gh-136616: Improve assert syntax error messages (#136653)

Lib/test/test_syntax.py

@@ -2686,6 +2686,71 @@ def f(x: *b)
     >>> f(x = 5, *:)
     Traceback (most recent call last):
     SyntaxError: Invalid star expression
+
+Asserts:
+
+    >>> assert (a := 1)  # ok
+    >>> # TODO(@sobolevn): improve this message in the next PR
+    >>> assert a := 1
+    Traceback (most recent call last):
+    SyntaxError: invalid syntax
+
+    >>> assert 1 = 2 = 3
+    Traceback (most recent call last):
+    SyntaxError: cannot assign to literal here. Maybe you meant '==' instead of '='?
+
+    >>> assert 1 = 2
+    Traceback (most recent call last):
+    SyntaxError: cannot assign to literal here. Maybe you meant '==' instead of '='?
+
+    >>> assert (1 = 2)
+    Traceback (most recent call last):
+    SyntaxError: cannot assign to literal here. Maybe you meant '==' instead of '='?
+
+    >>> assert 'a' = a
+    Traceback (most recent call last):
+    SyntaxError: cannot assign to literal here. Maybe you meant '==' instead of '='?
+
+    >>> assert x[0] = 1
+    Traceback (most recent call last):
+    SyntaxError: cannot assign to subscript here. Maybe you meant '==' instead of '='?
+
+    >>> assert (yield a) = 2
+    Traceback (most recent call last):
+    SyntaxError: cannot assign to yield expression here. Maybe you meant '==' instead of '='?
+
+    >>> assert a = 2
+    Traceback (most recent call last):
+    SyntaxError: cannot assign to name here. Maybe you meant '==' instead of '='?
+
+    >>> assert (a = 2)
+    Traceback (most recent call last):
+    SyntaxError: invalid syntax. Maybe you meant '==' or ':=' instead of '='?
+
+    >>> assert a = b
+    Traceback (most recent call last):
+    SyntaxError: cannot assign to name here. Maybe you meant '==' instead of '='?
+
+    >>> assert 1, 1 = b
+    Traceback (most recent call last):
+    SyntaxError: cannot assign to literal here. Maybe you meant '==' instead of '='?
+
+    >>> assert 1, (1 = b)
+    Traceback (most recent call last):
+    SyntaxError: cannot assign to literal here. Maybe you meant '==' instead of '='?
+
+    >>> assert 1, a = 1
+    Traceback (most recent call last):
+    SyntaxError: cannot assign to name here. Maybe you meant '==' instead of '='?
+
+    >>> assert 1, (a = 1)
+    Traceback (most recent call last):
+    SyntaxError: invalid syntax. Maybe you meant '==' or ':=' instead of '='?
+
+    >>> assert 1 = a, a = 1
+    Traceback (most recent call last):
+    SyntaxError: cannot assign to literal here. Maybe you meant '==' instead of '='?
+
 """
 
 import re