[core] Replace a damaged existing file in write_file_if_changed

esphome/helpers.py

@@ -550,9 +550,17 @@ def write_file_if_changed(path: Path, text: str) -> bool:
 
     Returns true if the file was changed.
     """
+    from esphome.core import EsphomeError
+
     src_content = None
     if path.is_file():
-        src_content = read_file(path)
+        try:
+            src_content = read_file(path)
+        except (EsphomeError, UnicodeDecodeError) as err:
+            # A damaged existing file (unreadable, non-UTF-8) must be
+            # replaced, not abort the regeneration that would fix it
+            _LOGGER.warning("Replacing damaged file %s: %s", path, err)
+            path.unlink(missing_ok=True)
     if src_content == text:
         return False
     write_file(path, text)

tests/unit_tests/test_helpers.py

@@ -1108,3 +1108,15 @@ def test_progressbar_enabled_on_pipe_with_dashboard(monkeypatch) -> None:
 def test_format_duration(seconds: float, expected: str) -> None:
     """Test that durations are rendered as short human-readable strings."""
     assert helpers.format_duration(seconds) == expected
+
+
+def test_write_file_if_changed_replaces_damaged_file(tmp_path, caplog) -> None:
+    """A non-UTF-8 or unreadable existing file is logged and overwritten;
+    aborting would block the very regeneration that fixes it."""
+    from esphome.helpers import write_file_if_changed
+
+    target = tmp_path / "generated.txt"
+    target.write_bytes(b"\xff\xfe")
+    assert write_file_if_changed(target, "fresh content") is True
+    assert target.read_text(encoding="utf-8") == "fresh content"
+    assert "Replacing damaged file" in caplog.text