dirstate.write: don't ignore stat data if mtime is in the future (issue1790)

This change narrows the race guard that was introduced by af3f26b6bba4
("dirstate: ignore stat data for files that were updated too recently")
to not discard the _map entry's stat data if the mtime is in the future.

Without this change, status locks files having odd mtimes in the future
into the 'unset' state, causing needless file compares later (admittedly
harmless), but also inflicting highly irritating sticky effects on
tools/plugins that directly read .hg/dirstate (e.g. TortoiseHg).

tests/test-dirstate-future

@@ -0,0 +1,13 b''
+#!/bin/sh
+
+hg init
+echo a > a
+hg add
+hg ci -m1
+
+# set mtime of a into the future
+touch -t 202101011200 a
+
+# status must not set a's entry to unset (issue1790)
+hg status
+hg debugstate

tests/test-dirstate-future.out

@@ -0,0 +1,2 b''
+adding a
+n 644          2 2021-01-01 12:00:00 a

mercurial/dirstate.py

@@ -377,9 +377,9 b' class dirstate(object):'
             gran = int(self._ui.config('dirstate', 'granularity', 1))
         except ValueError:
             gran = 1
-        limit = sys.maxint
         if gran > 0:
-            limit = util.fstat(st).st_mtime - gran
+            hlimit = util.fstat(st).st_mtime
+            llimit = hlimit - gran
 
         cs = cStringIO.StringIO()
         copymap = self._copymap
@@ -389,7 +389,8 b' class dirstate(object):'
         for f, e in self._map.iteritems():
             if f in copymap:
                 f = "%s\0%s" % (f, copymap[f])
-            if e[3] > limit and e[0] == 'n':
+            if gran > 0 and e[0] == 'n' and llimit < e[3] <= hlimit:
+                # file was updated too recently, ignore stat data
                 e = (e[0], 0, -1, -1)
             e = pack(_format, e[0], e[1], e[2], e[3], len(f))
             write(e)