dirstate-item: make sure we set the mtime-second-ambiguous on v2 write

We want to preserve the second-ambiguity alongside the ambiguous mtime. So we
use the decimated flag for that.

note: the C code was already doing so. No change was needed to it.

Differential Revision: https://phab.mercurial-scm.org/D11845

mercurial/pure/parsers.py

@@ -483,6 +483,8 b' class DirstateItem(object):'
                 flags |= DIRSTATE_V2_MODE_IS_SYMLINK
         if self._mtime_s is not None:
             flags |= DIRSTATE_V2_HAS_MTIME
+        if self._mtime_second_ambiguous:
+            flags |= DIRSTATE_V2_MTIME_SECOND_AMBIGUOUS
 
         if self._fallback_exec is not None:
             flags |= DIRSTATE_V2_HAS_FALLBACK_EXEC

rust/hg-core/src/dirstate/entry.rs

@@ -43,7 +43,10 b' pub struct TruncatedTimestamp {'
     truncated_seconds: u32,
     /// Always in the `0 .. 1_000_000_000` range.
     nanoseconds: u32,
-    second_ambiguous: bool,
+    /// TODO this should be in DirstateEntry, but the current code needs
+    /// refactoring to use DirstateEntry instead of TruncatedTimestamp for
+    /// comparison.
+    pub second_ambiguous: bool,
 }
 
 impl TruncatedTimestamp {

rust/hg-core/src/dirstate_tree/on_disk.rs

@@ -465,6 +465,9 b' impl Node {'
         };
         let mtime = if let Some(m) = mtime_opt {
             flags.insert(Flags::HAS_MTIME);
+            if m.second_ambiguous {
+                flags.insert(Flags::MTIME_SECOND_AMBIGUOUS);
+            };
             m.into()
         } else {
             PackedTruncatedTimestamp::null()