gh-142570: Check the file type before skipping the source first line

Lib/test/test_cmd_line_script.py

@@ -583,6 +583,23 @@ def test_non_ascii(self):
             'stdout=%r stderr=%r' % (stdout, stderr))
         self.assertEqual(0, rc)
 
+    def test_skip_source_first_line(self):
+        script = textwrap.dedent("""\
+            print("First line")
+            print("Second line")
+            """)
+        with os_helper.temp_dir() as script_dir:
+            script_name = _make_test_script(script_dir, 'script', script)
+            exitcode, stdout, stderr = assert_python_ok(script_name)
+            text = stdout.decode('ascii')
+            self.assertIn("First line", text)
+            self.assertIn("Second line", text)
+
+            exitcode, stdout, stderr = assert_python_ok('-x', script_name)
+            text = stdout.decode('ascii')
+            self.assertNotIn("First line", text)
+            self.assertIn("Second line", text)
+
     def test_issue20500_exit_with_exception_value(self):
         script = textwrap.dedent("""\
             import sys

Modules/main.c

@@ -380,6 +380,14 @@ pymain_run_file_obj(PyObject *program_name, PyObject *filename,
         return 2;
     }
 
+    struct _Py_stat_struct sb;
+    if (_Py_fstat_noraise(fileno(fp), &sb) == 0 && S_ISDIR(sb.st_mode)) {
+        PySys_FormatStderr("%S: %R is a directory, cannot continue\n",
+                           program_name, filename);
+        fclose(fp);
+        return 1;
+    }
+
     if (skip_source_first_line) {
         int ch;
         /* Push back first newline so line numbers remain the same */
@@ -391,14 +399,6 @@ pymain_run_file_obj(PyObject *program_name, PyObject *filename,
         }
     }
 
-    struct _Py_stat_struct sb;
-    if (_Py_fstat_noraise(fileno(fp), &sb) == 0 && S_ISDIR(sb.st_mode)) {
-        PySys_FormatStderr("%S: %R is a directory, cannot continue\n",
-                           program_name, filename);
-        fclose(fp);
-        return 1;
-    }
-
     // Call pending calls like signal handlers (SIGINT)
     if (Py_MakePendingCalls() == -1) {
         fclose(fp);