rust-dirstate-v2: save proper data size if no new data on append This is currently only triggered with the tests ran with `--rhg` without `--rust`, by "luck", there probably always was something to write, like an mtime when also using Rust extensions alongside `rhg`. Differential Revision: https://phab.mercurial-scm.org/D12580

procutil: avoid `+= None` when writing to full std{err,out} descriptor on py3 The write function returns `None` if there was no room to write the given data[1]. I don't like that this is effectively an infinite loop if there's never any progress emptying the underlying buffer, but we're no worse off than before, and it fixes random stacktrace popups seen in the py3 build of TortoiseHg. [1] https://docs.python.org/3/library/io.html#io.RawIOBase.write Differential Revision: https://phab.mercurial-scm.org/D12555

amend: don't remove unselected removals from memctx When there are removed files in the working copy and they are not selected to be amended into the parent, the `filectxfn` we create for the `memctx` would still return `None` before this patch. That's clearly incorrect; we should return the `filectx` from the unamended commit. Somehow it seems to not matter much except for the case with copies stored in changesets. Thanks to Kyle Lippincott for doing all the debugging and identifying the fix for this issue. Differential Revision: https://phab.mercurial-scm.org/D12573

tests: demonstrate crash on partial amend with copies in changesets See the fix in the next patch for explanation. Differential Revision: https://phab.mercurial-scm.org/D12572