rebase: allow rebase to ancestor (issue3010)

We only deny rebasing onto direct parent. Thanks to the ancestor argument of
merge. the "implementation" of this feature only consist in loosing the check
and imply detach when rebasing on ancestor.

hgext/rebase.py

@@ -536,11 +536,14 b' def buildstate(repo, dest, src, base, de'
 
     if src:
         commonbase = repo[src].ancestor(repo[dest])
-        samebranch = repo[src].branch() == repo[dest].branch()
         if commonbase == repo[src]:
             raise util.Abort(_('source is ancestor of destination'))
-        if samebranch and commonbase == repo[dest]:
-            raise util.Abort(_('source is descendant of destination'))
+        if commonbase == repo[dest]:
+            samebranch = repo[src].branch() == repo[dest].branch()
+            if samebranch and repo[src] in repo[dest].children():
+                raise util.Abort(_('source is a child of destination'))
+            # rebase on ancestor, force detach
+            detach = True
         source = repo[src].rev()
         if detach:
             # We need to keep track of source's ancestors up to the common base

tests/test-rebase-detach.t

@@ -281,3 +281,25 b' Rebasing across null as ancestor'
   |/
   o  0: 'A'
   
+
+  $ hg rebase -d 5 -s 7
+  saved backup bundle to $TESTTMP/a5/.hg/strip-backup/13547172c9c0-backup.hg
+  $ hg tglog
+  @  8: 'D'
+  |
+  o  7: 'C'
+  |
+  | o  6: 'B'
+  |/
+  o  5: 'extra branch'
+  
+  o  4: 'H'
+  |
+  | o  3: 'G'
+  |/|
+  o |  2: 'F'
+  | |
+  | o  1: 'E'
+  |/
+  o  0: 'A'
+  

tests/test-rebase-parameters.t

@@ -51,7 +51,7 b' These fail:'
   $ cd a1
 
   $ hg rebase -s 8 -d 7
-  abort: source is descendant of destination
+  abort: source is a child of destination
   [255]
 
   $ hg rebase --continue --abort

tests/test-rebase-scenario-global.t

@@ -212,7 +212,7 b' G onto F - rebase onto an ancestor:'
   $ cd a7
 
   $ hg rebase -s 6 -d 5
-  abort: source is descendant of destination
+  abort: source is a child of destination
   [255]
 
 F onto G - rebase onto a descendant:
@@ -248,3 +248,25 b' F onto G - rebase onto a descendant:'
   nothing to rebase
   [1]
 
+C onto A - rebase onto an ancestor:
+
+  $ hg rebase -d 0 -s 2
+  saved backup bundle to $TESTTMP/a7/.hg/strip-backup/5fddd98957c8-backup.hg
+  $ hg tglog
+  @  7: 'D'
+  |
+  o  6: 'C'
+  |
+  | o  5: 'H'
+  | |
+  | | o  4: 'G'
+  | |/|
+  | o |  3: 'F'
+  |/ /
+  | o  2: 'E'
+  |/
+  | o  1: 'B'
+  |/
+  o  0: 'A'
+  
+