refactor: resolve a device's config entry without the deprecated attribute

DeviceEntry.config_entries is deprecated in Core 2026.8 and removed in 2027.8 —
a device now belongs to exactly one config entry, exposed as config_entry_id.
Reading the old attribute on a new core writes a deprecation warning naming this
integration into the user's log, which is how another project's rename turns into
bug reports here.

Seven service handlers each carried a byte-identical copy of the same five-line
lookup. They now share _config_entry_id_for_device(), so the version handling
lives in one place — the same argument as the v1.3.5/v1.3.6 block-size bug, where
a fix applied to one of two identical blocks left the other raising every poll.

Selects on hasattr rather than on the value: the deprecated attribute still
exists behind a compatibility shim on a new core, so testing its value would
touch it and emit the warning being avoided.

Backwards compatible both ways — the legacy set is still read on cores below
2026.8, and a device spanning several integrations still resolves to whichever
entry is a loaded Growatt one.

No version bump; this rides along with the next release.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: 0xAHA

custom_components/growatt_modbus/diagnostic.py

@@ -47,6 +47,35 @@ def _coordinator_for_entry(hass: HomeAssistant, entry_id: str):
     return getattr(entry, "runtime_data", None) if entry else None
 
 
+def _config_entry_id_for_device(hass: HomeAssistant, device_entry) -> str | None:
+    """The loaded Growatt config entry backing a device, or None.
+
+    Every service that takes a `device_id` needs this, and each had its own copy of the
+    same five lines. That is the duplication pattern this project has been bitten by
+    before — v1.3.5 fixed a stored-format bug in one of two byte-identical blocks and
+    left the other raising on every poll.
+
+    It also isolates a deprecation. `DeviceEntry.config_entries` is a set of entry ids;
+    Core 2026.8 deprecates it in favour of the single `config_entry_id`, with removal in
+    2027.8, because a device now belongs to exactly one config entry. Reading the old
+    attribute on a new core writes a deprecation warning naming this integration into the
+    user's log — which is how somebody else's rename turns into bug reports here.
+
+    `hasattr` rather than a value check, deliberately: on a new core the old attribute
+    still exists behind a compatibility shim, so testing the value would touch it and
+    emit the warning we are avoiding.
+    """
+    if hasattr(device_entry, "config_entry_id"):
+        entry_ids = [device_entry.config_entry_id] if device_entry.config_entry_id else []
+    else:  # Core < 2026.8
+        entry_ids = list(device_entry.config_entries)
+
+    for entry_id in entry_ids:
+        if _coordinator_for_entry(hass, entry_id) is not None:
+            return entry_id
+    return None
+
+
 def _all_coordinators(hass: HomeAssistant):
     """Every loaded Growatt coordinator, as (entry_id, coordinator) pairs.
 
@@ -587,11 +616,7 @@ async def write_register(call: ServiceCall) -> None:
             raise ValueError(f"Device {device_id} not found")
 
         # Find the config entry for this device
-        config_entry_id = None
-        for entry_id in device_entry.config_entries:
-            if _coordinator_for_entry(hass, entry_id) is not None:
-                config_entry_id = entry_id
-                break
+        config_entry_id = _config_entry_id_for_device(hass, device_entry)
 
         if not config_entry_id:
             _LOGGER.error("No config entry found for device %s", device_id)
@@ -642,11 +667,7 @@ async def write_registers(call: ServiceCall) -> None:
             raise ValueError(f"Device {device_id} not found")
 
         # Find the config entry for this device
-        config_entry_id = None
-        for entry_id in device_entry.config_entries:
-            if _coordinator_for_entry(hass, entry_id) is not None:
-                config_entry_id = entry_id
-                break
+        config_entry_id = _config_entry_id_for_device(hass, device_entry)
 
         if not config_entry_id:
             _LOGGER.error("No config entry found for device %s", device_id)
@@ -683,11 +704,7 @@ async def detect_grid_orientation(call: ServiceCall) -> None:
             if not device_entry:
                 raise ValueError(f"Device {device_id} not found")
 
-            config_entry_id = None
-            for entry_id in device_entry.config_entries:
-                if _coordinator_for_entry(hass, entry_id) is not None:
-                    config_entry_id = entry_id
-                    break
+            config_entry_id = _config_entry_id_for_device(hass, device_entry)
 
             if not config_entry_id:
                 raise ValueError(f"No config entry found for device {device_id}")
@@ -890,11 +907,7 @@ async def read_register(call: ServiceCall) -> None:
             raise ValueError(f"Device {device_id} not found")
 
         # Find the config entry for this device
-        config_entry_id = None
-        for entry_id in device_entry.config_entries:
-            if _coordinator_for_entry(hass, entry_id) is not None:
-                config_entry_id = entry_id
-                break
+        config_entry_id = _config_entry_id_for_device(hass, device_entry)
 
         if not config_entry_id:
             _LOGGER.error("No config entry found for device %s", device_id)
@@ -1087,11 +1100,7 @@ async def set_battery_mode(call: ServiceCall) -> None:
             raise ValueError(f"Device {device_id} not found")
 
         # Find the config entry for this device
-        config_entry_id = None
-        for entry_id in device_entry.config_entries:
-            if _coordinator_for_entry(hass, entry_id) is not None:
-                config_entry_id = entry_id
-                break
+        config_entry_id = _config_entry_id_for_device(hass, device_entry)
 
         if not config_entry_id:
             raise ValueError(f"No config entry found for device {device_id}")
@@ -1192,11 +1201,7 @@ async def get_register_data(call: ServiceCall):
             raise ValueError(f"Device {device_id} not found")
 
         # Find the config entry for this device
-        config_entry_id = None
-        for entry_id in device_entry.config_entries:
-            if _coordinator_for_entry(hass, entry_id) is not None:
-                config_entry_id = entry_id
-                break
+        config_entry_id = _config_entry_id_for_device(hass, device_entry)
 
         if not config_entry_id:
             raise ValueError(f"No config entry found for device {device_id}")
@@ -1261,11 +1266,7 @@ async def sync_tou_schedule(call: ServiceCall) -> None:
         if not device_entry:
             raise ValueError(f"Device {device_id} not found")
 
-        config_entry_id = None
-        for entry_id in device_entry.config_entries:
-            if _coordinator_for_entry(hass, entry_id) is not None:
-                config_entry_id = entry_id
-                break
+        config_entry_id = _config_entry_id_for_device(hass, device_entry)
 
         if not config_entry_id:
             raise ValueError(f"No config entry found for device {device_id}")

tests/test_device_config_entry_lookup.py

@@ -0,0 +1,111 @@
+"""Resolving a device to its config entry, across Home Assistant versions.
+
+`DeviceEntry.config_entries` is a set of config entry ids. Core 2026.8 deprecates it in
+favour of a single `config_entry_id` — a device now belongs to exactly one config entry —
+with removal in Core 2027.8.
+
+Reading the deprecated attribute on a new core writes a warning naming this integration
+into the user's log. That is how another project's rename becomes bug reports here, so the
+old attribute must not be touched at all when the new one is available.
+
+Seven service handlers each carried their own byte-identical copy of this lookup. They now
+share one helper — the same de-duplication the v1.3.5/v1.3.6 block-size bug argued for,
+where a fix applied to one of two identical blocks left the other raising on every poll.
+"""
+from __future__ import annotations
+
+import importlib
+
+import pytest
+
+_diag = importlib.import_module("growatt_under_test.diagnostic")
+
+
+class _ModernDeviceEntry:
+    """Core >= 2026.8: one config entry, exposed singly."""
+
+    def __init__(self, entry_id):
+        self.config_entry_id = entry_id
+
+    @property
+    def config_entries(self):  # pragma: no cover - must never be reached
+        raise AssertionError(
+            "the deprecated config_entries attribute was read on a modern core"
+        )
+
+
+class _LegacyDeviceEntry:
+    """Core < 2026.8: a set, and no config_entry_id at all."""
+
+    def __init__(self, *entry_ids):
+        self.config_entries = set(entry_ids)
+
+
+class _Hass:
+    """Only what the helper touches: entry lookup returning runtime_data."""
+
+    def __init__(self, loaded):
+        self._loaded = loaded
+        self.config_entries = self
+
+    def async_get_entry(self, entry_id):
+        if entry_id not in self._loaded:
+            return None
+        return type("Entry", (), {"runtime_data": self._loaded[entry_id]})()
+
+
+def test_a_modern_core_uses_the_single_attribute():
+    hass = _Hass({"abc": object()})
+    assert _diag._config_entry_id_for_device(hass, _ModernDeviceEntry("abc")) == "abc"
+
+
+def test_a_modern_core_never_touches_the_deprecated_attribute():
+    """The point of the change. _ModernDeviceEntry raises if config_entries is read, so
+    this fails loudly rather than silently emitting a deprecation warning in production."""
+    hass = _Hass({"abc": object()})
+    _diag._config_entry_id_for_device(hass, _ModernDeviceEntry("abc"))  # must not raise
+
+
+def test_a_legacy_core_still_works():
+    hass = _Hass({"abc": object()})
+    assert _diag._config_entry_id_for_device(hass, _LegacyDeviceEntry("abc")) == "abc"
+
+
+def test_an_unloaded_entry_is_not_returned():
+    """A device can reference an entry that is disabled or not set up. Callers treat None
+    as 'no config entry found' and raise a clear error; returning the id would have them
+    resolve a coordinator that does not exist."""
+    hass = _Hass({})
+    assert _diag._config_entry_id_for_device(hass, _ModernDeviceEntry("abc")) is None
+    assert _diag._config_entry_id_for_device(hass, _LegacyDeviceEntry("abc")) is None
+
+
+def test_a_device_with_no_config_entry_is_handled():
+    """config_entry_id can be None on a modern core for an orphaned device."""
+    hass = _Hass({"abc": object()})
+    assert _diag._config_entry_id_for_device(hass, _ModernDeviceEntry(None)) is None
+
+
+def test_a_legacy_device_picks_the_entry_that_is_actually_ours():
+    """Before the single-entry rule a device could span several integrations. Only one of
+    them is a loaded Growatt entry, and that is the one to return."""
+    ours = object()
+    hass = _Hass({"growatt": ours})
+    device = _LegacyDeviceEntry("somebody_else", "growatt")
+    assert _diag._config_entry_id_for_device(hass, device) == "growatt"
+
+
+def test_the_duplicated_lookup_blocks_are_gone():
+    """Seven handlers had their own copy. Guards against a new service reintroducing one."""
+    from pathlib import Path
+
+    source = (Path(__file__).parent.parent / "custom_components" / "growatt_modbus"
+              / "diagnostic.py").read_text(encoding="utf-8")
+
+    assert "for entry_id in device_entry.config_entries:" not in source, (
+        "a service handler is reading DeviceEntry.config_entries directly again — it is "
+        "deprecated in Core 2026.8 and removed in 2027.8"
+    )
+    # The compatibility branch inside the helper is the one permitted read.
+    assert source.count("device_entry.config_entries") == 1
+    assert source.count("_config_entry_id_for_device(hass, device_entry)") == 7