match: override matchfn instead of __call__ for consistency The matchers that were recently moved into core from the sparse extension override __call__, while the previously existing matchers override matchfn. Let's switch to the latter for consistency.

match: express anypats(), not prefix(), in terms of the others When I added prefix() in 9789b4a7c595 (match: introduce boolean prefix() method, 2014-10-28), we already had always(), isexact(), and anypats(), so it made sense to write it in terms of them (a prefix matcher is one that isn't any of the other types). It's only now that I realize that it's much more natural to define prefix() explicitly (it's one that uses path: patterns, roughly speaking) and let anypats() be defined in terms of the others. Remember that these methods are all used for determining which fast paths are possible. anypats() simply means that no fast paths are possible (it could be called complex() instead). Further evidence is that rootfilesin:some/dir does not have any patterns, but it's still considered to be an anypats() matcher. That's because anypats() really just means that it's not a prefix() matcher (and not always() and not isexact()). This patch thus changes prefix() to return False by default and anypats() to return True only if the other three are False. Having anypats() be True by default also seems like a good thing, because it means forgetting to override it will lead only to performance bugs, not correctness bugs. Since the base class's implementation changes, we're also forced to update the subclasses. That change exposed and fixed a bug in the differencematcher: for example when both its two input matchers were prefix matchers, we would say that the result was also a prefix matcher, which is incorrect, because e.g "path:dir - path:dir/foo" no longer matches everything under "dir" (which is what prefix() means).

match: make nevermatcher an exact matcher and a prefix matcher The m.isexact() and m.prefix() methods are used by callers to determine whether m.files() can be used for fast paths. It seems safe to let callers to any fast paths it can that rely on the empty m.files().

revset: define successors revset This revset returns all successors, including transit nodes and the source nodes (to be consistent with existing revsets like "ancestors"). To filter out transit nodes, use `successors(X)-obsolete()`. To filter out divergent case, use `successors(X)-divergent()-obsolete()`. The revset could be useful to define rebase destination, like: `max(successors(BASE)-divergent()-obsolete())`. The `max` is to deal with splits. There are other implementations where `successors` returns just one level of successors, and `allsuccessors` returns everything. I think `successors` returning all successors by default is more user friendly. We have seen cases in production where people use 1-level `successors` while they really want `allsuccessors`. So it seems better to just have one single revset returning all successors by default to avoid user errors. In the future we might want to add `depth` keyword argument to it and for other revsets like `ancestors` etc. Or even build some flexible indexing syntax [1] to satisfy people having the depth limit requirement. [1]: https://www.mercurial-scm.org/pipermail/mercurial-devel/2017-July/101140.html

sparse: shorten try..except block in updateconfig() It now only covers refreshwdir(). This is what importfromfiles() does. I think it is the more appropriate behavior.

sparse: clean up updateconfig() * Use context manager for wlock * Rename oldsparsematch to oldmatcher * Always call parseconfig() because parsing an empty string yields the same result as the old code