[3.12] gh-110938: Fix error messages for indented blocks with functio… (#110990)

[3.12] gh-110938: Fix error messages for indented blocks with functions and classes with generic type parameters (GH-110973)
(cherry picked from commit 24e4ec7)

Co-authored-by: Pablo Galindo Salgado <Pablogsal@gmail.com>

Author: JelleZijlstra

Grammar/python.gram

@@ -1369,11 +1369,11 @@ invalid_for_stmt:
     | [ASYNC] a='for' star_targets 'in' star_expressions ':' NEWLINE !INDENT {
         RAISE_INDENTATION_ERROR("expected an indented block after 'for' statement on line %d", a->lineno) }
 invalid_def_raw:
-    | [ASYNC] a='def' NAME '(' [params] ')' ['->' expression] ':' NEWLINE !INDENT {
+    | [ASYNC] a='def' NAME [type_params] '(' [params] ')' ['->' expression] ':' NEWLINE !INDENT {
         RAISE_INDENTATION_ERROR("expected an indented block after function definition on line %d", a->lineno) }
 invalid_class_def_raw:
-    | 'class' NAME ['(' [arguments] ')'] NEWLINE { RAISE_SYNTAX_ERROR("expected ':'") }
-    | a='class' NAME ['(' [arguments] ')'] ':' NEWLINE !INDENT {
+    | 'class' NAME [type_params] ['(' [arguments] ')'] NEWLINE { RAISE_SYNTAX_ERROR("expected ':'") }
+    | a='class' NAME [type_params] ['(' [arguments] ')'] ':' NEWLINE !INDENT {
         RAISE_INDENTATION_ERROR("expected an indented block after class definition on line %d", a->lineno) }
 
 invalid_double_starred_kvpairs:

Lib/test/test_syntax.py

@@ -1446,11 +1446,21 @@
    Traceback (most recent call last):
    IndentationError: expected an indented block after function definition on line 1
 
+   >>> def foo[T](x, /, y, *, z=2):
+   ... pass
+   Traceback (most recent call last):
+   IndentationError: expected an indented block after function definition on line 1
+
    >>> class Blech(A):
    ... pass
    Traceback (most recent call last):
    IndentationError: expected an indented block after class definition on line 1
 
+   >>> class Blech[T](A):
+   ... pass
+   Traceback (most recent call last):
+   IndentationError: expected an indented block after class definition on line 1
+
    >>> match something:
    ... pass
    Traceback (most recent call last):

Misc/NEWS.d/next/Core and Builtins/2023-10-17-11-03-45.gh-issue-110938.X3sbMb.rst

@@ -0,0 +1,2 @@
+Fix error messages for indented blocks with functions and classes with
+generic type parameters. Patch by Pablo Galindo