Logging.EventSource tests failing on iOS with NullReferenceException in OnEventWritten

[github-actions]

Description

Microsoft.Extensions.Logging.EventSource.Tests failing on iOS and likely all mobile platforms with NullReferenceExceptions in EventSource.OnEventWritten.

Failure Pattern

All 8 failing tests report:

ERROR: Exception during EventSource.OnEventWritten: Object reference not set to an instance of an object.
Assert.Collection() Failure: Item comparison failure
Error: Event name does not match. Expected Message, event data is '{"__EVENT_NAME":"EventSourceMessage","message":"ERROR: Exception during EventSource.OnEventWritten: Object reference not set to an instance of an object."}'

Failing Tests

1. Logs_OnlyMessage_IfKeywordSet
2. Logs_TracingDetailsAsExpected_WithDefaults (4 theory variants)
3. Logs_OnlyFormattedMessage_IfKeywordSet
4. Logs_AsExpected_WithDefaults
5. Logs_AsExpected_WithDefaults_EnabledEarly

Platform Coverage

Confirmed on:

• iossimulator-arm64 CoreCLR

Likely affects all mobile platforms (tvOS, MacCatalyst, Android) based on failure pattern.

Failure Details

Build: https://dev.azure.com/dnceng-public/public/_build/results?buildId=1397424
Date: 2026-04-27

Helix Job: 7da59944-242f-4296-8a21-1a36fe1d0562
Work Item: Microsoft.Extensions.Logging.EventSource.Tests

Console log shows the EventSource implementation itself is throwing a NullReferenceException during event writing, not the test code.

Related

Likely related to recent changes around trimming, reflection, or EventSource handling on mobile/NativeAOT platforms. See also #127448 for concurrent DI/Hosting failures on the same build.

Note

🔒 Integrity filter blocked 3 items

The following items were blocked because they don't meet the GitHub integrity level.

• #126023 search_pull_requests: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".
• #124461 search_pull_requests: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".
• #108513 search_pull_requests: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".

To allow these resources, lower min-integrity in your GitHub frontmatter:

tools:
  github:
    min-integrity: approved  # merged | approved | unapproved | none

Generated by Mobile Platform Failure Scanner · ● 4.2M · ◷

[dotnet-policy-service]

Tagging subscribers to 'os-ios': @vitek-karas, @kotlarmilos, @steveisok, @akoeplinger
See info in area-owners.md if you want to be subscribed.

[dotnet-policy-service]

Tagging subscribers to 'os-maccatalyst': @vitek-karas, @kotlarmilos, @steveisok, @akoeplinger
See info in area-owners.md if you want to be subscribed.

[dotnet-policy-service]

Tagging subscribers to this area: @dotnet/area-extensions-logging
See info in area-owners.md if you want to be subscribed.

[dotnet-policy-service]

Tagging subscribers to 'arch-android': @vitek-karas, @simonrozsival, @steveisok, @akoeplinger
See info in area-owners.md if you want to be subscribed.

[dotnet-policy-service]

Tagging subscribers to 'os-tvos': @vitek-karas, @kotlarmilos, @steveisok, @akoeplinger
See info in area-owners.md if you want to be subscribed.

[tarekgh]

Looks the condition in

runtime/src/libraries/tests.proj

Line 381 in 14d3e32

<ItemGroup Condition="('$(TargetOS)' != 'browser' and '$(RunAOTCompilation)' == 'true' and '$(MonoForceInterpreter)' != 'true') or ('$(TargetOS)' == 'browser' and '$(BuildAOTTestsOnHelix)' == 'true' and '$(RunDisabledWasmTests)' != 'true') or (('$(TargetOS)' == 'ios' or '$(TargetOS)' == 'tvos' or '$(TargetOS)' == 'maccatalyst') and '$(BuildTestsOnHelix)' == 'true')">

is not correctly excluding the iossimulator and tvossimulator.

#127448 maybe similar root cause.

[tarekgh]

@vitek-karas @MichalStrehovsky do you think the trimming is aggressive? should preserve EventSource event metadata. The [DynamicDependency] and [UnconditionalSuppressMessage] attributes on LoggingEventSource may not be sufficient under aggressive trimming?