D4563: localrepo: create new function for instantiating a local repo object

indygreg (Gregory Szorc) phabricator at mercurial-scm.org
Thu Sep 13 16:30:04 UTC 2018


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

REVISION SUMMARY
  Today, there is a single local repository class - localrepository. Its
  __init__ is responsible for loading the .hg/requires file and taking
  different actions depending on what is present.
  
  In addition, extensions may define a "reposetup" function that
  monkeypatches constructed repository instances, often by implementing
  a derived type and changing the __class__ of the repo instance.
  
  Work around alternate storage backends and partial clone has made it
  clear to me that shoehorning all this logic into __init__ and operating
  on an existing instance is too convoluted. For example, localrepository
  assumes revlog storage and swapping in non-revlog storage requires
  overriding e.g. file() to return something that isn't a revlog. I've
  authored various patches that either:
  
  a) teach various methods (like file()) about different states and
  
    taking the appropriate code path at run-time
  
  b) create methods/attributes/callables used for instantiating things
  
    and populating these in __init__
  
  "a" incurs run-time performance penalties and makes code more
  complicated since various functions have a bunch of "if storage is X"
  branches.
  
  "b" makes localrepository quickly explode in complexity.
  
  My plan for tackling this problem is to make the local repository type
  more dynamic. Instead of a static localrepository class/type that
  supports all of the local repository configurations (revlogs vs other,
  revlogs with ellipsis, revlog v1 versus revlog v2, etc), we'll
  dynamically construct a type providing the implementations that are
  needed for the repository on disk, derived from the .hg/requires file
  and configuration options. The constructed repository type will be
  specialized and methods won't need to be taught about different
  implementations nor overloaded.
  
  We may also leverage this functionality for building types that don't
  implement all attributes. For example, the "intents" feature allows
  commands to declare that they are read only. By dynamically
  constructing a repository type, we could return a repository instance
  with no attributes related to mutating the repository. This could
  include things like a "changelog" property implementation that doesn't
  check whether it needs to invalidate the hidden revisions set on every
  access.
  
  This commit establishes a function for building a local repository
  instance. Future commits will start moving functionality from
  localrepository.__init__ to this function. Then we'll start dynamically
  changing the returned type depending on options that are present.
  
  This change may seem radical. But it should be fully compatible with
  the reposetup() model - at least for now.

REPOSITORY
  rHG Mercurial

REVISION DETAIL
  https://phab.mercurial-scm.org/D4563

AFFECTED FILES
  mercurial/localrepo.py
  tests/test-check-interfaces.py

CHANGE DETAILS

diff --git a/tests/test-check-interfaces.py b/tests/test-check-interfaces.py
--- a/tests/test-check-interfaces.py
+++ b/tests/test-check-interfaces.py
@@ -144,7 +144,7 @@
 
     ziverify.verifyClass(repository.completelocalrepository,
                          localrepo.localrepository)
-    repo = localrepo.localrepository(ui, rootdir)
+    repo = localrepo.makelocalrepository(ui, rootdir)
     checkzobject(repo)
 
     ziverify.verifyClass(wireprototypes.baseprotocolhandler,
diff --git a/mercurial/localrepo.py b/mercurial/localrepo.py
--- a/mercurial/localrepo.py
+++ b/mercurial/localrepo.py
@@ -376,6 +376,18 @@
 # set to reflect that the extension knows how to handle that requirements.
 featuresetupfuncs = set()
 
+def makelocalrepository(ui, path, intents=None):
+    """Create a local repository object.
+
+    Given arguments needed to construct a local repository, this function
+    derives a type suitable for representing that repository and returns an
+    instance of it.
+
+    The returned object conforms to the ``repository.completelocalrepository``
+    interface.
+    """
+    return localrepository(ui, path, intents=intents)
+
 @interfaceutil.implementer(repository.completelocalrepository)
 class localrepository(object):
 
@@ -2381,7 +2393,7 @@
     if create:
         createrepository(ui, localpath, createopts=createopts)
 
-    return localrepository(ui, localpath, intents=intents)
+    return makelocalrepository(ui, localpath, intents=intents)
 
 def islocal(path):
     return True



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