horrorshow/

macros.rs

// rustfmt doesn't like this file (lines too long, too hard to fix)
#![cfg_attr(rustfmt, rustfmt_skip)]

/// Create a new HTML template.
#[macro_export]
macro_rules! html {
    ($($inner:tt)*) => {{
        // Define this up here to prevent rust from saying:
        // Hey look, it's an FnOnce (this could be Fn/FnMut).
        let f = |__tmpl: &mut $crate::TemplateBuffer| -> () {
            $crate::append_html!(__tmpl, html, (), $($inner)*);
        };
        // Stringify the template content to get a hint at how much we should allocate...
        $crate::FnRenderer::with_capacity(stringify!($($inner)*).len(), f)
    }}
}

/// Create a new XML template.
#[macro_export]
macro_rules! xml {
    ($($inner:tt)*) => {{
        let f = |__tmpl: &mut $crate::TemplateBuffer| -> () {
            $crate::append_html!(__tmpl, xml, (), $($inner)*);
        };
        $crate::FnRenderer::with_capacity(stringify!($($inner)*).len(), f)
    }}
}

/// Create a new HTML template taking ownership of any variables used inside.
#[macro_export]
macro_rules! owned_html {
    ($($inner:tt)*) => {{
        // Define this up here to prevent rust from saying:
        // Hey look, it's an FnOnce (this could be Fn/FnMut).
        let f = move |__tmpl: &mut $crate::TemplateBuffer| -> () {
            $crate::append_html!(__tmpl, html, (), $($inner)*);
        };
        // Stringify the template content to get a hint at how much we should allocate...
        $crate::FnRenderer::with_capacity(stringify!($($inner)*).len(), f)
    }}
}

/// Create a new XML template taking ownership of any variables used inside.
#[macro_export]
macro_rules! owned_xml {
    ($($inner:tt)*) => {{
        let f = move |__tmpl: &mut $crate::TemplateBuffer| -> () {
            $crate::append_html!(__tmpl, xml, (), $($inner)*);
        };
        $crate::FnRenderer::with_capacity(stringify!($($inner)*).len(), f)
    }}
}

/// Create a new owned html template.
///
/// This template will be boxed and will own it's environment. If you need to return a template
/// from a function, use this.
///
/// Example:
///
/// ```rust
/// # #[macro_use]
/// # extern crate horrorshow;
///
/// # fn main() {
/// fn post<'a>(title: &'a str) -> Box<horrorshow::RenderBox + 'a> {
///     box_html! {
///         article {
///             title { h1 : title }
///             p : "This is one paragraph.";
///             p : "This is a second.";
///         }
///     }
/// }
/// println!("{}", html! {
///     html {
///         body {
///             : post("First Post");
///             |t| for i in 0..10 {
///                 // Waiting for non-lexical borrows!!!!
///                 let tmp = format!("Spam post {}", i);
///                 let post = post(&tmp);
///                 &mut *t << post;
///             };
///         }
///     }
/// });
/// # }
/// ```
#[macro_export]
macro_rules! box_html {
    ($($inner:tt)*) => {{
        Box::new($crate::owned_html!($($inner)*))
    }}
}

/// Append html to the current template.
/// Don't call this manually.
#[macro_export]
macro_rules! append_html {

    // Nop out close-tags for void elements.
    (@close_tag html area) => {">"};
    (@close_tag html base) => {">"};
    (@close_tag html br) => {">"};
    (@close_tag html col) => {">"};
    (@close_tag html embed) => {">"};
    (@close_tag html hr) => {">"};
    (@close_tag html img) => {">"};
    (@close_tag html input) => {">"};
    (@close_tag html link) => {">"};
    (@close_tag html meta) => {">"};
    (@close_tag html param) => {">"};
    (@close_tag html source) => {">"};
    (@close_tag html track) => {">"};
    (@close_tag html wbr) => {">"};
    (@close_tag html $($tag:ident)-+) => {
        concat!("></", $crate::append_html!(@stringify_compressed $($tag)-+), ">");
    };
    (@close_tag xml $($tag:ident)-+) => {
        "/>"
    };
    (@stringify_compressed $($tok:tt)*) => {
        concat!($(stringify!($tok)),*)
    };

    (@block_identity $b:block) => { $b };
    (@cont $tmpl:ident, $type:ident, ($s:stmt), $($next:tt)*) => {
        $s;
        $crate::append_html!($tmpl, $type, (), $($next)*);
    };
    (@write_const $tmpl:ident, $type:ident,) => {};
    (@write_const $tmpl:ident, $type:ident, $($p:expr),+) => {
        $tmpl.write_raw(concat!($($p),*));
    };
    (@expr_and_block $tmpl:ident, $type:ident, parse_match_block, (match $($prefix:tt)*), {$($pattern:pat => {$($inner:tt)*})*} $($next:tt)*) => {
        $crate::append_html!(@parse_match_block $tmpl, $type, (match ($($prefix)*) {$($pattern => {$($inner)*})*}), $($next)*);
    };
    (@expr_and_block $tmpl:ident, $type:ident, $goto:ident, ($($prefix:tt)*), {$($inner:tt)*} $($next:tt)*) => {
        $crate::append_html!(@$goto $tmpl, $type, ($($prefix)* {$crate::append_html!($tmpl, $type, (), $($inner)*);}), $($next)*);
    };
    (@expr_and_block $tmpl:ident, $type:ident, $goto:ident, ($($prefix:tt)*), $first:tt $($next:tt)*) => {
        $crate::append_html!(@expr_and_block $tmpl, $type, $goto, ($($prefix)* $first), $($next)*);
    };
    (@append_attrs $tmpl:ident, $type:ident, ($($p:expr),*), $($($attr:ident)-+):+ ?= $value:expr, $($rest:tt)+) => {
        $crate::append_html!(@append_attrs $tmpl, $type, ($($p),*), $($($attr)-+):+ ?= $value);
        $crate::append_html!(@append_attrs $tmpl, $type, (), $($rest)+);
    };
    (@append_attrs $tmpl:ident, $type:ident, ($($p:expr),*), $($($attr:ident)-+):+ ?= $value:expr) => {
        match $crate::BoolOption::bool_option($value) {
            (_, None) => {
                $crate::append_html!(@write_const $tmpl, $type, $($p),*);
            },
            (true, Some(_)) => { $crate::append_html!(@append_attrs $tmpl, $type, ($($p),*), $($($attr)-+):+); }
            (false, Some(v)) => { $crate::append_html!(@append_attrs $tmpl, $type, ($($p),*), $($($attr)-+):+ = v); }
        };
    };
    (@append_attrs $tmpl:ident, $type:ident, ($($p:expr),*), $($($attr:ident)-+):+ = $value:expr, $($rest:tt)+) => {
        $crate::append_html!(@append_attrs $tmpl, $type, ($($p),*), $($($attr)-+):+ = $value);
        $crate::append_html!(@append_attrs $tmpl, $type, (), $($rest)+);
    };
    (@append_attrs $tmpl:ident, $type:ident, ($($p:expr),*), $($($attr:ident)-+):+, $($rest:tt)+) => {
        $crate::append_html!(@append_attrs $tmpl, $type, ($($p),*), $($($attr)-+):+);
        $crate::append_html!(@append_attrs $tmpl, $type, (), $($rest)+);
    };
    (@append_attrs $tmpl:ident, $type:ident, ($($p:expr),*), $($($attr:ident)-+):+ = $value:expr) => {
        $tmpl.write_raw(concat!($($p,)* " ", $crate::append_html!(@stringify_compressed $($($attr)-+):+), "=\""));
        $crate::RenderOnce::render_once($value, $tmpl);
        $tmpl.write_raw("\"");
    };
    (@append_attrs $tmpl:ident, html, ($($p:expr),*), $($($attr:ident)-+):+) => {
        $tmpl.write_raw(concat!($($p,)* " ", $crate::append_html!(@stringify_compressed $($($attr)-+):+)));
    };
    (@append_attrs $tmpl:ident, xml, ($($p:expr),*), $($($attr:ident)-+):+) => {{
        $tmpl.write_raw(concat!($($p,)* " ",
            $crate::append_html!(@stringify_compressed $($($attr)-+):+),
            "=\"",
            $crate::append_html!(@stringify_compressed $($($attr)-+):+),
            "\""
        ));
    }};
    //////// IF CHAINS
    //// Begin
    (@parse_if $tmpl:ident, $type:ident, ($($prefix:tt)*), if let $v:pat = $e:tt $($next:tt)+) => {
        $crate::append_html!(@expr_and_block $tmpl, $type, parse_if_block, ($($prefix)* if let $v = $e), $($next)+);
    };
    (@parse_if $tmpl:ident, $type:ident, ($($prefix:tt)*), if $e:tt $($next:tt)+) => {
        $crate::append_html!(@expr_and_block $tmpl, $type, parse_if_block, ($($prefix)* if $e), $($next)+);
    };
    //// End
    // Else if
    (@parse_if_block $tmpl:ident, $type:ident, ($($prefix:tt)*), else if $($next:tt)*) => {
        $crate::append_html!(@parse_if $tmpl, $type, ($($prefix)* else), if $($next)*);
    };
    // Else
    (@parse_if_block $tmpl:ident, $type:ident, ($($prefix:tt)*), else {$($inner:tt)*} $($next:tt)*) => {
        $crate::append_html!(@cont $tmpl, $type, ($($prefix)* else {$crate::append_html!($tmpl, $type, (), $($inner)*);}), $($next)*);
    };
    // No else.
    (@parse_if_block $tmpl:ident, $type:ident, ($($prefix:tt)*), $($next:tt)*) => {
        $crate::append_html!(@cont $tmpl, $type, ($($prefix)*), $($next)*);
    };
    //////// MATCH
    (@parse_match_block $tmpl:ident, $type:ident, (match ($($prefix:tt)*) {$($pattern:pat => {$($inner:tt)*})*}), $($next:tt)*) => {
        $crate::append_html!(@cont $tmpl, $type, (match ($($prefix)*) {$(
            $pattern => { $crate::append_html!($tmpl, $type, (), $($inner)*); }
        )*}), $($next)*);
    };
    //// Condition
    ($tmpl:ident, $type:ident, ($($p:expr),*), @ if $($next:tt)+) => {
        $crate::append_html!(@write_const $tmpl, $type, $($p),*);
        $crate::append_html!(@parse_if $tmpl, $type, (), if $($next)*);
    };
    ($tmpl:ident, $type:ident, ($($p:expr),*), @ for $v:pat in $e:tt $($next:tt)*) => {
        $crate::append_html!(@write_const $tmpl, $type, $($p),*);
        $crate::append_html!(@expr_and_block $tmpl, $type, cont, (for $v in $e), $($next)*);
    };
    ($tmpl:ident, $type:ident, ($($p:expr),*), @ while let $v:pat = $e:tt $($next:tt)*) => {
        $crate::append_html!(@write_const $tmpl, $type, $($p),*);
        $crate::append_html!(@expr_and_block $tmpl, $type, cont, (while let $v = $e), $($next)*);
    };
    ($tmpl:ident, $type:ident, ($($p:expr),*), @ while $e:tt $($next:tt)*) => {
        $crate::append_html!(@write_const $tmpl, $type, $($p),*);
        $crate::append_html!(@expr_and_block $tmpl, $type, cont, (while $e), $($next)*);
    };
    ($tmpl:ident, $type:ident, ($($p:expr),*), @ match $e:tt $($next:tt)+) => {
        $crate::append_html!(@write_const $tmpl, $type, $($p),*);
        $crate::append_html!(@expr_and_block $tmpl, $type, parse_match_block, (match $e), $($next)*);
    };
    ($tmpl:ident, $type:ident, ($($p:expr),*), : {$($code:tt)*} $($next:tt)*) => {
        $crate::append_html!(@write_const, $tmpl, $type, $($p),*);
        $crate::RenderOnce::render_once({$($code)*}, $tmpl);
        $crate::append_html!($tmpl, $type, (), $($next)*);
    };
    ($tmpl:ident, $type:ident, ($($p:expr),*), : $code:expr; $($next:tt)* ) => {
        $crate::append_html!(@write_const $tmpl, $type, $($p),*);
        $crate::RenderOnce::render_once($code, $tmpl);
        $crate::append_html!($tmpl, $type, (), $($next)*);
    };
    ($tmpl:ident, $type:ident, ($($p:expr),*), : $code:expr ) => {
        $crate::append_html!(@write_const $tmpl, $type, $($p),*);
        $crate::RenderOnce::render_once($code, $tmpl);
    };
    ($tmpl:ident, $type:ident, ($($p:expr),*), |$var:ident| {$($code:tt)*} $($next:tt)*) => {
        $crate::append_html!(@write_const $tmpl, $type, $($p),*);
        {
            let $var: &mut $crate::TemplateBuffer = &mut *$tmpl;
            $crate::append_html!(@block_identity {$($code)*})
        }
        $crate::append_html!($tmpl, $type, (), $($next)*);
    };
    ($tmpl:ident, $type:ident, ($($p:expr),*), |mut $var:ident| {$($code:tt)*} $($next:tt)*) => {
        $crate::append_html!(@write_const $tmpl, $type, $($p),*);
        {
            let mut $var: &mut $crate::TemplateBuffer = &mut *$tmpl;
            $crate::append_html!(@block_identity {$($code)*})
        }
        $crate::append_html!($tmpl, $type, (), $($next)*);
    };
    ($tmpl:ident, $type:ident, ($($p:expr),*), |$var:ident| $code:stmt; $($next:tt)* ) => {
        $crate::append_html!(@write_const $tmpl, $type, $($p),*);
        {
            let $var: &mut $crate::TemplateBuffer = &mut *$tmpl;
            $code;
        }
        $crate::append_html!($tmpl, $type, (), $($next)*);
    };
    ($tmpl:ident, $type:ident, ($($p:expr),*), |mut $var:ident| $code:stmt; $($next:tt)* ) => {
        $crate::append_html!(@write_const $tmpl, $type, $($p),*);
        {
            let mut $var: &mut $crate::TemplateBuffer = &mut *$tmpl;
            $code;
        }
        $crate::append_html!($tmpl, $type, (), $($next)*);
    };
    ($tmpl:ident, $type:ident, ($($p:expr),*), |$var:ident| $code:stmt ) => {{
        $crate::append_html!(@write_const $tmpl, $type, $($p),*);
        let $var: &mut $crate::TemplateBuffer = &mut *$tmpl;
        $code;
    }};
    ($tmpl:ident, $type:ident, ($($p:expr),*), |mut $var:ident| $code:stmt ) => {{
        $crate::append_html!(@write_const $tmpl, $type, $($p),*);
        let mut $var: &mut $crate::TemplateBuffer = &mut *$tmpl;
        $code;
    }};
    ($tmpl:ident, $type:ident, ($($p:expr),*), $($tag:ident)-+($($attrs:tt)+) { $($children:tt)* } $($next:tt)* ) => {
        $crate::append_html!(@append_attrs $tmpl, $type, ($($p,)* "<", $crate::append_html!(@stringify_compressed $($tag)-+)), $($attrs)+);
        $crate::append_html!($tmpl, $type, (">"), $($children)*);
        $crate::append_html!($tmpl, $type, ("</", $crate::append_html!(@stringify_compressed $($tag)-+), ">"), $($next)*);
    };
    ($tmpl:ident, $type:ident, ($($p:expr),*), $($tag:ident)-+($($attr:tt)+) : $e:expr; $($next:tt)* ) => {
        $crate::append_html!($tmpl, $type, ($($p),*), $($tag)-+($($attr)+) { : $e; } $($next)* );
    };
    ($tmpl:ident, $type:ident, ($($p:expr),*), $($tag:ident)-+($($attr:tt)+) : $e:expr) => {
        $crate::append_html!($tmpl, $type, ($($p),*), $($tag)-+($($attr)+) { : $e });
    };
    ($tmpl:ident, $type:ident, ($($p:expr),*), $($tag:ident)-+($($attr:tt)+) : {$($code:tt)*} $($next:tt)* ) => {
        $crate::append_html!($tmpl, $type, ($($p),*), $($tag)-+($($attr)+) { : {$($code)*} } $($next)* );
    };
    ($tmpl:ident, $type:ident, ($($p:expr),*), $($tag:ident)-+($($attrs:tt)+); $($next:tt)*) => {
        $crate::append_html!(@append_attrs $tmpl, $type, ($($p,)* "<", $crate::append_html!(@stringify_compressed $($tag)-+)), $($attrs)+);
        $crate::append_html!($tmpl, $type, ($crate::append_html!(@close_tag $type $($tag)-+)), $($next)*);
    };
    ($tmpl:ident, $type:ident, ($($p:expr),*), $($tag:ident)-+($($attrs:tt)+)) => {
        $crate::append_html!(@append_attrs $tmpl, $type, ($($p,)* "<", $crate::append_html!(@stringify_compressed $($tag)-+)), $($attrs)+);
        $tmpl.write_raw($crate::append_html!(@close_tag $type $($tag)-+));
    };
    ($tmpl:ident, $type:ident, ($($p:expr),*), $($tag:ident)-+ { $($children:tt)* } $($next:tt)* ) => {
        $crate::append_html!($tmpl, $type, ($($p,)* "<", $crate::append_html!(@stringify_compressed $($tag)-+), ">"), $($children)*);
        $crate::append_html!($tmpl, $type, ("</", $crate::append_html!(@stringify_compressed $($tag)-+), ">"), $($next)*);
    };
    ($tmpl:ident, $type:ident, ($($p:expr),*), $($tag:ident)-+ : $e:expr; $($next:tt)* ) => {
        $crate::append_html!($tmpl, $type, ($($p),*), $($tag)-+ { : $e; } $($next)* );
    };
    ($tmpl:ident, $type:ident, ($($p:expr),*), $($tag:ident)-+ : {$($code:tt)*} $($next:tt)* ) => {
        $crate::append_html!($tmpl, $type, ($($p),*), $($tag)-+ { : {$($code)*} } $($next)* );
    };
    ($tmpl:ident, $type:ident, ($($p:expr),*), $($tag:ident)-+; $($next:tt)*) => {
        $crate::append_html!($tmpl, $type, ($($p,)* "<", $crate::append_html!(@stringify_compressed $($tag)-+), $crate::append_html!(@close_tag $type $($tag)-+)), $($next)*);
    };
    ($tmpl:ident, $type:ident, ($($p:expr),*), $($tag:ident)-+ : $e:expr) => {
        $crate::append_html!($tmpl, $type, ($($p),*), $($tag)-+ { : $e; });
    };
    ($tmpl:ident, $type:ident, ($($p:expr),*), $($tag:ident)-+) => {
        $crate::append_html!(@write_const $tmpl, $type, $($p,)* "<", $crate::append_html!(@stringify_compressed $($tag)-+), $crate::append_html!(@close_tag $type $($tag)-+));
    };
    ($tmpl:ident, $type:ident, ($($p:expr),*),) => {
        $crate::append_html!(@write_const $tmpl, $type, $($p),*);
    };
    ($tmpl:ident, $type:ident, ($($p:expr),*), $t:tt $($tr:tt)*) => {
        compile_error!(concat!("unexpected token tree: ", stringify!($t), "\n\nYou're probably missing a semicolon somewhere."));
    }
}

/// Create a new template.
///
/// This allows you to declare a template as follows:
///
/// ```
/// # #[macro_use]
/// # extern crate horrorshow;
/// template! {
///     MyTemplate(name: &str, age: &u32) {
///         p {
///            : "Hello, my name is ";
///            : name;
///            : " and I am ";
///            : age;
///            : " years old.";
///         }
///     }
/// }
/// # fn main() { }
/// ```
///
/// You can instantiate these templates by calling `new` on them:
///
/// ```
/// # #[macro_use]
/// # extern crate horrorshow;
/// # template! {
/// #     MyTemplate(name: &str, age: &u32) {
/// #         p {
/// #            : "Hello, my name is ";
/// #            : name;
/// #            : " and I am ";
/// #            : age;
/// #            : " years old.";
/// #         }
/// #     }
/// # }
///
/// # fn main() {
/// let age = 42;
/// let tmpl = MyTemplate::new("Not Me", &age);
/// # }
/// ```
///
/// These templates never own their content, they just borrow it. This is one of the reasons I call
/// this feature "experimental".
#[macro_export]
macro_rules! template {
    ($name:ident ($($field:ident : &$typ:ty),*) { $($tmpl:tt)* } $($rest:tt)*) => {
        struct $name<'a> { $( $field: &'a $typ),* }
        impl<'a> $name<'a> {
            pub fn new($($field: &'a $typ),*) -> Self {
                $name { $( $field: $field),* }
            }
        }
        impl<'a> $crate::RenderOnce for $name<'a> {
            fn render_once(self, tmpl: &mut $crate::TemplateBuffer) {
                $crate::Render::render(&self, tmpl);
            }
        }
        impl<'a> $crate::RenderMut for $name<'a> {
            fn render_mut(&mut self, tmpl: &mut $crate::TemplateBuffer) {
                $crate::Render::render(self, tmpl);
            }
        }
        impl<'a> $crate::Render for $name<'a> {
            fn render(&self, tmpl: &mut $crate::TemplateBuffer) {
                let &$name { $($field),* } = self;
                tmpl << $crate::html! { $($tmpl)* };
            }
        }
        $crate::template!($($rest)*);
    };
    (pub $name:ident ($($field:ident : &$typ:ty),*) { $($tmpl:tt)* } $($rest:tt)*) => {
        pub struct $name<'a> { $( $field: &'a $typ),* }
        impl<'a> $name<'a> {
            pub fn new($($field: &'a $typ),*) -> Self {
                $name { $( $field: $field),* }
            }
        }
        impl<'a> $crate::RenderOnce for $name<'a> {
            fn render_once(self, tmpl: &mut $crate::TemplateBuffer) {
                $crate::Render::render(&self, tmpl);
            }
        }
        impl<'a> $crate::RenderMut for $name<'a> {
            fn render_mut(&mut self, tmpl: &mut $crate::TemplateBuffer) {
                $crate::Render::render(self, tmpl);
            }
        }
        impl<'a> $crate::Render for $name<'a> {
            fn render(&self, tmpl: &mut $crate::TemplateBuffer) {
                let &$name { $($field),* } = self;
                tmpl << $crate::html! { $($tmpl)* };
            }
        }
        $crate::template!($($rest)*);
    };
    () => {}
}

/// Utility macro for generating a space-delimited string from a set of labels;
/// some of which may be conditionally included into the final string.
/// Labels are anything that implements the `RenderOnce` trait (e.g. `String` or `&str`).
///
/// This macro is an alias of: `labels_sep_by!(" "; maybe_label,...)`
///
/// Usage: `labels!(maybe_label,...)`
///
/// * `maybe_label` -- Either `label_expression`, or `label_expression => cond_test`.
///
/// * `label_expression` -- An expression that returns a label that implements
///   the `RenderOnce` trait (e.g. `String` or `&str`).
///
/// * `label_expression => cond_test` -- Conditionally include `label_expression` whenever `cond_test` is `true`.
///   `cond_test` is an expression that returns either `true` or `false`.
///
/// This useful in generating class attribute as follows:
///
/// ```
/// # #[macro_use]
/// # extern crate horrorshow;
/// # fn main() {
/// html! {
///     div(class = labels!("active" => true, "button-style")) {
///         : "This is a button"
///     }
/// }
/// # ;
/// # }
/// ```
///
#[macro_export]
macro_rules! labels {

    ($($tail:tt)+) => (
        $crate::labels_sep_by!(" "; $($tail)*)
    );

}

/// Utility macro for generating a delimited string from a set of labels;
/// some of which may be conditionally included into the final string.
/// The delimiter/seperator and labels are anything that implements
/// the `RenderOnce` trait (e.g. `String` or `&str`).
///
///
/// Usage: `labels_sep_by!(seperator; maybe_label,...)`
///
/// * `seperator` -- Delimiter/seperator that implements the `RenderOnce` trait (e.g. `String` or `&str`).
///
/// * `maybe_label` -- Either `label_expression`, or `label_expression => cond_test`.
///
/// * `label_expression` -- An expression that returns a label that implements
///   the `RenderOnce` trait (e.g. `String` or `&str`).
///
/// * `label_expression => cond_test` -- Conditionally include `label_expression` whenever `cond_test` is `true`.
///   `cond_test` is an expression that returns either `true` or `false`.
///
/// This useful in generating style attribute as follows:
///
/// ```
/// # #[macro_use]
/// # extern crate horrorshow;
/// # fn main() {
/// html! {
///     div(style = labels_sep_by!(";"; "color: #000" => true, "font-weight: bold")) {
///         : "This is a button"
///     }
/// }
/// # ;
/// # }
/// ```
///
#[macro_export]
macro_rules! labels_sep_by {

    (@inner_expand $has_before:expr; $sep:expr; $tmpl:ident $item:expr) => {
        if $has_before {
            $crate::RenderOnce::render_once($sep, $tmpl);
        }
        $crate::RenderOnce::render_once($item, $tmpl);
    };

    (@inner_expand $has_before:expr; $sep:expr; $tmpl:ident $item:expr => $should_include:expr) => {
        if $should_include {
            if $has_before {
                $crate::RenderOnce::render_once($sep, $tmpl);
            }
            $crate::RenderOnce::render_once($item, $tmpl);
        }
    };

    (@inner_expand $has_before:expr; $sep:expr; $tmpl:ident $item:expr, $($tail:tt)+) => {
        if $has_before {
            $crate::RenderOnce::render_once($sep, $tmpl);
        }
        $crate::RenderOnce::render_once($item, $tmpl);
        $crate::labels_sep_by!(@inner_expand true; $sep; $tmpl $($tail)*);
    };

    (@inner_expand $has_before:expr; $sep:expr; $tmpl:ident $item:expr => $should_include:expr, $($tail:tt)+) => {
        if $should_include {
            if $has_before {
                $crate::RenderOnce::render_once($sep, $tmpl);
            }
            $crate::RenderOnce::render_once($item, $tmpl);
        }
        $crate::labels_sep_by!(@inner_expand $has_before || $should_include; $sep; $tmpl $($tail)*);
    };

    // entries

    ($sep:expr; $item:expr) => {

        $crate::FnRenderer::new(|tmpl| {
            $crate::RenderOnce::render_once($item, tmpl);
        })

    };

    ($sep:expr; $item:expr => $should_include:expr) => {

        $crate::FnRenderer::new(|tmpl| {
            if $should_include {
                $crate::RenderOnce::render_once($item, tmpl);
            }
        })

    };

    ($sep:expr; $item:expr, $($tail:tt)+) => {

        $crate::FnRenderer::new(|tmpl| {
            $crate::RenderOnce::render_once($item, tmpl);
            $crate::labels_sep_by!(@inner_expand true; $sep; tmpl $($tail)*);
        })

    };

    ($sep:expr; $item:expr => $should_include:expr, $($tail:tt)+) => {

        $crate::FnRenderer::new(|tmpl| {
            if $should_include {
                $crate::RenderOnce::render_once($item, tmpl);
            }
            $crate::labels_sep_by!(@inner_expand $should_include; $sep; tmpl $($tail)*);
        })

    };

}