Merge pull request #36 from Kijewski/rest-pattern-struct#2

Add support for `..` in let pattern matching for structs (alternative take)

rinja_derive/src/generator.rs

@@ -12,10 +12,9 @@ use crate::input::{Source, TemplateInput};
 use crate::{CompileError, CRATE};
 
 use parser::node::{
-    Call, Comment, CondTest, FilterBlock, If, Include, Let, Lit, Loop, Match, Target, Whitespace,
-    Ws,
+    Call, Comment, CondTest, FilterBlock, If, Include, Let, Lit, Loop, Match, Whitespace, Ws,
 };
-use parser::{Expr, Filter, Node, WithSpan};
+use parser::{Expr, Filter, Node, Target, WithSpan};
 use quote::quote;
 
 pub(crate) struct Generator<'a> {
@@ -1788,8 +1787,8 @@ impl<'a> Generator<'a> {
         target: &Target<'a>,
     ) {
         match target {
-            Target::Name("_") => {
-                buf.write("_");
+            Target::Placeholder(s) | Target::Rest(s) => {
+                buf.write(s);
             }
             Target::Name(name) => {
                 let name = normalize_identifier(name);
@@ -1824,6 +1823,11 @@ impl<'a> Generator<'a> {
                 buf.write(SeparatedPath(path));
                 buf.write(" { ");
                 for (name, target) in targets {
+                    if let Target::Rest(s) = target {
+                        buf.write(s);
+                        continue;
+                    }
+
                     buf.write(normalize_identifier(name));
                     buf.write(": ");
                     self.visit_target(buf, initialized, false, target);

rinja_parser/src/lib.rs

@@ -22,6 +22,9 @@ pub mod expr;
 pub use expr::{Expr, Filter};
 pub mod node;
 pub use node::Node;
+
+mod target;
+pub use target::Target;
 #[cfg(test)]
 mod tests;
 

rinja_parser/src/node.rs

@@ -3,19 +3,15 @@ use std::str;
 use nom::branch::alt;
 use nom::bytes::complete::{tag, take_till};
 use nom::character::complete::char;
-use nom::combinator::{
-    complete, consumed, cut, eof, map, map_res, not, opt, peek, recognize, value,
-};
+use nom::combinator::{complete, consumed, cut, eof, map, not, opt, peek, recognize, value};
 use nom::error::ErrorKind;
 use nom::error_position;
-use nom::multi::{fold_many0, many0, many1, separated_list0, separated_list1};
-use nom::sequence::{delimited, pair, preceded, terminated, tuple};
+use nom::multi::{many0, many1, separated_list0};
+use nom::sequence::{delimited, pair, preceded, tuple};
 
-use crate::{not_ws, ErrorContext, ParseResult, WithSpan};
-
-use super::{
-    bool_lit, char_lit, filter, identifier, is_ws, keyword, num_lit, path_or_identifier, skip_till,
-    str_lit, ws, Expr, Filter, PathOrIdentifier, State,
+use crate::{
+    filter, identifier, is_ws, keyword, not_ws, skip_till, str_lit, ws, ErrorContext, Expr, Filter,
+    ParseResult, State, Target, WithSpan,
 };
 
 #[derive(Debug, PartialEq)]
@@ -177,150 +173,6 @@ impl<'a> Node<'a> {
     }
 }
 
-#[derive(Clone, Debug, PartialEq)]
-pub enum Target<'a> {
-    Name(&'a str),
-    Tuple(Vec<&'a str>, Vec<Target<'a>>),
-    Struct(Vec<&'a str>, Vec<(&'a str, Target<'a>)>),
-    NumLit(&'a str),
-    StrLit(&'a str),
-    CharLit(&'a str),
-    BoolLit(&'a str),
-    Path(Vec<&'a str>),
-    OrChain(Vec<Target<'a>>),
-}
-
-impl<'a> Target<'a> {
-    /// Parses multiple targets with `or` separating them
-    pub(super) fn parse(i: &'a str, s: &State<'_>) -> ParseResult<'a, Self> {
-        map(
-            separated_list1(ws(tag("or")), |i| s.nest(i, |i| Self::parse_one(i, s))),
-            |mut opts| match opts.len() {
-                1 => opts.pop().unwrap(),
-                _ => Self::OrChain(opts),
-            },
-        )(i)
-    }
-
-    /// Parses a single target without an `or`, unless it is wrapped in parentheses.
-    fn parse_one(i: &'a str, s: &State<'_>) -> ParseResult<'a, Self> {
-        let mut opt_opening_paren = map(opt(ws(char('('))), |o| o.is_some());
-        let mut opt_closing_paren = map(opt(ws(char(')'))), |o| o.is_some());
-        let mut opt_opening_brace = map(opt(ws(char('{'))), |o| o.is_some());
-
-        let (i, lit) = opt(Self::lit)(i)?;
-        if let Some(lit) = lit {
-            return Ok((i, lit));
-        }
-
-        // match tuples and unused parentheses
-        let (i, target_is_tuple) = opt_opening_paren(i)?;
-        if target_is_tuple {
-            let (i, is_empty_tuple) = opt_closing_paren(i)?;
-            if is_empty_tuple {
-                return Ok((i, Self::Tuple(Vec::new(), Vec::new())));
-            }
-
-            let (i, first_target) = Self::parse(i, s)?;
-            let (i, is_unused_paren) = opt_closing_paren(i)?;
-            if is_unused_paren {
-                return Ok((i, first_target));
-            }
-
-            let mut targets = vec![first_target];
-            let (i, _) = cut(tuple((
-                fold_many0(
-                    preceded(ws(char(',')), |i| Self::parse(i, s)),
-                    || (),
-                    |_, target| {
-                        targets.push(target);
-                    },
-                ),
-                opt(ws(char(','))),
-                ws(cut(char(')'))),
-            )))(i)?;
-            return Ok((i, Self::Tuple(Vec::new(), targets)));
-        }
-
-        let path = |i| {
-            map_res(path_or_identifier, |v| match v {
-                PathOrIdentifier::Path(v) => Ok(v),
-                PathOrIdentifier::Identifier(v) => Err(v),
-            })(i)
-        };
-
-        // match structs
-        let (i, path) = opt(path)(i)?;
-        if let Some(path) = path {
-            let i_before_matching_with = i;
-            let (i, _) = opt(ws(keyword("with")))(i)?;
-
-            let (i, is_unnamed_struct) = opt_opening_paren(i)?;
-            if is_unnamed_struct {
-                let (i, targets) = alt((
-                    map(char(')'), |_| Vec::new()),
-                    terminated(
-                        cut(separated_list1(ws(char(',')), |i| Self::parse(i, s))),
-                        pair(opt(ws(char(','))), ws(cut(char(')')))),
-                    ),
-                ))(i)?;
-                return Ok((i, Self::Tuple(path, targets)));
-            }
-
-            let (i, is_named_struct) = opt_opening_brace(i)?;
-            if is_named_struct {
-                let (i, targets) = alt((
-                    map(char('}'), |_| Vec::new()),
-                    terminated(
-                        cut(separated_list1(ws(char(',')), |i| Self::named(i, s))),
-                        pair(opt(ws(char(','))), ws(cut(char('}')))),
-                    ),
-                ))(i)?;
-                return Ok((i, Self::Struct(path, targets)));
-            }
-
-            return Ok((i_before_matching_with, Self::Path(path)));
-        }
-
-        // neither literal nor struct nor path
-        let (new_i, name) = identifier(i)?;
-        Ok((new_i, Self::verify_name(i, name)?))
-    }
-
-    fn lit(i: &'a str) -> ParseResult<'a, Self> {
-        alt((
-            map(str_lit, Self::StrLit),
-            map(char_lit, Self::CharLit),
-            map(num_lit, Self::NumLit),
-            map(bool_lit, Self::BoolLit),
-        ))(i)
-    }
-
-    fn named(init_i: &'a str, s: &State<'_>) -> ParseResult<'a, (&'a str, Self)> {
-        let (i, (src, target)) = pair(
-            identifier,
-            opt(preceded(ws(char(':')), |i| Self::parse(i, s))),
-        )(init_i)?;
-
-        let target = match target {
-            Some(target) => target,
-            None => Self::verify_name(init_i, src)?,
-        };
-
-        Ok((i, (src, target)))
-    }
-
-    fn verify_name(input: &'a str, name: &'a str) -> Result<Self, nom::Err<ErrorContext<'a>>> {
-        match name {
-            "self" | "writer" => Err(nom::Err::Failure(ErrorContext::new(
-                format!("cannot use `{name}` as a name"),
-                input,
-            ))),
-            _ => Ok(Self::Name(name)),
-        }
-    }
-}
-
 #[derive(Debug, PartialEq)]
 pub struct When<'a> {
     pub ws: Ws,
@@ -347,7 +199,7 @@ impl<'a> When<'a> {
             WithSpan::new(
                 Self {
                     ws: Ws(pws, nws),
-                    target: Target::Name("_"),
+                    target: Target::Placeholder("_"),
                     nodes,
                 },
                 start,

rinja_parser/src/target.rs

@@ -0,0 +1,213 @@
+use nom::branch::alt;
+use nom::bytes::complete::tag;
+use nom::character::complete::{char, one_of};
+use nom::combinator::{consumed, map, map_res, opt};
+use nom::multi::separated_list1;
+use nom::sequence::{pair, preceded};
+
+use crate::{
+    bool_lit, char_lit, identifier, keyword, num_lit, path_or_identifier, str_lit, ws,
+    ErrorContext, ParseErr, ParseResult, PathOrIdentifier, State,
+};
+
+#[derive(Clone, Debug, PartialEq)]
+pub enum Target<'a> {
+    Name(&'a str),
+    Tuple(Vec<&'a str>, Vec<Target<'a>>),
+    Struct(Vec<&'a str>, Vec<(&'a str, Target<'a>)>),
+    NumLit(&'a str),
+    StrLit(&'a str),
+    CharLit(&'a str),
+    BoolLit(&'a str),
+    Path(Vec<&'a str>),
+    OrChain(Vec<Target<'a>>),
+    Placeholder(&'a str),
+    Rest(&'a str),
+}
+
+impl<'a> Target<'a> {
+    /// Parses multiple targets with `or` separating them
+    pub(super) fn parse(i: &'a str, s: &State<'_>) -> ParseResult<'a, Self> {
+        map(
+            separated_list1(ws(tag("or")), |i| s.nest(i, |i| Self::parse_one(i, s))),
+            |mut opts| match opts.len() {
+                1 => opts.pop().unwrap(),
+                _ => Self::OrChain(opts),
+            },
+        )(i)
+    }
+
+    /// Parses a single target without an `or`, unless it is wrapped in parentheses.
+    fn parse_one(i: &'a str, s: &State<'_>) -> ParseResult<'a, Self> {
+        let mut opt_opening_paren = map(opt(ws(char('('))), |o| o.is_some());
+        let mut opt_opening_brace = map(opt(ws(char('{'))), |o| o.is_some());
+
+        let (i, lit) = opt(Self::lit)(i)?;
+        if let Some(lit) = lit {
+            return Ok((i, lit));
+        }
+
+        // match tuples and unused parentheses
+        let (i, target_is_tuple) = opt_opening_paren(i)?;
+        if target_is_tuple {
+            let (i, (singleton, mut targets)) = collect_targets(i, s, ')', Self::unnamed)?;
+            if singleton {
+                return Ok((i, targets.pop().unwrap()));
+            }
+            return Ok((i, Self::Tuple(Vec::new(), only_one_rest_pattern(targets)?)));
+        }
+
+        let path = |i| {
+            map_res(path_or_identifier, |v| match v {
+                PathOrIdentifier::Path(v) => Ok(v),
+                PathOrIdentifier::Identifier(v) => Err(v),
+            })(i)
+        };
+
+        // match structs
+        let (i, path) = opt(path)(i)?;
+        if let Some(path) = path {
+            let i_before_matching_with = i;
+            let (i, _) = opt(ws(keyword("with")))(i)?;
+
+            let (i, is_unnamed_struct) = opt_opening_paren(i)?;
+            if is_unnamed_struct {
+                let (i, (_, targets)) = collect_targets(i, s, ')', Self::unnamed)?;
+                return Ok((i, Self::Tuple(path, only_one_rest_pattern(targets)?)));
+            }
+
+            let (i, is_named_struct) = opt_opening_brace(i)?;
+            if is_named_struct {
+                let (i, (_, targets)) = collect_targets(i, s, '}', Self::named)?;
+                return Ok((i, Self::Struct(path, targets)));
+            }
+
+            return Ok((i_before_matching_with, Self::Path(path)));
+        }
+
+        // neither literal nor struct nor path
+        let (new_i, name) = identifier(i)?;
+        let target = match name {
+            "_" => Self::Placeholder(name),
+            _ => verify_name(i, name)?,
+        };
+        Ok((new_i, target))
+    }
+
+    fn lit(i: &'a str) -> ParseResult<'a, Self> {
+        alt((
+            map(str_lit, Self::StrLit),
+            map(char_lit, Self::CharLit),
+            map(num_lit, Self::NumLit),
+            map(bool_lit, Self::BoolLit),
+        ))(i)
+    }
+
+    fn unnamed(i: &'a str, s: &State<'_>) -> ParseResult<'a, Self> {
+        alt((Self::rest, |i| Self::parse(i, s)))(i)
+    }
+
+    fn named(init_i: &'a str, s: &State<'_>) -> ParseResult<'a, (&'a str, Self)> {
+        let (i, rest) = opt(consumed(Self::rest))(init_i)?;
+        if let Some(rest) = rest {
+            let (_, chr) = ws(opt(one_of(",:")))(i)?;
+            if let Some(chr) = chr {
+                return Err(nom::Err::Failure(ErrorContext::new(
+                    format!(
+                        "unexpected `{chr}` character after `..`\n\
+                         note that in a named struct, `..` must come last to ignore other members"
+                    ),
+                    i,
+                )));
+            }
+            return Ok((i, rest));
+        }
+
+        let (i, (src, target)) = pair(
+            identifier,
+            opt(preceded(ws(char(':')), |i| Self::parse(i, s))),
+        )(init_i)?;
+
+        if src == "_" {
+            return Err(nom::Err::Failure(ErrorContext::new(
+                "cannot use placeholder `_` as source in named struct",
+                init_i,
+            )));
+        }
+
+        let target = match target {
+            Some(target) => target,
+            None => verify_name(init_i, src)?,
+        };
+        Ok((i, (src, target)))
+    }
+
+    fn rest(i: &'a str) -> ParseResult<'a, Self> {
+        map(tag(".."), Self::Rest)(i)
+    }
+}
+
+fn verify_name<'a>(
+    input: &'a str,
+    name: &'a str,
+) -> Result<Target<'a>, nom::Err<ErrorContext<'a>>> {
+    match name {
+        "self" | "writer" => Err(nom::Err::Failure(ErrorContext::new(
+            format!("cannot use `{name}` as a name"),
+            input,
+        ))),
+        _ => Ok(Target::Name(name)),
+    }
+}
+
+fn collect_targets<'a, T>(
+    i: &'a str,
+    s: &State<'_>,
+    delim: char,
+    mut one: impl FnMut(&'a str, &State<'_>) -> ParseResult<'a, T>,
+) -> ParseResult<'a, (bool, Vec<T>)> {
+    let opt_comma = |i| map(ws(opt(char(','))), |o| o.is_some())(i);
+    let opt_end = |i| map(ws(opt(char(delim))), |o| o.is_some())(i);
+
+    let (i, has_end) = opt_end(i)?;
+    if has_end {
+        return Ok((i, (false, Vec::new())));
+    }
+
+    let (i, targets) = opt(separated_list1(ws(char(',')), |i| one(i, s)))(i)?;
+    let Some(targets) = targets else {
+        return Err(nom::Err::Failure(ErrorContext::new(
+            "expected comma separated list of members",
+            i,
+        )));
+    };
+
+    let (i, (has_comma, has_end)) = pair(opt_comma, opt_end)(i)?;
+    if !has_end {
+        let msg = match has_comma {
+            true => format!("expected member, or `{delim}` as terminator"),
+            false => format!("expected `,` for more members, or `{delim}` as terminator"),
+        };
+        return Err(nom::Err::Failure(ErrorContext::new(msg, i)));
+    }
+
+    let singleton = !has_comma && targets.len() == 1;
+    Ok((i, (singleton, targets)))
+}
+
+fn only_one_rest_pattern(targets: Vec<Target<'_>>) -> Result<Vec<Target<'_>>, ParseErr<'_>> {
+    let snd_wildcard = targets
+        .iter()
+        .filter_map(|t| match t {
+            Target::Rest(s) => Some(s),
+            _ => None,
+        })
+        .nth(1);
+    if let Some(snd_wildcard) = snd_wildcard {
+        return Err(nom::Err::Failure(ErrorContext::new(
+            "`..` can only be used once per tuple pattern",
+            snd_wildcard,
+        )));
+    }
+    Ok(targets)
+}

testing/tests/let_destructoring.rs

@@ -119,3 +119,73 @@ fn test_let_destruct_with_path_and_with_keyword() {
     };
     assert_eq!(t.render().unwrap(), "hello");
 }
+
+#[derive(Template)]
+#[template(
+    source = "
+{%- if let RestPattern2 { a, b } = x -%}hello {{ a }}{%- endif -%}
+{%- if let RestPattern2 { a, b, } = x -%}hello {{ b }}{%- endif -%}
+{%- if let RestPattern2 { a, .. } = x -%}hello {{ a }}{%- endif -%}
+",
+    ext = "html"
+)]
+struct RestPattern {
+    x: RestPattern2,
+}
+
+struct RestPattern2 {
+    a: u32,
+    b: u32,
+}
+
+#[test]
+fn test_has_rest_pattern() {
+    let t = RestPattern {
+        x: RestPattern2 { a: 0, b: 1 },
+    };
+    assert_eq!(t.render().unwrap(), "hello 0hello 1hello 0");
+}
+
+#[allow(dead_code)]
+struct X {
+    a: u32,
+    b: u32,
+}
+
+#[derive(Template)]
+#[template(
+    source = "
+{%- if let X { a, .. } = x -%}hello {{ a }}{%- endif -%}
+",
+    ext = "html"
+)]
+struct T1 {
+    x: X,
+}
+
+#[test]
+fn test_t1() {
+    let t = T1 {
+        x: X { a: 1, b: 2 },
+    };
+    assert_eq!(t.render().unwrap(), "hello 1");
+}
+
+#[derive(Template)]
+#[template(
+    source = "
+{%- if let X { .. } = x -%}hello{%- endif -%}
+",
+    ext = "html"
+)]
+struct T2 {
+    x: X,
+}
+
+#[test]
+fn test_t2() {
+    let t = T2 {
+        x: X { a: 1, b: 2 },
+    };
+    assert_eq!(t.render().unwrap(), "hello");
+}

testing/tests/rest_pattern.rs

@@ -0,0 +1,78 @@
+use rinja::Template;
+
+#[test]
+fn a() {
+    #[derive(Template)]
+    #[template(source = "{% if let (a, ..) = abc  %}-{{a}}-{% endif %}", ext = "txt")]
+    struct Tmpl {
+        abc: (u32, u32, u32),
+    }
+
+    assert_eq!(Tmpl { abc: (1, 2, 3) }.to_string(), "-1-");
+}
+
+#[test]
+fn ab() {
+    #[derive(Template)]
+    #[template(
+        source = "{% if let (a, b, ..) = abc  %}-{{a}}{{b}}-{% endif %}",
+        ext = "txt"
+    )]
+    struct Tmpl {
+        abc: (u32, u32, u32),
+    }
+
+    assert_eq!(Tmpl { abc: (1, 2, 3) }.to_string(), "-12-");
+}
+
+#[test]
+fn abc() {
+    #[derive(Template)]
+    #[template(
+        source = "{% if let (a, b, c, ..) = abc  %}-{{a}}{{b}}{{c}}-{% endif %}",
+        ext = "txt"
+    )]
+    struct Tmpl1 {
+        abc: (u32, u32, u32),
+    }
+
+    assert_eq!(Tmpl1 { abc: (1, 2, 3) }.to_string(), "-123-");
+
+    assert_eq!(Tmpl2 { abc: (1, 2, 3) }.to_string(), "-123-");
+
+    #[derive(Template)]
+    #[template(
+        source = "{% if let (a, b, c, ..) = abc  %}-{{a}}{{b}}{{c}}-{% endif %}",
+        ext = "txt"
+    )]
+    struct Tmpl2 {
+        abc: (u32, u32, u32),
+    }
+
+    assert_eq!(Tmpl2 { abc: (1, 2, 3) }.to_string(), "-123-");
+}
+
+#[test]
+fn bc() {
+    #[derive(Template)]
+    #[template(
+        source = "{% if let (.., b, c) = abc  %}-{{b}}{{c}}-{% endif %}",
+        ext = "txt"
+    )]
+    struct Tmpl {
+        abc: (u32, u32, u32),
+    }
+
+    assert_eq!(Tmpl { abc: (1, 2, 3) }.to_string(), "-23-");
+}
+
+#[test]
+fn c() {
+    #[derive(Template)]
+    #[template(source = "{% if let (.., c) = abc  %}-{{c}}-{% endif %}", ext = "txt")]
+    struct Tmpl {
+        abc: (u32, u32, u32),
+    }
+
+    assert_eq!(Tmpl { abc: (1, 2, 3) }.to_string(), "-3-");
+}

testing/tests/ui/let_destructuring_has_rest.rs

@@ -0,0 +1,48 @@
+use rinja::Template;
+
+struct X {
+    a: u32,
+    b: u32,
+}
+
+#[derive(Template)]
+#[template(source = "
+{%- if let X { a, .., } = x -%}hello {{ a }}{%- endif -%}
+", ext = "html")]
+struct T1 {
+    x: X,
+}
+
+#[derive(Template)]
+#[template(source = "
+{%- if let X { a .. } = x -%}hello {{ a }}{%- endif -%}
+", ext = "html")]
+struct T2 {
+    x: X,
+}
+
+#[derive(Template)]
+#[template(source = "
+{%- if let X { a, 1 } = x -%}hello {{ a }}{%- endif -%}
+", ext = "html")]
+struct T3 {
+    x: X,
+}
+
+#[derive(Template)]
+#[template(source = "
+{%- if let X { a, .., b } = x -%}hello {{ a }}{%- endif -%}
+", ext = "html")]
+struct T4 {
+    x: X,
+}
+
+#[derive(Template)]
+#[template(source = "
+{%- if let X { .., b } = x -%}hello {{ a }}{%- endif -%}
+", ext = "html")]
+struct T5 {
+    x: X,
+}
+
+fn main() {}

testing/tests/ui/let_destructuring_has_rest.stderr

@@ -0,0 +1,52 @@
+error: unexpected `,` character after `..`
+       note that in a named struct, `..` must come last to ignore other members
+       failed to parse template source at row 2, column 20 near:
+       ", } = x -%}hello {{ a }}{%- endif -%}\n"
+ --> tests/ui/let_destructuring_has_rest.rs:8:10
+  |
+8 | #[derive(Template)]
+  |          ^^^^^^^^
+  |
+  = note: this error originates in the derive macro `Template` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: expected `,` for more members, or `}` as terminator
+       failed to parse template source at row 2, column 17 near:
+       ".. } = x -%}hello {{ a }}{%- endif -%}\n"
+  --> tests/ui/let_destructuring_has_rest.rs:16:10
+   |
+16 | #[derive(Template)]
+   |          ^^^^^^^^
+   |
+   = note: this error originates in the derive macro `Template` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: expected member, or `}` as terminator
+       failed to parse template source at row 2, column 18 near:
+       "1 } = x -%}hello {{ a }}{%- endif -%}\n"
+  --> tests/ui/let_destructuring_has_rest.rs:24:10
+   |
+24 | #[derive(Template)]
+   |          ^^^^^^^^
+   |
+   = note: this error originates in the derive macro `Template` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: unexpected `,` character after `..`
+       note that in a named struct, `..` must come last to ignore other members
+       failed to parse template source at row 2, column 20 near:
+       ", b } = x -%}hello {{ a }}{%- endif -%}\n"
+  --> tests/ui/let_destructuring_has_rest.rs:32:10
+   |
+32 | #[derive(Template)]
+   |          ^^^^^^^^
+   |
+   = note: this error originates in the derive macro `Template` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: unexpected `,` character after `..`
+       note that in a named struct, `..` must come last to ignore other members
+       failed to parse template source at row 2, column 17 near:
+       ", b } = x -%}hello {{ a }}{%- endif -%}\n"
+  --> tests/ui/let_destructuring_has_rest.rs:40:10
+   |
+40 | #[derive(Template)]
+   |          ^^^^^^^^
+   |
+   = note: this error originates in the derive macro `Template` (in Nightly builds, run with -Z macro-backtrace for more info)