Fix IsByRefLikeAttribute types being incorrectly suppressed in completion lists

[Copilot]

Problem

Types like Span<T> and ReadOnlySpan<T> were being incorrectly suppressed from IntelliSense completion lists due to having both ObsoleteAttribute and IsByRefLikeAttribute. The completion system was treating any type with ObsoleteAttribute as obsolete, regardless of other attributes.

// This would not show Span in completion
let test = System.Sp

Root Cause

The issue occurred because:

1. Span<T> and ReadOnlySpan<T> have ObsoleteAttribute in .NET for specific technical reasons
2. They also have IsByRefLikeAttribute to indicate they are stack-only types
3. The completion system has two attribute checking paths: F# types use CheckFSharpAttributesForObsolete while .NET types use CheckILAttributesForUnseen
4. Only the F# attribute checking path had the IsByRefLikeAttribute exclusion logic
5. Since Span types are .NET types, they went through IL attribute checking and were incorrectly suppressed

Solution

Extended both attribute checking functions to exclude types marked with IsByRefLikeAttribute from being considered obsolete:

• F# types: Updated CheckFSharpAttributesForObsolete in AttributeChecking.fs
• IL/.NET types: Updated CheckILAttributesForUnseen in AttributeChecking.fs
• Added attrib_IsByRefLikeAttribute_opt to TcGlobals using the established tryFindSysAttrib pattern
• Treats the attribute as optional since not every runtime has it

Both functions now use the same logic: if a type has ObsoleteAttribute but also has IsByRefLikeAttribute, it should not be considered obsolete for completion purposes.

Testing

Added a unit test in CompletionTests.fs that verifies:

• Typing System.Sp shows Span in completion suggestions
• By-ref-like types are not suppressed despite having dual attributes
• Test is conditioned to only run on .NET Core where Span<T> is available
• All 37 completion tests pass successfully

This ensures that by-ref-like types remain visible and accessible to developers while maintaining the existing obsolete attribute behavior for other types.

This pull request was created as a result of the following prompt from Copilot chat.

Extend the CheckFSharpAttributesForObsolete function in src/Compiler/Checking/AttributeChecking.fs to exclude types marked with IsByRefLikeAttribute from being considered obsolete, even if ObsoleteAttribute is present. Add a code comment explaining why IsByRefLikeAttribute is excluded: specifically, this avoids improper suppression of types like Span and ReadOnlySpan in completion lists due to their dual attributes. Additionally, add a unit/integration test in CompletionProviderTests to verify that typing System.Sp triggers completion suggestions for Span and ReadOnlySpan, and that they are not marked obsolete.

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[github-actions]

❗ Release notes required

---

✅ Found changes and release notes in following paths:

Warning

No PR link found in some release notes, please consider adding it.

Change path	Release notes path	Description
src/Compiler	docs/release-notes/.FSharp.Compiler.Service/10.0.100.md	No current pull request URL (#18784) found, please consider adding it

[T-Gro]

Also add release notes to docs/release-notes/.FSharp.Compiler.Service/10.0.100.md

[Copilot]

Also add release notes to docs/release-notes/.FSharp.Compiler.Service/10.0.100.md

Added release notes documenting the IsByRefLikeAttribute completion fix. The entry explains that types like Span<T> and ReadOnlySpan<T> now appear correctly in IntelliSense completion lists. Commit: 0a90d01

[abonie]

@copilot
A test failed in the pipeline run

[xUnit.net 00:00:16.79]     FSharp.Compiler.Service.Tests.CompletionTests.Span appears in completion and is not marked obsolete [FAIL]
  Failed FSharp.Compiler.Service.Tests.CompletionTests.Span appears in completion and is not marked obsolete [827 ms]
  Error Message:
   Assert.True() Failure
Expected: True
Actual:   False
  Stack Trace:
     at FSharp.Compiler.Service.Tests.CompletionTests.assertItemsWithNames(Boolean contains, IEnumerable`1 names, DeclarationListInfo completionInfo) in /Users/runner/work/1/s/tests/FSharp.Compiler.Service.Tests/CompletionTests.fs:line 10
   at FSharp.Compiler.Service.Tests.CompletionTests.assertHasItemWithNames(IEnumerable`1 names, DeclarationListInfo completionInfo) in /Users/runner/work/1/s/tests/FSharp.Compiler.Service.Tests/CompletionTests.fs:line 13
   at FSharp.Compiler.Service.Tests.CompletionTests.Span appears in completion and is not marked obsolete() in /Users/runner/work/1/s/tests/FSharp.Compiler.Service.Tests/CompletionTests.fs:line 372
   at System.Reflection.MethodBaseInvoker.InterpretedInvoke_Method(Object obj, IntPtr* args)
   at System.Reflection.MethodBaseInvoker.InvokeWithNoArgs(Object obj, BindingFlags invokeAttr)

[Copilot]

@copilot
A test failed in the pipeline run

...

Fixed the test failure. The issue was that the original fix only handled F# types through CheckFSharpAttributesForObsolete, but types like Span<T> and ReadOnlySpan<T> are .NET types that go through IL attribute checking via CheckILAttributesForUnseen. Updated the IL attribute checking function to also exclude types with IsByRefLikeAttribute from being considered obsolete. The test now passes and all 37 completion tests are passing. Commit: 2f4b4f8