refactor: prefer checks against nullrev over nullid A common pattern is using a changeset context and obtaining the node to compare against nullid. Change this to obtain the nullrev instead. In the future, the nullid becomes a property of the repository and is no longer a global constant, so using nullrev is much easier to reason about. Python function call overhead makes the difference moot, but future changes will result in more dictionary lookups otherwise, so prefer the simpler pattern. Differential Revision: https://phab.mercurial-scm.org/D10290

refactor: prefer lookup by revision, even for null While the nullid lookup is a special case, it is still more complicated. The common pattern is to lookup via nullrev so be consistent here. Differential Revision: https://phab.mercurial-scm.org/D10280

setdiscovery: simplify by using tiprev directly tip() uses tiprev() and reads the node from it, so drop a layer of indirection. Differential Revision: https://phab.mercurial-scm.org/D10289

test: enforce master to be the default branch in test Newer git issue a message about this. Differential Revision: https://phab.mercurial-scm.org/D10281

fix: merge imports Differential Revision: https://phab.mercurial-scm.org/D10277

tests: update divergence test for `hg fix` to actually result in divergence We have a test that checks that `hg fix` errors out if it might cause divergence. However, the test simply prunes the commit it then tries to fix, so fixing it wouldn't actually cause divergence. That works because the implementation is simple enough that it doesn't notice the difference. I'm about to make the implementation smarter, so let's fix the test first. Differential Revision: https://phab.mercurial-scm.org/D10267

rebase: don't call rewriteutil.precheck() with to-be-skipped commits It's clearly incorrect to call `rewriteutil.precheck()` for commits that we're not about to rewrite. We haven't noticed yet because the function doesn't check for divergence, but I'm about to teach it to do that. Differential Revision: https://phab.mercurial-scm.org/D10259

reabase: call rewriteutil.precheck() a bit later We now filter out descendants of divergence-causing commits in `_handleskippingobsolete()`. The filtered-out commits are removed from the rebase set (`destmap` and `state`). We should therefore call `rewriteutil.precheck()` after `_handleskippingobsolete()`. This patch does that. It hasn't mattered so far because `rewriteutil.precheck()` doesn't yet check for divergence, but it will soon. This affects one test where we now fail because the user is trying to rebase an ancestor instead of failing because they tried to rebase a public commit. We have several similar tests just after, where we still fail because of the phase, so that seems fine. The difference in behavior also seems fine to me. Differential Revision: https://phab.mercurial-scm.org/D10258

rebase: set `prepared = True` at very end of `_preparenewrebase()` Once we've set `rebaseruntime.prepared = True`, `rebaseruntime.repo` starts returning the unfiltered repo. That will make my next patch break, because that patch moves the call to `rewriteutil.precheck()` after the call to `_handleskippingobsolete()`, which current happens after `prepared = True`. We therefore need to prepare by moving `prepared = True` a bit later, after `_handleskippingobsolete()`. I don't think that matters for that call. Differential Revision: https://phab.mercurial-scm.org/D10257

rebase: filter out descendants of divergence-causing commits earlier `hg rebase` treats obsolete commits differently depending what has happened to the commit: 1) Obsolete commit without non-obsolete successors: Skipped, and a note is printed ("it has no successor"). 2) Obsolete commit with a successor in the destination (ancestor of it): Skipped, and a note is printed ("already in destination"). 3) Obsolete commit with a successor in the rebase set: The commit and its descendants are skipped, and a note is printed ("not rebasing <commit> and its descendants as this would cause divergence"), unless `allowdivergence` config set. 4) Obsolete commit with a successor elsewhere: Error ("this rebase will cause divergences"), unless `allowdivergence` config set. Before this patch, we did all those checks up front, except for (3), which was checked later. The later check consisted of two parts: 1) filtering out of descendants, and 2) conditionally printing message if the `allowdivergence` config was not set. This patch makes it so we do the filtering early. A consequence of filtering out divergence-causing commits earlier is that we rebase commits in slightly different order, which has some impact on tests. Differential Revision: https://phab.mercurial-scm.org/D10249