rebase: factor out nothing to rebase return code

A rebase call that results in nothing to rebase might be considered successful
in some contexts. This factors out the return code from places where hg
determines that there is nothing to rebase, so an extenion might change this
return code to be something that would allow scripts to run without seeing this
as an error.

hgext/rebase.py

@@ -41,6 +41,9 b' command = cmdutil.command(cmdtable)'
 # leave the attribute unspecified.
 testedwith = 'internal'
 
+def _nothingtorebase():
+    return 1
+
 def _savegraft(ctx, extra):
     s = ctx.extra().get('source', None)
     if s is not None:
@@ -290,13 +293,13 b' def rebase(ui, repo, **opts):'
                 if not rebaseset:
                     ui.status(_('empty "rev" revision set - '
                                 'nothing to rebase\n'))
-                    return 1
+                    return _nothingtorebase()
             elif srcf:
                 src = scmutil.revrange(repo, [srcf])
                 if not src:
                     ui.status(_('empty "source" revision set - '
                                 'nothing to rebase\n'))
-                    return 1
+                    return _nothingtorebase()
                 rebaseset = repo.revs('(%ld)::', src)
                 assert rebaseset
             else:
@@ -304,7 +307,7 b' def rebase(ui, repo, **opts):'
                 if not base:
                     ui.status(_('empty "base" revision set - '
                                 "can't compute rebase set\n"))
-                    return 1
+                    return _nothingtorebase()
                 commonanc = repo.revs('ancestor(%ld, %d)', base, dest).first()
                 if commonanc is not None:
                     rebaseset = repo.revs('(%d::(%ld) - %d)::',
@@ -337,7 +340,7 b' def rebase(ui, repo, **opts):'
                     else: # can it happen?
                         ui.status(_('nothing to rebase from %s to %s\n') %
                                   ('+'.join(str(repo[r]) for r in base), dest))
-                    return 1
+                    return _nothingtorebase()
 
             allowunstable = obsolete.isenabled(repo, obsolete.allowunstableopt)
             if (not (keepf or allowunstable)
@@ -365,7 +368,7 b' def rebase(ui, repo, **opts):'
             if not result:
                 # Empty state built, nothing to rebase
                 ui.status(_('nothing to rebase\n'))
-                return 1
+                return _nothingtorebase()
 
             root = min(rebaseset)
             if not keepf and not repo[root].mutable():