path: error out if the `path://` reference point to an unknown path

Differential Revision: https://phab.mercurial-scm.org/D10265

mercurial/ui.py

@@ -2339,7 +2339,12 b' class path(object):'
     def chain_path(self, ui, paths):
         if self.url.scheme == b'path':
             assert self.url.path is None
-            subpath = paths[self.url.host]
+            try:
+                subpath = paths[self.url.host]
+            except KeyError:
+                m = _('cannot use `%s`, "%s" is not a known path')
+                m %= (self.rawloc, self.url.host)
+                raise error.Abort(m)
             if subpath.raw_url.scheme == b'path':
                 m = _('cannot use `%s`, "%s" is also define as a `path://`')
                 m %= (self.rawloc, self.url.host)

tests/test-paths.t

@@ -370,3 +370,18 b' Doing an actual circle should always be '
   $ hg pull chain_path
   abort: cannot use `path://other_default`, "other_default" is also define as a `path://`
   [255]
+
+Test basic error cases
+----------------------
+
+  $ cat << EOF > .hg/hgrc
+  > [paths]
+  > error-missing=path://unknown
+  > EOF
+  $ hg path
+  abort: cannot use `path://unknown`, "unknown" is not a known path
+  [255]
+  $ hg pull error-missing
+  abort: cannot use `path://unknown`, "unknown" is not a known path
+  [255]
+