From 1332226b32da44087a55e1d71990ee6899dfd28a Mon Sep 17 00:00:00 2001
From: Pablo Galindo <Pablogsal@gmail.com>
Date: Mon, 27 Jul 2020 23:46:59 +0100
Subject: [PATCH] Validate the AST produced by the parser in debug mode
 (GH-21643)

This will improve the debug experience if something fails in the produced AST. Previously, errors in the produced AST can be felt much later like in the garbage collector or the compiler, making debugging them much more difficult.
---
 Parser/pegen.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/Parser/pegen.c b/Parser/pegen.c
index e2cbf8ba246..f615907f5f5 100644
--- a/Parser/pegen.c
+++ b/Parser/pegen.c
@@ -4,6 +4,7 @@
 
 #include "pegen.h"
 #include "string_parser.h"
+#include "ast.h"
 
 PyObject *
 _PyPegen_new_type_comment(Parser *p, char *s)
@@ -1137,6 +1138,14 @@ _PyPegen_run_parser(Parser *p)
         return RAISE_SYNTAX_ERROR("multiple statements found while compiling a single statement");
     }
 
+#if defined(Py_DEBUG) && defined(Py_BUILD_CORE)
+    if (p->start_rule == Py_single_input ||
+        p->start_rule == Py_file_input ||
+        p->start_rule == Py_eval_input)
+    {
+        assert(PyAST_Validate(res));
+    }
+#endif
     return res;
 }