Add AttributeTargets.Interface to ExcludeFromCodeCoverageAttribute and StackTraceHiddenAttribute

[Copilot]

Description

Interfaces with default implementation members (C# 8+) can contain executable code that appears in code coverage reports. This PR adds AttributeTargets.Interface to both attributes as approved in API review.

Changes

• Implementation: Added AttributeTargets.Interface to ExcludeFromCodeCoverageAttribute and StackTraceHiddenAttribute in System.Private.CoreLib
• NativeAOT: Updated StackTraceHiddenAttribute in Test.CoreLib
• Reference assembly: Updated System.Runtime.cs
• API compat: Added suppressions in ApiCompatBaseline.NetCoreAppLatestStable.xml (one entry per assembly where the attribute is type-forwarded: System.Diagnostics.Tools.dll, System.Runtime.dll, netstandard.dll, and System.dll) and ApiCompatBaseline.netstandard2.1.xml
• Tests: Added behavioral test verifying that default interface methods marked with [StackTraceHidden] are actually hidden from stack traces

API Diff

namespace System.Diagnostics.CodeAnalysis
{
-    [AttributeUsage(AttributeTargets.Assembly | AttributeTargets.Class | ... | AttributeTargets.Event, ...)]
+    [AttributeUsage(AttributeTargets.Assembly | AttributeTargets.Class | ... | AttributeTargets.Event | AttributeTargets.Interface, ...)]
    public sealed class ExcludeFromCodeCoverageAttribute : Attribute;
}

namespace System.Diagnostics
{
-    [AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Constructor | AttributeTargets.Method, ...)]
+    [AttributeUsage(AttributeTargets.Class | ... | AttributeTargets.Method | AttributeTargets.Interface, ...)]
    public sealed class StackTraceHiddenAttribute : Attribute;
}

Example

[ExcludeFromCodeCoverage]
public interface ILogger
{
    void Log(string message);

    // Default interface method now excluded from coverage
    void LogWarning(string message) => Log($"[WARN] {message}");
}

Original prompt

---

This section details on the original issue you should resolve

<issue_title>ExcludeFromCodeCoverageAttribute can't be applied to interfaces</issue_title>
<issue_description>### Description

With interfaces now having the ability to have default implementations members, they can now contain code, which can show up on a code coverage report. The AttributeUsage attribute on ExcludeFromCodeCoverageAttribute does not specify AttributeTargets.Interface so applying the attribute to an interface will cause a compiler error.

Reproduction Steps

Try to compile the following code:

[ExcludeFromCodeCoverage]
public interface ILogger
{
    void Log(string message);

    // Default interface method (C# 8+)
    void LogWarning(string message)
        => Log($"[WARN] {message}");
}

Expected behavior

The provided sample code to be compiled without error.

Actual behavior

You will get a compilation error as ExcludeFromCodeCoverageAttribute can't be applied to an interface.

Regression?

No regression

Known Workarounds

I would expect applying the attribute to the individual method implementations would work.

Configuration

All versions of .NET, any OS, any architecture.

Other information

Missing AttributeTargets.Interface on the AttributeUsage attribute of ExcludeFromCodeCoverageAttribute.</issue_description>

<agent_instructions>Implement the approved APIs, updating the ref assemblies as well</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@bartonjs [Video](https://www.youtube.com/watch?v=qkCNatTijWg&t=1h38m59s)

Looks good as proposed.

Actually, we went ahead and pre-approved StackTraceHidden, too.

namespace System.Diagnostics.CodeAnalysis
{
-    [AttributeUsage(AttributeTargets.Assembly | AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Constructor | AttributeTargets.Method | AttributeTargets.Property | AttributeTargets.Event, Inherited = false, AllowMultiple = false)]
+    [AttributeUsage(AttributeTargets.Assembly | AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Constructor | AttributeTargets.Method | AttributeTargets.Property | AttributeTargets.Event | AttributeTargets.Interface, Inherited = false, AllowMultiple = false)]
    public sealed class ExcludeFromCodeCoverageAttribute : Attribute;
}

namespace System.Diagnostics
{
-    [AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Constructor | AttributeTargets.Method, Inherited = false)]
+    [AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Constructor | AttributeTargets.Method | AttributeTargets.Interface, Inherited = false)]
    public sealed class StackTraceHiddenAttribute : Attribute;
}
```</body></comment_new>
</comments>

• Fixes ExcludeFromCodeCoverageAttribute can't be applied to interfaces #123405

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[Copilot]

Pull request overview

This PR adds AttributeTargets.Interface to both ExcludeFromCodeCoverageAttribute and StackTraceHiddenAttribute to support interfaces with default implementation members (C# 8+) that contain executable code.

Changes:

• Added AttributeTargets.Interface to ExcludeFromCodeCoverageAttribute and StackTraceHiddenAttribute in implementation and reference assemblies
• Added API compatibility suppressions for the attribute usage changes
• Added tests verifying the attributes can be applied to interfaces

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/libraries/System.Private.CoreLib/src/System/Diagnostics/CodeAnalysis/ExcludeFromCodeCoverageAttribute.cs	Added AttributeTargets.Interface to the attribute usage declaration in alphabetical order
src/libraries/System.Private.CoreLib/src/System/Diagnostics/StackTraceHiddenAttribute.cs	Added AttributeTargets.Interface to the attribute usage declaration in alphabetical order
src/coreclr/nativeaot/Test.CoreLib/src/System/Diagnostics/StackTraceHiddenAttribute.cs	Added AttributeTargets.Interface to maintain consistency with the main implementation
src/libraries/System.Runtime/ref/System.Runtime.cs	Updated reference assembly to reflect the attribute usage changes for both attributes
src/libraries/apicompat/ApiCompatBaseline.NetCoreAppLatestStable.xml	Added suppressions for CP0015 diagnostic due to attribute usage changes across multiple assemblies
src/libraries/apicompat/ApiCompatBaseline.netstandard2.1.xml	Added suppression for CP0015 diagnostic for netstandard compatibility
src/libraries/System.Runtime/tests/System.Diagnostics.Tools.Tests/System/Diagnostics/CodeAnalysis/ExcludeFromCodeCoverageAttributeTests.cs	Added test verifying ExcludeFromCodeCoverageAttribute can be applied to interfaces
src/libraries/System.Runtime/tests/System.Runtime.Tests/System/Diagnostics/StackTraceHiddenAttributeTests.cs	Added test verifying StackTraceHiddenAttribute can be applied to interfaces

[MichalStrehovsky]

Should we instead have a test that checks the methods on the interface are actually hidden in stack traces?

The tests in this file all tests the actual behavior (Exception.StackTrace/Environment.StackTrace). This added test is more of a reflection test than anything else and I'm pretty sure we have such coverage elsewhere.

[Copilot]

Replaced the reflection test with a behavioral test (InterfaceHidden_EnvironmentStackTrace) that verifies default interface methods are actually hidden from stack traces, consistent with the other tests in this file. Commit b572aee.

[stephentoub]

@copilot

[stephentoub]

@copilot can you add a similar INotHiddenInterface and validate that with exactly the same setup except for the attribute that those stacktraces do contain the relevant method names?

[stephentoub]

@copilot?