subrepo: fix default implementation of forget() (issue3404)

mercurial/subrepo.py

@@ -366,7 +366,7 b' class abstractsubrepo(object):'
         pass
 
     def forget(self, ui, match, prefix):
-        return []
+        return ([], [])
 
     def revert(self, ui, substate, *pats, **opts):
         ui.warn('%s: reverting %s subrepos is unsupported\n' \

tests/test-subrepo-git.t

@@ -507,3 +507,8 b' Test subrepo already at intended revisio'
   da5f5b1d8ffcf62fb8327bcd3c89a4367a6018e7
   $ cd ..
 
+Test forgetting files, not implemented in git subrepo, used to
+traceback
+  $ hg forget 'notafile*'
+  notafile*: No such file or directory
+  [1]

tests/test-subrepo-svn.t

@@ -548,3 +548,10 b' Test archive'
   archiving (s): 2/2 files (100.00%)
   archiving (recreated): 0/1 files (0.00%)
   archiving (recreated): 1/1 files (100.00%)
+
+Test forgetting files, not implemented in svn subrepo, used to
+traceback
+
+  $ hg forget 'notafile*'
+  notafile*: No such file or directory
+  [1]