urlutil: add a `get_clone_path` function

We add a new function with a semantic focussed on `clone` operation (so without
an existing repository). I am not certain the return type is the best, but this
is what we need for now. Once all caller are migrated we might start thinking
about that the API should be. For now that will do.

Differential Revision: https://phab.mercurial-scm.org/D10401

mercurial/hg.py

@@ -672,8 +672,8 b' def clone('
     """
 
     if isinstance(source, bytes):
-        origsource = ui.expandpath(source)
-        source, branches = urlutil.parseurl(origsource, branch)
+        src = urlutil.get_clone_path(ui, source, branch)
+        origsource, source, branches = src
         srcpeer = peer(ui, peeropts, source)
     else:
         srcpeer = source.peer()  # in case we were called with a localrepo

mercurial/utils/urlutil.py

@@ -471,6 +471,13 b' def get_pull_paths(repo, ui, sources, de'
         yield parseurl(url, default_branches)
 
 
+def get_clone_path(ui, source, default_branches=()):
+    """return the `(origsource, path, branch)` selected as clone source"""
+    url = ui.expandpath(source)
+    path, branch = parseurl(url, default_branches)
+    return url, path, branch
+
+
 def parseurl(path, branches=None):
     '''parse url#branch, returning (url, (branch, branches))'''
     u = url(path)