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exchange: ensure all outgoing subrepo references are present before pushing
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Authored by mharbison72 on Dec 12 2019, 1:54 PM.

Details

Summary

We've run into occasional problems with people committing a repo, and then
amending or rebasing in the subrepo. That makes it so that the revision in the
parent can't be checked out, and the problem gets propagated on push. Mercurial
already tries to defend against this sort of dangling reference by pushing *all*
subrepo revisions first. This reuses the checks that trigger warnings in
hg verify to bail on the push unless using --force.

I thought about putting this on the server side, but at that point, all of the
data has been transferred, only to bail out. Additionally, SCM Manager hosts
subrepos in a location that isn't nested in the parent, so normal subrepo code
would complain that the subrepo is missing when run on the server.

Because the push command pushes subrepos before calling this exchange code, a
subrepo will be pushed before the parent is verified. Not great, but no
dangling references are exchanged, so it solves the problem. This code isn't in
the loop that pushes the subrepos because:

  1. the list of outgoing revisions is needed to limit the scope of the check
  2. the loop only accesses the current revision, and therefore can miss subrepos that were dropped in previous commits
  3. this code is called when pushing a subrepo, so the protection is recursive

I'm not sure if there's a cheap check for the list of files in the outgoing
bundle. If there is, that would provide a fast path to bypass this check for
people not using subrepos (or if no subrepo changes were made). There's
probably also room for verifying other references like tags. But since that
doesn't break checkouts, it's much less of a problem.

Diff Detail

Repository
rHG Mercurial
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Unit
Unit Tests Skipped

Event Timeline

mharbison72 created this revision.Dec 12 2019, 1:54 PM
pulkit accepted this revision.Dec 17 2019, 7:03 AM
This revision is now accepted and ready to land.Dec 17 2019, 7:03 AM