Add trim analyzer support for C# 14 extensions

[sbomer]

Fixes #115949

This adds Roslyn analyzer support for C# 14 extensions. A few notes on the behavior:

• DAM is supported on method return/params, including on property accessor return/param.
• DAM is not supported on extension properties (see DAM on extension properties is silently ignored #119113)
• DAM is not supported on extension methods (this produces IL2041)
• There's still a bug with the behavior for ILLink/ILC due to the annotations not being preserved into the implementation when lowering: "return" attributes on extension property accessors not emitted on implementation roslyn#80017.

Includes an update to Microsoft.CodeAnalysis for new analyzer APIs involving extension members. #119159 tracks fixing new warnings that are suppressed for now.

New tests uncovered an analyzer issue with operators in the (extension or not): #119110. This change includes test coverage for non-extension operators.
They also uncovered an issue that looks like a race condition in ILC: #119155.

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[Copilot]

Pull Request Overview

This PR adds trim analyzer support for C# 14 extensions by implementing comprehensive handling of the new extension syntax introduced in C# 14. The key changes enable proper data flow analysis and warning generation for extension members while addressing compiler-generated artifacts.

• Adds test coverage for both traditional extension methods and new C# 14 extension members
• Updates the trim analysis infrastructure to handle extension parameters on types
• Implements workarounds for compiler-generated types that inherit attributes from extension members

Reviewed Changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/tools/illink/test/Mono.Linker.Tests/TestCasesRunner/ResultChecker.cs	Adds workaround to skip attribute validation for compiler-generated extension member types
src/tools/illink/test/Mono.Linker.Tests.Cases/DataFlow/ExtensionsDataFlow.cs	New test case for traditional extension method data flow analysis
src/tools/illink/test/Mono.Linker.Tests.Cases/DataFlow/ExtensionMembersDataFlow.cs	New test case for C# 14 extension members data flow analysis
src/tools/illink/test/ILLink.RoslynAnalyzer.Tests/DataFlowTests.cs	Adds test methods for the new extension data flow test cases
src/tools/illink/src/ILLink.RoslynAnalyzer/TrimAnalysis/TrimAnalysisVisitor.cs	Updates parameter handling to support extension parameters on types
src/tools/illink/src/ILLink.RoslynAnalyzer/TrimAnalysis/ParameterProxy.cs	Enhances parameter proxy to handle extension parameters with proper indexing
src/tools/illink/src/ILLink.RoslynAnalyzer/TrimAnalysis/MethodParameterValue.cs	Removes obsolete constructors for method parameter values
src/tools/illink/src/ILLink.RoslynAnalyzer/TrimAnalysis/FlowAnnotations.cs	Updates parameter annotation retrieval for extension methods
src/tools/illink/src/ILLink.RoslynAnalyzer/IMethodSymbolExtensions.cs	Adds extension parameter detection and parameter counting logic
src/tools/illink/src/ILLink.RoslynAnalyzer/ILLink.RoslynAnalyzer.csproj	Reorders NoWarn directives and removes conditional compilation warning suppression
src/tools/illink/src/ILLink.RoslynAnalyzer/DataFlow/LocalDataFlowVisitor.cs	Updates method and property call handling for extension parameters
src/coreclr/tools/aot/ILCompiler.Trimming.Tests/TestCasesRunner/ResultChecker.cs	Duplicates the compiler-generated type workaround for NativeAOT testing
eng/Versions.props	Updates Microsoft.CodeAnalysis version from 4.8.0 to 4.14.0

[jtschuster]

Thank you!

[tannergooding]

Will this need backport to .NET 10?

[sbomer]

@jkoritzinsky does the version update look OK to you?

[jkoritzinsky]

Version update looks good!

[jtschuster]

Good catch on the operators!

[sbomer]

/backport to release/10.0

[github-actions]

Started backporting to release/10.0: https://github.com/dotnet/runtime/actions/runs/17307689788

[github-actions]

@sbomer backporting to "release/10.0" failed, the patch most likely resulted in conflicts:

$ git am --3way --empty=keep --ignore-whitespace --keep-non-patch changes.patch

Applying: Add ExtensionsDataFlow test
Applying: Add support for extension members
Applying: Add property tests and arguments fix
Applying: Fix ILCompiler.Trimming.Tests infra
Applying: Update MicrosoftCodeAnalysisVersion_LatestVS
Applying: Update MicrosoftCodeAnalysisVersion_LatestVS
Using index info to reconstruct a base tree...
M	eng/Versions.props
Falling back to patching base and 3-way merge...
No changes -- Patch already applied.
Applying: Reorganize tests, fix setter arguments
Applying: Don't propagate extension property annotations
Applying: Avoid conflict warning for DAM on property
Applying: Add coverage for operators
Applying: Add comment about property annotations
Applying: Silence warnings
Using index info to reconstruct a base tree...
M	src/tools/illink/src/ILLink.RoslynAnalyzer/ILLink.RoslynAnalyzer.csproj
Falling back to patching base and 3-way merge...
Auto-merging src/tools/illink/src/ILLink.RoslynAnalyzer/ILLink.RoslynAnalyzer.csproj
CONFLICT (content): Merge conflict in src/tools/illink/src/ILLink.RoslynAnalyzer/ILLink.RoslynAnalyzer.csproj
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
hint: When you have resolved this problem, run "git am --continue".
hint: If you prefer to skip this patch, run "git am --skip" instead.
hint: To restore the original branch and stop patching, run "git am --abort".
hint: Disable this message with "git config set advice.mergeConflict false"
Patch failed at 0012 Silence warnings
Error: The process '/usr/bin/git' failed with exit code 128

Please backport manually!

[pentp]

It seems this commit is causing local builds to fail with error IDE0031: Null check can be simplified (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0031) [C:\dev\runtime\src\tools\illink\src\ILLink.RoslynAnalyzer\ILLink.RoslynAnalyzer.csproj

[sbomer]

error IDE0031

I haven't been able to reproduce this (tried on a couple machines). If anyone else hits this please let me know. Repro steps, run outside of VS (confirmed with @pentp):

> git checkout 7eacd692219e1f5eefc143a2dbb3d342f9978c03
> git clean -xfd
> .\build.cmd -s tools.illink

[sbomer]

Looks like #119391 (comment) is a potential explanation for the inconsistent repro.