dirstate: add test for exceptions during updates

Adds a test that checks if the working copy parent and the working copy are in a
good state if an exception happens between the time the working copy parent is
set and the time the actual updates are recorded in the dirstate.

tests/test-dirstate.t

@@ -1,63 +1,88 b''
 ------ Test dirstate._dirs refcounting
 
   $ hg init t
   $ cd t
   $ mkdir -p a/b/c/d
   $ touch a/b/c/d/x
   $ touch a/b/c/d/y
   $ touch a/b/c/d/z
   $ hg ci -Am m
   adding a/b/c/d/x
   adding a/b/c/d/y
   adding a/b/c/d/z
   $ hg mv a z
   moving a/b/c/d/x to z/b/c/d/x (glob)
   moving a/b/c/d/y to z/b/c/d/y (glob)
   moving a/b/c/d/z to z/b/c/d/z (glob)
 
 Test name collisions
 
   $ rm z/b/c/d/x
   $ mkdir z/b/c/d/x
   $ touch z/b/c/d/x/y
   $ hg add z/b/c/d/x/y
   abort: file 'z/b/c/d/x' in dirstate clashes with 'z/b/c/d/x/y'
   [255]
   $ rm -rf z/b/c/d
   $ touch z/b/c/d
   $ hg add z/b/c/d
   abort: directory 'z/b/c/d' already in dirstate
   [255]
 
   $ cd ..
 
 Issue1790: dirstate entry locked into unset if file mtime is set into
 the future
 
 Prepare test repo:
 
   $ hg init u
   $ cd u
   $ echo a > a
   $ hg add
   adding a
   $ 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
   n 644          2 2021-01-01 12:00:00 a
 
 Test modulo storage/comparison of absurd dates:
 
 #if no-aix
   $ touch -t 195001011200 a
   $ hg st
   $ hg debugstate
   n 644          2 2018-01-19 15:14:08 a
 #endif
+
+Verify that exceptions during a dirstate change leave the dirstate
+coherent (issue4353)
+
+  $ cat > ../dirstateexception.py <<EOF
+  > from mercurial import merge, extensions, util
+  > 
+  > def wraprecordupdates(orig, repo, actions, branchmerge):
+  >     raise util.Abort("simulated error while recording dirstateupdates")
+  > 
+  > def reposetup(ui, repo):
+  >     extensions.wrapfunction(merge, 'recordupdates', wraprecordupdates)
+  > EOF
+
+  $ hg rm a
+  $ hg commit -m 'rm a'
+  $ echo "[extensions]" >> .hg/hgrc
+  $ echo "dirstateex=../dirstateexception.py" >> .hg/hgrc
+  $ hg up 0
+  abort: simulated error while recording dirstateupdates
+  [255]
+  $ hg log -r . -T '{rev}\n'
+  1
+  $ hg status
+  ? a