bpo-30858: Improve error location for expressions with assignments

pablogsal · pablogsal · commit 6efa4681cfcb · 2020-12-13T15:29:00.000Z
diff --git a/Grammar/python.gram b/Grammar/python.gram
@@ -646,9 +646,9 @@ invalid_arguments:
         RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "Generator expression must be parenthesized") }
     | a=args ',' args { _PyPegen_arguments_parsing_error(p, a) }
 invalid_kwarg:
-    | a=expression '=' {
+    | a=expression b='=' {
         RAISE_SYNTAX_ERROR_KNOWN_LOCATION(
-            a, "expression cannot contain assignment, perhaps you meant \"==\"?") }
+            b, "expression cannot contain assignment, perhaps you meant \"==\"?") }
 invalid_named_expression:
     | a=expression ':=' expression {
         RAISE_SYNTAX_ERROR_KNOWN_LOCATION(
diff --git a/Lib/test/test_syntax.py b/Lib/test/test_syntax.py
@@ -802,6 +802,13 @@ def _check_error(self, code, errtext,
         else:
             self.fail("compile() did not raise SyntaxError")
 
+    def test_expression_with_assignment(self):
+        self._check_error(
+            "print(end1 + end2 = ' ')",
+            'expression cannot contain assignment, perhaps you meant "=="?',
+            offset=19
+        )
+
     def test_curly_brace_after_primary_raises_immediately(self):
         self._check_error("f{", "invalid syntax", mode="single")
 
diff --git a/Misc/NEWS.d/next/Core and Builtins/2020-12-13-15-23-09.bpo-30858.-f9G4z.rst b/Misc/NEWS.d/next/Core and Builtins/2020-12-13-15-23-09.bpo-30858.-f9G4z.rst
@@ -0,0 +1,2 @@
+Improve error location in expressions that contain assignments. Patch by
+Pablo Galindo and Lysandros Nikolaou.
diff --git a/Parser/parser.c b/Parser/parser.c
@@ -14562,16 +14562,16 @@ invalid_kwarg_rule(Parser *p)
             return NULL;
         }
         D(fprintf(stderr, "%*c> invalid_kwarg[%d-%d]: %s\n", p->level, ' ', _mark, p->mark, "expression '='"));
-        Token * _literal;
         expr_ty a;
+        Token * b;
         if (
             (a = expression_rule(p))  // expression
             &&
-            (_literal = _PyPegen_expect_token(p, 22))  // token='='
+            (b = _PyPegen_expect_token(p, 22))  // token='='
         )
         {
             D(fprintf(stderr, "%*c+ invalid_kwarg[%d-%d]: %s succeeded!\n", p->level, ' ', _mark, p->mark, "expression '='"));
-            _res = RAISE_SYNTAX_ERROR_KNOWN_LOCATION ( a , "expression cannot contain assignment, perhaps you meant \"==\"?" );
+            _res = RAISE_SYNTAX_ERROR_KNOWN_LOCATION ( b , "expression cannot contain assignment, perhaps you meant \"==\"?" );
             if (_res == NULL && PyErr_Occurred()) {
                 p->error_indicator = 1;
                 D(p->level--);

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,2 @@`
	`1`	`+Improve error location in expressions that contain assignments. Patch by`
	`2`	`+Pablo Galindo and Lysandros Nikolaou.`