backup: fix issue when the backup end up in a different directory

Because of store encoding, we might end up with the backup in a different
directory than the initial copy (for example if the backup path make it cross
the 120 char limit).

This can create crash, especially since 6.4 where backup are used during revlog
split.

Making sure the directory exists fixes these crash We added a test covering this
case.

Strictly speaking, this has always been broken, however the new code in 6.4
triggers it more easily.

mercurial/transaction.py

@@ -414,6 +414,11 b' class transaction(util.transactional):'
         if vfs.exists(file):
             filepath = vfs.join(file)
             backuppath = vfs.join(backupfile)
+            # store encoding may result in different directory here.
+            # so we have to ensure the destination directory exist
+            final_dir_name = os.path.dirname(backuppath)
+            util.makedirs(final_dir_name, mode=vfs.createmode, notindexed=True)
+            # then we can copy the backup
             util.copyfile(filepath, backuppath, hardlink=hardlink)
         else:
             backupfile = b''

tests/test-transaction-rollback-on-revlog-split.t

@@ -1,6 +1,9 b''
 Test correctness of revlog inline -> non-inline transition
 ----------------------------------------------------------
 
+We test various file length and naming pattern as this created issue in the
+past.
+
 Helper extension to intercept renames and kill process
 
   $ cat > $TESTTMP/intercept_before_rename.py << EOF
@@ -80,6 +83,7 b' setup a repository for tests'
   > file
   > Directory_With,Special%Char/Complex_File.babar
   > foo/bar/babar_celeste/foo
+  > 1234567890/1234567890/1234567890/1234567890/1234567890/1234567890/1234567890/1234567890/1234567890/1234567890/f
   > "
   $ for f in $files; do
   >     mkdir -p `dirname $f`
@@ -179,7 +183,7 b' recover is rolling the split back, the f'
   $ f -s .hg/store/data/file*
   .hg/store/data/file.i: size=1174
   $ hg tip
-  changeset:   1:272bd31be9b8
+  changeset:   1:cc8dfb126534
   tag:         tip
   user:        test
   date:        Thu Jan 01 00:00:00 1970 +0000
@@ -249,7 +253,7 b' recover is rolling the split back, the f'
   $ f -s .hg/store/data/file*
   .hg/store/data/file.i: size=1174
   $ hg tip
-  changeset:   1:272bd31be9b8
+  changeset:   1:cc8dfb126534
   tag:         tip
   user:        test
   date:        Thu Jan 01 00:00:00 1970 +0000
@@ -313,7 +317,7 b' recover is rolling the split back, the f'
   $ f -s .hg/store/data/file*
   .hg/store/data/file.i: size=1174
   $ hg tip
-  changeset:   1:272bd31be9b8
+  changeset:   1:cc8dfb126534
   tag:         tip
   user:        test
   date:        Thu Jan 01 00:00:00 1970 +0000
@@ -353,7 +357,7 b' The split was rollback'
 
 
   $ hg tip
-  changeset:   1:272bd31be9b8
+  changeset:   1:cc8dfb126534
   tag:         tip
   user:        test
   date:        Thu Jan 01 00:00:00 1970 +0000