status: gather fixup info at comparison time

This is still racy, but on a much small windows. In addition, the API now make
it possible for it to not be racy. This also unlock other cleanups that we are
about to do regarding mtime ambiguity at gathering time.

Differential Revision: https://phab.mercurial-scm.org/D11785

mercurial/context.py

@@ -46,6 +46,9 b' from .utils import ('
     dateutil,
     stringutil,
 )
+from .dirstateutils import (
+    timestamp,
+)
 
 propertycache = util.propertycache
 
@@ -1814,7 +1817,21 b' class workingctx(committablectx):'
                 ):
                     modified.append(f)
                 else:
-                    fixup.append(f)
+                    # XXX note that we have a race windows here since we gather
+                    # the stats after we compared so the file might have
+                    # changed.
+                    #
+                    # However this have always been the case and the
+                    # refactoring moving the code here is improving the
+                    # situation by narrowing the race and moving the two steps
+                    # (comparison + stat) in the same location.
+                    #
+                    # Making this code "correct" is now possible.
+                    s = self[f].lstat()
+                    mode = s.st_mode
+                    size = s.st_size
+                    mtime = timestamp.mtime_of(s)
+                    fixup.append((f, (mode, size, mtime)))
             except (IOError, OSError):
                 # A file become inaccessible in between? Mark it as deleted,
                 # matching dirstate behavior (issue5584).
@@ -1842,13 +1859,13 b' class workingctx(committablectx):'
                     if dirstate.identity() == oldid:
                         if fixup:
                             if dirstate.pendingparentchange():
-                                normal = lambda f: dirstate.update_file(
+                                normal = lambda f, pfd: dirstate.update_file(
                                     f, p1_tracked=True, wc_tracked=True
                                 )
                             else:
                                 normal = dirstate.set_clean
-                            for f in fixup:
-                                normal(f)
+                            for f, pdf in fixup:
+                                normal(f, pdf)
                             # write changes out explicitly, because nesting
                             # wlock at runtime may prevent 'wlock.release()'
                             # after this block from doing so for subsequent
@@ -1890,7 +1907,7 b' class workingctx(committablectx):'
             s.deleted.extend(deleted2)
 
             if fixup and clean:
-                s.clean.extend(fixup)
+                s.clean.extend((f for f, _ in fixup))
 
         self._poststatusfixup(s, fixup)