Add support for macro args type annotations

[GuillaumeGomez]

Fixes #514.

Does it look good to you @seijikun ?

[seijikun]

Awesome, thank you for working on this!

I just tried the following:

use askama::Template;

struct ComplexStruct {
    title: String,
    icon: String,
}

#[derive(Template)]
#[template(
    source = r#"
        {%- macro test(entries: &[ComplexStruct]) -%}{% endmacro -%}
        {{ test(&entries) }}
    "#,
    ext = "txt"
)]
struct Page {
    entries: Vec<ComplexStruct>,
}

fn main() {
    let page = Page {
        entries: vec![ComplexStruct {
            title: "title".to_string(),
            icon: "icon".to_string(),
        }],
    };
    page.render().unwrap();
}

But am getting this error:

error: expected `)` to close macro argument list
         --> <source attribute>:2:22
       "(entries: &[ComplexStruct]) -%}{% endmacro -%}\n        {{ test(entries) }}\n    "
  --> src/main.rs:10:14
   |
10 |       source = r#"
   |  ______________^
11 | |         {%- macro test(entries: &[ComplexStruct]) -%}{% endmacro -%}
12 | |         {{ test(entries) }}
13 | |     "#,
   | |______^

[GuillaumeGomez]

Updated with new tests (including yours). Can you give it another try please?

[seijikun]

Looks good!
I'd personally prefer the implementation to take the type verbatim instead of forcefully injecting a & - so the behavior is a bit more predictable.
But I guess you probably had a good reason for taking all arguments as reference(?)

[seijikun]

It might make sense to also test the short call syntax in the tests:

{{ test(y) }}

[GuillaumeGomez]

Adding a test for it.

[GuillaumeGomez]

I'd personally prefer the implementation to take the type verbatim instead of forcefully injecting a & - so the behavior is a bit more predictable.
But I guess you probably had a good reason for taking all arguments as reference(?)

Sadly it comes from the current limitations of the proc-macros error reporting. If we don't add a reference, it will then take ownership, leading to hard to track errors. So for now, it's simply a better user experience. Hopefully, once the proc-macro Span API evolves, we can change it.

[GuillaumeGomez]

@seijikun Added the test you suggested, thanks for that!

Also realized I forgot to add docs for it so added it as well. Seems like PR is ready to go. Merging once CI is happy.