TypeError is raised from Chrome.get_navigation_items() with Babel

[Jun Omae]

I encountered the following error while developing ​th:AccountManagerPlugin with Trac 1.5.x and Python 3.

2023-03-25 06:14:25,244 Trac[main] ERROR: [127.0.0.1] Internal Server Error: <RequestWithSession "POST '/prefs/account'">, referrer 'http://127.0.0.1:46741/trac/prefs/account'
Traceback (most recent call last):
  File "/home/jun66j5/src/accountmanagerplugin.git/.tox/py39-trac15/lib/python3.9/site-packages/trac/web/main.py", line 610, in dispatch_request
    dispatcher.dispatch(req)
  File "/home/jun66j5/src/accountmanagerplugin.git/.tox/py39-trac15/lib/python3.9/site-packages/trac/web/main.py", line 302, in dispatch
    raise e
  File "/home/jun66j5/src/accountmanagerplugin.git/.tox/py39-trac15/lib/python3.9/site-packages/trac/web/main.py", line 248, in dispatch
    resp = chosen_handler.process_request(req)
  File "/home/jun66j5/src/accountmanagerplugin.git/.tox/py39-trac15/lib/python3.9/site-packages/trac/prefs/web_ui.py", line 108, in process_request
    resp = chosen_provider.render_preference_panel(req, panel_id)
  File "/home/jun66j5/src/accountmanagerplugin.git/acct_mgr/web_ui.py", line 136, in render_preference_panel
    data.update(self._do_account(req))
  File "/home/jun66j5/src/accountmanagerplugin.git/acct_mgr/web_ui.py", line 248, in _do_account
    if self._do_change_password(req) and force_change_password:
  File "/home/jun66j5/src/accountmanagerplugin.git/acct_mgr/web_ui.py", line 286, in _do_change_password
    add_notice(req, _("Password updated successfully."))
  File "/home/jun66j5/src/accountmanagerplugin.git/.tox/py39-trac15/lib/python3.9/site-packages/trac/web/chrome.py", line 213, in add_notice
    _add_message(req, 'notices', msg, args)
  File "/home/jun66j5/src/accountmanagerplugin.git/.tox/py39-trac15/lib/python3.9/site-packages/trac/web/chrome.py", line 221, in _add_message
    if msg not in req.chrome[name]:
  File "/home/jun66j5/src/accountmanagerplugin.git/.tox/py39-trac15/lib/python3.9/site-packages/trac/web/api.py", line 569, in __getattr__
    value = self.callbacks[name](self)
  File "/home/jun66j5/src/accountmanagerplugin.git/.tox/py39-trac15/lib/python3.9/site-packages/trac/web/chrome.py", line 818, in prepare_request
    chrome['nav'] = self.get_navigation_items(req, handler)
  File "/home/jun66j5/src/accountmanagerplugin.git/.tox/py39-trac15/lib/python3.9/site-packages/trac/web/chrome.py", line 938, in get_navigation_items
    if attributes['enabled'] and attributes['link'] and \
  File "/home/jun66j5/src/accountmanagerplugin.git/.tox/py39-trac15/lib/python3.9/site-packages/babel/support.py", line 207, in __len__
    return len(self.value)
TypeError: object of type 'Fragment' has no len()

The root cause is that babal.support.LazyProxy doesn't have __bool__ method. However, we should check whether the instance is a LazyProxy before checking whether the instance is a Fragment or Element.

trac/util/html.py

@@ -95 +95 @@
     """
     if isinstance(text, Markup):
         return text
+    if LazyProxy and isinstance(text, LazyProxy):
+        text = text.value
     if isinstance(text, Fragment):
         return Markup(text)
     e = escape_quotes(text)
@@ -968 +970 @@
     :param keeplinebreaks: optionally keep linebreaks
 
     """
+    if LazyProxy and isinstance(text, LazyProxy):
+        text = text.value
     if isinstance(text, Fragment):
         text = text.as_text()
     else:
@@ -982 +986 @@
     attribute, class or tag, using a preorder depth-first search.
 
     """
+    if LazyProxy and isinstance(frag, LazyProxy):
+        frag = frag.value
     if isinstance(frag, Element):
         if attr is not None and attr in frag.attrib:
             return frag

trac/web/chrome.py

@@ -34 +34 @@
 
 from jinja2 import FileSystemLoader
 
+try:
+    import babel
+except ImportError:
+    babel = LazyProxy = None
+else:
+    from babel.support import LazyProxy
+
 from trac.api import IEnvironmentSetupParticipant, ISystemInfoProvider
 from trac.config import *
 from trac.core import *
@@ -640 +647 @@
         info = get_pkginfo(jinja2).get('version')
         yield 'Jinja2', info
         # Optional Babel
-        try:
-            import babel
-        except ImportError:
-            babel = None
         if babel is not None:
             info = get_pkginfo(babel).get('version')
             if not get_available_locales():
@@ -877 +880 @@
             label = section.get(name + '.label')
             if href and href.startswith('/'):
                 href = req.href + href
+            if LazyProxy and isinstance(text, LazyProxy):
+                text = text.value
             if isinstance(text, Element) and text.tag == 'a':
                 link = text
                 if label:

[Jun Omae]

The same issue exists in Trac 1.4.

$ ~/venv/trac/1.4.3/bin/python
>>> from trac.util.html import find_element, tag
>>> from trac.util.translation import tag_
>>> find_element(tag('logged in as ', tag.b('admin')), tag='b')
<trac.util.html.Element object at 0x7f3ff0c31fa0>
>>> find_element(tag_("logged in as %(name)s", name=tag.b('admin')), tag='b')
>>> #=> should be a Element object

[Jun Omae]

Fixed in [17693] and merged in [17694].