diff --git a/hgext/highlight/__init__.py b/hgext/highlight/__init__.py
--- a/hgext/highlight/__init__.py
+++ b/hgext/highlight/__init__.py
@@ -77,6 +77,7 @@
 
     return orig(web)
 
+@webcommands.webcommand('highlightcss')
 def generate_css(web):
     pg_style = web.config('web', 'pygments_style', 'colorful')
     fmter = highlight.HtmlFormatter(style=pg_style)
@@ -91,6 +92,4 @@
     # monkeypatch in the new version
     extensions.wrapfunction(webcommands, '_filerevision',
                             filerevision_highlight)
-    extensions.wrapfunction(webcommands, 'annotate', annotate_highlight)
-    webcommands.highlightcss = generate_css
-    webcommands.__all__.append('highlightcss')
+    webcommands.wrapwebcommand('annotate', annotate_highlight)
diff --git a/hgext/keyword.py b/hgext/keyword.py
--- a/hgext/keyword.py
+++ b/hgext/keyword.py
@@ -740,7 +740,7 @@
     extensions.wrapfunction(cmdutil, 'copy', kw_copy)
     extensions.wrapfunction(cmdutil, 'dorecord', kw_dorecord)
     for c in nokwwebcommands.split():
-        extensions.wrapfunction(webcommands, c, kwweb_skip)
+        webcommands.wrapwebcommand(c, kwweb_skip)
 
 def reposetup(ui, repo):
     '''Sets up repo as kwrepo for keyword substitution.'''
diff --git a/hgext/largefiles/uisetup.py b/hgext/largefiles/uisetup.py
--- a/hgext/largefiles/uisetup.py
+++ b/hgext/largefiles/uisetup.py
@@ -151,7 +151,7 @@
     extensions.wrapfunction(archival, 'archive', overrides.overridearchive)
     extensions.wrapfunction(subrepo.hgsubrepo, 'archive',
                             overrides.hgsubrepoarchive)
-    extensions.wrapfunction(webcommands, 'archive', overrides.hgwebarchive)
+    webcommands.wrapwebcommand('archive', overrides.hgwebarchive)
     extensions.wrapfunction(cmdutil, 'bailifchanged',
                             overrides.overridebailifchanged)
 
diff --git a/mercurial/hgweb/hgweb_mod.py b/mercurial/hgweb/hgweb_mod.py
--- a/mercurial/hgweb/hgweb_mod.py
+++ b/mercurial/hgweb/hgweb_mod.py
@@ -354,7 +354,7 @@
                 cmd = cmd[style + 1:]
 
             # avoid accepting e.g. style parameter as command
-            if util.safehasattr(webcommands, cmd):
+            if cmd in webcommands.commands:
                 req.qsparams['cmd'] = cmd
 
             if cmd == 'static':
@@ -416,7 +416,7 @@
 
                 res.headers['ETag'] = tag
 
-            if cmd not in webcommands.__all__:
+            if cmd not in webcommands.commands:
                 msg = 'no such method: %s' % cmd
                 raise ErrorResponse(HTTP_BAD_REQUEST, msg)
             else:
@@ -424,7 +424,7 @@
                 # override easily enough.
                 res.status = '200 Script output follows'
                 res.headers['Content-Type'] = ctype
-                return getattr(webcommands, cmd)(rctx)
+                return webcommands.commands[cmd](rctx)
 
         except (error.LookupError, error.RepoLookupError) as err:
             msg = pycompat.bytestr(err)
diff --git a/mercurial/hgweb/webcommands.py b/mercurial/hgweb/webcommands.py
--- a/mercurial/hgweb/webcommands.py
+++ b/mercurial/hgweb/webcommands.py
@@ -8,6 +8,7 @@
 from __future__ import absolute_import
 
 import copy
+import functools
 import mimetypes
 import os
 import re
@@ -47,7 +48,6 @@
     webutil,
 )
 
-__all__ = []
 commands = {}
 
 class webcommand(object):
@@ -77,10 +77,34 @@
         self.name = name
 
     def __call__(self, func):
-        __all__.append(self.name)
         commands[self.name] = func
         return func
 
+def wrapwebcommand(command, wrapper):
+    """Utility to wrap functions defined as webcommands
+
+    Wrap the webcommand 'command' using the specified wrapper.
+    The wrapper function should have the signature
+
+      wrapper(orig, web)
+
+    where 'orig' is the webcommand to be wrapped, and 'web' is the
+    requestcontext instance that will be passed to the webcommand
+    at runtime."""
+
+    if command not in commands:
+        raise error.ProgrammingError('no webcommand named %s' % command)
+
+    if not callable(wrapper):
+        raise error.ProgrammingError('wrapper must be a callable')
+
+    # Create the new webcommand
+    orig = commands[command]
+    newfunc = functools.partial(wrapper, orig)
+
+    # Overwrite the old webcommand with the new one
+    commands[command] = newfunc
+
 @webcommand('log')
 def log(web):
     """
diff --git a/tests/hgweberror.py b/tests/hgweberror.py
--- a/tests/hgweberror.py
+++ b/tests/hgweberror.py
@@ -6,6 +6,7 @@
     webcommands,
 )
 
+@webcommands.webcommand('raiseerror')
 def raiseerror(web):
     '''Dummy web command that raises an uncaught Exception.'''
 
@@ -18,7 +19,3 @@
         web.res.getbodyfile().write(b'partial content\n')
 
     raise AttributeError('I am an uncaught error!')
-
-def extsetup(ui):
-    setattr(webcommands, 'raiseerror', raiseerror)
-    webcommands.__all__.append('raiseerror')