destutil: if wdp is obsolete, update to the closest non-obsolete ancestor

As the original comments suggest, using prune as a model here was an existing
idea, and now this patch implements it.

I think it would be even better to do what solveobswdp() from evolve does (in
short, it allows to update to a successor of the closest ancestor even if that
ancestor is obsolete), but that is outside of this series' scope.

Differential Revision: https://phab.mercurial-scm.org/D12099

mercurial/destutil.py

@@ -65,9 +65,8 b' def _destupdateobs(repo, clean):'
         # replaced changesets: same as divergent except we know there
         # is no conflict
         #
-        # pruned changeset: no update is done; though, we could
-        #     consider updating to the first non-obsolete parent,
-        #     similar to what is current done for 'hg prune'
+        # pruned changeset: update to the closest non-obsolete ancestor,
+        # similar to what 'hg prune' currently does
 
         if successors:
             # flatten the list here handles both divergent (len > 1)
@@ -77,11 +76,15 b' def _destupdateobs(repo, clean):'
             # get the max revision for the given successors set,
             # i.e. the 'tip' of a set
             node = repo.revs(b'max(%ln)', successors).first()
-            if bookmarks.isactivewdirparent(repo):
-                movemark = repo[b'.'].node()
         else:
-            # TODO: copy hg prune logic
-            node = repo[b'.'].node()
+            p1 = p1.p1()
+            while p1.obsolete():
+                p1 = p1.p1()
+            node = p1.node()
+
+        if node is not None and bookmarks.isactivewdirparent(repo):
+            movemark = repo[b'.'].node()
+
     return node, movemark, None
 
 

tests/test-update-branches.t

@@ -696,9 +696,8 b' Test that 5 is not detected as a valid d'
   (commit or update --clean to discard changes)
   [255]
 
-Test that we don't crash when updating from a pruned changeset (i.e. has no
-successors). Behavior should probably be that we update to the first
-non-obsolete parent but that will be decided later.
+Test that we update to the closest non-obsolete ancestor when updating from a
+pruned changeset (i.e. that has no successors)
   $ hg id --debug -r 2
   bd10386d478cd5a9faf2e604114c8e6da62d3889
   $ hg up --quiet 0
@@ -706,21 +705,18 b' non-obsolete parent but that will be dec'
   $ hg debugobsolete bd10386d478cd5a9faf2e604114c8e6da62d3889
   1 new obsolescence markers
   obsoleted 1 changesets
+  $ hg log -r '_destupdate()'
+  1:0786582aa4b1 1 (no-eol)
   $ hg up
-  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
-
-Test experimental revset support
-
-  $ hg log -r '_destupdate()'
-  2:bd10386d478c 2 (no-eol)
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
 
 Test that boolean flags allow --no-flag specification to override [defaults]
   $ cat >> $HGRCPATH <<EOF
   > [defaults]
   > update = --check
   > EOF
-  $ hg co 2
+  $ hg co 1
   abort: uncommitted changes
   [20]
-  $ hg co --no-check 2
+  $ hg co --no-check 1
   0 files updated, 0 files merged, 0 files removed, 0 files unresolved