log: add config for making `hg log -G` always topo-sorted

I (and everyone else at Google) have an log alias that adds graph mode
and templating. I have another one that builds on the first and also
restricts the set of revisions to only show those I'm most likely to
care about. This second alias also adds topological sorting. I still
sometimes use the first one. When I do, it very often bothers me that
it's not topologically sorted (branches are interleaved). This patch
adds a config option for always using topological sorting with graph
log.

The revision set is sorted eagerly, which seems like a bad idea, but
it doesn't seem to make a big difference in the hg repo (150ms). I
initially tried to instead wrap the user's revset in sort(...,topo),
but that seemed much harder.

Differential Revision: https://phab.mercurial-scm.org/D6331

mercurial/configitems.py

@@ -529,6 +529,9 coreconfigitem('experimental', 'evolutio
 coreconfigitem('experimental', 'evolution.bundle-obsmarker',
     default=False,
 )
+coreconfigitem('experimental', 'log.topo',
+    default=False,
+)
 coreconfigitem('experimental', 'evolution.report-instabilities',
     default=True,
 )

mercurial/logcmdutil.py

@@ -746,7 +746,12 def getrevs(repo, pats, opts):
     if opts.get('graph'):
         # User-specified revs might be unsorted, but don't sort before
         # _makerevset because it might depend on the order of revs
-        if not (revs.isdescending() or revs.istopo()):
+        if repo.ui.configbool('experimental', 'log.topo'):
+            if not revs.istopo():
+                revs = dagop.toposort(revs, repo.changelog.parentrevs)
+                # TODO: try to iterate the set lazily
+                revs = revset.baseset(list(revs))
+        elif not (revs.isdescending() or revs.istopo()):
             revs.sort(reverse=True)
     if expr:
         matcher = revset.match(None, expr)

relnotes/next

@@ -3,6 +3,16
  * New config `commands.commit.post-status` shows status after successful
  commit.
 
+
+== New Experimental Features ==
+
+ * New config `experimental.log.topo` makes `hg log -G` use
+   topological sorting. This is especially useful for aliases since it
+   lets the alias accept an `-r` option while still using topological
+   sorting with or without the `-r` (unlike if you use the `sort(...,
+   topo)` revset).
+
+
 == Bug Fixes  ==
 
 

tests/test-glog-topological.t

@@ -114,3 +114,41 later.
   |/
   o  0
   
+
+Topological sort can be turned on via config
+
+  $ cat >> $HGRCPATH << EOF
+  > [experimental]
+  > log.topo=true
+  > EOF
+
+  $ hg log -G
+  o  8
+  |
+  o  3
+  |
+  o  2
+  |
+  o  1
+  |
+  | o  7
+  | |
+  | o  6
+  | |
+  | o  5
+  | |
+  | o  4
+  |/
+  o  0
+  
+Does not affect non-graph log
+  $ hg log -T '{rev}\n'
+  8
+  7
+  6
+  5
+  4
+  3
+  2
+  1
+  0