--- a/mercurial/dirstateutils/timestamp.py Tue Nov 23 18:11:42 2021 +0100
+++ b/mercurial/dirstateutils/timestamp.py Tue Nov 23 18:03:51 2021 +0100
@@ -99,3 +99,28 @@
subsec_nanos = nanos % billion
return timestamp((secs, subsec_nanos))
+
+
+def reliable_mtime_of(stat_result, present_mtime):
+ """same as `mtime_of`, but return None if the date might be ambiguous
+
+ A modification time is reliable if it is older than "present_time" (or
+ sufficiently in the futur).
+
+ Otherwise a concurrent modification might happens with the same mtime.
+ """
+ file_mtime = mtime_of(stat_result)
+ file_second = file_mtime[0]
+ boundary_second = present_mtime[0]
+ # If the mtime of the ambiguous file is younger (or equal) to the starting
+ # point of the `status` walk, we cannot garantee that another, racy, write
+ # will not happen right after with the same mtime and we cannot cache the
+ # information.
+ #
+ # However is the mtime is far away in the future, this is likely some
+ # mismatch between the current clock and previous file system operation. So
+ # mtime more than one days in the future are considered fine.
+ if boundary_second <= file_second < (3600 * 24 + boundary_second):
+ return None
+ else:
+ return file_mtime