gh-137376: ensure that SyntaxError are properly detected in REPL

Include/internal/pycore_global_strings.h

@@ -441,6 +441,7 @@ struct _Py_global_strings {
         STRUCT_FOR_ID(fd)
         STRUCT_FOR_ID(fd2)
         STRUCT_FOR_ID(fdel)
+        STRUCT_FOR_ID(feature_version)
         STRUCT_FOR_ID(fget)
         STRUCT_FOR_ID(fields)
         STRUCT_FOR_ID(file)

Lib/_pyrepl/console.py

@@ -20,10 +20,12 @@
 from __future__ import annotations
 
 import _colorize
+import _symtable
 
 from abc import ABC, abstractmethod
 import ast
 import code
+import codeop
 import linecache
 from dataclasses import dataclass, field
 import os.path
@@ -211,6 +213,17 @@ def runsource(self, source, filename="<input>", symbol="single"):
         except (OverflowError, ValueError):
             self.showsyntaxerror(filename, source=source)
             return False
+
+        try:
+            # validate stuff that cannot be validated with AST parsing only
+            flags = self.compile.compiler.flags
+            flags &= ~codeop.PyCF_DONT_IMPLY_DEDENT
+            flags &= ~codeop.PyCF_ALLOW_INCOMPLETE_INPUT
+            _symtable.symtable(source, filename, "exec", flags=flags)
+        except (SyntaxError, OverflowError, ValueError):
+            self.showsyntaxerror(filename, source=source)
+            return False
+
         if tree.body:
             *_, last_stmt = tree.body
         for stmt in tree.body:

Lib/test/test_pyrepl/test_interact.py

@@ -131,6 +131,15 @@ def test_runsource_shows_syntax_error_for_failed_compilation(self):
             console.runsource(source)
             mock_showsyntaxerror.assert_called_once()
 
+    def test_runsource_shows_syntax_error_for_failed_symtable_checks(self):
+        # Some checks cannot be performed by AST parsing only.
+        # See https://github.com/python/cpython/issues/137376.
+        console = InteractiveColoredConsole()
+        source = "x = 1; global x; x = 2"
+        with patch.object(console, "showsyntaxerror") as mock_showsyntaxerror:
+            console.runsource(source)
+            mock_showsyntaxerror.assert_called_once()
+
     def test_runsource_survives_null_bytes(self):
         console = InteractiveColoredConsole()
         source = "\x00\n"

Misc/NEWS.d/next/Library/2025-08-04-14-38-28.gh-issue-137376.iHSKBL.rst

@@ -0,0 +1,3 @@
+Ensure that :exc:`SyntaxError` is raised when given incorrect REPL inputs
+that are only detected when processing symbol tables. Patch by Bénédikt
+Tran.

Modules/symtablemodule.c

@@ -16,22 +16,33 @@ _symtable.symtable
     filename:  object(converter='PyUnicode_FSDecoder')
     startstr:  str
     /
+    *
+    flags: int = 0
+    feature_version: int = 0
 
 Return symbol and scope dictionaries used internally by compiler.
 [clinic start generated code]*/
 
 static PyObject *
 _symtable_symtable_impl(PyObject *module, PyObject *source,
-                        PyObject *filename, const char *startstr)
-/*[clinic end generated code: output=59eb0d5fc7285ac4 input=9dd8a50c0c36a4d7]*/
+                        PyObject *filename, const char *startstr, int flags,
+                        int feature_version)
+/*[clinic end generated code: output=1e766ac3387e156a input=5ccfb94e8a19a975]*/
 {
     struct symtable *st;
     PyObject *t;
     int start;
     PyCompilerFlags cf = _PyCompilerFlags_INIT;
     PyObject *source_copy = NULL;
 
-    cf.cf_flags = PyCF_SOURCE_IS_UTF8;
+    cf.cf_flags = flags | PyCF_SOURCE_IS_UTF8;
+    if (feature_version >= 0 && (flags & PyCF_ONLY_AST)) {
+        cf.cf_feature_version = feature_version;
+    }
+    if (flags & ~(PyCF_MASK | PyCF_MASK_OBSOLETE | PyCF_COMPILE_MASK)) {
+        PyErr_SetString(PyExc_ValueError, "_symtable.symtable(): unrecognised flags");
+        return NULL;
+    }
 
     const char *str = _Py_SourceAsString(source, "symtable", "string or bytes", &cf, &source_copy);
     if (str == NULL) {