path: forbid chaining `path://` definitions

To have `path://xxx` referencing paths that use `path://` too, we need to
analyze dependencies to initialize them in the right order (and to detect
cycle).

I don't want to deal with that right now, so I just disallow it for now.

Differential Revision: https://phab.mercurial-scm.org/D10264

mercurial/ui.py

@@ -2317,6 +2317,8 b' class path(object):'
             u.fragment = None
 
         self.url = u
+        # the url from the config/command line before dealing with `path://`
+        self.raw_url = u.copy()
         self.branch = branch
 
         self.name = name
@@ -2338,6 +2340,10 b' class path(object):'
         if self.url.scheme == b'path':
             assert self.url.path is None
             subpath = paths[self.url.host]
+            if subpath.raw_url.scheme == b'path':
+                m = _('cannot use `%s`, "%s" is also define as a `path://`')
+                m %= (self.rawloc, self.url.host)
+                raise error.Abort(m)
             self.url = subpath.url
             self.rawloc = subpath.rawloc
             self.loc = subpath.loc

mercurial/util.py

@@ -3144,6 +3144,21 b' class url(object):'
             if v is not None:
                 setattr(self, a, urlreq.unquote(v))
 
+    def copy(self):
+        u = url(b'temporary useless value')
+        u.path = self.path
+        u.scheme = self.scheme
+        u.user = self.user
+        u.passwd = self.passwd
+        u.host = self.host
+        u.path = self.path
+        u.query = self.query
+        u.fragment = self.fragment
+        u._localpath = self._localpath
+        u._hostport = self._hostport
+        u._origpath = self._origpath
+        return u
+
     @encoding.strmethod
     def __repr__(self):
         attrs = []

tests/test-paths.t

@@ -334,3 +334,39 b' test inheritance of the suboptions'
   adding manifests
   adding file changes
   added 5 changesets with 0 changes to 0 files (+1 heads)
+
+Test chaining path:// definition
+--------------------------------
+
+This is currently unsupported, but feel free to implement the necessary
+dependency detection.
+
+  $ cat << EOF >> .hg/hgrc
+  > chain_path=path://other_default
+  > EOF
+
+  $ hg id
+  000000000000
+  $ hg path
+  abort: cannot use `path://other_default`, "other_default" is also define as a `path://`
+  [255]
+  $ hg pull chain_path
+  abort: cannot use `path://other_default`, "other_default" is also define as a `path://`
+  [255]
+
+Doing an actual circle should always be an issue
+
+  $ cat << EOF >> .hg/hgrc
+  > rock=path://cissors
+  > cissors=path://paper
+  > paper=://rock
+  > EOF
+
+  $ hg id
+  000000000000
+  $ hg path
+  abort: cannot use `path://other_default`, "other_default" is also define as a `path://`
+  [255]
+  $ hg pull chain_path
+  abort: cannot use `path://other_default`, "other_default" is also define as a `path://`
+  [255]