Implement AOP at IL level (like PostSharp)

[vbcodec]

There are two proposals to implement AOP like #5561 and #5292. First proposal operates on Roslyn level, and require access to AST and/or generating code as string. This way is very messy and look like workaround than solution. Certainly, this is not what average coders want from AOP. Second proposal that use superseding is better, but require language improvement and there are issues how to implement it in right way.
Unfortunately, both proposals are overkill and have shortcomings compared to IL - level. Implementing AOP as IL codegen, do not require heavy Roslyn improvements, nor language changes (with fear of polluting language with non mature specific concept), and have very big advantage - ability to handle members that exist in libraries. This - IL - way is enough for most scenarios, simply to understand and use. Extensions and other features work in this way, and work very well.

[MgSam]

Those proposals are complementary, not alternatives. IL codegen is extremely messy and means that you have no way to verify what the behavior of your code is until runtime (or by inspecting the re-written IL). The proposals you mention neatly deal with that issue by making the injected code available for perusal at design time.

[tmat]

One of the big problems with IL rewriting is that is degrades debugging experience. The rewriter generally doesn't have enough information (which is only present in source) to produce the correct debugging information.

[gafter]

This is kind of out-of-scope for Roslyn, which is a compiler and language analysis framework for C# and VB.

[Inverness]

I've been working on a project using Fody as a way of achieving AOP with IL weaving.

Fody basically sets up a system that lets you easily utilize IL weaving libraries at build time. Mono.Cecil is used to edit the assemblies and preserve debugging information.

I don't think is something Roslyn needs to handle.

[m0sa]

Still, CSharpCompilation.Emit is very closed down. It would be great if there would be an extension point to hook into the process of creating IL and pdb.