gh-111488: Changed error message in case of no 'in' keyword after 'for' in cmp (#113656)

Author: grigoriev-semyon

Grammar/python.gram

@@ -968,6 +968,8 @@ for_if_clause[comprehension_ty]:
         CHECK_VERSION(comprehension_ty, 6, "Async comprehensions are", _PyAST_comprehension(a, b, c, 1, p->arena)) }
     | 'for' a=star_targets 'in' ~ b=disjunction c[asdl_expr_seq*]=('if' z=disjunction { z })* {
         _PyAST_comprehension(a, b, c, 0, p->arena) }
+    | 'async'? 'for' (bitwise_or (',' bitwise_or)* [',']) !'in' {
+        RAISE_SYNTAX_ERROR("'in' expected after for-loop variables") }
     | invalid_for_target
 
 listcomp[expr_ty]:

Lib/test/test_syntax.py

@@ -259,6 +259,36 @@
 Traceback (most recent call last):
 SyntaxError: invalid syntax
 
+Comprehensions without 'in' keyword:
+
+>>> [x for x if range(1)]
+Traceback (most recent call last):
+SyntaxError: 'in' expected after for-loop variables
+
+>>> tuple(x for x if range(1))
+Traceback (most recent call last):
+SyntaxError: 'in' expected after for-loop variables
+
+>>> [x for x() in a]
+Traceback (most recent call last):
+SyntaxError: cannot assign to function call
+
+>>> [x for a, b, (c + 1, d()) in y]
+Traceback (most recent call last):
+SyntaxError: cannot assign to expression
+
+>>> [x for a, b, (c + 1, d()) if y]
+Traceback (most recent call last):
+SyntaxError: 'in' expected after for-loop variables
+
+>>> [x for x+1 in y]
+Traceback (most recent call last):
+SyntaxError: cannot assign to expression
+
+>>> [x for x+1, x() in y]
+Traceback (most recent call last):
+SyntaxError: cannot assign to expression
+
 Comprehensions creating tuples without parentheses
 should produce a specialized error message:
 

Misc/ACKS

@@ -666,6 +666,7 @@ Eddy De Greef
 Duane Griffin
 Grant Griffin
 Andrea Griffini
+Semyon Grigoryev
 Duncan Grisby
 Olivier Grisel
 Fabian Groffen

Misc/NEWS.d/next/Core and Builtins/2024-01-02-17-22-57.gh-issue-111488.EJH3Oh.rst

@@ -0,0 +1,2 @@
+Changed error message in case of no 'in' keyword after 'for' in list
+comprehensions