Refactor code structure and add test for multiple CR cases

Author: mohsinm-dev

Lib/test/test_io/test_textio.py

@@ -704,6 +704,46 @@ def test_tell_after_readline_with_cr(self):
             remaining = f.read()
             self.assertEqual(remaining, "")
 
+    def test_tell_after_readline_with_multiple_cr(self):
+        # Test for gh-141314: TextIOWrapper.tell() assertion failure
+        # when dealing with multiple standalone carriage returns
+        test_cases = [
+            (b'line1\r\rline2\r', ['line1\n', '\n', 'line2\n']),
+            (b'line1\r\r\rline2\r', ['line1\n', '\n', '\n', 'line2\n']),
+            (b'line1\rline2\rline3\r', ['line1\n', 'line2\n', 'line3\n']),
+            (b'\r\rdata\r', ['\n', '\n', 'data\n']),
+        ]
+        
+        for data, expected_lines in test_cases:
+            with self.subTest(data=data):
+                with self.open(os_helper.TESTFN, "wb") as f:
+                    f.write(data)
+                
+                with self.open(os_helper.TESTFN, "r") as f:
+                    # Read all lines and call tell() after each
+                    lines_read = []
+                    positions = []
+                    while True:
+                        pos_before = f.tell()
+                        line = f.readline()
+                        if not line:
+                            break
+                        lines_read.append(line)
+                        # This should not cause an assertion failure
+                        pos_after = f.tell()
+                        positions.append((pos_before, pos_after))
+                    
+                    # Verify lines read correctly
+                    self.assertEqual(lines_read, expected_lines)
+                    
+                    # Verify we can seek back to each position
+                    f.seek(0)
+                    for i, (pos_before, pos_after) in enumerate(positions):
+                        f.seek(pos_before)
+                        line = f.readline()
+                        self.assertEqual(line, expected_lines[i])
+                        self.assertEqual(f.tell(), pos_after)
+
     def test_seek_with_encoder_state(self):
         f = self.open(os_helper.TESTFN, "w", encoding="euc_jis_2004")
         f.write("\u00e6\u0300")

Modules/_io/textio.c

@@ -2847,12 +2847,12 @@ _io_TextIOWrapper_tell_impl(textio *self)
     /* Skip the optimization if next_input is empty */
     if (PyBytes_GET_SIZE(next_input) == 0) {
         skip_bytes = 0;
-    }
-    else {
+    } else {
         skip_back = 1;
         assert(skip_back <= PyBytes_GET_SIZE(next_input));
         input = PyBytes_AS_STRING(next_input);
-        while (skip_bytes > 0) {
+    }
+    while (skip_bytes > 0) {
         /* Decode up to temptative start point */
         if (_textiowrapper_decoder_setstate(self, &cookie) < 0)
             goto fail;
@@ -2875,7 +2875,6 @@ _io_TextIOWrapper_tell_impl(textio *self)
             skip_back *= 2;
         }
     }
-    }
     if (skip_bytes <= 0) {
         skip_bytes = 0;
         if (_textiowrapper_decoder_setstate(self, &cookie) < 0)