hg: use "os.path.join()" to join path components which may be empty (issue4203)

Changset 2d0ab571b822 rewriting "hg.copystore()" with vfs uses
'dstbase + "/lock"' instead of "os.path.join()", because target files
given from "store.copyfiles()" already uses "/" as path separator

But in the repository using revlog format 0, "dstbase" becomes empty
("data" directory is located under ".hg" directly), and 'dstbase +
"/lock"' is treated as "/lock": in almost all cases, write access to
"/lock" causes "permission denied".

This patch uses "os.path.join()" to join path components which may be
empty in "hg.copystore()".

mercurial/hg.py

@@ -213,8 +213,10 b' def copystore(ui, srcrepo, destpath):'
                 dstvfs.mkdir(dstbase)
             if srcvfs.exists(f):
                 if f.endswith('data'):
+                    # 'dstbase' may be empty (e.g. revlog format 0)
+                    lockfile = os.path.join(dstbase, "lock")
                     # lock to avoid premature writing to the target
-                    destlock = lock.lock(dstvfs, dstbase + "/lock")
+                    destlock = lock.lock(dstvfs, lockfile)
                 hardlink, n = util.copyfiles(srcvfs.join(f), dstvfs.join(f),
                                              hardlink)
                 num += n

tests/test-clone.t

@@ -621,3 +621,17 b' re-enable perm to allow deletion'
 #endif
 
   $ cd ..
+
+Test clone from the repository in (emulated) revlog format 0 (issue4203):
+
+  $ mkdir issue4203
+  $ mkdir -p src/.hg
+  $ echo foo > src/foo
+  $ hg -R src add src/foo
+  $ hg -R src commit -m '#0'
+  $ hg -R src log -q
+  0:e1bab28bca43
+  $ hg clone -U -q src dst
+  $ hg -R dst log -q
+  0:e1bab28bca43
+  $ cd ..