'string_if_invalid' option does not work with custom filter

[JOSEPH KIM]

I use 'string_if_invalid' option to debug invalid context variable.

However, custom filter does not work when a context variable is invalid.

I attached sample project and you can see custom filter works when the context variables is valid.

[JOSEPH KIM]

sample project of custom filter with 'string if invalid' option

[JOSEPH KIM]

tested other filters like 'lower' but, it doesn't work with other filters either.

[Tim Graham]

I see this output. What output do you expect?

with filter
    __FOO__
    filter works with valid foo context
with tag
    tag works with __FOO__
    tag works with valid foo context 

[JOSEPH KIM]

if filter works with "string_if_invalid" option
the output should be

with filter
    filter works with __FOO__
    filter works with valid foo context
with tag
    tag works with __FOO__
    tag works with valid foo context 

[Tim Graham]

I don't see an advantage to running string_if_valid through template filters -- they might transform the value to some other output which would make it more difficult debug.

[JOSEPH KIM]

"string_if_invalid" option works perfectly with context variables, however, with request parameters, it makes redundant code.

Actually, I am supposed to get null string ("") when I don't need string of "string_if_invalid" especially handle request parameters.

for example, to get null string (or to escape invalid string)

as is

<input name="foo" type="text" value="{% if request.GET.foo %}{{ request.GET.foo }}{% endif %}">

want to

<input name="foo" type="text" value="{{ request.GET.foo|or_null }}">

[Tim Graham]

I'm having trouble understanding how your last comment relates to our previous discussion.

Have you read the "​For debug purposes only" note about string_if_invalid? I get the sense that you may be trying to use string_if_invalid for more than it's designed for.