urlutil: add a new `get_unique_push_path`

This function is dedicated to call that needs a single destination. Currently
most caller actually need that since few actually support multiple destinations
(the most importants `hg push` and `hg outgoing` do). So having a clear API
point for that will be important when the time comes to have a single `[paths]`
alias resolving to multiple urls.

Differential Revision: https://phab.mercurial-scm.org/D10407

mercurial/utils/urlutil.py

@@ -471,6 +471,25 b' def get_pull_paths(repo, ui, sources, de'
         yield parseurl(url, default_branches)
 
 
+def get_unique_push_path(action, repo, ui, dest=None):
+    """return a unique `path` or abort if multiple are found
+
+    This is useful for command and action that does not support multiple
+    destination (yet).
+
+    Note that for now, we cannot get multiple destination so this function is "trivial".
+
+    The `action` parameter will be used for the error message.
+    """
+    if dest is None:
+        dests = []
+    else:
+        dests = [dest]
+    dests = list(get_push_paths(repo, ui, dests))
+    assert len(dests) == 1
+    return dests[0]
+
+
 def get_unique_pull_path(action, repo, ui, source=None, default_branches=()):
     """return a unique `(path, branch)` or abort if multiple are found