log: add obsfate by default in changeset printer

Having an obsfate by default in log will be useful for users to understand why
they have obsolete and unstable changesets. Obsfate will only be shown for
obsolete changesets, which only happens if people opt-in to experimental feature.

But when obsolete changeset are visible, it is very useful to understand where
they are. Having it in log could be sufficient for most people, so they don't
have to learn a new command (like obslog which is itself useful in case of
divergences).

For example, when pulling and working directory parent become obsolete:

  $ hg pull
  ...
  working directory parent is obsolete! (f936c1697205)

This message comes from the Evolve extension.

Obsfate would comes handy:

  $ hg log -G
  o  changeset:   2:6f91013c5136
  |  tag:         tip
  |  parent:      0:4ef7b558f3ec
  |  user:        Boris Feld <[e-mail]>
  |  date:        Mon Oct 09 16:00:27 2017 +0200
  |  summary:     A
  |
  | @  changeset:   1:f936c1697205
  |/   user:        Boris Feld <[e-mail]>
  |    date:        Mon Oct 09 16:00:27 2017 +0200
  |    obsfate:     rewritten using amend as 2:6f91013c5136
  |    summary:     -A
  |
  o  changeset:   0:feb4dd822b8c
     user:        Boris Feld <[e-mail]>
     date:        Tue Oct 09 16:00:00 2017 +0200
     summary:     ROOT

And once we update, we don't have an obsolete changeset in the log anymore so
we don't show obsfate anymore, most users won't see obsfate often if they
don't have obsolete changeset often:

  @  changeset:   2:6f91013c5136
  |  tag:         tip
  |  parent:      0:4ef7b558f3ec
  |  user:        Boris Feld <[e-mail]>
  |  date:        Mon Oct 09 16:00:27 2017 +0200
  |  summary:     A
  |
  o  changeset:   0:feb4dd822b8c
     user:        Boris Feld <[e-mail]>
     date:        Tue Oct 09 16:00:00 2017 +0200
     summary:     ROOT

mercurial/cmdutil.py

@@ -1665,6 +1665,9 b' class changeset_printer(object):'
             self.ui.write(_("instability: %s\n") % ', '.join(instabilities),
                           label='log.instability')
 
+        elif ctx.obsolete():
+            self._showobsfate(ctx)
+
         self._exthook(ctx)
 
         if self.ui.debugflag:
@@ -1713,6 +1716,15 b' class changeset_printer(object):'
 
         self.showpatch(ctx, matchfn)
 
+    def _showobsfate(self, ctx):
+        obsfate = templatekw.showobsfate(repo=self.repo, ctx=ctx, ui=self.ui)
+
+        if obsfate:
+            for obsfateline in obsfate:
+                # i18n: column positioning for "hg log"
+                self.ui.write(_("obsfate:     %s\n") % obsfateline,
+                              label='log.obsfate')
+
     def _exthook(self, ctx):
         '''empty method used by extension as a hook point
         '''

tests/test-commandserver.t

@@ -535,6 +535,7 b' changelog and manifest would have invali'
   tag:         tip
   user:        test
   date:        Thu Jan 01 00:00:00 1970 +0000
+  obsfate:     pruned
   summary:     .
   
   changeset:   0:eff892de26ec

tests/test-obsmarker-template.t

@@ -58,11 +58,13 b' Test setup'
   |/   parent:      0:ea207398892e
   |    user:        test
   |    date:        Thu Jan 01 00:00:00 1970 +0000
+  |    obsfate:     rewritten using amend as 3:d004c8f274b9 by test2
   |    summary:     A1
   |
   | x  changeset:   1:471f378eab4c
   |/   user:        test
   |    date:        Thu Jan 01 00:00:00 1970 +0000
+  |    obsfate:     rewritten using amend as 2:a468dc9b3633
   |    summary:     A0
   |
   o  changeset:   0:ea207398892e
@@ -103,6 +105,26 b' Predecessors template should show curren'
   |/     Obsfate: rewritten using amend as 3:d004c8f274b9 by test, test2
   o  ea207398892e
   
+
+  $ hg log -G --config ui.logtemplate=
+  o  changeset:   3:d004c8f274b9
+  |  tag:         tip
+  |  parent:      0:ea207398892e
+  |  user:        test
+  |  date:        Thu Jan 01 00:00:00 1970 +0000
+  |  summary:     A2
+  |
+  | @  changeset:   1:471f378eab4c
+  |/   user:        test
+  |    date:        Thu Jan 01 00:00:00 1970 +0000
+  |    obsfate:     rewritten using amend as 3:d004c8f274b9 by test2
+  |    summary:     A0
+  |
+  o  changeset:   0:ea207398892e
+     user:        test
+     date:        Thu Jan 01 00:00:00 1970 +0000
+     summary:     ROOT
+  
   $ hg up 'desc(A1)' --hidden
   1 files updated, 0 files merged, 0 files removed, 0 files unresolved
 
@@ -294,6 +316,7 b' Test templates with splitted commit'
   | x  changeset:   1:471597cad322
   |/   user:        test
   |    date:        Thu Jan 01 00:00:00 1970 +0000
+  |    obsfate:     split as 2:337fec4d2edc, 3:f257fde29c7a
   |    summary:     A0
   |
   o  changeset:   0:ea207398892e
@@ -469,11 +492,13 b' Simulate a fold'
   | x  changeset:   2:0dec01379d3b
   | |  user:        test
   | |  date:        Thu Jan 01 00:00:00 1970 +0000
+  | |  obsfate:     rewritten as 3:eb5a0daa2192
   | |  summary:     B0
   | |
   | x  changeset:   1:471f378eab4c
   |/   user:        test
   |    date:        Thu Jan 01 00:00:00 1970 +0000
+  |    obsfate:     rewritten as 3:eb5a0daa2192
   |    summary:     A0
   |
   o  changeset:   0:ea207398892e
@@ -640,6 +665,7 b' Test setup'
   | x  changeset:   1:471f378eab4c
   |/   user:        test
   |    date:        Thu Jan 01 00:00:00 1970 +0000
+  |    obsfate:     rewritten using amend as 2:fdf9bde5129a
   |    summary:     A0
   |
   o  changeset:   0:ea207398892e
@@ -669,6 +695,8 b' Test setup'
   | x  changeset:   1:471f378eab4c
   |/   user:        test
   |    date:        Thu Jan 01 00:00:00 1970 +0000
+  |    obsfate:     rewritten using amend as 2:fdf9bde5129a
+  |    obsfate:     rewritten using amend as 3:65b757b745b9
   |    summary:     A0
   |
   o  changeset:   0:ea207398892e
@@ -690,6 +718,7 b' Test setup'
   |/   parent:      0:ea207398892e
   |    user:        test
   |    date:        Thu Jan 01 00:00:00 1970 +0000
+  |    obsfate:     rewritten using amend as 4:019fadeab383
   |    summary:     A2
   |
   | o  changeset:   2:fdf9bde5129a
@@ -702,6 +731,8 b' Test setup'
   | x  changeset:   1:471f378eab4c
   |/   user:        test
   |    date:        Thu Jan 01 00:00:00 1970 +0000
+  |    obsfate:     rewritten using amend as 2:fdf9bde5129a
+  |    obsfate:     rewritten using amend as 3:65b757b745b9
   |    summary:     A0
   |
   o  changeset:   0:ea207398892e
@@ -880,6 +911,7 b' Test setup'
   | x  changeset:   2:0dec01379d3b
   |/   user:        test
   |    date:        Thu Jan 01 00:00:00 1970 +0000
+  |    obsfate:     rewritten using amend as 3:b7ea6d14e664
   |    summary:     B0
   |
   o  changeset:   1:471f378eab4c
@@ -918,16 +950,19 b' Test setup'
   | |  parent:      1:471f378eab4c
   | |  user:        test
   | |  date:        Thu Jan 01 00:00:00 1970 +0000
+  | |  obsfate:     rewritten as 4:eb5a0daa2192
   | |  summary:     B1
   | |
   | | x  changeset:   2:0dec01379d3b
   | |/   user:        test
   | |    date:        Thu Jan 01 00:00:00 1970 +0000
+  | |    obsfate:     rewritten using amend as 3:b7ea6d14e664
   | |    summary:     B0
   | |
   | x  changeset:   1:471f378eab4c
   |/   user:        test
   |    date:        Thu Jan 01 00:00:00 1970 +0000
+  |    obsfate:     rewritten as 4:eb5a0daa2192
   |    summary:     A0
   |
   o  changeset:   0:ea207398892e
@@ -1166,11 +1201,13 b' Test setup'
   |/   parent:      0:ea207398892e
   |    user:        test
   |    date:        Thu Jan 01 00:00:00 1970 +0000
+  |    obsfate:     rewritten using amend as 3:7a230b46bf61
   |    summary:     A1
   |
   | x  changeset:   1:471f378eab4c
   |/   user:        test
   |    date:        Thu Jan 01 00:00:00 1970 +0000
+  |    obsfate:     rewritten using amend as 2:fdf9bde5129a
   |    summary:     A0
   |
   o  changeset:   0:ea207398892e
@@ -1201,6 +1238,7 b' Test setup'
   | @  changeset:   1:471f378eab4c
   |/   user:        test
   |    date:        Thu Jan 01 00:00:00 1970 +0000
+  |    obsfate:     rewritten using amend as 2:7a230b46bf61
   |    summary:     A0
   |
   o  changeset:   0:ea207398892e
@@ -1608,6 +1646,8 b' Diverge one of the splitted commit'
   | x  changeset:   6:4a004186e638
   |/   user:        test
   |    date:        Thu Jan 01 00:00:00 1970 +0000
+  |    obsfate:     rewritten using amend as 8:b18bc8331526
+  |    obsfate:     rewritten using amend as 9:0b997eb7ceee
   |    summary:     Add A,B,C
   |
   o  changeset:   5:dd800401bd8c
@@ -2051,6 +2091,7 b' Test templates with splitted and pruned '
   |  tag:         tip
   |  user:        test
   |  date:        Thu Jan 01 00:00:00 1970 +0000
+  |  obsfate:     pruned
   |  summary:     A2
   |
   o  changeset:   2:617adc3a144c
@@ -2062,6 +2103,7 b' Test templates with splitted and pruned '
   | x  changeset:   1:471597cad322
   |/   user:        test
   |    date:        Thu Jan 01 00:00:00 1970 +0000
+  |    obsfate:     split as 2:617adc3a144c, 3:0d0ef4bdf70e
   |    summary:     A0
   |
   o  changeset:   0:ea207398892e

tests/test-obsolete.t

@@ -975,6 +975,7 b' test the obsolete labels'
   [log.parent changeset.draft|parent:      3:6f9641995072]
   [log.user|user:        test]
   [log.date|date:        Thu Jan 01 00:00:00 1970 +0000]
+  [log.obsfate|obsfate:     pruned]
   [log.summary|summary:     add obsolete_e]