Support universal_newlines and use _translate_newlines in run_pipeline

- Factor out _translate_newlines() as a module-level function, have
  Popen's method delegate to it for code sharing
- Remove rejection of universal_newlines kwarg in run_pipeline(), treat
  it the same as text=True (consistent with Popen behavior)
- Use _translate_newlines() for text mode decoding in run_pipeline()
  to properly handle \r\n and \r newline sequences
- Update documentation to remove mention of universal_newlines rejection
- Update test to verify universal_newlines=True works like text=True

Co-authored-by: Claude <noreply@anthropic.com>

Author: gpshead

Doc/library/subprocess.rst

@@ -317,9 +317,6 @@ underlying :class:`Popen` interface can be used directly.
    in the returned :class:`PipelineResult`'s :attr:`~PipelineResult.stdout`
    attribute. Other keyword arguments are passed to each :class:`Popen` call.
 
-   Unlike :func:`run`, this function does not accept *universal_newlines*.
-   Use ``text=True`` instead.
-
    Examples::
 
       >>> import subprocess

Lib/subprocess.py

@@ -354,6 +354,12 @@ def _make_input_view(input_data):
     return memoryview(input_data)
 
 
+def _translate_newlines(data, encoding, errors):
+    """Decode bytes to str and translate newlines to \n."""
+    data = data.decode(encoding, errors)
+    return data.replace("\r\n", "\n").replace("\r", "\n")
+
+
 def _communicate_io_posix(selector, stdin, input_view, input_offset,
                           output_buffers, endtime):
     """
@@ -984,13 +990,6 @@ def run_pipeline(*commands, input=None, capture_output=False, timeout=None,
     if len(commands) < 2:
         raise ValueError('run_pipeline requires at least 2 commands')
 
-    # Reject universal_newlines - use text= instead
-    if kwargs.get('universal_newlines') is not None:
-        raise TypeError(
-            "run_pipeline() does not support 'universal_newlines'. "
-            "Use 'text=True' instead."
-        )
-
     # Validate no conflicting arguments
     if input is not None:
         if kwargs.get('stdin') is not None:
@@ -1071,8 +1070,9 @@ def run_pipeline(*commands, input=None, capture_output=False, timeout=None,
         else:
             endtime = None
 
-        # Determine if we're in text mode
-        text_mode = kwargs.get('text') or kwargs.get('encoding') or kwargs.get('errors')
+        # Determine if we're in text mode (text= or universal_newlines=)
+        text_mode = (kwargs.get('text') or kwargs.get('universal_newlines')
+                     or kwargs.get('encoding') or kwargs.get('errors'))
         encoding = kwargs.get('encoding')
         errors_param = kwargs.get('errors', 'strict')
         if text_mode and encoding is None:
@@ -1115,13 +1115,11 @@ def run_pipeline(*commands, input=None, capture_output=False, timeout=None,
         stdout = results.get(last_proc.stdout)
         stderr = results.get(stderr_reader)
 
-        # Decode stdout if in text mode (Popen text mode only applies to
-        # streams it creates, but we read via _communicate_streams which
-        # always returns bytes)
+        # Translate newlines if in text mode (decode and convert \r\n to \n)
         if text_mode and stdout is not None:
-            stdout = stdout.decode(encoding, errors_param)
+            stdout = _translate_newlines(stdout, encoding, errors_param)
         if text_mode and stderr is not None:
-            stderr = stderr.decode(encoding, errors_param)
+            stderr = _translate_newlines(stderr, encoding, errors_param)
 
         # Wait for all processes to complete (use remaining time from deadline)
         returncodes = []
@@ -1686,8 +1684,7 @@ def universal_newlines(self, universal_newlines):
         self.text_mode = bool(universal_newlines)
 
     def _translate_newlines(self, data, encoding, errors):
-        data = data.decode(encoding, errors)
-        return data.replace("\r\n", "\n").replace("\r", "\n")
+        return _translate_newlines(data, encoding, errors)
 
     def __enter__(self):
         return self

Lib/test/test_subprocess.py

@@ -2123,16 +2123,16 @@ def test_pipeline_capture_output_conflict(self):
             )
         self.assertIn('capture_output', str(cm.exception))
 
-    def test_pipeline_rejects_universal_newlines(self):
-        """Test that universal_newlines is not supported"""
-        with self.assertRaises(TypeError) as cm:
-            subprocess.run_pipeline(
-                [sys.executable, '-c', 'pass'],
-                [sys.executable, '-c', 'pass'],
-                universal_newlines=True
-            )
-        self.assertIn('universal_newlines', str(cm.exception))
-        self.assertIn('text=True', str(cm.exception))
+    def test_pipeline_universal_newlines(self):
+        """Test that universal_newlines=True works like text=True"""
+        result = subprocess.run_pipeline(
+            [sys.executable, '-c', 'print("hello")'],
+            [sys.executable, '-c', 'import sys; print(sys.stdin.read().upper())'],
+            capture_output=True, universal_newlines=True
+        )
+        self.assertIsInstance(result.stdout, str)
+        self.assertIn('HELLO', result.stdout)
+        self.assertEqual(result.returncodes, [0, 0])
 
     def test_pipeline_result_repr(self):
         """Test PipelineResult string representation"""