[PATCH 1 of 2 sparse-ext maybe-for-stable] sparse: properly error out when absolute paths are used

[Kostia Balytskyi]

# HG changeset patch
# User Kostia Balytskyi <ikostia at fb.com>
# Date 1501109970 25200
#      Wed Jul 26 15:59:30 2017 -0700
# Branch stable
# Node ID 681f8819475ed5546e712d9ce04116b8b5a04f9b
# Parent  f9769619b640af5952060ca101d39bc09a7149a8
sparse: properly error out when absolute paths are used

Current logic is misleading (it says it drops only absolute paths, but
it actually drops all of them), not cross-platform (does not support Windows)
and IMO just wrong (as it should just error out if absolute paths are given).

This commit fixes it.

diff --git a/mercurial/sparse.py b/mercurial/sparse.py
--- a/mercurial/sparse.py
+++ b/mercurial/sparse.py
@@ -636,10 +636,10 @@ def updateconfig(repo, pats, opts, inclu
             newexclude = set(oldexclude)
             newprofiles = set(oldprofiles)
 
-        if any(pat.startswith('/') for pat in pats):
-            repo.ui.warn(_('warning: paths cannot start with /, ignoring: %s\n')
-                         % ([pat for pat in pats if pat.startswith('/')]))
-        elif include:
+        if any(os.path.isabs(pat) for pat in pats):
+            raise error.Abort(_('paths cannot be absolute'))
+
+        if include:
             newinclude.update(pats)
         elif exclude:
             newexclude.update(pats)
diff --git a/tests/test-sparse.t b/tests/test-sparse.t
--- a/tests/test-sparse.t
+++ b/tests/test-sparse.t
@@ -29,11 +29,13 @@ Absolute paths outside the repo should j
 
 #if no-windows
   $ hg debugsparse --include /foo/bar
-  warning: paths cannot start with /, ignoring: ['/foo/bar']
+  abort: paths cannot be absolute
+  [255]
   $ hg debugsparse --include '$TESTTMP/myrepo/hide'
 
   $ hg debugsparse --include '/root'
-  warning: paths cannot start with /, ignoring: ['/root']
+  abort: paths cannot be absolute
+  [255]
 #else
 TODO: See if this can be made to fail the same way as on Unix
   $ hg debugsparse --include /c/foo/bar