression b=for_if_clauses '}' { _Py_SetComp(a, b, EXTRA) }
| '{' a=expression ~ b=for_if_clauses '}' { _Py_SetComp(a, b, EXTRA) }
| invalid_comprehension
dict[expr_ty]:
| '{' a=[double_starred_kvpairs] '}' {
Expand All @@ -516,10 +523,11 @@ kvpair[KeyValuePair*]: a=expression ':' b=expression { _PyPegen_key_value_pair(p
for_if_clauses[asdl_seq*]:
| for_if_clause+
for_if_clause[comprehension_ty]:
| ASYNC 'for' a=star_targets 'in' b=disjunction c=('if' z=disjunction { z })* {
| ASYNC 'for' a=star_targets 'in' ~ b=disjunction c=('if' z=disjunction { z })* {
CHECK_VERSION(6, "Async comprehensions are", _Py_comprehension(a, b, c, 1, p->arena)) }
| 'for' a=star_targets 'in' b=disjunction c=('if' z=disjunction { z })* {
| 'for' a=star_targets 'in' ~ b=disjunction c=('if' z=disjunction { z })* {
_Py_comprehension(a, b, c, 0, p->arena) }
| invalid_for_target

yield_expr[expr_ty]:
| 'yield' 'from' a=expression { _Py_YieldFrom(a, EXTRA) }
Expand Down Expand Up @@ -589,19 +597,15 @@ single_subscript_attribute_target[expr_ty]:
| a=t_primary '[' b=slices ']' !t_lookahead { _Py_Subscript(a, b, Store, EXTRA) }

del_targets[asdl_seq*]: a=','.del_target+ [','] { a }
# The lookaheads to del_target_end ensure that we don't match expressions where a prefix of the
# expression matches our rule, thereby letting these cases fall through to invalid_del_target.
del_target[expr_ty] (memo):
| a=t_primary '.' b=NAME &del_target_end { _Py_Attribute(a, b->v.Name.id, Del, EXTRA) }
| a=t_primary '[' b=slices ']' &del_target_end { _Py_Subscript(a, b, Del, EXTRA) }
| a=t_primary '.' b=NAME !t_lookahead { _Py_Attribute(a, b->v.Name.id, Del, EXTRA) }
| a=t_primary '[' b=slices ']' !t_lookahead { _Py_Subscript(a, b, Del, EXTRA) }
| del_t_atom
del_t_atom[expr_ty]:
| a=NAME &del_target_end { _PyPegen_set_expr_context(p, a, Del) }
| a=NAME { _PyPegen_set_expr_context(p, a, Del) }
| '(' a=del_target ')' { _PyPegen_set_expr_context(p, a, Del) }
| '(' a=[del_targets] ')' { _Py_Tuple(a, Del, EXTRA) }
| '[' a=[del_targets] ']' { _Py_List(a, Del, EXTRA) }
| invalid_del_target
del_target_end: ')' | ']' | ',' | ';' | NEWLINE

targets[asdl_seq*]: a=','.target+ [','] { a }
target[expr_ty] (memo):
Expand Down Expand Up @@ -652,16 +656,23 @@ invalid_assignment:
RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "illegal target for annotation") }
| (star_targets '=')* a=star_expressions '=' {
RAISE_SYNTAX_ERROR_KNOWN_LOCATION(
_PyPegen_get_invalid_target(a),
"cannot assign to %s", _PyPegen_get_expr_name(_PyPegen_get_invalid_target(a))) }
GET_INVALID_TARGET(a),
"cannot assign to %s", _PyPegen_get_expr_name(GET_INVALID_TARGET(a))) }
| (star_targets '=')* a=yield_expr '=' { RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "assignment to yield expression not possible") }
| a=star_expressions augassign (yield_expr | star_expressions) {
RAISE_SYNTAX_ERROR_KNOWN_LOCATION(
a,
"'%s' is an illegal expression for augmented assignment",
_PyPegen_get_expr_name(a)
)}

invalid_del_stmt:
| 'del' a=star_expressions {
GET_INVALID_DEL_TARGET(a) != NULL ?
RAISE_SYNTAX_ERROR_KNOWN_LOCATION(
GET_INVALID_DEL_TARGET(a),
"cannot delete %s", _PyPegen_get_expr_name(GET_INVALID_DEL_TARGET(a))
) :
RAISE_SYNTAX_ERROR("invalid syntax") }
invalid_block:
| NEWLINE !INDENT { RAISE_INDENTATION_ERROR("expected an indented block") }
invalid_comprehension:
Expand All @@ -684,9 +695,25 @@ invalid_lambda_star_etc:
invalid_double_type_comments:
| TYPE_COMMENT NEWLINE TYPE_COMMENT NEWLINE INDENT {
RAISE_SYNTAX_ERROR("Cannot have two type comments on def") }
invalid_del_target:
| a=star_expression &del_target_end {
RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "cannot delete %s", _PyPegen_get_expr_name(a)) }
invalid_with_item:
| expression 'as' a=expression {
RAISE_SYNTAX_ERROR_KNOWN_LOCATION(
GET_INVALID_TARGET(a),
"cannot assign to %s", _PyPegen_get_expr_name(GET_INVALID_TARGET(a))
) }

invalid_for_target:
| ASYNC? 'for' a=star_expressions {
GET_INVALID_FOR_TARGET(a) != NULL ?
RAISE_SYNTAX_ERROR_KNOWN_LOCATION(
GET_INVALID_FOR_TARGET(a),
"cannot assign to %s", _PyPegen_get_expr_name(GET_INVALID_FOR_TARGET(a))
) :
RAISE_SYNTAX_ERROR("invalid syntax") }

invalid_group:
| '(' a=starred_expression ')' {
RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "can't use starred expression here") }
invalid_import_from_targets:
| import_from_as_names ',' {
RAISE_SYNTAX_ERROR("trailing comma not allowed without surrounding parentheses") }
2 changes: 1 addition & 1 deletion Lib/test/test_exceptions.py
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Original file line number Diff line number Diff line change
Expand Up @@ -253,7 +253,7 @@ def baz():
check('foo(x for x in range(10), 100)', 1, 5)
check('(yield i) = 2', 1, 1 if support.use_old_parser() else 2)
check('def f(*):\n pass', 1, 7 if support.use_old_parser() else 8)
check('for 1 in []: pass', 1, 5 if support.use_old_parser() else 7)
check('for 1 in []: pass', 1, 5)

@cpython_only
def testSettingException(self):
Expand Down
57 changes: 56 additions & 1 deletion Lib/test/test_syntax.py
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Expand Up @@ -160,6 +160,61 @@
Traceback (most recent call last):
SyntaxError: 'list' is an illegal expression for augmented assignment

Invalid targets in `for` loops and `with` statements should also
produce a specialized error message

>>> for a() in b: pass
Traceback (most recent call last):
SyntaxError: cannot assign to function call

>>> for (a, b()) in b: pass
Traceback (most recent call last):
SyntaxError: cannot assign to function call

>>> for [a, b()] in b: pass
Traceback (most recent call last):
SyntaxError: cannot assign to function call

>>> for (*a, b, c+1) in b: pass
Traceback (most recent call last):
SyntaxError: cannot assign to operator

>>> for (x, *(y, z.d())) in b: pass
Traceback (most recent call last):
SyntaxError: cannot assign to function call

>>> for a, b() in c: pass
Traceback (most recent call last):
SyntaxError: cannot assign to function call

>>> for i < (): pass
Traceback (most recent call last):
SyntaxError: invalid syntax

>>> with a as b(): pass
Traceback (most recent call last):
SyntaxError: cannot assign to function call

>>> with a as (b, c()): pass
Traceback (most recent call last):
SyntaxError: cannot assign to function call

>>> with a as [b, c()]: pass
Traceback (most recent call last):
SyntaxError: cannot assign to function call

>>> with a as (*b, c, d+1): pass
Traceback (most recent call last):
SyntaxError: cannot assign to operator

>>> with a as (x, *(y, z.d())): pass
Traceback (most recent call last):
SyntaxError: cannot assign to function call

>>> with a as b, c as d(): pass
Traceback (most recent call last):
SyntaxError: cannot assign to function call

>>> p = p =
Traceback (most recent call last):
SyntaxError: invalid syntax
Expand Down Expand Up @@ -736,7 +791,7 @@ def test_assign_del(self):
self._check_error("del (1, 2)", "delete literal")
self._check_error("del None", "delete None")
self._check_error("del *x", "delete starred")
self._check_error("del (*x)", "delete starred")
self._check_error("del (*x)", "use starred expression")
self._check_error("del (*x,)", "delete starred")
self._check_error("del [*x,]", "delete starred")
self._check_error("del f()", "delete function call")
Expand Down
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