How to get and transform all attributes that inherit from another attribute?

[Windows11CE]

I currently have this piece of code that I use to collect and transform all my "custom attributes" before passing it down to my source generator:

var customAttributes = context.SyntaxProvider
	.ForAttributeWithMetadataName(
		"Namespace.CustomAttribute",
		(node, _) => node is CompilationUnitSyntax,
		TransformCustomAttributes
	)
	.SelectMany((x, _) => x)
	.Collect();

However I want to also get ahold of attributes that inherit from this specific attribute, how would I do that? I currently have a IncrementalGeneratorInitializationContext and so I tried to create a compilation context to do it but couldn't get around it.

[333fred]

I want to also get ahold of attributes that inherit from this specific attribute,

You cannot, plain and simple. This is not something supported by FAWMN, and cannot be, as that would break the caching it uses to be as fast as possible.

[333fred]

On the order of seconds, which is critical in live IDE scenarios where source generators run. I seriously cannot stress enough that our strong recommendation is that you do not support this.

[CyrusNajmabadi]

But what does 100 times slower means in actual numbers?

Note: the 100x is both in time (which may be on the order of seconds on medium to large projects). But it's much worse in terms of memory. This approach will realize every syntax node in every file when the generator runs. Every time. We see GBs of allocations per second caused by this approach in real world cases. Those geebies of allocations have a dramatic and detrimental effect on virtually all parts of tooling, causing GC thrashing, UI delays, and all sorts of pain.

I ended up fixing at least a dozen cases of SGs doing this. The problem is real. The solution is intentional. You are free to ignore and go your own route. But that would be against our recommendations and we will not be able to help you if perf issues arise for any of your users. We will only be able to say: write this as a separate tool, or use FAWMN if you want performance.

[m-gasser]

As a case in point, the HotChocolate source generator is scanning for custom attributes, that can be applied in various places. If you really want to do this, you can have a look there, how it is done. But as others said, it is very expensive. This is actually how I know about the implementation of that source generator. It has a relatively high impact on our build time, despite only a few usages. I had a go at improving performance but was not able to.
That said, if your source generator is only used internally and only in relatively small projects, you might be fine.

[333fred]

@m-gasser, being perfectly honest; that generator is going to cause a lot of performance issues in the IDE, not just in CLI scenarios. It stores symbols in various model classes, and while it doesn't include those symbols in equality, that is in some ways worse: you're now rooting arbitrary old compilations for indefinite amounts of time.

[m-gasser]

@333fred I remember checking for accidentally cached symbols back then and I did not see any. Now that you mentioned this, I had a look again and the place I found was added since then.
Is there some way to get some statistics, which source generator is slowing things down by how much when run in the IDE? This would help catching regressions in caching, that are not visible in MSBuild Log Viewer. It would also be helpful for our our own source generators. Currently we have no idea whether we messed up and are slowing the IDE down.