Macro arguments sometimes would need type info

[seijikun]

Something I encountered multiple times when creating macro blocks with optional parameters was the following situation:

{% macro test(title = None) %}
    {% if let Some(title) = title %}
        Title: {{title}}
    {% endif %}
{% endmacro %}

The following case works, since when explicitly supplying Some(<value>), the Option<ValueType> is clearly specified:

{% call test(title = Some("My awesome title!")) %}{% endcall %}

However when using the default value of None, the Option's template parameter can not be automatically inferenced and the variable is thus underspecified:

{% call test() %}{% endcall %}

I tried explicitly specifying the generic parameter, like: Option::<&'static str>::None, but for everything I tried, the syntax was denied by askama.

---

Is there something I've been missing on this?
Is there a suggested way to deal with this?

[GuillaumeGomez]

You tried with the not-yet released version or with the last released version? If the current not-yet released version doesn't allow you to do it, then we should add support for it.

[seijikun]

The following templates fail with the current master branch:

{% macro test(title = Option::<&'static str>::None) %}
    {% if let Some(title) = title %}
        Title: {{title}}
    {% endif %}
{% endmacro %}

{% call test() %}{% endcall %}

{% macro test(title: Option<&'static str> = None) %}
    {% if let Some(title) = title %}
        Title: {{title}}
    {% endif %}
{% endmacro %}

{% call test() %}{% endcall %}

error: failed to parse template source
         --> templates/page.jinja:1:31
       "&'static str>::None) %}\n    {% if let Some(title) = title %}\n        Title: {{ti"...
 --> src/main.rs:4:19

Which of the two would you suggest to support? Both?

[GuillaumeGomez]

The first for sure. The second would be up to debate. What about opening issues for both of them? Like that we can decide whether or not we want the second one.