diff: don't crash when merged-in addition is copied Similar to what was explained in the previous commit, the diff code expected copy source to be in "ctx1", which is not always the case during a merge. This has been broken since before hg 2.0. Also similar to the previous commit, we fix the problem by fixing up the copy dict.

diff: don't crash when merged-in addition was removed (issue4786) During a merge, if the user removes a file that came from parent 2 and did not exist in parent 1, the file's status will be "removed". This surprises the diff code, which crashes because it expects removed files exist in parent 1. This has been broken since 377124ba6b10 (trydiff: use 'not in addedset' for symmetry with 'not in removedset', 2014-12-23). Fix by fixing up the list of removed file, similar to how we currently fix up the list of modified and added files during a merge.

diff: move status fixup earlier, out of _filepairs() This prepares for future patches, and it also lets us remove the ugly "ctx1" argument to _filepairs() (ugly because of its assymmetry -- there's no "ctx2" argument).

graft: warn when -r is combined with revisions as positional arguments The behaviour in this case is undefined. Instead of silently doing something "random" and surprising, at least issue a warning. (This should perhaps be considered a "deprecation" and turned into an error in a future release.)

graft: clarify in help that `-r` is not just optional Positional parameters are also treated as revisions, but the order of revisions matters and it will often be wrong if the user understands it as `-r` taking multiple revisions as `-r REV1 REV2`. (Alternatively, `-r` could be turned into a no-op flag as the documentation suggests. That would however be less "semantic markup" and I agree with the implementation in 55e7f352b1d3 but not the documentation.)

streamclone: use backgroundfilecloser (issue4889) Closing files that have been appended to is slow on Windows/NTFS. CloseHandle() calls on this platform often take 1-10ms - and that's on my i7-6700K Skylake processor with a modern and fast SSD. Contrast with other I/O operations, such as writing data, which take <100us. This means that creating/appending thousands of files can add significant overhead. For example, cloning mozilla-central creates ~232,000 revlog files. Assuming 1ms per CloseHandle(), that yields 232s (3:52) of wall time waiting for file closes! The impact of this overhead can be measured most directly when applying stream clone bundles. Applying these files is effectively uncompressing a tar archive (read: it's very fast). Using a RAM disk (read: no I/O wait), the difference in wall time for a `hg debugapplystreamclonebundle` for a ~1731 MB mozilla-central bundle between Windows and Linux from the same machine is drastic: Linux: ~12.8s (128MB/s) Windows: ~352.0s (4.7MB/s) Windows is ~27.5x slower. Yikes! After this patch: Linux: ~12.8s (128MB/s) Windows: ~102.1s (16.1MB/s) Windows is now ~3.4x faster. Unfortunately, it is still ~8x slower than Linux. Profiling reveals a few hot code paths that could likely be improved. But those are for other patches. This patch introduces test-clone-uncompressed.t because existing tests of `clone --uncompressed` are scattered about and adding a variation for background thread closing to e.g. test-http.t doesn't feel correct.

streamclone: indent code This will make the subsequent patch easier to read.

scmutil: support background file closing Closing files that have been appended to is relatively slow on Windows/NTFS. This makes several Mercurial operations slower on Windows. The workaround to this issue is conceptually simple: use multiple threads for I/O. Unfortunately, Python doesn't scale well to multiple threads because of the GIL. And, refactoring our code to use threads everywhere would be a huge undertaking. So, we decide to tackle this problem by starting small: establishing a thread pool for closing files. This patch establishes a mechanism for closing file handles on separate threads. The coordinator object is basically a queue of file handles to operate on and a thread pool consuming from the queue. When files are opened through the VFS layer, the caller can specify that delay closing is allowed. A proxy class for file handles has been added. We must use a proxy because it isn't possible to modify __class__ on built-in types. This adds some overhead. But as future patches will show, this overhead is cancelled out by the benefit of closing file handles on background threads.