extensions: recommend against using wrapfunction for repo methods

Instead, all extensions should use the "dynamic subclass" trick:
subclass repo.__class__ and then replace repo.__class__ with your new
subclass.  This avoids conflicts that happen when one extension uses
wrapfunction and another uses subclassing to extend the same method of
localrepository.

mercurial/extensions.py

@@ -1,254 +1,286 b''
 # extensions.py - extension handling for mercurial
 #
 # Copyright 2005-2007 Matt Mackall <[e-mail]>
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 import imp, os
 import util, cmdutil, help, error
 from i18n import _, gettext
 
 _extensions = {}
 _order = []
 
 def extensions():
     for name in _order:
         module = _extensions[name]
         if module:
             yield name, module
 
 def find(name):
     '''return module with given extension name'''
     try:
         return _extensions[name]
     except KeyError:
         for k, v in _extensions.iteritems():
             if k.endswith('.' + name) or k.endswith('/' + name):
                 return v
         raise KeyError(name)
 
 def loadpath(path, module_name):
     module_name = module_name.replace('.', '_')
     path = util.expandpath(path)
     if os.path.isdir(path):
         # module/__init__.py style
         d, f = os.path.split(path.rstrip('/'))
         fd, fpath, desc = imp.find_module(f, [d])
         return imp.load_module(module_name, fd, fpath, desc)
     else:
         return imp.load_source(module_name, path)
 
 def load(ui, name, path):
     # unused ui argument kept for backwards compatibility
     if name.startswith('hgext.') or name.startswith('hgext/'):
         shortname = name[6:]
     else:
         shortname = name
     if shortname in _extensions:
         return
     _extensions[shortname] = None
     if path:
         # the module will be loaded in sys.modules
         # choose an unique name so that it doesn't
         # conflicts with other modules
         mod = loadpath(path, 'hgext.%s' % name)
     else:
         def importh(name):
             mod = __import__(name)
             components = name.split('.')
             for comp in components[1:]:
                 mod = getattr(mod, comp)
             return mod
         try:
             mod = importh("hgext.%s" % name)
         except ImportError:
             mod = importh(name)
     _extensions[shortname] = mod
     _order.append(shortname)
 
 def loadall(ui):
     result = ui.configitems("extensions")
     newindex = len(_order)
     for (name, path) in result:
         if path:
             if path[0] == '!':
                 continue
         try:
             load(ui, name, path)
         except KeyboardInterrupt:
             raise
         except Exception, inst:
             if path:
                 ui.warn(_("*** failed to import extension %s from %s: %s\n")
                         % (name, path, inst))
             else:
                 ui.warn(_("*** failed to import extension %s: %s\n")
                         % (name, inst))
             if ui.traceback():
                 return 1
 
     for name in _order[newindex:]:
         uisetup = getattr(_extensions[name], 'uisetup', None)
         if uisetup:
             uisetup(ui)
 
     for name in _order[newindex:]:
         extsetup = getattr(_extensions[name], 'extsetup', None)
         if extsetup:
             try:
                 extsetup(ui)
             except TypeError:
                 if extsetup.func_code.co_argcount != 0:
                     raise
                 extsetup() # old extsetup with no ui argument
 
 def wrapcommand(table, command, wrapper):
     aliases, entry = cmdutil.findcmd(command, table)
     for alias, e in table.iteritems():
         if e is entry:
             key = alias
             break
 
     origfn = entry[0]
     def wrap(*args, **kwargs):
         return util.checksignature(wrapper)(
             util.checksignature(origfn), *args, **kwargs)
 
     wrap.__doc__ = getattr(origfn, '__doc__')
     wrap.__module__ = getattr(origfn, '__module__')
 
     newentry = list(entry)
     newentry[0] = wrap
     table[key] = tuple(newentry)
     return entry
 
 def wrapfunction(container, funcname, wrapper):
+    '''Wrap the function named funcname in container
+
+    It is replacing with your wrapper. The container is typically a
+    module, class, or instance.
+
+    The wrapper will be called like
+
+      wrapper(orig, *args, **kwargs)
+
+    where orig is the original (wrapped) function, and *args, **kwargs
+    are the arguments passed to it.
+
+    Wrapping methods of the repository object is not recommended since
+    it conflicts with extensions that extend the repository by
+    subclassing. All extensions that need to extend methods of
+    localrepository should use this subclassing trick: namely,
+    reposetup() should look like
+
+      def reposetup(ui, repo):
+          class myrepo(repo.__class__):
+              def whatever(self, *args, **kwargs):
+                  [...extension stuff...]
+                  super(myrepo, self).whatever(*args, **kwargs)
+                  [...extension stuff...]
+
+          repo.__class__ = myrepo
+
+    In general, combining wrapfunction() with subclassing does not
+    work. Since you cannot control what other extensions are loaded by
+    your end users, you should play nicely with others by using the
+    subclass trick.
+    '''
     def wrap(*args, **kwargs):
         return wrapper(origfn, *args, **kwargs)
 
     origfn = getattr(container, funcname)
     setattr(container, funcname, wrap)
     return origfn
 
 def _disabledpaths(strip_init=False):
     '''find paths of disabled extensions. returns a dict of {name: path}
     removes /__init__.py from packages if strip_init is True'''
     import hgext
     extpath = os.path.dirname(os.path.abspath(hgext.__file__))
     try: # might not be a filesystem path
         files = os.listdir(extpath)
     except OSError:
         return {}
 
     exts = {}
     for e in files:
         if e.endswith('.py'):
             name = e.rsplit('.', 1)[0]
             path = os.path.join(extpath, e)
         else:
             name = e
             path = os.path.join(extpath, e, '__init__.py')
             if not os.path.exists(path):
                 continue
             if strip_init:
                 path = os.path.dirname(path)
         if name in exts or name in _order or name == '__init__':
             continue
         exts[name] = path
     return exts
 
 def _disabledhelp(path):
     '''retrieve help synopsis of a disabled extension (without importing)'''
     try:
         file = open(path)
     except IOError:
         return
     else:
         doc = help.moduledoc(file)
         file.close()
 
     if doc: # extracting localized synopsis
         return gettext(doc).splitlines()[0]
     else:
         return _('(no help text available)')
 
 def disabled():
     '''find disabled extensions from hgext
     returns a dict of {name: desc}, and the max name length'''
 
     paths = _disabledpaths()
     if not paths:
         return None, 0
 
     exts = {}
     maxlength = 0
     for name, path in paths.iteritems():
         doc = _disabledhelp(path)
         if not doc:
             continue
 
         exts[name] = doc
         if len(name) > maxlength:
             maxlength = len(name)
 
     return exts, maxlength
 
 def disabledext(name):
     '''find a specific disabled extension from hgext. returns desc'''
     paths = _disabledpaths()
     if name in paths:
         return _disabledhelp(paths[name])
 
 def disabledcmd(cmd, strict=False):
     '''import disabled extensions until cmd is found.
     returns (cmdname, extname, doc)'''
 
     paths = _disabledpaths(strip_init=True)
     if not paths:
         raise error.UnknownCommand(cmd)
 
     def findcmd(cmd, name, path):
         try:
             mod = loadpath(path, 'hgext.%s' % name)
         except Exception:
             return
         try:
             aliases, entry = cmdutil.findcmd(cmd,
                 getattr(mod, 'cmdtable', {}), strict)
         except (error.AmbiguousCommand, error.UnknownCommand):
             return
         for c in aliases:
             if c.startswith(cmd):
                 cmd = c
                 break
         else:
             cmd = aliases[0]
         return (cmd, name, mod)
 
     # first, search for an extension with the same name as the command
     path = paths.pop(cmd, None)
     if path:
         ext = findcmd(cmd, cmd, path)
         if ext:
             return ext
 
     # otherwise, interrogate each extension until there's a match
     for name, path in paths.iteritems():
         ext = findcmd(cmd, name, path)
         if ext:
             return ext
 
     raise error.UnknownCommand(cmd)
 
 def enabled():
     '''return a dict of {name: desc} of extensions, and the max name length'''
     exts = {}
     maxlength = 0
     for ename, ext in extensions():
         doc = (gettext(ext.__doc__) or _('(no help text available)'))
         ename = ename.split('.')[-1]
         maxlength = max(len(ename), maxlength)
         exts[ename] = doc.splitlines()[0].strip()
 
     return exts, maxlength