LFT-2910: Detect mutability from primary class constructors

[j3parker]

No description provided.

[j3parker]

There is some open chatter in the compiler about exposing more of this stuff via the semantic model but the current situation is you need to go into the syntax.

[j3parker]

You might wonder like don't they show up as properties or something in the GetMembers() call earlier, and the answer is that no they don't.

[omsmith]

So, this is only the case if the parameters get used outside of field initializers. Really we just want the Roslyn team's RS0062, or to add an equivalent.

https://andrewlock.net/blocking-primary-constructor-member-capture-using-an-analyzer/

using System;

sealed class A( string P ) {
    void M() {
        Console.WriteLine( P );
    }
}


sealed class B( string P ) {
    private readonly string m_p = P;

    void M() {
        Console.WriteLine( m_p );
    }
}

using System;
using System.Diagnostics;
using System.Reflection;
using System.Runtime.CompilerServices;
using System.Security;
using System.Security.Permissions;

[assembly: CompilationRelaxations(8)]
[assembly: RuntimeCompatibility(WrapNonExceptionThrows = true)]
[assembly: Debuggable(DebuggableAttribute.DebuggingModes.Default | DebuggableAttribute.DebuggingModes.IgnoreSymbolStoreSequencePoints | DebuggableAttribute.DebuggingModes.EnableEditAndContinue | DebuggableAttribute.DebuggingModes.DisableOptimizations)]
[assembly: SecurityPermission(SecurityAction.RequestMinimum, SkipVerification = true)]
[assembly: AssemblyVersion("0.0.0.0")]
[module: UnverifiableCode]
[module: RefSafetyRules(11)]
[NullableContext(1)]
[Nullable(0)]
internal sealed class A
{
	public A(string P)
	{
		<P>P = P;
		base..ctor();
	}

	private void M()
	{
		Console.WriteLine(<P>P);
	}
}
[NullableContext(1)]
[Nullable(0)]
internal sealed class B
{
	private readonly string m_p;

	public B(string P)
	{
		m_p = P;
		base..ctor();
	}

	private void M()
	{
		Console.WriteLine(m_p);
	}
}

https://lab.razor.fyi/#43rPyMUVUJSfXpSYq5dcLPSAsbQ4My9dIbiyuCQ115qLqzg1MSc1RSE5J7G4WMFRQ6G4pAgkH6CgqVDNpaCgoFCWn5mi4KsB44KAc35ecX5Oql54UWZJqk9mXqoGSL01WL6Wq5YLzVQnLKYWFGWWJZakKhSlJqbk5-VUwlTkxhco2CoEWHORYDdID8J2L6bk4ihOji3zu25fTBdgSWCsYAQA

[omsmith]

If you want to do this as a first pass though, 👍

[j3parker]

I'm not sure I agree with

Really we just want the Roslyn team's RS0062, or to add an equivalent.

In that I think this analyzer should stand on it's own (if that counts as "adding an equivalent" then OK).

As written this will prevent okay usages of primary class constructors for immutable types, so I do agree that this is a "first pass" in that sense (I wasn't planning to do any more of it, though -- this was motivated by the thread in Slack and existing (probably benign) usages that have snuck through).

[j3parker]

I guess this is probably 99% agreement, I'll chat with you on Slack about next steps