storageutil: invert logic of file data comparison IMO things make more sense when the function is explicitly a test for file data equivalence. Not bothering with API since the function was introduced by the previous commit. Differential Revision: https://phab.mercurial-scm.org/D4802

storageutil: extract filelog.cmp() to a standalone function As part of implementing an alternate storage backend, I found myself reimplementing this code. With a little massaging, we can extract filelog.cmp() to a standalone function. As part of this, the call to revlog.cmp() was inlined (it is just a 2-line function). I also tweaked some variable names to improve readability. I'll further tweak names in a subsequent commit. Differential Revision: https://phab.mercurial-scm.org/D4801

storageutil: extract copy metadata retrieval out of filelog As part of implementing an alternate storage backend, I found myself reinventing this wheel. Let's create a utility function for doing the work. Differential Revision: https://phab.mercurial-scm.org/D4800

storageutil: extract functionality for resolving strip revisions I found myself having to copy this method as part of implementing a new storage backend. With a little tweaking, we can extract it to a standalone function so it can be reused easily. We'll likely want to implement a better method for removing revisions on the storage interface someday. But until then, let's use what we have. Differential Revision: https://phab.mercurial-scm.org/D4799

storageutil: consistently raise LookupError (API) The interface docs say this is supposed to raise LookupError on failure. But for invalid revision number input, it could raise IndexError because ifileindex.node() is documented to raise IndexError. lookup() for files isn't used that much (pretty much just in basefilectx in core AFAICT). And callers should already be catching LookupError. So I don't anticipate that much fallout from this change. Differential Revision: https://phab.mercurial-scm.org/D4798

storageutil: implement file identifier resolution method (BC) revlog.lookup() has a number of advanced features, including partial node matching. These advanced features aren't needed for file id lookup because file identifiers are almost always from internal sources. (An exception to this is hgweb, which appears to have some code paths that attempt to resolve a user-supplied string to a node.) This commit implements a new function for resolving file identifiers to nodes. It behaves like revlog.lookup() but without the advanced features. Tests reveal behavior changes: * Partial hex nodes are no longer resolved to nodes. * "-1" now returns nullid instead of raising LookupError. * "0" on an empty store now raises LookupError instead of returning nullid. I'm not sure why "-1" wasn't recognized before. But it seems reasonable to accept it as a value since integer -1 resolves to nullid. These changes all seem reasonable to me. And with the exception of partial hex node matching, we may want to consider changing revlog.lookup() as well. Differential Revision: https://phab.mercurial-scm.org/D4797

testing: add more testing for ifileindex.lookup() The tests demonstrate some... questionable behavior of revlog.lookup(). Differential Revision: https://phab.mercurial-scm.org/D4796

dagop: extract DAG local heads functionality from revlog As part of implementing an alternate storage backend, I found myself having to reimplement this function. The DAG traversal logic is generic and can be factored out into a standalone function. We could probably combine this with headrevs(). But I'll leave that for another time. Differential Revision: https://phab.mercurial-scm.org/D4795