diff -r 8fd9b56e8d7c -r 45bfcd16f27e mercurial/subrepo.py
--- a/mercurial/subrepo.py	Fri Mar 09 15:53:41 2018 +0100
+++ b/mercurial/subrepo.py	Sat Mar 10 12:33:19 2018 +0530
@@ -348,7 +348,7 @@
         matched by the match function
         '''
 
-    def forget(self, match, prefix):
+    def forget(self, match, prefix, dryrun):
         return ([], [])
 
     def removefiles(self, matcher, prefix, after, force, subrepos, warnings):
@@ -811,9 +811,10 @@
         return ctx.walk(match)
 
     @annotatesubrepoerror
-    def forget(self, match, prefix):
+    def forget(self, match, prefix, dryrun):
         return cmdutil.forget(self.ui, self._repo, match,
-                              self.wvfs.reljoin(prefix, self._path), True)
+                              self.wvfs.reljoin(prefix, self._path),
+                              True, dryrun=dryrun)
 
     @annotatesubrepoerror
     def removefiles(self, matcher, prefix, after, force, subrepos, warnings):