proc-macro derive panicked on range-based for loop.

[sbwtw]

{% for i in *start..*end %}
    {{ i }},
{% endfor %}

#[derive(Template)]
#[template(path = "for-range.html")]
struct ForRangeTemplate {
    start: usize,
    end: usize,
}

#[test]
fn test_for_range() {
    let s = ForTemplate {
        start:0, end: 3
    };
    assert_eq!(s.render().unwrap(), "0,1,2,");
}

output:

C:\Windows\system32\cmd.exe /c (cargo test -- test_for_range)
   Compiling askama_testing v0.1.0 (E:\Projects\askama\testing)
error: proc-macro derive panicked
  --> testing\tests\loops.rs:20:10
   |
20 | #[derive(Template)]
   |          ^^^^^^^^
   |
   = help: message: unable to parse template:

           "{% for i in *start..*end %}\r\n    {{ i }},\r\n{% endfor %}\r"

error: aborting due to previous error

error: Could not compile `askama_testing`.

To learn more, run the command again with --verbose.
shell returned 101
Hit any key to close this window...

[djc]

Yeah, Askama does not support & or * prefixes. It tries to do the right thing automatically there, but it probably doesn't always get it right. Did you try with just start and end, and if so, what error message do you get in that case?

[sbwtw]

@djc
for i in start..end

error[E0308]: mismatched types
  --> src\main.rs:62:10
   |
62 | #[derive(Template)]
   |          ^^^^^^^^
   |          |
   |          expected &usize, found usize
   |          help: consider borrowing here: `&Template`
   |
   = note: expected type `&usize`
              found type `usize`

error[E0599]: no method named `into_iter` found for type `std::ops::Range<&usize
>` in the current scope
  --> src\main.rs:62:10
   |
62 | #[derive(Template)]
   |          ^^^^^^^^
   |
   = note: the method `into_iter` exists but the following trait bounds were not
 satisfied:
           `std::ops::Range<&usize> : std::iter::IntoIterator`
           `&std::ops::Range<&usize> : std::iter::IntoIterator`
           `&mut std::ops::Range<&usize> : std::iter::IntoIterator`

error: aborting due to 2 previous errors

Some errors occurred: E0308, E0599.
For more information about an error, try `rustc --explain E0308`.

and even literal integer for i in 0..3 is not work too:

error[E0308]: mismatched types
  --> src\main.rs:62:10
   |
62 | #[derive(Template)]
   |          ^^^^^^^^
   |          |
   |          expected &{integer}, found integral variable
   |          help: consider borrowing here: `&Template`
   |
   = note: expected type `&{integer}`
              found type `{integer}`

error[E0599]: no method named `into_iter` found for type `std::ops::Range<&{inte
ger}>` in the current scope
  --> src\main.rs:62:10
   |
62 | #[derive(Template)]
   |          ^^^^^^^^
   |
   = note: the method `into_iter` exists but the following trait bounds were not
 satisfied:
           `std::ops::Range<&{integer}> : std::iter::IntoIterator`
           `&std::ops::Range<&{integer}> : std::iter::IntoIterator`
           `&mut std::ops::Range<&{integer}> : std::iter::IntoIterator`

error: aborting due to 2 previous errors

Some errors occurred: E0308, E0599.
For more information about an error, try `rustc --explain E0308`.

[zzau13]

@djc You have to treat the ranges separately, like

 match iter {
            Expr::Range(_, _, _) => buf.writeln(&format!(") in ({}).enumerate() {{", expr_code)),
            _ => buf.writeln(&format!(") in (&{}).into_iter().enumerate() {{", expr_code)),
        };

I add coverage to this part and do the pull request

[zzau13]

The problem is that we can not differentiate between iterator and vector. We should always use iterators. And force the user to use them. It would be necessary to change several tests by adding .into_iter() to the html. Same of #107. I add to that pull request?

[djc]

This has been fixed by @botika in #118. @sbwtw thanks for reporting, and @botika thanks for fixing!

@botika I don't want to require users to force users to pass actual Iterators into templates. Ideally we'd make it work in general for things that are IntoIterator as well as for things that are Iterator. Maybe we could do this by coming up with a more general internal trait?