issue2550683 Allow indexargs_form filter variable exclusion.

Patch generated by Bruce Tulloch (bruce). Applied and docstring for
indexargs_form updated by John Rouillard. Full patch description is
in CHANGES.txt file. I added the use case description.

Code should be backwards compatible. There are not existing tests of
indexargs_form that I can adopt to test, but it didn't cause tests/test_cgi
tests/test_template to fail and the demo tracker ran properly.

Author: rouilj

CHANGES.txt

@@ -40,6 +40,33 @@ Features:
 - issue2109308 - Allow subject of nosy messages be changed from reactor
   Adds a subject parameter to nosymessage function. Patch initally
   generated by Frank Niessink. Tests, adaptation by John Rouillard.
+- issue2550683 Allow indexargs_form filter variable exclusion.
+  Patch generated by Bruce Tulloch (bruce). Applied and docstring for
+  indexargs_form updated by John Rouillard. Patch description is:
+  This is required to allow indexargs_form to be used in conjunction with
+  other form variables which *replace* some filterspec parameters.
+
+  One must exclude all variables from the indexargs_form call which are to
+  be replaced with values that are derived from other form input elements,
+  otherwise they will clash with the "hidden" input elements generated by
+  indexargs_form itself.
+
+  For example:
+    <tal:block replace="structure python:request.indexargs_form(
+                      sort=0,group=0,filter=0,columns=0,
+                      exclude=['type','status','assignedto'])"/>
+  where the variables type, status and assignedto are supplied via other
+  form input elements. Without the new exclude argument to indexargs_form,
+  all hidden input elements otherwise generated by this call would need to
+  be manually added to the template code. Further, given that the template
+  may not know what other variables may be defined, it may not even be
+  possible to code this without some python helpers.
+    [ rouilj I think this is an example usecase. Possible assignedto
+    users need to have a specific role. Create TAL that
+    filters the users to the select few. Defines a select list for
+    assignedto. Use exclude=['assignedto'] to prevent the
+    indexargs_form from generating a confliciting assignedto field
+    which lists all users regardless of the role.]
 
 Fixed:
 

roundup/cgi/templating.py

@@ -2681,8 +2681,15 @@ def __str__(self):
 """%d
 
     def indexargs_form(self, columns=1, sort=1, group=1, filter=1,
-            filterspec=1, search_text=1):
-        """ return the current index args as form elements """
+            filterspec=1, search_text=1, exclude=[]):
+        """ return the current index args as form elements
+
+            This routine generates an html form with hidden elements.
+            If you want to have visible form elements in your tal/jinja
+            generated templates use the exclude aray to list the names for
+            these elements. This wll prevent the function from creating
+            these elements in its output.
+        """
         l = []
         sc = self.special_char
         def add(k, v):
@@ -2710,6 +2717,8 @@ def add(k, v):
         if self.classname and filterspec:
             cls = self.client.db.getclass(self.classname)
             for k,v in self.filterspec.items():
+                if k in exclude:
+                    continue
                 if type(v) == type([]):
                     if isinstance(cls.get_transitive_prop(k), hyperdb.String):
                         add(k, ' '.join(v))