gh-131927: Prevent emitting optimizer warnings twice in the REPL

Include/cpython/warnings.h

@@ -18,3 +18,9 @@ PyAPI_FUNC(int) PyErr_WarnExplicitFormat(
 
 // DEPRECATED: Use PyErr_WarnEx() instead.
 #define PyErr_Warn(category, msg) PyErr_WarnEx((category), (msg), 1)
+
+int _PyErr_WarnExplicitObjectWithContext(
+ PyObject *category,
+ PyObject *message,
+ PyObject *filename,
+ int lineno);

Lib/test/test_compile.py

@@ -1646,6 +1646,24 @@ class WeirdDict(dict):
 
  self.assertRaises(NameError, ns['foo'])
 
+ def test_compile_warnings(self):
+ # See gh-131927
+ # Compile warnings originating from the same file and
+ # line are now only emitted once.
+ with warnings.catch_warnings(record=True) as caught:
+ warnings.simplefilter("default")
+ compile('1 is 1', '<stdin>', 'eval')
+ compile('1 is 1', '<stdin>', 'eval')
+
+ self.assertEqual(len(caught), 1)
+
+ with warnings.catch_warnings(record=True) as caught:
+ warnings.simplefilter("always")
+ compile('1 is 1', '<stdin>', 'eval')
+ compile('1 is 1', '<stdin>', 'eval')
+
+ self.assertEqual(len(caught), 2)
+
 class TestBooleanExpression(unittest.TestCase):
  class Value:
  def __init__(self):

Lib/test/test_pyrepl/test_interact.py

@@ -1,6 +1,7 @@
 import contextlib
 import io
 import unittest
+import warnings
 from unittest.mock import patch
 from textwrap import dedent
 
@@ -273,3 +274,28 @@ def test_incomplete_statement(self):
  code = "if foo:"
  console = InteractiveColoredConsole(namespace, filename="<stdin>")
  self.assertTrue(_more_lines(console, code))
+
+
+class TestWarnings(unittest.TestCase):
+ def test_pep_765_warning(self):
+ """
+ Test that a SyntaxWarning emitted from the
+ AST optimizer is only shown once in the REPL.
+ """
+ # gh-131927
+ console = InteractiveColoredConsole()
+ code = dedent("""\
+ def f():
+ try:
+ return 1
+ finally:
+ return 2
+ """)
+
+ with warnings.catch_warnings(record=True) as caught:
+ warnings.simplefilter("default")
+ console.runsource(code)
+
+ count = sum("'return' in a 'finally' block" in str(w.message)
+ for w in caught)
+ self.assertEqual(count, 1)

Python/_warnings.c

@@ -1479,6 +1479,28 @@ PyErr_WarnExplicitObject(PyObject *category, PyObject *message,
  return 0;
 }
 
+/* Like PyErr_WarnExplicitObject, but automatically sets up context */
+int
+_PyErr_WarnExplicitObjectWithContext(PyObject *category, PyObject *message,
+ PyObject *filename, int lineno)
+{
+ PyObject *unused_filename, *module, *registry;
+ int unused_lineno;
+ int stack_level = 1;
+
+ if (!setup_context(stack_level, NULL, &unused_filename, &unused_lineno,
+ &module, &registry)){
+ return -1;
+ }
+
+ int rc = PyErr_WarnExplicitObject(category, message, filename, lineno,
+ module, registry);
+ Py_DECREF(unused_filename);
+ Py_DECREF(registry);
+ Py_DECREF(module);
+ return rc;
+}
+
 int
 PyErr_WarnExplicit(PyObject *category, const char *text,
  const char *filename_str, int lineno,

Python/errors.c

@@ -1906,8 +1906,8 @@ int
 _PyErr_EmitSyntaxWarning(PyObject *msg, PyObject *filename, int lineno, int col_offset,
  int end_lineno, int end_col_offset)
 {
- if (PyErr_WarnExplicitObject(PyExc_SyntaxWarning, msg, filename,
-lineno, NULL, NULL) < 0)
+ if (_PyErr_WarnExplicitObjectWithContext(PyExc_SyntaxWarning, msg,
+ filename, lineno) < 0)
 {
  if (PyErr_ExceptionMatches(PyExc_SyntaxWarning)){
  /* Replace the SyntaxWarning exception with a SyntaxError