filelog: wrap revlog instead of inheriting it (API) The revlog base class exposes a ton of methods. Inheriting the revlog class for filelog will make it difficult to expose a clean interface. There will be abstraction violations. This commit breaks the inheritance of revlog by the filelog class. Filelog instances now contain a reference to a revlog instance. Various properties and methods are now proxied to that instance. There is precedence for doing this: manifestlog does something similar. Although, manifestlog has a cleaner interface than filelog. We'll get there with filelog... The new filelog class exposes a handful of extra properties and methods that aren't part of the declared filelog interface. Every extra item was added in order to get a test to pass. The set of tests that failed without these extra proxies has significant overlap with the set of tests that don't work with the simple store repo. There should be no surprise there. Hopefully the hardest part about this commit to review are the changes to bundlerepo and unionrepo. Both repository types define a custom revlog or revlog-like class and then have a custom filelog that inherits from both filelog and their custom revlog. This code has been changed so the filelog types don't inherit from revlog. Instead, they replace the revlog instance on the created filelog. This is super hacky. I plan to fix this in a future commit by parameterizing filelog.__init__. Because Python function call overhead is a thing, this change could impact performance by introducing a nearly empty proxy function for various methods and properties. I would gladly measure the performance impact of it, but I'm not sure what operations have tight loops over filelog attribute lookups or function calls. I know some of the DAG traversal code can be sensitive about the performance of e.g. parentrevs(). However, many of these functions are implemented on the revlog class and therefore have direct access to self.parentrevs() and aren't going through a proxy. .. api:: filelog.filelog is now a standalone class and doesn't inherit from revlog. Instead, it wraps a revlog instance at self._revlog. This change was made in an attempt to formalize storage APIs and prevent revlog implementation details leaking through to callers. Differential Revision: https://phab.mercurial-scm.org/D3154