diff mercurial/repository.py @ 39231:b41d023a412a

repository: establish API for emitting revision deltas

With our revision delta and revision delta request interfaces
defined, it is now time to define a method on storage interfaces
for using them.

So far, the only storage interface that is well-defined and used
is file storage. So that is the only interface we need to add a
method on.

We define an ``emitrevisiondeltas()`` method that takes an
iterable of ``irevisiondeltarequest``s and turns them into
``irevisiondelta`` instances.

changegroup._handlerevisiondeltarequest() and the looping logic
from changegroup.deltagroup() has effectively been moved to
revlog.emitrevisiondeltas().

Our filelog wrapper class proxies its emitrevisiondeltas() to
the internal revlog instance.

The simple store test extension used to verify sanity of storage
abstractions has also implemented emitrevisiondeltas() for
file storage and the test harness when run with this extension doesn't
seem to exhibit any regressions.

Rather than create a shared type to represent revision deltas,
each storage backend has its own type and the class name identifies
where the revision delta was derived from.

Differential Revision: https://phab.mercurial-scm.org/D4226

--- a/mercurial/repository.py	Thu Aug 09 15:40:14 2018 -0700
+++ b/mercurial/repository.py	Thu Aug 09 16:02:14 2018 -0700
@@ -621,6 +621,30 @@
         revision data.
         """
 
+    def emitrevisiondeltas(requests):
+        """Produce ``irevisiondelta`` from ``irevisiondeltarequest``s.
+
+        Given an iterable of objects conforming to the ``irevisiondeltarequest``
+        interface, emits objects conforming to the ``irevisiondelta``
+        interface.
+
+        This method is a generator.
+
+        ``irevisiondelta`` should be emitted in the same order of
+        ``irevisiondeltarequest`` that was passed in.
+
+        The emitted objects MUST conform by the results of
+        ``irevisiondeltarequest``. Namely, they must respect any requests
+        for building a delta from a specific ``basenode`` if defined.
+
+        When sending deltas, implementations must take into account whether
+        the client has the base delta before encoding a delta against that
+        revision. A revision encountered previously in ``requests`` is
+        always a suitable base revision. An example of a bad delta is a delta
+        against a non-ancestor revision. Another example of a bad delta is a
+        delta against a censored revision.
+        """
+
 class ifilemutation(interfaceutil.Interface):
     """Storage interface for mutation events of a tracked file."""