From ff6f1d8b1b61247dc8170555eabadd833c0e971e Mon Sep 17 00:00:00 2001
From: fan wu <336798967+FanWu-ai@users.noreply.github.com>
Date: Sun, 4 Oct 2026 21:22:44 -0700
Subject: [PATCH] Clean up temporary files when closing a rewrite fails

---
 CHANGELOG.md       |  1 +
 src/dotenv/main.py | 35 +++++++++++++-------------
 tests/test_main.py | 63 ++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 81 insertions(+), 18 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index e5f25414..5d1f5aeb 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,7 @@ project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ### Fixed
 
+- Remove temporary files when a buffered write fails while closing the file during `set_key` or `unset_key`.
 - Fix a package build deprecation warning caused by a non-string `license` value in `pyproject.toml` by [@kurtmckee] in [#648]
 - `set_key`, `unset_key` and the `dotenv set`/`unset` commands now name the `.env` path instead of an internal temporary file when its directory is missing or not writable, and the CLI prints a short error and exits with code 2 instead of a traceback by [@jamalkamaladdin] in [#711]
 - `set_key` and `unset_key` no longer leave a `.tmp_*` file behind on Windows when writing a read-only `.env` fails, and the error raised is the one from the failed write rather than from cleaning up the temporary file by [@MohammedAlkindi] in [#686]
diff --git a/src/dotenv/main.py b/src/dotenv/main.py
index 5faa7f0e..10226017 100644
--- a/src/dotenv/main.py
+++ b/src/dotenv/main.py
@@ -197,28 +197,27 @@ def rewrite(
         err.filename = os.fspath(path)
         raise
 
-    with temp_file as dest:
-        dest_path = pathlib.Path(dest.name)
-        error = None
+    dest_path = pathlib.Path(temp_file.name)
+    try:
+        with temp_file as dest:
+            error = None
 
-        try:
-            with source:
-                yield (source, dest)
-        except BaseException as err:
-            error = err
+            try:
+                with source:
+                    yield (source, dest)
+            except BaseException as err:
+                error = err
 
-    if error is None:
-        try:
-            if original_mode is not None:
-                os.chmod(dest_path, original_mode)
+        if error is not None:
+            raise error from None
 
-            os.replace(dest_path, path)
-        except BaseException:
-            _discard_temp_file(dest_path)
-            raise
-    else:
+        if original_mode is not None:
+            os.chmod(dest_path, original_mode)
+
+        os.replace(dest_path, path)
+    except BaseException:
         _discard_temp_file(dest_path)
-        raise error from None
+        raise
 
 
 def set_key(
diff --git a/tests/test_main.py b/tests/test_main.py
index 930ab171..49772553 100644
--- a/tests/test_main.py
+++ b/tests/test_main.py
@@ -238,6 +238,69 @@ def test_rewrite_reports_original_error_when_cleanup_fails(dotenv_path, caplog):
     ]
 
 
+@pytest.mark.parametrize(
+    "before,rewrite",
+    [
+        (None, lambda path: dotenv.set_key(path, "a", "new")),
+        ("a=old\n", lambda path: dotenv.set_key(path, "a", "new")),
+        ("a=old\nb=keep\n", lambda path: dotenv.unset_key(path, "a")),
+    ],
+    ids=["set_key_new_file", "set_key", "unset_key"],
+)
+def test_rewrite_close_failure_leaves_no_temp_file(tmp_path, before, rewrite):
+    dotenv_path = tmp_path / ".env"
+    if before is not None:
+        dotenv_path.write_text(before)
+    close_error = OSError("buffered write failed while closing")
+    real_temp_file = dotenv.main.tempfile.NamedTemporaryFile
+    opened_files = []
+
+    def failing_temp_file(*args, **kwargs):
+        temp_file = real_temp_file(*args, **kwargs)
+        opened_files.append(temp_file)
+        wrapper = mock.MagicMock(wraps=temp_file)
+        wrapper.name = temp_file.name
+        wrapper.__enter__.return_value = temp_file
+
+        def close(*exc):
+            temp_file.close()
+            raise close_error
+
+        wrapper.__exit__.side_effect = close
+        return wrapper
+
+    with mock.patch("dotenv.main.tempfile.NamedTemporaryFile", failing_temp_file):
+        with mock.patch("dotenv.main.os.replace") as replace:
+            with pytest.raises(OSError) as exc_info:
+                rewrite(dotenv_path)
+
+    assert exc_info.value is close_error
+    assert all(temp_file.closed for temp_file in opened_files)
+    replace.assert_not_called()
+    if before is None:
+        assert not dotenv_path.exists()
+    else:
+        assert dotenv_path.read_text() == before
+    assert list(tmp_path.glob(".tmp_*")) == []
+
+
+@pytest.mark.parametrize("error_type", [ValueError, KeyboardInterrupt])
+def test_rewrite_body_failure_preserves_error_and_target(dotenv_path, error_type):
+    dotenv_path.write_text("a=old\n")
+    error = error_type("rewrite interrupted")
+
+    with pytest.raises(error_type) as exc_info:
+        with dotenv.main.rewrite(dotenv_path, encoding="utf-8") as (source, dest):
+            dest.write("a=new\n")
+            raise error
+
+    assert exc_info.value is error
+    assert source.closed
+    assert dest.closed
+    assert dotenv_path.read_text() == "a=old\n"
+    assert list(dotenv_path.parent.glob(".tmp_*")) == []
+
+
 def test_set_key_missing_directory(tmp_path):
     dotenv_path = tmp_path / "nx_dir" / ".env"