Ingore null loggers returned by LogProviders in ELoggerFactory

[petrroll]

Port of dotnet/runtime#117334

Microsoft Reviewers: Open in CodeFlow

[Copilot]

Pull Request Overview

This PR ports logic to ignore null loggers from LogProviders in ExtendedLoggerFactory and adds a corresponding test to verify the behavior.

• Filter out NullLogger.Instance providers in CreateLoggers
• Add NullLoggerProvider to the provider list and verify it’s ignored
• Import Microsoft.Extensions.Logging.Abstractions where needed

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/Libraries/Microsoft.Extensions.Telemetry/Logging/ExtendedLoggerFactory.cs	Change CreateLoggers to use a list, skip NullLogger.Instance, and return an array
test/Libraries/Microsoft.Extensions.Telemetry.Tests/Logging/ExtendedLoggerFactoryTests.cs	Add a test (NullLoggerByProviderIsIgnored) to ensure null loggers are not included

Comments suppressed due to low confidence (3)

src/Libraries/Microsoft.Extensions.Telemetry/Logging/ExtendedLoggerFactory.cs:232

• The comment mentions NullLogger<T>.Instance but the code only filters NullLogger.Instance. Update the comment to accurately reflect what the code is checking or adjust the code to match the comment.

            // We do not need to check for NullLogger<T>.Instance as no provider would reasonably return it (the <T> handling is at

test/Libraries/Microsoft.Extensions.Telemetry.Tests/Logging/ExtendedLoggerFactoryTests.cs:548

• [nitpick] The test checks only the count of MessageLoggers. To make it more robust, assert that the remaining logger is indeed from the non-null Provider and not a NullLogger instance.

        var logger1 = (ExtendedLogger)factory.CreateLogger("C1");

src/Libraries/Microsoft.Extensions.Telemetry/Logging/ExtendedLoggerFactory.cs:234

• Comparing only against NullLogger.Instance will not catch other possible null-logger types (e.g., NullLogger<T>). Consider using a type check like if (!(loggerInformation.Logger is NullLogger)) to filter all null loggers.

            if (loggerInformation.Logger != NullLogger.Instance)

[evgenyfedorov2]

@geeknoid FYI