largefiles: always create the cache and standin directories when cloning

The standin matcher only works if the .hglf directory exists (and it won't exist
if 'clone -U' is used, unless --all-largefiles is also specified).  Since not
even 'update -r null' will get rid of the standin directory, this ensures that
the standin directory always exists if the repo has the 'largefiles'
requirement.  This requirement is only set after a largefile is committed, so
these directories will not be created for repos that have the extension enabled
but have not committed a largefile.

With the standin directory in place, 'lfconvert --to-normal' will now be able to
download the required largefiles when converting a repo that was created with
'clone -U', and whose files are not in the usercache.

The downloadlfiles command could probably be put inside the 'largefiles'
requirement conditional too, but given that the user specified --all-largefiles,
there is likely an expectation to print out the number of largefiles downloaded,
even if it is 0.

hgext/largefiles/overrides.py

@@ -733,20 +733,25 b' def overrideclone(orig, ui, source, dest'
 def hgclone(orig, ui, opts, *args, **kwargs):
     result = orig(ui, opts, *args, **kwargs)
 
-    if result is not None and opts.get('all_largefiles'):
+    if result is not None:
         sourcerepo, destrepo = result
         repo = destrepo.local()
 
         # The .hglf directory must exist for the standin matcher to match
         # anything (which listlfiles uses for each rev), and .hg/largefiles is
         # assumed to exist by the code that caches the downloaded file.  These
-        # directories exist if clone updated to any rev.
+        # directories exist if clone updated to any rev.  (If the repo does not
+        # have largefiles, download never gets to the point of needing
+        # .hg/largefiles, and the standin matcher won't match anything anyway.)
+        if 'largefiles' in repo.requirements:
         if opts.get('noupdate'):
             util.makedirs(repo.pathto(lfutil.shortname))
             util.makedirs(repo.join(lfutil.longname))
 
         # Caching is implicitly limited to 'rev' option, since the dest repo was
-        # truncated at that point.
+        # truncated at that point.  The user may expect a download count with
+        # this option, so attempt whether or not this is a largefile repo.
+        if opts.get('all_largefiles'):
         success, missing = lfcommands.downloadlfiles(ui, repo, None)
 
         if missing != 0:

tests/test-lfconvert.t

@@ -276,10 +276,21 b' round-trip: converting back to a normal '
 
 Avoid a traceback if a largefile isn't available (issue3519)
 
+Ensure the largefile can be cached in the source if necessary
   $ hg clone -U largefiles-repo issue3519
   $ rm "${USERCACHE}"/*
   $ hg lfconvert --to-normal issue3519 normalized3519
   initializing destination normalized3519
+
+Ensure the abort message is useful if a largefile is entirely unavailable
+  $ rm -rf normalized3519
+  $ rm "${USERCACHE}"/*
+  $ rm issue3519/.hg/largefiles/*
+  $ rm largefiles-repo/.hg/largefiles/*
+  $ hg lfconvert --to-normal issue3519 normalized3519
+  initializing destination normalized3519
+  large: can't get file locally
+  (no default or default-push path set in hgrc)
   abort: missing largefile 'large' from revision d4892ec57ce212905215fad1d9018f56b99202ad
   [255]