From 442486c7108f245fefc880bf6464b89a0f3e0339 Mon Sep 17 00:00:00 2001
From: Christopher Krah <48338417+chrikrah@users.noreply.github.com>
Date: Mon, 12 Oct 2026 07:52:10 +0200
Subject: [PATCH] =?UTF-8?q?=F0=9F=90=9B=20Keep=20`CliRunner`=20output=20bu?=
 =?UTF-8?q?ffers=20open=20when=20its=20stream=20wrappers=20close?=
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Port the `typer/testing.py` part of pallets/click#3139, released in Click 8.3.2.
`_NamedTextIOWrapper` gets an empty `close()`, so dropping the wrapper no longer
closes the `StreamMixer` buffer that `invoke()` reads afterwards, and
`StreamMixer.__del__` goes, so a stream captured inside the command stays writable
after `invoke()` returns.
---
 tests/test_termui.py | 35 ++++++++++++++++++++++++++++++++++-
 typer/testing.py     | 11 +++++------
 2 files changed, 39 insertions(+), 7 deletions(-)

diff --git a/tests/test_termui.py b/tests/test_termui.py
index 8f908923db..edc4abd37f 100644
--- a/tests/test_termui.py
+++ b/tests/test_termui.py
@@ -5,8 +5,9 @@
 
 import io
 import os
+import sys
 from contextlib import contextmanager
-from typing import Literal
+from typing import Literal, TextIO
 
 import pytest
 import typer
@@ -103,6 +104,38 @@ def main() -> None:
     assert os.environ.get(env_key) == "present"
 
 
+def test_clirunner_stream_replaced_during_invoke() -> None:
+    # pytest's live logging suspends capturing mid-command: it swaps sys.stdout
+    # and sys.stderr, which drops the last reference to the runner's wrappers
+    runner = CliRunner()
+    app = typer.Typer()
+
+    @app.command()
+    def main() -> None:
+        sys.stdout = io.StringIO()
+        sys.stderr = io.StringIO()
+
+    result = runner.invoke(app, [])
+    assert result.exit_code == 0, result.output
+    assert result.output == ""
+
+
+def test_clirunner_stream_usable_after_invoke() -> None:
+    # A logging.StreamHandler created inside the command keeps writing here
+    runner = CliRunner()
+    app = typer.Typer()
+    streams: list[TextIO] = []
+
+    @app.command()
+    def main() -> None:
+        streams.append(sys.stderr)
+
+    result = runner.invoke(app, [])
+    assert result.exit_code == 0, result.output
+    streams[0].write("late")
+    streams[0].flush()
+
+
 @pytest.mark.parametrize(
     ("exit_value", "expected_exit_code", "expected_stdout"),
     [
diff --git a/typer/testing.py b/typer/testing.py
index 7ecc0e693c..aebd459caa 100644
--- a/typer/testing.py
+++ b/typer/testing.py
@@ -53,12 +53,6 @@ def __init__(self) -> None:
         self.stdout: io.BytesIO = BytesIOCopy(copy_to=self.output)
         self.stderr: io.BytesIO = BytesIOCopy(copy_to=self.output)
 
-    def __del__(self) -> None:
-        """Guarantee that file-like objects are closed in a predictable order"""
-        self.stderr.close()
-        self.stdout.close()
-        self.output.close()
-
 
 class _NamedTextIOWrapper(io.TextIOWrapper):
     def __init__(self, buffer: BinaryIO, name: str, mode: str, **kwargs: Any) -> None:
@@ -66,6 +60,11 @@ def __init__(self, buffer: BinaryIO, name: str, mode: str, **kwargs: Any) -> Non
         self._name = name
         self._mode = mode
 
+    def close(self) -> None:
+        """The buffer belongs to `StreamMixer`, so keep it open when the
+        wrapper is closed or garbage collected.
+        """
+
     @property
     def name(self) -> str:
         return self._name  # pragma: no cover