remove stdout=subprocess.PIPE from env._call, see #7698

src/poetry/utils/env.py

@@ -1537,9 +1537,8 @@ def _run(self, cmd: list[str], **kwargs: Any) -> int | str:
                     **kwargs,
                 ).stdout
             elif call:
-                return subprocess.call(
-                    cmd, stdout=subprocess.PIPE, stderr=stderr, env=env, **kwargs
-                )
+                assert stderr != subprocess.PIPE
+                return subprocess.call(cmd, stderr=stderr, env=env, **kwargs)
             else:
                 output = subprocess.check_output(cmd, stderr=stderr, env=env, **kwargs)
         except CalledProcessError as e:

tests/utils/test_env.py

@@ -5,6 +5,7 @@
 import sys
 
 from pathlib import Path
+from threading import Thread
 from typing import TYPE_CHECKING
 from typing import Any
 
@@ -1009,6 +1010,31 @@ def test_check_output_with_called_process_error(
     assert "some error" in str(error.value)
 
 
+@pytest.mark.parametrize("out", ["sys.stdout", "sys.stderr"])
+def test_call_does_not_block_on_full_pipe(
+    tmp_path: Path, tmp_venv: VirtualEnv, out: str
+):
+    """see https://github.com/python-poetry/poetry/issues/7698"""
+    script = tmp_path / "script.py"
+    script.write_text(
+        f"""\
+import sys
+for i in range(10000):
+    print('just print a lot of text to fill the buffer', file={out})
+"""
+    )
+
+    def target(result: list[int]) -> None:
+        result.append(tmp_venv.run("python", str(script), call=True))
+
+    results = []
+    # use a separate thread, so that the test does not block in case of error
+    thread = Thread(target=target, args=(results,))
+    thread.start()
+    thread.join(1)  # must not block
+    assert results and results[0] == 0
+
+
 def test_run_python_script_called_process_error(
     tmp_dir: str, tmp_venv: VirtualEnv, mocker: MockerFixture
 ):