C#: Tracer support for invoking csc directly.

[michaelnebel]

There appears to be a change in .NET 10 RC2 on how dotnet invokes the compiler.
I tested the following on a simple console application that can be build using dotnet build.

In .NET 9 / .NET 10 RC 1, the tracer sees the following intercept candidates

• dotnet build (we intercept and disable shared compilation)
• dotnet exec csc.dll ... <- This is the compiler invocation that we catch in the tracer and use to call the extractor.

However, in .NET RC 2, the tracer sees the following intercept candicates

• dotnet build (we intercept and disable shared compilation)
• csc ... <-- This is the compiler invocation, but it "falls through" the patterns in the tracer.

In this PR we

• Add tracer support on MacOS and Linux when csc invoked directly. This also requires some special handling in the extractor to "detect" the correct compiler version information.
• Add integration tests for windows and linux for creating a database using .NET 10 RC 2. Without modifying the integration test workflow, we need to rely on the autobuilder to install (and source) a dotnet installation. Unfortunately, this step fails for .NET 10 RC 2 on the Mac OS test runner - which is why it has been excluded from the integration test. It is possible for me to execute the test locally on my Mac when .NET 10 RC 2 is already installed. I don't think we should invest more time before we get the release version of .NET 10.

DCA looks good.

[Copilot]

Pull Request Overview

This PR adds tracer support for .NET 10 RC2, which changed how dotnet invokes the C# compiler. Instead of using dotnet exec csc.dll, RC2 directly invokes csc, which the tracer previously didn't handle. The changes enable proper tracing and extraction on macOS and Linux when csc is invoked directly.

Key Changes:

• Added pattern matcher in tracer configuration to intercept direct csc invocations
• Updated compiler version detection to handle csc binary by reading version info from csc.dll
• Added release note documenting the new tracing capability

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
csharp/tools/tracing-config.lua	Adds pattern matcher for direct csc compiler invocations
csharp/ql/lib/change-notes/2025-10-21-dotnet-rc2-tracing.md	Documents the new tracer support for .NET 10 RC2
csharp/extractor/Semmle.Extraction.CSharp/Extractor/CompilerVersion.cs	Updates version detection to read from csc.dll when compiler name is csc

[Copilot]

The EndsWith check is too broad and could incorrectly match paths ending with 'csc' that aren't the compiler binary (e.g., /path/to/misc). Use Path.GetFileNameWithoutExtension(SpecifiedCompiler) == "csc" to ensure only the actual csc compiler binary is matched.

Suggested change

	var compilerBinaryName = SpecifiedCompiler.EndsWith("csc") ? $"{SpecifiedCompiler}.dll" : SpecifiedCompiler;
	var compilerBinaryName = Path.GetFileNameWithoutExtension(SpecifiedCompiler) == "csc" ? $"{SpecifiedCompiler}.dll" : SpecifiedCompiler;

[michaelnebel]

Good suggestion - we do however need to take the file extension into account.

[michaelnebel]

And we also need to make sure not to read the version information from a non-existing file 😄

[hvitved]

Thanks for fixing this; tracer issues are annoying to debug. Could we add an integration test?

[hvitved]

Why not just include '^csc$' in the list above?

[michaelnebel]

Due to the quotation in the above.

[michaelnebel]

As per our offline discussion, the matchers have been merged, which means that the quotation has been removed for the .exe cases.