Hello *, I've put in place a new server-side validation hook a few days ago, and since nobody seemed to have complained yet, I assume it didn't have any adverse effects so far :-) It will only be triggered when Git submodule references are touched by a commit; you can find some preliminary (but incomplete) documentation and a sample session triggering validation-failure on purpose at https://ghc.haskell.org/trac/ghc/ticket/8251#comment:4 (this will be turned into a proper wiki-page once #8251 is completed; there's some minor details wrt some corner cases that still need to be looked at) So, this mostly addresses the server-side requirements for migrating to a proper git-submodule set-up for ghc.git; The next steps, however, include taking care of the client-side work-flow for working with a fully "submoduled" ghc.git setup. Personally, I'm quite comfortable using direct git commands to manage such a construct, but I'm well aware not everyone is (as previous discussions here have shown). Also, as my time is rather limited, I'd like to ask interested parties to join in and help formulate the future client-side work-flow[1] and/or update (or rewrite) the 'sync-all' to provide a seamless or at least smooth transition for those GHC devs who want to keep using "sync-all" instead of using direct Git commands. [1]: There's some difference in how tracked upstream packages and GHC-HQ owned sub-repos are to be handled workflow-wise, to avoid ending up with a noisy ghc.git history. For instance, having ghc.git with submodules is not the same as having a huge monolithic ghc.git repository with all subrepos embedded. specifically, it might not be sensible to propagate *every* single subrepo-commit as a separate ghc.git submod-ref update, but rather in logical batches (N.B.: using submodules gives the additional ability to git bisect within subrepos instead of having to bisect always only at top-level). This is one example of things to discuss/consider when designing the new work-flow. Cheers, hvr