localrepo: iteratively derive local repository type This commit implements the dynamic local repository type derivation that was explained in the recent commit bfeab472e3c0 "localrepo: create new function for instantiating a local repo object." Instead of a static localrepository class/type which must be customized after construction, we now dynamically construct a type by building up base classes/types to represent specific repository interfaces. Conceptually, the end state is similar to what was happening when various extensions would monkeypatch the __class__ of newly-constructed repo instances. However, the approach is inverted. Instead of making the instance then customizing it, we do the customization up front by influencing the behavior of the type then we instantiate that custom type. This approach gives us much more flexibility. For example, we can use completely separate classes for implementing different aspects of the repository. For example, we could have one class representing revlog-based file storage and another representing non-revlog based file storage. When then choose which implementation to use based on the presence of repo requirements. A concern with this approach is that it creates a lot more types and complexity and that complexity adds overhead. Yes, it is true that this approach will result in more types being created. Yes, this is more complicated than traditional "instantiate a static type." However, I believe the alternatives to supporting alternate storage backends are just as complicated. (Before I arrived at this solution, I had patches storing factory functions on local repo instances for e.g. constructing a file storage instance. We ended up having a handful of these. And this was logically identical to assigning custom methods. Since we were logically changing the type of the instance, I figured it would be better to just use specialized types instead of introducing levels of abstraction at run-time.) On the performance front, I don't believe that having N base classes has any significant performance overhead compared to just a single base class. Intuition says that Python will need to iterate the base classes to find an attribute. However, CPython caches method lookups: as long as the __class__ or MRO isn't changing, method attribute lookup should be constant time after first access. And non-method attributes are stored in __dict__, of which there is only 1 per object, so the number of base classes for __dict__ is irrelevant. Anyway, this commit splits up the monolithic completelocalrepository interface into sub-interfaces: 1 for file storage and 1 representing everything else. We've taught ``makelocalrepository()`` to call a series of factory functions which will produce types implementing specific interfaces. It then calls type() to create a new type from the built-up list of base types. This commit should be considered a start and not the end state. I suspect we'll hit a number of problems as we start to implement alternate storage backends: * Passing custom arguments to __init__ and setting custom attributes on __dict__. * Customizing the set of interfaces that are needed. e.g. the "readonly" intent could translate to not requesting an interface providing methods related to writing. * More ergonomic way for extensions to insert themselves so their callbacks aren't unconditionally called. * Wanting to modify vfs instances, other arguments passed to __init__. That being said, this code is usable in its current state and I'm convinced future commits will demonstrate the value in this approach. Differential Revision: https://phab.mercurial-scm.org/D4642

localrepo: pass root manifest into manifestlog.__init__ Today, localrepository has a method that can be overloaded which returns an instance of the root manifest storage object. When a manifestlog is created, it calls this private method and stores the root manifest object on it. This "hook" on localrepository isn't part of the documented interface. It isn't compatible with our desire to make repo storage determined before the repo object is constructed. This commit changes manifestlog.__init__ to accept the root storage object instead of calling into the repo to construct it. By doing things this way, the repo instance is responsible for constructing the manifest storage object directly. This does mean that other derived repo types need to overload manifestlog(). But they should have been doing this already, as manifestlog() is typically decorated in a storage-specific way. e.g. localrepository.manifestlog() is decorated as @storecache('00manifest.i'). And this assumes that a 00manifest.i file exists in the store vfs. This condition may not hold for repository types using non-revlog storage. So it is important for special repo types to override manifestlog() to remove this file association. The code changed in perf is wrong because it isn't compatible with older Mercurial versions. But I'm pretty sure the code was broken on older versions before this commit. It only affects `hg perftags`. I don't care enough to fix that at this time. .. api:: ``manifest.manifestlog.__init__()`` now receives the root manifest storage instance instead of calling into a private method on the repo object to obtain it. Differential Revision: https://phab.mercurial-scm.org/D4641