dirstate: store mtimes with nanosecond precision in memory Keep integer seconds since the Unix epoch, together with integer nanoseconds in the `0 <= n < 1e9` range. For now, nanoseconds are still always zero. This commit is about data structure changes. Differential Revision: https://phab.mercurial-scm.org/D11684

rust: remove now-unused DirstateEntry::clear_ambiguous_mtime method Differential Revision: https://phab.mercurial-scm.org/D11696

dirstate: align Rust function name to `need_delay` The rest of the code use this name. It is not a great name, but it is better to stay consistent. Differential Revision: https://phab.mercurial-scm.org/D11699

dirstate: rename a `very_likely_equal` method to `likely_equal` No need to oversell it. Differential Revision: https://phab.mercurial-scm.org/D11691

backout: backed out changeset 2f2107c01dee After discussion on the original phab patch, we've decided to wait until Python 2 support is dropped to do this since the behavior differs for relatively obscure reasons. Differential Revision: https://phab.mercurial-scm.org/D11692

backout: backed out changeset 6edc8800dbc3 Same as the previous changeset. Differential Revision: https://phab.mercurial-scm.org/D11693

dirstate-v2: preserve the fallback values on disk When the fallback values are set, they are now read and written to disk. See format documentation for details. Differential Revision: https://phab.mercurial-scm.org/D11688

dirstate: make DirstateItem constructor accept fallback value This could arguably goes in the previous changeset, but I wanted to keep that previous changeset small to focus more on the user code and the documentation. Differential Revision: https://phab.mercurial-scm.org/D11687

dirstate: add a concept of "fallback" flags to dirstate item The concept is defined and "used" by the flag code, but it is neither persisted nor set anywhere yet. We currently focus on defining the semantic of the attribute. More to come in the next changesets Check the inline documentation for details. Differential Revision: https://phab.mercurial-scm.org/D11686

dirstate-v2: adds two flag to track the presence of some unrecorded files Right now, we don't record ignored or unknown files in the dirstate. However the structure would allow it. So we introduce two flags that can be used to clarify whether all unknown/ignored children are recorded or not. This will allow for more information to be stored in the future if this end up being relevant. Differential Revision: https://phab.mercurial-scm.org/D11682

dirstate-v2: adds a flag to mark a file as modified Right now, a files with a file system state that requires a lookup (same size, different mtime) will requires a lookup. If the result of that lookup is a modified files, it will remains ambiguous, requiring a lookup on the next status run too. To fix this, we introduce a dedicated flag in the new format. Such flag will allow to record such file as "known modified" avoiding an extra lookup later. As None of the associate code currently exist in the status code, we do the minimal implementation: if we read a dirstate entry with this flag set, we make it as "ambiguous" so that the next status code has to look it up. The same as it would have to without this flag existing anyway. Differential Revision: https://phab.mercurial-scm.org/D11681

rhg: simplify split_metadata It turns out that it's possible to implement `FilelogEntry.into_data` on top of `split`, as proposed by @spectral. Differential Revision: https://phab.mercurial-scm.org/D11689