How to find undeclared variables?

[buremba]

The original API has a method for finding out the undeclared variables. See: http://jinja.pocoo.org/docs/dev/api/#jinja2.meta.find_undeclared_variables

Is there a way to do that in Jinjava? If not, I would like to implement it. What's the best way to start implementing it given that I'm not familiar with the codebase?

[buremba]

@ilkerc

[xuchaoyong]

I am also demanding the undeclared variables. Is there anyway to do it in Jinjava?

[bnat1]

I was trying the different configuration options, and found withFailOnUnknownTokens, and it works.

JinjavaConfig jinjavaConfig = JinjavaConfig.newBuilder().withFailOnUnknownTokens(true).build();
Jinjava jinjava = new Jinjava(jinjavaConfig);

If there is an undefined variable, it throws an UnknownTokenException, which has the name of the undefined variable.

I haven't found anything that finds all of the undeclared variables at once though.

[jonathannaguin]

I would also like this functionality on the API, any guidance on how we can implement this?

[boulter]

You could look at all the places where we throw UnknownToken exceptions and track them in the Context object.

[jonathannaguin]

I was able to use the Jinja interpreter in a loop like this:

 Map<String, Object> binding = new HashMap<>();
JinjavaConfig config = JinjavaConfig.newBuilder()
                                    .withFailOnUnknownTokens(true)
                                    .build();

Jinjava jinjava = new Jinjava(config);
Context context = new Context(jinjava.getGlobalContext(), binding, config.getDisabled());
JinjavaInterpreter interpreter = config.getInterpreterFactory()
                                       .newInstance(jinjava, context, config);

boolean terminated = false;
do
{
    try
    {
        interpreter.render(content);
        terminated = true;
    }
    catch (UnknownTokenException e)
    {
        binding.put(e.getToken(), "");
    }
}
while (!terminated);

After it finishes, the binding map will contain all the undefined variables.
However, even though that works fine for simple templates like Hello {{user}}, it does not parse templates like:

{%- if GENDER == 'male' -%}
    {%- set greeting = "Good Morning Sir" -%}
{%- elif GENDER == 'female' -%}
    {%- set greeting = "Good Morning Madam" -%}
{%- else -%}
    {%- set greeting = "Good Morning" -%}
{%- endif -%}

Is there a way to parse the above too?

Thanks!

[GregDThomas]

I have submitted a PR at #572 which sort of solves this problem.

Rather than providing a context that (hopefully) contains a list of all your variables, you can supply a VariableFunction. This is a function that is supplied by the caller takes the name of a token, and returns it's value. It's invoked as the template is parsed.

Probably more easily explained from the test case at https://github.com/HubSpot/jinjava/pull/572/files#diff-dd8f89332b7f565f4eda09b58d91342a61ec8ea1729e2b7b280adf8d158707b1R23

Using your more complex example, it would be called with a parameter of "GENDER", twice. Your function could keep track of its invocations, and then you would know the variables in the template.

Note that this won't find all variables - only those in the paths determine from earlier results. e.g. if your "GENDER" returns "male", then only variables rendered in the {%- if GENDER == 'male' -%} ... {%-...} block would be requested.