largefiles: use "normallookup", if "mtime" of standin is unset

Before this patch, largefiles gotten from "other" revision (without
conflict) at "hg merge" become "clean" unexpectedly in steps below:

    1. "merge.update()" is invoked
      1-1 standinfile SF is updated in the working directory
      1-2 "dirstate" entry for SF is "normallookup"-ed

    2. "lfcommands.updatelfiles()" is invoked (by "overrides.hgmerge()")
      2-1 largefile LF (for SF) is updated in the working directory
      2-2 "dirstate" returns "n" for SF (by 1-2)
      2-3 "lfdirstate" entry for LF is "normal"-ed
      2-4 "lfdirstate" is written into ".hg/largefiles/dirstate", and
          timestamp of LF is stored into "lfdirstate" file
          (ASSUMPTION: timestamp of LF differs from one of "lfdirstate" file)

Then, "hs status" treats LF as "clean", even though LF is updated by
"other" revision (by 2-1), because "lfilesrepo.status()" always treats
"normal"-ed files (by 2-3 and 2-4) as "clean".

When timestamp is not set (= negative value) for standinfile in
"dirstate", largefile should be "normallookup"-ed regardless of
rebasing or not, because "n" state in "dirstate" doesn't ensure
"clean"-ness of a standinfile at that time.

This patch uses "normallookup" instead of "normal", if "mtime" of
standin is unset

This is a temporary way to fix with less changes. For fundamental
resolution of this kind of problems in the future, "lfdirstate" should
be updated with "dirstate" simultaneously while "merge.update"
execution: maybe by hooking "recordupdates"

It is also why this patch (temporarily) uses internal field "_map" of
"dirstate" directly.

This patch uses "[debug] dirstate.delaywrite" feature in the test, to
ensure that timestamp of the largefile gotten from "other" revision is
stored into ".hg/largefiles/dirstate". (for ASSUMPTION at 2-4)

This patch newly adds "test-largefiles-update.t", to avoid increasing
cost to run other tests for largefiles by subsequent patches
(especially, "[debug] dirstate.delaywrite" causes so).

tests/test-largefiles-update.t

@@ -0,0 +1,53 b''
+This file focuses mainly on updating largefiles in the working
+directory (and ".hg/largefiles/dirstate")
+
+  $ cat >> $HGRCPATH <<EOF
+  > [ui]
+  > merge = internal:fail
+  > [extensions]
+  > largefiles =
+  > EOF
+
+  $ hg init repo
+  $ cd repo
+
+  $ echo large1 > large1
+  $ echo large2 > large2
+  $ hg add --large large1 large2
+  $ echo normal1 > normal1
+  $ hg add normal1
+  $ hg commit -m '#0'
+  $ echo 'large1 in #1' > large1
+  $ echo 'normal1 in #1' > normal1
+  $ hg commit -m '#1'
+  $ hg update -q -C 0
+  $ echo 'large2 in #2' > large2
+  $ hg commit -m '#2'
+  created new head
+
+Test that "hg merge" updates largefiles from "other" correctly
+
+(getting largefiles from "other" normally)
+
+  $ hg status -A large1
+  C large1
+  $ cat large1
+  large1
+  $ cat .hglf/large1
+  4669e532d5b2c093a78eca010077e708a071bb64
+  $ hg merge --config debug.dirstate.delaywrite=2
+  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  (branch merge, don't forget to commit)
+  getting changed largefiles
+  1 largefiles updated, 0 removed
+  $ hg status -A large1
+  M large1
+  $ cat large1
+  large1 in #1
+  $ cat .hglf/large1
+  58e24f733a964da346e2407a2bee99d9001184f5
+  $ hg diff -c 1 --nodates .hglf/large1 | grep '^[+-][0-9a-z]'
+  -4669e532d5b2c093a78eca010077e708a071bb64
+  +58e24f733a964da346e2407a2bee99d9001184f5
+
+  $ cd ..

hgext/largefiles/lfcommands.py

@@ -509,12 +509,15 b' def updatelfiles(ui, repo, filelist=None'
 
             updated += update1
 
-            state = repo.dirstate[lfutil.standin(lfile)]
+            standin = lfutil.standin(lfile)
+            if standin in repo.dirstate:
+                stat = repo.dirstate._map[standin]
+                state, mtime = stat[0], stat[3]
+            else:
+                state, mtime = '?', -1
             if state == 'n':
-                # When rebasing, we need to synchronize the standin and the
-                # largefile, because otherwise the largefile will get reverted.
-                # But for commit's sake, we have to mark the file as unclean.
-                if getattr(repo, "_isrebasing", False):
+                if mtime < 0:
+                    # state 'n' doesn't ensure 'clean' in this case
                     lfdirstate.normallookup(lfile)
                 else:
                     lfdirstate.normal(lfile)