#3117: backport r55087, fixes segfault with lambda (None,): None.

Lib/test/test_grammar.py

@@ -277,6 +277,7 @@ l5 = lambda x, y, z=2: x + y + z
 verify(l5(1, 2) == 5)
 verify(l5(1, 2, 3) == 6)
 check_syntax("lambda x: x = 2")
+check_syntax("lambda (None,): None")
 
 ### stmt: simple_stmt | compound_stmt
 # Tested below

Python/ast.c

@@ -249,6 +249,8 @@ PyAST_FromNode(const node *n, PyCompilerFlags *flags, const char *filename,
 		    goto error;
                 asdl_seq_SET(stmts, 0, Pass(n->n_lineno, n->n_col_offset,
                                             arena));
+                if (!asdl_seq_GET(stmts, 0))
+                    goto error;
                 return Interactive(stmts, arena);
             }
             else {
@@ -679,6 +681,8 @@ ast_for_arguments(struct compiling *c, const node *n)
 		    if (NCH(ch) != 1) {
 			/* We have complex arguments, setup for unpacking. */
 			asdl_seq_SET(args, k++, compiler_complex_args(c, ch));
+			if (!asdl_seq_GET(args, k-1))
+			    goto error;
 		    } else {
 			/* def foo((x)): setup for checking NAME below. */
 			/* Loop because there can be many parens and tuple