D4557: hg: don't reuse repo instance after unshare()

[indygreg (Gregory Szorc)]

indygreg created this revision.
Herald added a subscriber: mercurial-devel.
Herald added a reviewer: hg-reviewers.

REVISION SUMMARY
  Unsharing a repository is a pretty invasive procedure and fundamentally
  changes the behavior of the repository.
  
  Currently, hg.unshare() calls into localrepository.__init__ to
  re-initialize the repository instance. This is a bit hacky. And
  future commits that refactor how localrepository instances are
  constructed will make this difficult to support.
  
  This commit changes unshare() so it constructs a new repo instance
  once the unshare I/O has completed. It then poisons the old repo
  instance so any further use will result in error.
  
  Surprisingly, nothing in core appears to access a repo instance
  after it has been unshared!
  
  .. api::
  
    ``hg.unshare()`` now poisons the repo instance so it can't be used.
    
    It also returns a new repo instance suitable for interacting with
    the unshared repository.

REPOSITORY
  rHG Mercurial

REVISION DETAIL
  https://phab.mercurial-scm.org/D4557

AFFECTED FILES
  mercurial/hg.py
  mercurial/localrepo.py

CHANGE DETAILS

diff --git a/mercurial/localrepo.py b/mercurial/localrepo.py
--- a/mercurial/localrepo.py
+++ b/mercurial/localrepo.py
@@ -2503,3 +2503,28 @@
                      b'layout')
 
     scmutil.writerequires(hgvfs, requirements)
+
+def poisonrepository(repo):
+    """Poison a repository instance so it can no longer be used."""
+    # Perform any cleanup on the instance.
+    repo.close()
+
+    # Our strategy is to replace the type of the object with one that
+    # has all attribute lookups result in error.
+    #
+    # But we have to allow the close() method because some constructors
+    # of repos call close() on repo references.
+    class poisonedrepository(object):
+        def __getattribute__(self, item):
+            if item == r'close':
+                return object.__getattribute__(self, item)
+
+            raise error.ProgrammingError('repo instances should not be used '
+                                         'after unshare')
+
+        def close(self):
+            pass
+
+    # We may have a repoview, which intercepts __setattr__. So be sure
+    # we operate at the lowest level possible.
+    object.__setattr__(repo, r'__class__', poisonedrepository)
diff --git a/mercurial/hg.py b/mercurial/hg.py
--- a/mercurial/hg.py
+++ b/mercurial/hg.py
@@ -307,6 +307,11 @@
     """convert a shared repository to a normal one
 
     Copy the store data to the repo and remove the sharedpath data.
+
+    Returns a new repository object representing the unshared repository.
+
+    The passed repository object is not usable after this function is
+    called.
     """
 
     destlock = lock = None
@@ -329,16 +334,22 @@
         destlock and destlock.release()
         lock and lock.release()
 
-    # update store, spath, svfs and sjoin of repo
-    repo.unfiltered().__init__(repo.baseui, repo.root)
+    # Removing share changes some fundamental properties of the repo instance.
+    # So we instantiate a new repo object and operate on it rather than
+    # try to keep the existing repo usable.
+    newrepo = repository(repo.baseui, repo.root, create=False)
 
     # TODO: figure out how to access subrepos that exist, but were previously
     #       removed from .hgsub
-    c = repo['.']
+    c = newrepo['.']
     subs = c.substate
     for s in sorted(subs):
         c.sub(s).unshare()
 
+    localrepo.poisonrepository(repo)
+
+    return newrepo
+
 def postshare(sourcerepo, destrepo, bookmarks=True, defaultpath=None):
     """Called after a new shared repo is created.
 



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