context: move reuse of context object to repo.__getitem__ (API) As an example of how weird the basectx.__new__ is: whenever you create a workingctx, basectx.__new__ gets called first. Since our __new__ has a "changeid" argument as second parameter, when create the workingctx(repo, text="blah"), the text gets bound to "changeid". Since a string isn't a basectx, our __new__ ends up not doing anything funny, but that's still very confusing code. Another case is metadataonlyctx.__new__(), which I think exists in order to prevent metadataonlyctx.__init__'s third argument (originalctx) from being interpreted as a changeid in basectx.__new__(), thereby getting reused. Let's move this to repo.__getitem__ instead, where it will be pretty obvious what the code does. After this patch, changectx(ctx) will be an error (it will fail when trying to see if it's a 20-byte string). Differential Revision: https://phab.mercurial-scm.org/D2969

--- a/mercurial/localrepo.py	Thu Mar 29 22:22:51 2018 -0700
+++ b/mercurial/localrepo.py	Thu Mar 29 22:51:45 2018 -0700
@@ -782,6 +782,8 @@
     def __getitem__(self, changeid):
         if changeid is None:
             return context.workingctx(self)
+        if isinstance(changeid, context.basectx):
+            return changeid
         if isinstance(changeid, slice):
             # wdirrev isn't contiguous so the slice shouldn't include it
             return [context.changectx(self, i)