rebase: clean up rebasestate from active transaction

Previously, rebase assumes the following pattern:

    rebase:
        with transaction as tr: # top-level
            ...
        tr.__close__ writes rebasestate
        unlink('rebasestate')

However it's possible that "rebase" was called inside a transaction:

    with transaction as tr1:
        rebase:
            with transaction as tr2: # not top-level
                ...
            tr2.__close__ does not write rebasestate
            unlink('rebasestate')
    tr1.__close__ writes rebasestate

That leaves a rebasestate on disk incorrectly.

This patch adds "removefilegenerator" to notify transaction code that the
state file is no longer needed therefore fixes the issue.

hgext/rebase.py

@@ -1148,6 +1148,10 b' def restorecollapsemsg(repo, isabort):'
 def clearstatus(repo):
     'Remove the status files'
     _clearrebasesetvisibiliy(repo)
+    # Make sure the active transaction won't write the state file
+    tr = repo.currenttransaction()
+    if tr:
+        tr.removefilegenerator('rebasestate')
     repo.vfs.unlinkpath("rebasestate", ignoremissing=True)
 
 def needupdate(repo, state):

mercurial/transaction.py

@@ -292,6 +292,12 b' class transaction(object):'
         # but for bookmarks that are handled outside this mechanism.
         self._filegenerators[genid] = (order, filenames, genfunc, location)
 
+    @active
+    def removefilegenerator(self, genid):
+        """reverse of addfilegenerator, remove a file generator function"""
+        if genid in self._filegenerators:
+            del self._filegenerators[genid]
+
     def _generatefiles(self, suffix='', group=gengroupall):
         # write files registered for generation
         any = False

tests/test-rebase-scenario-global.t

@@ -954,4 +954,4 b' Testing rebase being called inside anoth'
   rebasing 2:dc0947a82db8 "C" (C tip)
 
   $ [ -f .hg/rebasestate ] && echo 'WRONG: rebasestate should not exist'
-  WRONG: rebasestate should not exist
+  [1]