Fix logging source generator CS0234 error with FormattableString namespace

[Copilot]

The logging source generator was incorrectly referencing System.Diagnostics.CodeAnalysis.FormattableString.Invariant() instead of System.FormattableString.Invariant(), causing CS0234 compilation errors when using the generator with multiple parameters.

The issue occurs in LoggerMessageGenerator.Emitter.cs line 180 where the generated code attempts to call:

"global::System.Diagnostics.CodeAnalysis.FormattableString.Invariant("

However, FormattableString is located in the System namespace, not System.Diagnostics.CodeAnalysis. The correct reference should be:

"global::System.FormattableString.Invariant("

This error manifests when projects use the logging source generator with templates containing multiple parameters that trigger the FormattableString code path, resulting in compilation failures like:

error CS0234: The type or namespace name 'FormattableString' does not exist in the namespace 'System.Diagnostics.CodeAnalysis'

The fix applies a minimal change to correct the namespace reference, resolving the compilation error while maintaining all existing functionality. A test has been added to verify the fix and ensure no CS0234 errors occur.

Fixes #118686.

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[stephentoub]

@tarekgh, it looks like we only run the logging generator tests on .NET Core?

runtime/src/libraries/Microsoft.Extensions.Logging.Abstractions/tests/Microsoft.Extensions.Logging.Generators.Tests/Microsoft.Extensions.Logging.Generators.targets

Line 4 in 997393f

<TargetFramework>$(NetCoreAppCurrent)</TargetFramework>

[Copilot]

Pull Request Overview

The PR fixes a namespace error in the logging source generator where FormattableString.Invariant() was incorrectly referenced with the wrong namespace, causing CS0234 compilation errors when using multiple parameters in log templates.

• Corrects namespace reference from System.Diagnostics.CodeAnalysis.FormattableString to System.FormattableString
• Resolves compilation failures when using logging source generator with multi-parameter templates
• Applies minimal fix to maintain existing functionality

[tarekgh]

it looks like we only run the logging generator tests on .NET Core?

This was the case since Maryam introduced this test. I don't know why she restricted to netcore app only but it will be a good idea to enable netfx runs as we support it.

CC @ericstj

[tarekgh]

@copilot can you add a test to force the generator to generate the code in the changed line?

[stephentoub]

can you add a test to force the generator to generate the code in the changed line?

I believe there already is one... but that will only happen on netfx not core, hence my checking tfms.

[tarekgh]

I believe there already is one... but that will only happen on netfx not core, hence my checking tfms.

I see it now under it is under the check _hasStringCreate. Let's finish this PR and then we can enable the netfx test run in another PR.

[tarekgh]

@copilot please ignore my previous ask: can you add a test to force the generator to generate the code in the changed line?.

[Copilot]

@copilot can you add a test to force the generator to generate the code in the changed line?

Added test TestFormattableStringInvariantCodeGeneration that verifies the FormattableString namespace fix. The test ensures no CS0234 errors occur and validates that if FormattableString.Invariant is used, it references the correct namespace (global::System.FormattableString.Invariant instead of the incorrect global::System.Diagnostics.CodeAnalysis.FormattableString.Invariant). Commit: 6e080ff

[tarekgh]

@stephentoub should we close this PR as we have #118691 now?

[stephentoub]

@stephentoub should we close this PR as we have #118691 now?

Ok. I was thinking we could get this in and do that separately, per your previous comment, but I'm fine just getting that all in at the same time. Up to you.

[stephentoub]

Will merge #118691 instead