registrar: introduce new class for registration to replace funcregistrar

_funcregistrarbase differs from funcregistrar in points below:

  - every code paths should use same class derived from
    _funcregistrarbase to register functions in a same category

    funcregistrar expects (3rd party) extensions to use (a class
    derived from) delayregistrar.

  - actual extra setup should be executed in another function

    For example, marking revset predicate as "safe" is executed in a
    class derived from _funcregistrarbase, but putting name of "safe"
    predicate into safesymbols is executed in another function for it.

    funcregistrar expects derived classes to do so.

New class is named as module private one, because code paths, which
register functions, should use not it directly but one derived from
it.

mercurial/registrar.py

@@ -126,3 +126,82 b' class delayregistrar(object):'
         while self._list:
             func, decorator = self._list.pop(0)
             decorator(func)
+
+class _funcregistrarbase(object):
+    """Base of decorator to register a fuction for specific purpose
+
+    This decorator stores decorated functions into own dict 'table'.
+
+    The least derived class can be defined by overriding 'formatdoc',
+    for example::
+
+        class keyword(_funcregistrarbase):
+            _docformat = ":%s: %s"
+
+    This should be used as below:
+
+        keyword = registrar.keyword()
+
+        @keyword('bar')
+        def barfunc(*args, **kwargs):
+            '''Explanation of bar keyword ....
+            '''
+            pass
+
+    In this case:
+
+    - 'barfunc' is stored as 'bar' in '_table' of an instance 'keyword' above
+    - 'barfunc.__doc__' becomes ":bar: Explanation of bar keyword"
+    """
+    def __init__(self, table=None):
+        if table is None:
+            self._table = {}
+        else:
+            self._table = table
+
+    def __call__(self, decl, *args, **kwargs):
+        return lambda func: self._doregister(func, decl, *args, **kwargs)
+
+    def _doregister(self, func, decl, *args, **kwargs):
+        name = self._getname(decl)
+
+        if func.__doc__ and not util.safehasattr(func, '_origdoc'):
+            doc = func.__doc__.strip()
+            func._origdoc = doc
+            func.__doc__ = self._formatdoc(decl, doc)
+
+        self._table[name] = func
+        self._extrasetup(name, func, *args, **kwargs)
+
+        return func
+
+    def _parsefuncdecl(self, decl):
+        """Parse function declaration and return the name of function in it
+        """
+        i = decl.find('(')
+        if i >= 0:
+            return decl[:i]
+        else:
+            return decl
+
+    def _getname(self, decl):
+        """Return the name of the registered function from decl
+
+        Derived class should override this, if it allows more
+        descriptive 'decl' string than just a name.
+        """
+        return decl
+
+    _docformat = None
+
+    def _formatdoc(self, decl, doc):
+        """Return formatted document of the registered function for help
+
+        'doc' is '__doc__.strip()' of the registered function.
+        """
+        return self._docformat % (decl, doc)
+
+    def _extrasetup(self, name, func):
+        """Execute exra setup for registered function, if needed
+        """
+        pass