bpo-42128: Add 'missing :' syntax error message to match statements (GH-24733)

Author: pablogsal

Grammar/python.gram

@@ -211,13 +211,15 @@ finally_block[asdl_stmt_seq*]: 'finally' ':' a=block { a }
 match_stmt[stmt_ty]:
     | "match" subject=subject_expr ':' NEWLINE INDENT cases[asdl_match_case_seq*]=case_block+ DEDENT {
         CHECK_VERSION(stmt_ty, 10, "Pattern matching is", _Py_Match(subject, cases, EXTRA)) }
+    | invalid_match_stmt
 subject_expr[expr_ty]:
     | value=star_named_expression ',' values=star_named_expressions? {
         _Py_Tuple(CHECK(asdl_expr_seq*, _PyPegen_seq_insert_in_front(p, value, values)), Load, EXTRA) }
     | named_expression
 case_block[match_case_ty]:
     | "case" pattern=patterns guard=guard? ':' body=block {
         _Py_match_case(pattern, guard, body, p->arena) }
+    | invalid_case_block
 guard[expr_ty]: 'if' guard=named_expression { guard }
 
 patterns[expr_ty]:
@@ -853,3 +855,9 @@ invalid_except_block:
         RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "exception group must be parenthesized") }
     | 'except' expression ['as' NAME ] &&':'
     | 'except' &&':' 
+
+invalid_match_stmt:
+    | "match" subject_expr !':' { CHECK_VERSION(void*, 10, "Pattern matching is", RAISE_SYNTAX_ERROR("expected ':'") ) }
+
+invalid_case_block:
+    | "case" patterns guard? !':' { RAISE_SYNTAX_ERROR("expected ':'") }

Lib/test/test_syntax.py

@@ -825,6 +825,24 @@
    Traceback (most recent call last):
    SyntaxError: expected ':'
 
+   >>> match x
+   ...   case list():
+   ...       pass
+   Traceback (most recent call last):
+   SyntaxError: expected ':'
+
+   >>> match x:
+   ...   case list()
+   ...       pass
+   Traceback (most recent call last):
+   SyntaxError: expected ':'
+
+   >>> match x:
+   ...   case [y] if y > 0
+   ...       pass
+   Traceback (most recent call last):
+   SyntaxError: expected ':'
+
 Make sure that the old "raise X, Y[, Z]" form is gone:
    >>> raise X, Y
    Traceback (most recent call last):
@@ -1159,6 +1177,24 @@ def test_error_parenthesis(self):
         for paren in ")]}":
             self._check_error(paren + "1 + 2", f"unmatched '\\{paren}'")
 
+    def test_match_call_does_not_raise_syntax_error(self):
+        code = """
+def match(x):
+    return 1+1
+
+match(34)
+"""
+        compile(code, "<string>", "exec")
+
+    def test_case_call_does_not_raise_syntax_error(self):
+        code = """
+def case(x):
+    return 1+1
+
+case(34)
+"""
+        compile(code, "<string>", "exec")
+
 
 def test_main():
     support.run_unittest(SyntaxTestCase)