rewriteutil: add devel warning if precheck is called with contexts

I'm trying to upstream parts from the evolve extension. This check
exists there.

Differential Revision: https://phab.mercurial-scm.org/D10515

mercurial/rewriteutil.py

@@ -21,6 +21,7 b' from . import ('
     obsutil,
     revset,
     scmutil,
+    util,
 )
 
 
@@ -38,6 +39,10 b" def precheck(repo, revs, action=b'rewrit"
         hint = _(b"no changeset checked out")
         raise error.InputError(msg, hint=hint)
 
+    if any(util.safehasattr(r, 'rev') for r in revs):
+        repo.ui.develwarn(b"rewriteutil.precheck called with ctx not revs")
+        revs = (r.rev() for r in revs)
+
     if len(repo[None].parents()) > 1:
         raise error.StateError(_(b"cannot %s while merging") % action)