bpo-40614: Respect feature version for f-string debug expressions (GH-20196)

Co-authored-by: Lysandros Nikolaou <[email protected]>
Co-authored-by: Pablo Galindo <[email protected]>

Author: 3 people

Lib/test/test_ast.py

@@ -663,6 +663,11 @@ def test_ast_asdl_signature(self):
         expressions[0] = f"expr = {ast.expr.__subclasses__()[0].__doc__}"
         self.assertCountEqual(ast.expr.__doc__.split("\n"), expressions)
 
+    def test_issue40614_feature_version(self):
+        ast.parse('f"{x=}"', feature_version=(3, 8))
+        with self.assertRaises(SyntaxError):
+            ast.parse('f"{x=}"', feature_version=(3, 7))
+
 
 class ASTHelpers_Test(unittest.TestCase):
     maxDiff = None

Misc/NEWS.d/next/Library/2020-05-18-22-41-02.bpo-40614.8j3kmq.rst

@@ -0,0 +1 @@
+:func:`ast.parse` will not parse self documenting expressions in f-strings when passed ``feature_version`` is less than ``(3, 8)``.

Parser/pegen/parse_string.c

@@ -928,6 +928,11 @@ fstring_find_expr(Parser *p, const char **str, const char *end, int raw, int rec
     /* Check for =, which puts the text value of the expression in
        expr_text. */
     if (**str == '=') {
+        if (p->feature_version < 8) {
+            RAISE_SYNTAX_ERROR("f-string: self documenting expressions are "
+                               "only supported in Python 3.8 and greater");
+            goto error;
+        }
         *str += 1;
 
         /* Skip over ASCII whitespace.  No need to test for end of string

Python/ast.c

@@ -5069,6 +5069,12 @@ fstring_find_expr(const char **str, const char *end, int raw, int recurse_lvl,
     /* Check for =, which puts the text value of the expression in
        expr_text. */
     if (**str == '=') {
+        if (c->c_feature_version < 8) {
+            ast_error(c, n,
+                      "f-string: self documenting expressions are "
+                      "only supported in Python 3.8 and greater");
+            goto error;
+        }
         *str += 1;
 
         /* Skip over ASCII whitespace.  No need to test for end of string