Strip parens from filter params list

This isn't necessary, we will always know that the second item within
the filter list is the set of filter parameters.

This also ensures that any time the filter separator is detected,
we force parsing the next token as a filter parameter.

tatsu_grammar.txt

@@ -83,8 +83,26 @@ variable_filter
     =
     {SP}* "|" {SP}* @:filter
     ;
-filter                  = @+:IDENTIFIER [@+:filter_parameters];
-filter_parameters       = "(" [@+:filter_parameter {"," {SP}* @+:filter_parameter}*] ")";
+filter =
+    @+:IDENTIFIER
+    [@+:filter_parameters]
+    ;
+
+filter_parameters
+    =
+    "("
+        @:[filter_parameter_list]
+    ")"
+    ;
+filter_parameter_list
+    =
+    @+:filter_parameter {filter_parameter_separator ~ @+:filter_parameter}*
+    ;
+
+filter_parameter_separator
+    =
+    {SP}* "," {SP}*
+    ;
 filter_parameter        = {!"," !")" CHAR}* ;
 
 comment_expression      = comment_open comment_content comment_close ;
@@ -96,7 +114,7 @@ content                 = !(block_open | variable_open | comment_open) CHAR ;
 
 IDENTIFIER
     =
-    /[a-zA-Z]+/
+    /[a-zA-Z][a-zA-Z0-9]*/
     ;
 
 ALPHA

test_template.jinja

@@ -1,8 +1,10 @@
 {% with key=val %}
-{{ kkk  |test(first,second, third)|filter}}
+{{ kkk  |test(first ,second, third)|filter | lastFilter}}
 {%block single key=val param=value %}
 test {{var}}
 {%endblock%}
 {# comment contents
 across lines #}
-{% raw %}{% block %}fake content{{ fake vars }}{% endraw %}
+{% raw %}
+    {% block %}fake content{{ fake vars }}
+{% endraw %}