--- a/CHANGELOG	Wed Jan 01 21:36:21 2020 +0530
+++ b/CHANGELOG	Mon Nov 04 01:30:50 2019 +0530
@@ -11,6 +11,8 @@
   * obslog: make templatable
   * compat: cleanup some compatibility code for mercurial < 4.5
   * compat: compatibility with some changes of the upcoming Mercurial 5.3
+  * evolve: add content divergence checking to the standard pre-rewrite check,
+  * evolve: improve the message associated with content divergence.
 
 9.2.2 - in progress
 -------------------

--- a/hgext3rd/evolve/rewriteutil.py	Wed Jan 01 21:36:21 2020 +0530
+++ b/hgext3rd/evolve/rewriteutil.py	Mon Nov 04 01:30:50 2019 +0530
@@ -77,6 +77,31 @@
         msg %= (action, len(newunstable))
         hint = _(b"see 'hg help evolution.instability'")
         raise error.Abort(msg, hint=hint)
+    divrisk = revs_hascontentdivrisk(repo, revs)
+    allowdivergence = repo.ui.configbool(b'experimental',
+                                         b'evolution.allowdivergence')
+    if divrisk and not allowdivergence:
+        localdiv = repo[divrisk[0]]
+        otherdiv, base = repo[divrisk[1][0]], repo[divrisk[1][1]]
+        msg = _(b"%s of %s creates content-divergence "
+                b"with %s") % (action, localdiv, otherdiv)
+        if localdiv.rev() != base.rev():
+            msg += _(b', from %s') % base
+        hint = _(b"add --verbose for details or see "
+                 b"'hg help evolution.instability'")
+        if repo.ui.verbose:
+            if localdiv.rev() != base.rev():
+                msg += _(b'\n    changeset %s is an evolution of '
+                         b'changeset %s') % (localdiv, base)
+            msg += _(b'\n    changeset %s already have a successors as '
+                     b'changeset %s\n'
+                     b'    rewriting changeset %s would create '
+                     b'"content-divergence"\n'
+                     b'    set experimental.evolution.allowdivergence=True to '
+                     b'overwrite this check') % (base, otherdiv, localdiv)
+            hint = _(b"see 'hg help evolution.instability' for details "
+                     b"on content-divergence")
+        raise error.Abort(msg, hint=hint)
 
 def bookmarksupdater(repo, oldid, tr):
     """Return a callable update(newid) updating the current bookmark
@@ -89,6 +114,14 @@
             repo._bookmarks.applychanges(repo, tr, bmchanges)
     return updatebookmarks
 
+def revs_hascontentdivrisk(repo, revs):
+    obsrevs = repo.revs(b'%ld and obsolete()', revs)
+    for r in obsrevs:
+        div = precheck_contentdiv(repo, repo[r])
+        if div:
+            return [r, div]
+    return []
+
 def disallowednewunstable(repo, revs):
     """Check that editing <revs> will not create disallowed unstable
 
@@ -257,10 +290,12 @@
         lockmod.release(tr, lock, wlock)
 
 def precheck_contentdiv(repo, ctx):
-    """logic to check if rewriting an obsolete cset will create divergence"""
+    """return divergent revision if rewriting an obsolete cset (ctx) will
+    create divergence"""
     # We need to check two cases that can cause divergence:
     # case 1: the rev being rewritten has a non-obsolete successor (easily
     #     detected by successorssets)
+    divergent = [] # contains [divergent_cset, common_precursor]
     sset = obsutil.successorssets(repo, ctx.node())
     nodivergencerisk = (len(sset) == 0
                         or (len(sset) == 1
@@ -271,6 +306,13 @@
         # case 2: one of the precursors of the rev being revived has a
         #     non-obsolete successor (we need divergentsets for this)
         from . import evolvecmd
-        if evolvecmd.divergentsets(repo, ctx):
-            nodivergencerisk = False
-    return not nodivergencerisk
+        divsets = evolvecmd.divergentsets(repo, ctx)
+        if divsets:
+            nsuccset = divsets[0][b'divergentnodes']
+            divergent.append(nsuccset[0])
+            prec = divsets[0][b'commonprecursor']
+            divergent.append(prec)
+    else:
+        divergent.append(sset[0][0])
+        divergent.append(ctx.node())
+    return divergent

--- a/tests/test-amend.t	Wed Jan 01 21:36:21 2020 +0530
+++ b/tests/test-amend.t	Mon Nov 04 01:30:50 2019 +0530
@@ -121,6 +121,9 @@
   update: (current)
   phases: 3 draft
 
+setting the user after we have performed the test with no username
+  $ HGUSER=test
+
 Check the help
   $ hg amend -h
   hg amend [OPTION]... [FILE]...
@@ -170,3 +173,63 @@
   $ hg amend --patch --extract
   abort: cannot use both --patch and --extract
   [255]
+
+  $ cd ..
+
+Check the pre-check logic for content-divergence
+  $ hg init precheckrepo
+  $ cd precheckrepo
+  $ echo a > a
+  $ hg ci -Am "added a"
+  adding a
+  $ echo newchanges > a
+  $ hg amend
+  $ hg up 0 --hidden -q
+  updated to hidden changeset 9092f1db7931
+  (hidden revision '9092f1db7931' was rewritten as: aafaf407b00d)
+  working directory parent is obsolete! (9092f1db7931)
+
+when rewritting an already rewritten changeset (i.e cset being rewritten will
+be the base of divergence)
+  $ hg amend -m "i am gonna create divergence"
+  abort: amend of 9092f1db7931 creates content-divergence with aafaf407b00d
+  (add --verbose for details or see 'hg help evolution.instability')
+  [255]
+  $ hg amend -m "i am gonna create divergence" --verbose
+  abort: amend of 9092f1db7931 creates content-divergence with aafaf407b00d
+      changeset 9092f1db7931 already have a successors as changeset aafaf407b00d
+      rewriting changeset 9092f1db7931 would create "content-divergence"
+      set experimental.evolution.allowdivergence=True to overwrite this check
+  (see 'hg help evolution.instability' for details on content-divergence)
+  [255]
+
+when rewritting a cset which has a predecessor with non-obsolete successor
+
+to prepare the repo
+1) create content-divergence
+2) remove divergence by pruning one of the divergent cset
+  $ echo edited_a > a
+  $ hg ci -m "edited a"
+  1 new orphan changesets
+  $ hg debugobsolete $(hg id -ir 0 --debug) $(hg id -ir 2 --debug)
+  1 new obsolescence markers
+  2 new content-divergent changesets
+
+remove divergence by pruning one side of divergenence
+  $ hg debugobsolete $(hg id -ir 2 --debug)
+  1 new obsolescence markers
+  obsoleted 1 changesets
+
+  $ hg evolve -l
+  $ hg amend -m "i am gonna create divergence"
+  abort: amend of f8c05838af90 creates content-divergence with aafaf407b00d, from 9092f1db7931
+  (add --verbose for details or see 'hg help evolution.instability')
+  [255]
+  $ hg amend -m "i am gonna create divergence" --verbose
+  abort: amend of f8c05838af90 creates content-divergence with aafaf407b00d, from 9092f1db7931
+      changeset f8c05838af90 is an evolution of changeset 9092f1db7931
+      changeset 9092f1db7931 already have a successors as changeset aafaf407b00d
+      rewriting changeset f8c05838af90 would create "content-divergence"
+      set experimental.evolution.allowdivergence=True to overwrite this check
+  (see 'hg help evolution.instability' for details on content-divergence)
+  [255]

--- a/tests/test-evolve-content-divergent-basic.t	Wed Jan 01 21:36:21 2020 +0530
+++ b/tests/test-evolve-content-divergent-basic.t	Mon Nov 04 01:30:50 2019 +0530
@@ -21,6 +21,8 @@
   > unified = 0
   > [ui]
   > logtemplate = {rev}:{node|short}@{branch}({phase}) {desc|firstline} [{instabilities}]\n
+  > [experimental]
+  > evolution.allowdivergence = True
   > [extensions]
   > EOF
   $ echo "evolve=$(echo $(dirname $TESTDIR))/hgext3rd/evolve/" >> $HGRCPATH

--- a/tests/test-evolve-content-divergent-corner-cases.t	Wed Jan 01 21:36:21 2020 +0530
+++ b/tests/test-evolve-content-divergent-corner-cases.t	Mon Nov 04 01:30:50 2019 +0530
@@ -21,6 +21,8 @@
   > unified = 0
   > [ui]
   > logtemplate = {rev}:{node|short}@{branch}({phase}) {desc|firstline} [{instabilities}]\n
+  > [experimental]
+  > evolution.allowdivergence = True
   > [extensions]
   > EOF
   $ echo "evolve=$(echo $(dirname $TESTDIR))/hgext3rd/evolve/" >> $HGRCPATH

--- a/tests/test-evolve-content-divergent-first-changeset.t	Wed Jan 01 21:36:21 2020 +0530
+++ b/tests/test-evolve-content-divergent-first-changeset.t	Mon Nov 04 01:30:50 2019 +0530
@@ -1,6 +1,11 @@
   $ . $TESTDIR/testlib/pythonpath.sh
-  $ echo "[extensions]" >> $HGRCPATH
-  $ echo "evolve=" >> $HGRCPATH
+  $ cat >> $HGRCPATH << EOF
+  > [extensions]
+  > evolve=
+  > [experimental]
+  > evolution.allowdivergence = True
+  > EOF
+
 
 This test file tests the case of content-divergence resolution of changesets
 that have the null revision as the parent.

--- a/tests/test-evolve-content-divergent-interrupted.t	Wed Jan 01 21:36:21 2020 +0530
+++ b/tests/test-evolve-content-divergent-interrupted.t	Mon Nov 04 01:30:50 2019 +0530
@@ -24,6 +24,8 @@
   > publish = False
   > [alias]
   > glog = log -GT "{rev}:{node|short} {desc}\n ({bookmarks}) {phase}"
+  > [experimental]
+  > evolution.allowdivergence = True
   > [extensions]
   > EOF
   $ echo "evolve=$(echo $(dirname $TESTDIR))/hgext3rd/evolve/" >> $HGRCPATH

--- a/tests/test-evolve-content-divergent-meta.t	Wed Jan 01 21:36:21 2020 +0530
+++ b/tests/test-evolve-content-divergent-meta.t	Mon Nov 04 01:30:50 2019 +0530
@@ -12,6 +12,8 @@
   > glog = log -GT "{rev}:{node|short} {desc|firstline}\n {phase} {instabilities}\n\n"
   > [phases]
   > publish = False
+  > [experimental]
+  > evolution.allowdivergence = True
   > [extensions]
   > rebase =
   > strip =

--- a/tests/test-evolve-obshistory-content-divergent.t	Wed Jan 01 21:36:21 2020 +0530
+++ b/tests/test-evolve-obshistory-content-divergent.t	Mon Nov 04 01:30:50 2019 +0530
@@ -5,6 +5,10 @@
 ============
 
   $ . $TESTDIR/testlib/obshistory_setup.sh
+  $ cat >> $HGRCPATH << EOF
+  > [experimental]
+  > evolution.allowdivergence = True
+  > EOF
 
 Test output with content-divergence
 ===================================

--- a/tests/test-evolve-order.t	Wed Jan 01 21:36:21 2020 +0530
+++ b/tests/test-evolve-order.t	Mon Nov 04 01:30:50 2019 +0530
@@ -15,6 +15,8 @@
   > unified = 0
   > [ui]
   > logtemplate = {rev}:{node|short}@{branch}({phase}) {desc|firstline}\n
+  > [experimental]
+  > evolution.allowdivergence = True
   > [extensions]
   > EOF
   $ echo "evolve=$(echo $(dirname $TESTDIR))/hgext3rd/evolve/" >> $HGRCPATH

--- a/tests/test-evolve-public-content-divergent-corner-cases.t	Wed Jan 01 21:36:21 2020 +0530
+++ b/tests/test-evolve-public-content-divergent-corner-cases.t	Mon Nov 04 01:30:50 2019 +0530
@@ -12,6 +12,8 @@
   > glog = log -GT "{rev}:{node|short} {desc|firstline}\n {phase} {instabilities}\n\n"
   > [phases]
   > publish = False
+  > [experimental]
+  > evolution.allowdivergence = True
   > [extensions]
   > rebase =
   > EOF

--- a/tests/test-evolve-public-content-divergent-discard.t	Wed Jan 01 21:36:21 2020 +0530
+++ b/tests/test-evolve-public-content-divergent-discard.t	Mon Nov 04 01:30:50 2019 +0530
@@ -17,6 +17,8 @@
   > glog = log -GT "{rev}:{node|short} {desc|firstline}\n {phase} {instabilities}\n\n"
   > [phases]
   > publish = False
+  > [experimental]
+  > evolution.allowdivergence = True
   > [extensions]
   > rebase =
   > EOF

--- a/tests/test-evolve-public-content-divergent-main.t	Wed Jan 01 21:36:21 2020 +0530
+++ b/tests/test-evolve-public-content-divergent-main.t	Mon Nov 04 01:30:50 2019 +0530
@@ -15,6 +15,8 @@
   > glog = log -GT "{rev}:{node|short} {desc|firstline}\n {phase} {instabilities}\n\n"
   > [phases]
   > publish = False
+  > [experimental]
+  > evolution.allowdivergence = True
   > [extensions]
   > rebase =
   > EOF

--- a/tests/test-evolve-templates.t	Wed Jan 01 21:36:21 2020 +0530
+++ b/tests/test-evolve-templates.t	Mon Nov 04 01:30:50 2019 +0530
@@ -9,6 +9,8 @@
   > interactive = true
   > [phases]
   > publish=False
+  > [experimental]
+  > evolution.allowdivergence = True
   > [extensions]
   > evolve =
   > [alias]

--- a/tests/test-fold.t	Wed Jan 01 21:36:21 2020 +0530
+++ b/tests/test-fold.t	Mon Nov 04 01:30:50 2019 +0530
@@ -405,8 +405,8 @@
 
   $ hg fold --exact -r 'desc("A")::desc("B")' -m 'second fold' \
   >         --config experimental.evolution.allowdivergence=no
-  abort: folding obsolete revisions may cause divergence
-  (set experimental.evolution.allowdivergence=yes to allow folding them)
+  abort: fold of 4b34ecfb0d56 creates content-divergence with fcfd42a7fa46
+  (add --verbose for details or see 'hg help evolution.instability')
   [255]
 
 but if we allow divergence, this should work and should create new content-divergent changesets

--- a/tests/test-topic-stack-complex.t	Wed Jan 01 21:36:21 2020 +0530
+++ b/tests/test-topic-stack-complex.t	Mon Nov 04 01:30:50 2019 +0530
@@ -7,6 +7,7 @@
   $ cat << EOF >> $HGRCPATH
   > [experimental]
   > evolution = all
+  > evolution.allowdivergence = True
   > [ui]
   > interactive = True
   > [extensions]

--- a/tests/test-touch.t	Wed Jan 01 21:36:21 2020 +0530
+++ b/tests/test-touch.t	Mon Nov 04 01:30:50 2019 +0530
@@ -6,6 +6,8 @@
   > amend=-d "0 0"
   > [alias]
   > glog = log -GT "{rev}: {desc}"
+  > [experimental]
+  > evolution.allowdivergence = True
   > [extensions]
   > hgext.rebase=
   > EOF

--- a/tests/test-uncommit.t	Wed Jan 01 21:36:21 2020 +0530
+++ b/tests/test-uncommit.t	Mon Nov 04 01:30:50 2019 +0530
@@ -1,4 +1,6 @@
   $ cat >> $HGRCPATH <<EOF
+  > [experimental]
+  > evolution.allowdivergence = True
   > [extensions]
   > EOF
   $ echo "evolve=$(echo $(dirname $TESTDIR))/hgext3rd/evolve/" >> $HGRCPATH