Fix LightSwitch crash in update_sun_times due to unhandled WinRT exception by Copilot · Pull Request #47394 · microsoft/PowerToys

Copilot · 2026-04-29T08:51:11Z

Summary of the Pull Request

PowerToys.LightSwitchService.exe crashes with FAST_FAIL_FATAL_APP_EXIT when update_sun_times calls add_property on a PowerToyValues object loaded from a settings file that lacks the "properties" JSON key. The WinRT exception thrown by GetNamedObject is not a std::exception subclass and escapes the catch (const std::exception&) guard, killing the process.

Fix 1 — src/common/SettingsAPI/settings_objects.h: Guard add_property against a missing or corrupted "properties" key (e.g. fresh install, corrupted file). load_from_settings_file loads raw JSON with no schema guarantee, so the key may not exist or may have a non-Object type. The guard now uses json::has(..., JsonValueType::Object) to handle both cases — a missing key and a key present with a non-Object type (null/array/string/number) — replacing properties with a fresh JsonObject when needed.

// Before — throws winrt::hresult_error when "properties" key absent or wrong type
m_json.GetNamedObject(L"properties").SetNamedValue(name, prop_value);

// After — ensures "properties" is a valid JsonObject before writing
if (!json::has(m_json, L"properties", json::JsonValueType::Object))
{
    m_json.SetNamedValue(L"properties", json::JsonObject{});
}
m_json.GetNamedObject(L"properties").SetNamedValue(name, prop_value);

Fix 2 — src/modules/LightSwitch/LightSwitchService/LightSwitchStateManager.cpp: Expand exception handling in update_sun_times with typed catches for maximum diagnostics, plus a final catch-all as defense-in-depth. winrt::hresult_error is caught first and logs both the HRESULT code and WinRT message; std::exception logs what(); the final catch (...) handles any other unexpected exception type.

PR Checklist

Detailed Description of the Pull Request / Additional comments

Crash chain:

LightSwitch Sun mode triggers update_sun_times on a new day or mode switch.
It calls PowerToyValues::load_from_settings_file(L"LightSwitch"), which loads the raw JSON blob without validating its schema.
add_property calls m_json.GetNamedObject(L"properties") — if the key is absent or has a non-Object type (first run, migration, corruption), the WinRT JSON API throws winrt::hresult_error.
winrt::hresult_error does not inherit from std::exception, so the catch (const std::exception&) guard is bypassed.
The exception propagates unhandled → terminate() → FAST_FAIL_FATAL_APP_EXIT (0xC0000409).

Note: has_property (in settings_objects.cpp) already handled this safely via json::has(..., JsonValueType::Object). add_property now follows the same pattern.

Validation Steps Performed

Code review of crash call stack against source confirmed the exact failure path.
Verified winrt::hresult_error is not derived from std::exception (confirming the catch miss).
Confirmed has_property already uses json::has(..., JsonValueType::Object); add_property now follows suit.
Verified json::has checks both key presence and value type, handling corrupted properties values (null/array/string/number) in addition to the missing-key case.
Confirmed catch order is correct (most-derived before catch-all) and winrt types are available through the json.h include chain.

…uard add_property against missing properties key Agent-Logs-Url: https://github.com/microsoft/PowerToys/sessions/8940919c-1eef-4a10-9abc-a0defbc156d8 Co-authored-by: MuyuanMS <116717757+MuyuanMS@users.noreply.github.com>

Copilot

Pull request overview

Fixes a crash in the LightSwitch service caused by WinRT JSON APIs throwing exceptions that were not handled by the existing std::exception catch, particularly when settings JSON does not contain the expected "properties" object.

Changes:

Harden PowerToyValues::add_property to create the "properties" JSON object when missing.
Broaden exception handling in LightSwitch update_sun_times to prevent unhandled termination on non-std::exception throws.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/modules/LightSwitch/LightSwitchService/LightSwitchStateManager.cpp	Broadens exception handling around sun-time settings update to avoid process termination.
src/common/SettingsAPI/settings_objects.h	Makes `PowerToyValues::add_property` resilient to missing `"properties"` key in loaded settings JSON.

MuyuanMS · 2026-05-14T08:24:32Z

+            if (!m_json.HasKey(L"properties"))
+            {
+                m_json.SetNamedValue(L"properties", json::JsonObject{});
+            }


Fixed in 53dcab7.

add_property now uses json::has(..., JsonValueType::Object) before calling GetNamedObject, so corrupted properties values (null/array/string/etc.) get replaced with a fresh object instead of throwing.

MuyuanMS · 2026-05-14T08:24:34Z

+    catch (...)
    {
-        std::string msg = e.what();
-        std::wstring wmsg(msg.begin(), msg.end());
-        Logger::error(L"[LightSwitchService] Exception during sun time update: {}", wmsg);
+        Logger::error(L"[LightSwitchService] Exception during sun time update.");
    }


Fixed in 53dcab7.

update_sun_times now catches winrt::hresult_error first and logs both the HRESULT and WinRT message, keeps a std::exception catch for what(), and leaves the final catch-all to log an unknown exception.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

MuyuanMS · 2026-05-14T08:31:59Z

@copilot please re-review the latest changes.

Copilot · 2026-05-14T08:50:36Z

@copilot please re-review the latest changes.

Reviewed commit 53dcab7. Both changes look correct:

settings_objects.h — json::has(m_json, L"properties", json::JsonValueType::Object) correctly handles both a missing key and a key present with a non-Object type (null/array/string). It's consistent with the has_property helper in settings_objects.cpp. ✅

LightSwitchStateManager.cpp — The three-catch chain (winrt::hresult_error → std::exception → ...) is correctly ordered, provides full diagnostic detail for every exception type, and winrt is transitively available through the json.h include chain. ✅

No issues found. Ready to merge.

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MuyuanMS · 2026-05-24T11:06:43Z

This PR doesn't seem to be addressing the root cause, as original issue comments indicate properties field is not missing from the settings json.

Initial plan

9ba06a5

Copilot AI assigned Copilot and MuyuanMS Apr 29, 2026

Copilot started work on behalf of MuyuanMS April 29, 2026 11:31 View session

Copilot AI linked an issue Apr 29, 2026 that may be closed by this pull request

v0.95.0 - Light Switch - Crash - PowerToys_LightSwitchService!update_sun_times<LightSwitchConfig const > / CxxThrowException #42511

Open

Copilot AI changed the title ~~[WIP] Fix crash in Light Switch service for PowerToys 0.95.0~~ Fix LightSwitch crash in update_sun_times due to unhandled WinRT exception Apr 29, 2026

Copilot finished work on behalf of MuyuanMS April 29, 2026 11:40

Copilot AI requested a review from MuyuanMS April 29, 2026 11:40

niels9001 added the Product-LightSwitch label Apr 29, 2026

MuyuanMS requested a review from Copilot May 14, 2026 03:09

Copilot AI reviewed May 14, 2026

View reviewed changes

Address review: validate settings type and preserve exception details

53dcab7

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot started work on behalf of MuyuanMS May 14, 2026 08:45 View session

Copilot finished work on behalf of MuyuanMS May 14, 2026 08:51

MuyuanMS closed this May 24, 2026

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Fix LightSwitch crash in update_sun_times due to unhandled WinRT exception#47394

Fix LightSwitch crash in update_sun_times due to unhandled WinRT exception#47394
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Summary of the Pull Request

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Copilot AI commented Apr 29, 2026 •

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