largefiles: use the core file copy logic to validate the destination path

The destination is validated by pathutil.canonpath() for illegal components, and
that it is in the repository.  The logic for creating the standin directory tree
was calling this before cmdutil.copy(), but without the destination file name
component.  The cmdutil.copy() logic also calls pathutil.canonpath(), but with
the file name component.  By always calling the core logic first, the error
message is always consistent.  Specifically, the old behavior for these tests
was to say '.hg' contains an illegal component, and '..' is not under root.

A user wasn't likely to notice the discrepancy, but this eliminates a needless
difference when running the test suite with --config extensions.largefiles=.

hgext/largefiles/overrides.py

@@ -559,16 +559,6 b' def overridecopy(orig, ui, repo, pats, o'
         # this isn't legal, let the original function deal with it
         return orig(ui, repo, pats, opts, rename)
 
-    def makestandin(relpath):
-        path = pathutil.canonpath(repo.root, repo.getcwd(), relpath)
-        return os.path.join(repo.wjoin(lfutil.standin(path)))
-
-    fullpats = scmutil.expandpats(pats)
-    dest = fullpats[-1]
-
-    if os.path.isdir(dest):
-        if not os.path.isdir(makestandin(dest)):
-            os.makedirs(makestandin(dest))
     # This could copy both lfiles and normal files in one command,
     # but we don't want to do that. First replace their matcher to
     # only match normal files and run it, then replace it to just
@@ -595,6 +585,17 b' def overridecopy(orig, ui, repo, pats, o'
     except OSError:
         return result
 
+    def makestandin(relpath):
+        path = pathutil.canonpath(repo.root, repo.getcwd(), relpath)
+        return os.path.join(repo.wjoin(lfutil.standin(path)))
+
+    fullpats = scmutil.expandpats(pats)
+    dest = fullpats[-1]
+
+    if os.path.isdir(dest):
+        if not os.path.isdir(makestandin(dest)):
+            os.makedirs(makestandin(dest))
+
     try:
         try:
             # When we call orig below it creates the standins but we don't add

tests/test-rename.t

@@ -620,10 +620,16 b' check illegal path components'
   $ hg rename d1/d11/a1 .hg
   abort: path contains illegal component: .hg/a1 (glob)
   [255]
+  $ hg --config extensions.largefiles= rename d1/d11/a1 .hg
+  abort: path contains illegal component: .hg/a1 (glob)
+  [255]
   $ hg status -C
   $ hg rename d1/d11/a1 ..
   abort: ../a1 not under root '$TESTTMP' (glob)
   [255]
+  $ hg --config extensions.largefiles= rename d1/d11/a1 ..
+  abort: ../a1 not under root '$TESTTMP' (glob)
+  [255]
   $ hg status -C
 
   $ mv d1/d11/a1 .hg