urlutil: add a `get_push_paths` to perform the push destination logic

As is this changeset does not change anything. However having an official empty
point will help unifying the logic and encapsulate the details and update the
logic to support path definition pointing to multiple other path.

Differential Revision: https://phab.mercurial-scm.org/D10377

mercurial/commands.py

@@ -5720,12 +5720,9 b' def push(ui, repo, *dests, **opts):'
                 # this lets simultaneous -r, -b options continue working
                 opts.setdefault(b'rev', []).append(b"null")
 
-    if not dests:
-        dests = [None]
     some_pushed = False
     result = 0
-    for dest in dests:
-        path = ui.getpath(dest, default=(b'default-push', b'default'))
+    for path in urlutil.get_push_paths(repo, ui, dests):
         if not path:
             raise error.ConfigError(
                 _(b'default repository not configured!'),

mercurial/utils/urlutil.py

@@ -445,6 +445,14 b' def removeauth(u):'
     return bytes(u)
 
 
+def get_push_paths(repo, ui, dests):
+    """yields all the `path` selected as push destination by `dests`"""
+    if not dests:
+        dests = [None]
+    for dest in dests:
+        yield ui.getpath(dest, default=(b'default-push', b'default'))
+
+
 def parseurl(path, branches=None):
     '''parse url#branch, returning (url, (branch, branches))'''
     u = url(path)