Add option to include symbols for runtime packs when running ILLink

[vitek-karas]

Currently when the SDK runs ILLink it will only produce updated pdbs for assemblies which it has pdbs for. Which basically excludes all framework assemblies (from runtime packs). But ILLink will modify the framework assemblies. So after trimming there's no way to get the new pdbs for the trimmed framework anymore.

There should be an option (MSBuild property) which will tell SDK to gather symbols for everything it can before running ILLink so that trimming can also produce matching PDBs and allow full debugging experience across all assemblies.

[sbomer]

The way I would imagine this working is that we would ship Microsoft.SymbolStore in the SDK with a task that can fetch symbols matching the framework version we are publishing (and maybe also third-party nugets?). It could be useful independently of the linker, so maybe the option could be called PublishWithSymbols or similar.

@mikem8361 @wli3 does this seem like a reasonable approach?

[mikem8361]

Yes, the Microsoft.SymbolStore code could be used to create a download symbol msbuild task. What I'm confused about is what PDB is being downloaded: the original PDB for the untrimmed assembly or the PDB for the trimmed ones? What get published to the symbol server?

[vitek-karas]

We would download the untrimmed symbols - the exact same one which are already published to symbol server today. The trimmed ones are produced locally when trimming the app. Trimming the app trims framework assemblies - for that one app alone - so it will produce a "trimmed" version of the symbols locally. In order to do that, it needs the original untrimmed symbols (just like it consumes the untrimmed assemblies on input).

[mikem8361]

I understand. It wouldn't take much for someone to write a msbuild task using Microsoft.SymbolStore to do this download.

[wli3]

@KathleenDollard @dsplaisted Microsoft.SymbolStore is only 71KB. And the scenario is very useful. I think we should go ahead. What do you think?

[dsplaisted]

Seems reasonable to me.

[mikem8361]

FYI Microsoft.SymbolStore does have a dependency on Microsoft.FileFormats (99K)

[vitek-karas]

We should do this in such a way that it also happens for NativeAOT, since it has the same problem.