Create a product source build layout from a repo sha

[mmitche]

Using darc and given a repo at a sha, we should be able to evaluate the set of repo+sha's that are required to create any dependencies needed to build that sha. For instance, core-setup depends on corefx's output packages (among others). Those corefx input packages were produced from an official build of corefx, which was done at a specific sha. Following this transitively from that corefx sha, we then can determine the input coreclr versions, etc.

Using this information, we should be able to git clone and provide a source drop layout of the product subtree starting with the input repo.

When this is done, given a repo+sha combo darc should be able to:

• Display all input shas
• Clone all repos at the input shas

[mmitche]

T-shirt size: Small

Requires all repos to be on darc for the version info, though.

[dagood]

Requires all repos to be on darc for the version info

We talked about this in a source-build planning meeting, and I think we could reasonably use this functionality even if only certain sets of repos were fetchable like this. We could keep our submodules up to the root(s) of the subtree(s) and use Darc beyond that.

[markwilkie]

@mmitche - what's the latest on this issue?

[mmitche]

We have the support to determine the sha set in darc now...just waiting for more repos to onboard,

[markwilkie]

Can (should) this issue be closed then? Sounds like the functionality is there, and we're waiting for folks to finish onboarding... thoughts?

[mmitche]

@dagood Are you fine taking the darc output as the input to create layout, or do you want the ability to create the layout natively in the tool?

[dagood]

To me that's mainly a resourcing question and of course it would be better for someone primarily working on Arcade to do it 😄, but technically I think it's perfectly reasonable to expect us to (edit: be able to) do that and probably contribute it to the tool to do natively.

[mmitche]

@dagood Required for preview 2?

[dagood]

I think the graph alone will make it significantly more reasonable to ship preview2 from source-build. Manual work would still be required to update the submodules (or temporary automation coded up) but the detective work that was needed to find preview1 commit hashes wouldn't be necessary.

We also aren't using Darc in our build yet, so the effort to integrate it might not even make sense for preview2 anyway.

[jcagme]

• @crummel

After the later talks do you think using the output graph would be enough? If this is the case, could we close this?

[crummel]

Yes, I think the output graph is enough and we can close this.