Enable using live ref pack in source generator unit tests

[elinor-fung]

Currently, source generator unit tests either directly reference implementation assemblies or use a non-live ref pack. To enable using live ref assemblies in source generator unit tests, we should add infrastructure to zip the live ref assemblies, include in the Helix payload, and unzip / resolve against in the unit tests

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Issue Details

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Currently, source generator unit tests either directly reference implementation assemblies or use a non-live ref pack. To enable using live ref assemblies in source generator unit tests, we should add infrastructure to zip the live ref assemblies, include in the Helix payload, and unzip / resolve against in the unit tests

Author:	elinor-fung
Assignees:	-
Labels:	area-Infrastructure-libraries
Milestone:	7.0.0

[ViktorHofer]

To enable using live ref assemblies in source generator unit tests, we should add infrastructure to zip the live ref assemblies, include in the Helix payload

As the targeting pack (ref pack) is only needed for building and not running, why would we need that on a Helix machine? Do we actually build on Helix now?

[jkoritzinsky]

The ref pack is needed to add to a Roslyn Compilation object so we can run our analyzer/source-generator/code-fix tests against the actual assemblies our customers will compile against.

So yes, in a sense we're building code on Helix now, just as part of tests that hook into our customer's compilation experience.

[ViktorHofer]

we should add infrastructure to zip the live ref assemblies, include in the Helix payload, and unzip / resolve against in the unit tests

Can you just use the live built targeting pack nuget package? That's the common path that our customers use as well. We should be able to build the targeting pack package as part of the libraries build as there are no dependencies on the runtime.

[jkoritzinsky]

Using the package is actually more annoying than using the zip. We’d still need to upload it to Helix since it wouldn’t be on a feed yet, and we’d need to calculate the version to restore. Additionally, we would need to continue to override the NUGET_PACKAGES environment variable to a new value every run since each local build has the same version (7.0.0-dev). Using a zip of the ref assemblies is actually significantly easier.