Pass encoding to AtomicWriter in write_utf8_file_atomic (#164015)

homeassistant/util/file.py

@@ -32,8 +32,11 @@ def write_utf8_file_atomic(
     Using this function frequently will significantly
     negatively impact performance.
     """
+    encoding = "utf-8" if "b" not in mode else None
     try:
-        with AtomicWriter(filename, mode=mode, overwrite=True).open() as fdesc:
+        with AtomicWriter(  # type: ignore[call-arg]  # atomicwrites-stubs is outdated, encoding is a valid kwarg
+            filename, mode=mode, overwrite=True, encoding=encoding
+        ).open() as fdesc:
             if not private:
                 os.fchmod(fdesc.fileno(), 0o644)
             fdesc.write(utf8_data)

tests/util/test_file.py

@@ -83,6 +83,19 @@ def test_write_utf8_file_fails_at_rename_and_remove(
     assert "File replacement cleanup failed" in caplog.text
 
 
+@pytest.mark.parametrize("func", [write_utf8_file, write_utf8_file_atomic])
+def test_write_utf8_file_with_non_ascii_content(tmp_path: Path, func) -> None:
+    """Test files with non-ASCII content can be written even when locale is ASCII."""
+    test_file = tmp_path / "test.json"
+    non_ascii_data = '{"name":"自动化","emoji":"🏠"}'
+
+    with patch("locale.getpreferredencoding", return_value="ascii"):
+        func(test_file, non_ascii_data, False)
+
+    file_text = test_file.read_text(encoding="utf-8")
+    assert file_text == non_ascii_data
+
+
 def test_write_utf8_file_atomic_fails(tmpdir: py.path.local) -> None:
     """Test OSError from write_utf8_file_atomic is rethrown as WriteError."""
     test_dir = tmpdir.mkdir("files")