dirstate-item: implement the comparison logic for mtime-second-ambiguous

dirstate-item: implement the comparison logic for mtime-second-ambiguous

If the flag is set we now process it properly.

We "just" need to actually set it and persist it.

Differential Revision: https://phab.mercurial-scm.org/D11843

--- a/mercurial/cext/parsers.c	Wed Nov 24 04:40:00 2021 +0100
+++ b/mercurial/cext/parsers.c	Wed Nov 24 04:51:05 2021 +0100
@@ -335,10 +335,20 @@
 	                      &other_second_ambiguous)) {
 		return NULL;
 	}
-	if ((self->flags & dirstate_flag_has_mtime) &&
-	    self->mtime_s == other_s &&
-	    (self->mtime_ns == other_ns || self->mtime_ns == 0 ||
-	     other_ns == 0)) {
+	if (!(self->flags & dirstate_flag_has_mtime)) {
+		Py_RETURN_FALSE;
+	}
+	if (self->mtime_s != other_s) {
+		Py_RETURN_FALSE;
+	}
+	if (self->mtime_ns == 0 || other_ns == 0) {
+		if (self->flags & dirstate_flag_mtime_second_ambiguous) {
+			Py_RETURN_FALSE;
+		} else {
+			Py_RETURN_TRUE;
+		}
+	}
+	if (self->mtime_ns == other_ns) {
 		Py_RETURN_TRUE;
 	} else {
 		Py_RETURN_FALSE;

--- a/mercurial/pure/parsers.py	Wed Nov 24 04:40:00 2021 +0100
+++ b/mercurial/pure/parsers.py	Wed Nov 24 04:51:05 2021 +0100
@@ -310,9 +310,21 @@
             return False
         self_ns = self._mtime_ns
         other_sec, other_ns, second_ambiguous = other_mtime
-        return self_sec == other_sec and (
-            self_ns == other_ns or self_ns == 0 or other_ns == 0
-        )
+        if self_sec != other_sec:
+            # seconds are different theses mtime are definitly not equal
+            return False
+        elif other_ns == 0 or self_ns == 0:
+            # at least one side as no nano-seconds information
+
+            if self._mtime_second_ambiguous:
+                # We cannot trust the mtime in this case
+                return False
+            else:
+                # the "seconds" value was reliable on its own. We are good to go.
+                return True
+        else:
+            # We have nano second information, let us use them !
+            return self_ns == other_ns
 
     @property
     def state(self):

--- a/rust/hg-core/src/dirstate/entry.rs	Wed Nov 24 04:40:00 2021 +0100
+++ b/rust/hg-core/src/dirstate/entry.rs	Wed Nov 24 04:51:05 2021 +0100
@@ -130,10 +130,17 @@
     /// in that way, doing a simple comparison would cause many false
     /// negatives.
     pub fn likely_equal(self, other: Self) -> bool {
-        self.truncated_seconds == other.truncated_seconds
-            && (self.nanoseconds == other.nanoseconds
-                || self.nanoseconds == 0
-                || other.nanoseconds == 0)
+        if self.truncated_seconds != other.truncated_seconds {
+            false
+        } else if self.nanoseconds == 0 || other.nanoseconds == 0 {
+            if self.second_ambiguous {
+                false
+            } else {
+                true
+            }
+        } else {
+            self.nanoseconds == other.nanoseconds
+        }
     }
 
     pub fn likely_equal_to_mtime_of(