ui: move URL and path detection into path API

ui.expandpath() has code for recognizing URLs or local filesystem
paths. Our goal is to use ``path`` class instances everywhere a path
is represented.

Changing ui.expandpath() to return path instances is a lot of work.
Our goal is to slowly marginalize it by moving logic into the paths
API and to convert callers to the paths API.

Many callers of ui.expandpath() pass in a value that could be a
local filesystem path or URI. We move the detection of these strings
from ui.expandpath() to paths.getpath() and path.__init__(). To do
this properly in a way that is compatible with future callers, we
need to parse the "#branch" syntax out of locations. This is a bit
complicated, but it is necessary.

The code for URL parsing is essentially a copy of hg.parseurl().
Once all consumers are speaking the paths API, it is likely that
this function won't be called any more and it can be deleted.

mercurial/ui.py

@@ -550,12 +550,9 b' class ui(object):'
 
     def expandpath(self, loc, default=None):
         """Return repository location relative to cwd or from [paths]"""
-        if util.hasscheme(loc) or os.path.isdir(os.path.join(loc, '.hg')):
-            return loc
-
         p = self.paths.getpath(loc, default=default)
         if p:
-            return p.loc
+            return p.rawloc
         return loc
 
     @util.propertycache
@@ -1002,7 +999,10 b' class paths(dict):'
             self[name] = path(name, rawloc=loc)
 
     def getpath(self, name, default=None):
-        """Return a ``path`` for the specified name, falling back to a default.
+        """Return a ``path`` from a string, falling back to a default.
+
+        ``name`` can be a named path or locations. Locations are filesystem
+        paths or URIs.
 
         Returns the first of ``name`` or ``default`` that is present, or None
         if neither is present.
@@ -1010,6 +1010,12 b' class paths(dict):'
         try:
             return self[name]
         except KeyError:
+            # Try to resolve as a local path or URI.
+            try:
+                return path(None, rawloc=name)
+            except ValueError:
+                pass
+
             if default is not None:
                 try:
                     return self[default]
@@ -1026,10 +1032,34 b' class path(object):'
 
         ``name`` is the symbolic name of the path.
         ``rawloc`` is the raw location, as defined in the config.
+
+        If ``name`` is not defined, we require that the location be a) a local
+        filesystem path with a .hg directory or b) a URL. If not,
+        ``ValueError`` is raised.
         """
+        if not rawloc:
+            raise ValueError('rawloc must be defined')
+
+        # Locations may define branches via syntax <base>#<branch>.
+        u = util.url(rawloc)
+        branch = None
+        if u.fragment:
+            branch = u.fragment
+            u.fragment = None
+
+        self.url = u
+        self.branch = branch
+
         self.name = name
-        # We'll do more intelligent things with rawloc in the future.
-        self.loc = rawloc
+        self.rawloc = rawloc
+        self.loc = str(u)
+
+        # When given a raw location but not a symbolic name, validate the
+        # location is valid.
+        if (not name and not u.scheme
+            and not os.path.isdir(os.path.join(str(u), '.hg'))):
+            raise ValueError('location is not a URL or path to a local '
+                             'repo: %s' % rawloc)
 
 # we instantiate one globally shared progress bar to avoid
 # competing progress bars when multiple UI objects get created