--- a/mercurial/dispatch.py	Fri Mar 11 04:14:54 2016 +0900
+++ b/mercurial/dispatch.py	Fri Mar 11 04:14:54 2016 +0900
@@ -31,6 +31,7 @@
     error,
     extensions,
     fancyopts,
+    fileset,
     hg,
     hook,
     revset,
@@ -753,6 +754,7 @@
 #   extraobj) arguments
 extraloaders = [
     ('cmdtable', commands, 'loadcmdtable'),
+    ('filesetpredicate', fileset, 'loadpredicate'),
     ('revsetpredicate', revset, 'loadpredicate'),
 ]
 

--- a/mercurial/fileset.py	Fri Mar 11 04:14:54 2016 +0900
+++ b/mercurial/fileset.py	Fri Mar 11 04:14:54 2016 +0900
@@ -560,5 +560,15 @@
 def prettyformat(tree):
     return parser.prettyformat(tree, ('string', 'symbol'))
 
+def loadpredicate(ui, extname, registrarobj):
+    """Load fileset predicates from specified registrarobj
+    """
+    for name, func in registrarobj._table.iteritems():
+        symbols[name] = func
+        if func._callstatus:
+            _statuscallers.add(name)
+        if func._callexisting:
+            _existingcallers.add(name)
+
 # tell hggettext to extract docstrings from these functions:
 i18nfunctions = symbols.values()

--- a/mercurial/registrar.py	Fri Mar 11 04:14:54 2016 +0900
+++ b/mercurial/registrar.py	Fri Mar 11 04:14:54 2016 +0900
@@ -122,3 +122,42 @@
 
     def _extrasetup(self, name, func, safe=False):
         func._safe = safe
+
+class filesetpredicate(_funcregistrarbase):
+    """Decorator to register fileset predicate
+
+    Usage::
+
+        filesetpredicate = registrar.filesetpredicate()
+
+        @filesetpredicate('mypredicate()')
+        def mypredicatefunc(mctx, x):
+            '''Explanation of this fileset predicate ....
+            '''
+            pass
+
+    The first string argument is used also in online help.
+
+    Optional argument 'callstatus' indicates whether a predicate
+     implies 'matchctx.status()' at runtime or not (False, by
+     default).
+
+    Optional argument 'callexisting' indicates whether a predicate
+    implies 'matchctx.existing()' at runtime or not (False, by
+    default).
+
+    'filesetpredicate' instance in example above can be used to
+    decorate multiple functions.
+
+    Decorated functions are registered automatically at loading
+    extension, if an instance named as 'filesetpredicate' is used for
+    decorating in extension.
+
+    Otherwise, explicit 'fileset.loadpredicate()' is needed.
+    """
+    _getname = _funcregistrarbase._parsefuncdecl
+    _docformat = "``%s``\n    %s"
+
+    def _extrasetup(self, name, func, callstatus=False, callexisting=False):
+        func._callstatus = callstatus
+        func._callexisting = callexisting

--- a/tests/test-fileset.t	Fri Mar 11 04:14:54 2016 +0900
+++ b/tests/test-fileset.t	Fri Mar 11 04:14:54 2016 +0900
@@ -351,9 +351,10 @@
 Test detection of unintentional 'matchctx.existing()' invocation
 
   $ cat > $TESTTMP/existingcaller.py <<EOF
-  > from mercurial import fileset
+  > from mercurial import registrar
   > 
-  > @fileset.predicate('existingcaller()', callexisting=False)
+  > filesetpredicate = registrar.filesetpredicate()
+  > @filesetpredicate('existingcaller()', callexisting=False)
   > def existingcaller(mctx, x):
   >     # this 'mctx.existing()' invocation is unintentional
   >     return [f for f in mctx.existing()]