gh-138944: Fix SyntaxError message for invalid syntax following valid import-as statement (#138945)

Author: brianschubert

Grammar/python.gram

@@ -1416,11 +1416,11 @@ invalid_import:
     | 'import' token=NEWLINE {
         RAISE_SYNTAX_ERROR_STARTING_FROM(token, "Expected one or more names after 'import'") }
 invalid_dotted_as_name:
-    | dotted_name 'as' !(NAME (',' | ')' | NEWLINE)) a=expression {
+    | dotted_name 'as' !(NAME (',' | ')' | ';' | NEWLINE)) a=expression {
         RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a,
             "cannot use %s as import target", _PyPegen_get_expr_name(a)) }
 invalid_import_from_as_name:
-    | NAME 'as' !(NAME (',' | ')' | NEWLINE)) a=expression {
+    | NAME 'as' !(NAME (',' | ')' | ';' | NEWLINE)) a=expression {
         RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a,
             "cannot use %s as import target", _PyPegen_get_expr_name(a)) }
 

Lib/test/test_syntax.py

@@ -2163,6 +2163,25 @@
 Traceback (most recent call last):
 SyntaxError: cannot use subscript as import target
 
+# Check that we don't raise a "cannot use name as import target" error
+# if there is an error in an unrelated statement after ';'
+
+>>> import a as b; None = 1
+Traceback (most recent call last):
+SyntaxError: cannot assign to None
+
+>>> import a, b as c; d = 1; None = 1
+Traceback (most recent call last):
+SyntaxError: cannot assign to None
+
+>>> from a import b as c; None = 1
+Traceback (most recent call last):
+SyntaxError: cannot assign to None
+
+>>> from a import b, c as d; e = 1; None = 1
+Traceback (most recent call last):
+SyntaxError: cannot assign to None
+
 # Check that we dont raise the "trailing comma" error if there is more
 # input to the left of the valid part that we parsed.
 

Misc/NEWS.d/next/Core_and_Builtins/2025-09-15-13-06-11.gh-issue-138944.PeCgLb.rst

@@ -0,0 +1,3 @@
+Fix :exc:`SyntaxError` message when invalid syntax appears on the same line
+as a valid ``import ... as ...`` or ``from ... import ... as ...``
+statement. Patch by Brian Schubert.