Implement enum variants

.github/workflows/rust.yml

@@ -172,7 +172,8 @@ jobs:
         with:
           tool: cargo-nextest
       - uses: Swatinem/rust-cache@v2
-      - run: cd ${{ matrix.package }} && cargo nextest run --no-tests=warn
+      - run: cd ${{ matrix.package }} && cargo build --all-targets
+      - run: cd ${{ matrix.package }} && cargo nextest run --all-targets --no-fail-fast --no-tests=warn
       - run: cd ${{ matrix.package }} && cargo clippy --all-targets -- -D warnings
 
   MSRV:

rinja/src/helpers.rs

@@ -269,3 +269,11 @@ impl<L: FastWritable, R: FastWritable> FastWritable for Concat<L, R> {
         self.1.write_into(dest)
     }
 }
+
+pub trait EnumVariantTemplate {
+    fn render_into_with_values<W: fmt::Write + ?Sized>(
+        &self,
+        writer: &mut W,
+        values: &dyn crate::Values,
+    ) -> crate::Result<()>;
+}

rinja_derive/src/generator.rs

@@ -25,9 +25,12 @@ pub(crate) fn template_to_string(
     input: &TemplateInput<'_>,
     contexts: &HashMap<&Arc<Path>, Context<'_>, FxBuildHasher>,
     heritage: Option<&Heritage<'_, '_>>,
-    target: Option<&str>,
+    tmpl_kind: TmplKind,
 ) -> Result<usize, CompileError> {
-    let ctx = &contexts[&input.path];
+    if tmpl_kind == TmplKind::Struct {
+        buf.write("const _: () = { extern crate rinja as rinja;");
+    }
+
     let generator = Generator::new(
         input,
         contexts,
@@ -36,13 +39,27 @@ pub(crate) fn template_to_string(
         input.block.is_some(),
         0,
     );
-    let mut result = generator.build(ctx, buf, target);
-    if let Err(err) = &mut result {
-        if err.span.is_none() {
+    let size_hint = match generator.impl_template(buf, tmpl_kind) {
+        Err(mut err) if err.span.is_none() => {
             err.span = input.source_span;
+            Err(err)
         }
+        result => result,
+    }?;
+
+    if tmpl_kind == TmplKind::Struct {
+        impl_everything(input.ast, buf);
+        buf.write("};");
     }
-    result
+    Ok(size_hint)
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub(crate) enum TmplKind {
+    /// [`rinja::Template`]
+    Struct,
+    /// [`rinja::helpers::EnumVariantTemplate`]
+    Variant,
 }
 
 struct Generator<'a, 'h> {
@@ -97,31 +114,18 @@ impl<'a, 'h> Generator<'a, 'h> {
         }
     }
 
-    // Takes a Context and generates the relevant implementations.
-    fn build(
-        mut self,
-        ctx: &Context<'a>,
-        buf: &mut Buffer,
-        target: Option<&str>,
-    ) -> Result<usize, CompileError> {
-        if target.is_none() {
-            buf.write("const _: () = { extern crate rinja as rinja;");
-        }
-        let size_hint = self.impl_template(ctx, buf, target.unwrap_or("rinja::Template"))?;
-        if target.is_none() {
-            impl_everything(self.input.ast, buf);
-            buf.write("};");
-        }
-        Ok(size_hint)
-    }
-
     // Implement `Template` for the given context struct.
     fn impl_template(
-        &mut self,
-        ctx: &Context<'a>,
+        mut self,
         buf: &mut Buffer,
-        target: &str,
+        tmpl_kind: TmplKind,
     ) -> Result<usize, CompileError> {
+        let ctx = &self.contexts[&self.input.path];
+
+        let target = match tmpl_kind {
+            TmplKind::Struct => "rinja::Template",
+            TmplKind::Variant => "rinja::helpers::EnumVariantTemplate",
+        };
         write_header(self.input.ast, buf, target);
         buf.write(
             "fn render_into_with_values<RinjaW>(\
@@ -161,12 +165,12 @@ impl<'a, 'h> Generator<'a, 'h> {
 
         let size_hint = self.impl_template_inner(ctx, buf)?;
 
-        buf.write(format_args!(
-            "\
-                rinja::Result::Ok(())\
-            }}\
-            const SIZE_HINT: rinja::helpers::core::primitive::usize = {size_hint}usize;",
-        ));
+        buf.write("rinja::Result::Ok(()) }");
+        if tmpl_kind == TmplKind::Struct {
+            buf.write(format_args!(
+                "const SIZE_HINT: rinja::helpers::core::primitive::usize = {size_hint}usize;",
+            ));
+        }
 
         buf.write('}');
         Ok(size_hint)

rinja_derive/src/input.rs

@@ -271,6 +271,63 @@ impl TemplateInput<'_> {
     }
 }
 
+pub(crate) enum AnyTemplateArgs {
+    Struct(TemplateArgs),
+    Enum {
+        enum_args: Option<PartialTemplateArgs>,
+        vars_args: Vec<Option<PartialTemplateArgs>>,
+        has_default_impl: bool,
+    },
+}
+
+impl AnyTemplateArgs {
+    pub(crate) fn new(ast: &syn::DeriveInput) -> Result<Self, CompileError> {
+        let syn::Data::Enum(enum_data) = &ast.data else {
+            return Ok(Self::Struct(TemplateArgs::new(ast)?));
+        };
+
+        let enum_args = PartialTemplateArgs::new(ast, &ast.attrs)?;
+        let vars_args = enum_data
+            .variants
+            .iter()
+            .map(|variant| PartialTemplateArgs::new(ast, &variant.attrs))
+            .collect::<Result<Vec<_>, _>>()?;
+        if vars_args.is_empty() {
+            return Ok(Self::Struct(TemplateArgs::from_partial(ast, enum_args)?));
+        }
+
+        let mut needs_default_impl = vars_args.len();
+        let enum_source = enum_args.as_ref().and_then(|v| v.source.as_ref());
+        for (variant, var_args) in enum_data.variants.iter().zip(&vars_args) {
+            if var_args
+                .as_ref()
+                .and_then(|v| v.source.as_ref())
+                .or(enum_source)
+                .is_none()
+            {
+                return Err(CompileError::new_with_span(
+                    #[cfg(not(feature = "code-in-doc"))]
+                    "either all `enum` variants need a `path` or `source` argument, \
+                    or the `enum` itself needs a default implementation",
+                    #[cfg(feature = "code-in-doc")]
+                    "either all `enum` variants need a `path`, `source` or `in_doc` argument, \
+                    or the `enum` itself needs a default implementation",
+                    None,
+                    Some(variant.ident.span()),
+                ));
+            } else if !var_args.is_none() {
+                needs_default_impl -= 1;
+            }
+        }
+
+        Ok(Self::Enum {
+            enum_args,
+            vars_args,
+            has_default_impl: needs_default_impl > 0,
+        })
+    }
+}
+
 #[derive(Debug)]
 pub(crate) struct TemplateArgs {
     pub(crate) source: (Source, Option<Span>),
@@ -626,6 +683,17 @@ pub(crate) enum PartialTemplateArgsSource {
     InDoc(Span, Source),
 }
 
+impl PartialTemplateArgsSource {
+    pub(crate) fn span(&self) -> Span {
+        match self {
+            Self::Path(s) => s.span(),
+            Self::Source(s) => s.span(),
+            #[cfg(feature = "code-in-doc")]
+            Self::InDoc(s, _) => s.span(),
+        }
+    }
+}
+
 // implement PartialTemplateArgs::new()
 const _: () = {
     impl PartialTemplateArgs {

rinja_derive/src/integration.rs

@@ -1,7 +1,16 @@
 use std::fmt::{Arguments, Display, Write};
 
-use quote::quote;
-use syn::DeriveInput;
+use proc_macro2::{TokenStream, TokenTree};
+use quote::{ToTokens, quote};
+use syn::spanned::Spanned;
+use syn::{
+    Data, DeriveInput, Fields, GenericParam, Generics, Ident, Lifetime, LifetimeParam, Token, Type,
+    Variant, parse_quote,
+};
+
+use crate::generator::TmplKind;
+use crate::input::{PartialTemplateArgs, TemplateArgs};
+use crate::{CompileError, build_template_item};
 
 /// Implement every integration for the given item
 pub(crate) fn impl_everything(ast: &DeriveInput, buf: &mut Buffer) {
@@ -223,3 +232,291 @@ fn string_escape(dest: &mut String, src: &str) {
     }
     dest.extend(&src[last..]);
 }
+
+pub(crate) fn build_template_enum(
+    buf: &mut Buffer,
+    enum_ast: &DeriveInput,
+    mut enum_args: Option<PartialTemplateArgs>,
+    vars_args: Vec<Option<PartialTemplateArgs>>,
+    has_default_impl: bool,
+) -> Result<usize, CompileError> {
+    let Data::Enum(enum_data) = &enum_ast.data else {
+        unreachable!();
+    };
+
+    buf.write("const _: () = { extern crate rinja as rinja;");
+    impl_everything(enum_ast, buf);
+
+    let enum_id = &enum_ast.ident;
+    let enum_span = enum_id.span();
+    let lifetime = Lifetime::new(&format!("'__Rinja_{enum_id}"), enum_span);
+
+    let mut generics = enum_ast.generics.clone();
+    if generics.lt_token.is_none() {
+        generics.lt_token = Some(Token![<](enum_span));
+    }
+    if generics.gt_token.is_none() {
+        generics.gt_token = Some(Token![>](enum_span));
+    }
+    generics
+        .params
+        .insert(0, GenericParam::Lifetime(LifetimeParam::new(lifetime)));
+
+    let mut biggest_size_hint = 0;
+    let mut render_into_arms = TokenStream::new();
+    let mut size_hint_arms = TokenStream::new();
+    for (var, var_args) in enum_data.variants.iter().zip(vars_args) {
+        let Some(mut var_args) = var_args else {
+            continue;
+        };
+
+        let var_ast = type_for_enum_variant(enum_ast, &generics, var);
+        buf.write(quote!(#var_ast).to_string());
+
+        // not inherited: template, meta_docs, block, print
+        if let Some(enum_args) = &mut enum_args {
+            set_default(&mut var_args, enum_args, |v| &mut v.source);
+            set_default(&mut var_args, enum_args, |v| &mut v.escape);
+            set_default(&mut var_args, enum_args, |v| &mut v.ext);
+            set_default(&mut var_args, enum_args, |v| &mut v.syntax);
+            set_default(&mut var_args, enum_args, |v| &mut v.config);
+            set_default(&mut var_args, enum_args, |v| &mut v.whitespace);
+        }
+        let size_hint = biggest_size_hint.max(build_template_item(
+            buf,
+            &var_ast,
+            &TemplateArgs::from_partial(&var_ast, Some(var_args))?,
+            TmplKind::Variant,
+        )?);
+        biggest_size_hint = biggest_size_hint.max(size_hint);
+
+        variant_as_arm(
+            &var_ast,
+            var,
+            size_hint,
+            &mut render_into_arms,
+            &mut size_hint_arms,
+        );
+    }
+    if has_default_impl {
+        let size_hint = build_template_item(
+            buf,
+            enum_ast,
+            &TemplateArgs::from_partial(enum_ast, enum_args)?,
+            TmplKind::Variant,
+        )?;
+        biggest_size_hint = biggest_size_hint.max(size_hint);
+
+        render_into_arms.extend(quote! {
+            ref __rinja_arg => {
+                <_ as rinja::helpers::EnumVariantTemplate>::render_into_with_values(
+                    __rinja_arg,
+                    __rinja_writer,
+                    __rinja_values,
+                )
+            }
+        });
+        size_hint_arms.extend(quote! {
+            _ => {
+                #size_hint
+            }
+        });
+    }
+
+    write_header(enum_ast, buf, "rinja::Template");
+    buf.write(format_args!(
+        "\
+        fn render_into_with_values<RinjaW>(\
+            &self,\
+            __rinja_writer: &mut RinjaW,\
+            __rinja_values: &dyn rinja::Values,\
+        ) -> rinja::Result<()>\
+        where \
+            RinjaW: rinja::helpers::core::fmt::Write + ?rinja::helpers::core::marker::Sized\
+        {{\
+            match *self {{\
+                {render_into_arms}\
+            }}\
+        }}",
+    ));
+
+    #[cfg(feature = "alloc")]
+    buf.write(format_args!(
+        "\
+        fn render_with_values(\
+            &self,\
+            __rinja_values: &dyn rinja::Values,\
+        ) -> rinja::Result<rinja::helpers::alloc::string::String> {{\
+            let size_hint = match self {{\
+                {size_hint_arms}\
+            }};\
+            let mut buf = rinja::helpers::alloc::string::String::new();\
+            let _ = buf.try_reserve(size_hint);\
+            self.render_into_with_values(&mut buf, __rinja_values)?;\
+            rinja::Result::Ok(buf)\
+        }}",
+    ));
+
+    buf.write(format_args!(
+        "\
+        const SIZE_HINT: rinja::helpers::core::primitive::usize = {biggest_size_hint}usize;\
+        }}\
+        }};",
+    ));
+    Ok(biggest_size_hint)
+}
+
+fn set_default<S, T, A>(dest: &mut S, parent: &mut S, mut access: A)
+where
+    T: Clone,
+    A: FnMut(&mut S) -> &mut Option<T>,
+{
+    let dest = access(dest);
+    if dest.is_none() {
+        if let Some(parent) = access(parent) {
+            *dest = Some(parent.clone());
+        }
+    }
+}
+
+/// Generates a `struct` to contain the data of an enum variant
+fn type_for_enum_variant(
+    enum_ast: &DeriveInput,
+    enum_generics: &Generics,
+    var: &Variant,
+) -> DeriveInput {
+    let enum_id = &enum_ast.ident;
+    let (_, ty_generics, _) = enum_ast.generics.split_for_impl();
+    let lt = enum_generics.params.first().unwrap();
+
+    let id = &var.ident;
+    let span = id.span();
+    let id = Ident::new(&format!("__Rinja__{enum_id}__{id}"), span);
+
+    let phantom: Type = parse_quote! {
+        rinja::helpers::core::marker::PhantomData < &#lt #enum_id #ty_generics >
+    };
+    let fields = match &var.fields {
+        Fields::Named(fields) => {
+            let mut fields = fields.clone();
+            for f in fields.named.iter_mut() {
+                let ty = &f.ty;
+                f.ty = parse_quote!(&#lt #ty);
+            }
+            let id = Ident::new(&format!("__Rinja__{enum_id}__phantom"), span);
+            fields.named.push(parse_quote!(#id: #phantom));
+            Fields::Named(fields)
+        }
+        Fields::Unnamed(fields) => {
+            let mut fields = fields.clone();
+            for f in fields.unnamed.iter_mut() {
+                let ty = &f.ty;
+                f.ty = parse_quote!(&#lt #ty);
+            }
+            fields.unnamed.push(parse_quote!(#phantom));
+            Fields::Unnamed(fields)
+        }
+        Fields::Unit => Fields::Unnamed(parse_quote!((#phantom))),
+    };
+    let semicolon = match &var.fields {
+        Fields::Named(_) => None,
+        _ => Some(Token![;](span)),
+    };
+
+    parse_quote! {
+        #[rinja::helpers::core::prelude::rust_2021::derive(
+            rinja::helpers::core::prelude::rust_2021::Clone,
+            rinja::helpers::core::prelude::rust_2021::Copy,
+            rinja::helpers::core::prelude::rust_2021::Debug
+        )]
+        #[allow(dead_code, non_camel_case_types, non_snake_case)]
+        struct #id #enum_generics #fields #semicolon
+    }
+}
+
+/// Generates a `match` arm for an `enum` variant, that calls `<_ as EnumVariantTemplate>::render_into()`
+/// for that type and data
+fn variant_as_arm(
+    var_ast: &DeriveInput,
+    var: &Variant,
+    size_hint: usize,
+    render_into_arms: &mut TokenStream,
+    size_hint_arms: &mut TokenStream,
+) {
+    let var_id = &var_ast.ident;
+    let ident = &var.ident;
+    let span = ident.span();
+
+    let generics = var_ast.generics.clone();
+    let (_, ty_generics, _) = generics.split_for_impl();
+    let ty_generics: TokenStream = ty_generics
+        .as_turbofish()
+        .to_token_stream()
+        .into_iter()
+        .enumerate()
+        .map(|(idx, token)| match idx {
+            // 0 1 2 3 4   =>   : : < ' __Rinja_Foo
+            4 => TokenTree::Ident(Ident::new("_", span)),
+            _ => token,
+        })
+        .collect();
+
+    let Data::Struct(ast_data) = &var_ast.data else {
+        unreachable!();
+    };
+    let mut src = TokenStream::new();
+    let mut this = TokenStream::new();
+    match &var.fields {
+        Fields::Named(fields) => {
+            for (idx, field) in fields.named.iter().enumerate() {
+                let arg = Ident::new(&format!("__rinja_arg_{idx}"), field.span());
+                let id = field.ident.as_ref().unwrap();
+                src.extend(quote!(#id: ref #arg,));
+                this.extend(quote!(#id: #arg,));
+            }
+
+            let phantom = match &ast_data.fields {
+                Fields::Named(fields) => fields
+                    .named
+                    .iter()
+                    .next_back()
+                    .unwrap()
+                    .ident
+                    .as_ref()
+                    .unwrap(),
+                Fields::Unnamed(_) | Fields::Unit => unreachable!(),
+            };
+            this.extend(quote!(#phantom: rinja::helpers::core::marker::PhantomData {},));
+        }
+
+        Fields::Unnamed(fields) => {
+            for (idx, field) in fields.unnamed.iter().enumerate() {
+                let span = field.ident.span();
+                let arg = Ident::new(&format!("__rinja_arg_{idx}"), span);
+                let idx = syn::LitInt::new(&format!("{idx}"), span);
+                src.extend(quote!(#idx: ref #arg,));
+                this.extend(quote!(#idx: #arg,));
+            }
+            let idx = syn::LitInt::new(&format!("{}", fields.unnamed.len()), span);
+            this.extend(quote!(#idx: rinja::helpers::core::marker::PhantomData {},));
+        }
+
+        Fields::Unit => {
+            this.extend(quote!(0: rinja::helpers::core::marker::PhantomData {},));
+        }
+    };
+    render_into_arms.extend(quote! {
+        Self :: #ident { #src } => {
+            <_ as rinja::helpers::EnumVariantTemplate>::render_into_with_values(
+                & #var_id #ty_generics { #this },
+                __rinja_writer,
+                __rinja_values,
+            )
+        }
+    });
+    size_hint_arms.extend(quote! {
+        Self :: #ident { .. } => {
+            #size_hint
+        }
+    });
+}

rinja_derive/src/lib.rs

@@ -19,10 +19,10 @@ use std::path::Path;
 use std::sync::Mutex;
 
 use config::{Config, read_config_file};
-use generator::template_to_string;
+use generator::{TmplKind, template_to_string};
 use heritage::{Context, Heritage};
-use input::{Print, TemplateArgs, TemplateInput};
-use integration::Buffer;
+use input::{AnyTemplateArgs, Print, TemplateArgs, TemplateInput};
+use integration::{Buffer, build_template_enum};
 use parser::{Parsed, strip_common};
 #[cfg(not(feature = "__standalone"))]
 use proc_macro::TokenStream as TokenStream12;
@@ -159,7 +159,7 @@ fn build_skeleton(buf: &mut Buffer, ast: &syn::DeriveInput) -> Result<usize, Com
     let mut contexts = HashMap::default();
     let parsed = parser::Parsed::default();
     contexts.insert(&input.path, Context::empty(&parsed));
-    template_to_string(buf, &input, &contexts, None, None)
+    template_to_string(buf, &input, &contexts, None, TmplKind::Struct)
 }
 
 /// Takes a `syn::DeriveInput` and generates source code for it
@@ -173,11 +173,28 @@ pub(crate) fn build_template(
     buf: &mut Buffer,
     ast: &syn::DeriveInput,
 ) -> Result<usize, CompileError> {
-    let template_args = TemplateArgs::new(ast)?;
-    let mut result = build_template_item(buf, ast, &template_args, None);
+    let err_span;
+    let mut result = match AnyTemplateArgs::new(ast)? {
+        AnyTemplateArgs::Struct(item) => {
+            err_span = item.source.1.or(item.template_span);
+            build_template_item(buf, ast, &item, TmplKind::Struct)
+        }
+        AnyTemplateArgs::Enum {
+            enum_args,
+            vars_args,
+            has_default_impl,
+        } => {
+            err_span = enum_args
+                .as_ref()
+                .and_then(|v| v.source.as_ref())
+                .map(|s| s.span())
+                .or_else(|| enum_args.as_ref().map(|v| v.template.span()));
+            build_template_enum(buf, ast, enum_args, vars_args, has_default_impl)
+        }
+    };
     if let Err(err) = &mut result {
         if err.span.is_none() {
-            err.span = template_args.source.1.or(template_args.template_span);
+            err.span = err_span;
         }
     }
     result
@@ -187,7 +204,7 @@ fn build_template_item(
     buf: &mut Buffer,
     ast: &syn::DeriveInput,
     template_args: &TemplateArgs,
-    target: Option<&str>,
+    tmpl_kind: TmplKind,
 ) -> Result<usize, CompileError> {
     let config_path = template_args.config_path();
     let s = read_config_file(config_path, template_args.config_span)?;
@@ -230,7 +247,7 @@ fn build_template_item(
     }
 
     let mark = buf.get_mark();
-    let size_hint = template_to_string(buf, &input, &contexts, heritage.as_ref(), target)?;
+    let size_hint = template_to_string(buf, &input, &contexts, heritage.as_ref(), tmpl_kind)?;
     if input.print == Print::Code || input.print == Print::All {
         eprintln!("{}", buf.marked_text(mark));
     }

testing/tests/enum.rs

@@ -0,0 +1,113 @@
+use std::any::type_name_of_val;
+use std::fmt::{Debug, Display};
+
+use rinja::Template;
+
+#[test]
+fn test_simple_enum() {
+    #[derive(Template, Debug)]
+    #[template(
+        ext = "txt",
+        source = "{{ self::type_name_of_val(self) }} | {{ self|fmt(\"{:?}\") }}"
+    )]
+    enum SimpleEnum<'a, B: Display + Debug> {
+        #[template(source = "A")]
+        A,
+        #[template(source = "B()")]
+        B(),
+        #[template(source = "C({{self.0}}, {{self.1}})")]
+        C(u32, u32),
+        #[template(source = "D {}")]
+        D {},
+        #[template(source = "E { a: {{a}}, b: {{b}} }")]
+        E {
+            a: &'a str,
+            b: B,
+        },
+        // uses default source with `SimpleEnum` as `Self`
+        F,
+        // uses default source with a synthetic type `__Rinja__SimpleEnum__G` as `Self`
+        #[template()]
+        G,
+    }
+
+    let tmpl: SimpleEnum<'_, X> = SimpleEnum::A;
+    assert_eq!(tmpl.render().unwrap(), "A");
+
+    let tmpl: SimpleEnum<'_, X> = SimpleEnum::B();
+    assert_eq!(tmpl.render().unwrap(), "B()");
+
+    let tmpl: SimpleEnum<'_, X> = SimpleEnum::C(12, 34);
+    assert_eq!(tmpl.render().unwrap(), "C(12, 34)");
+
+    let tmpl: SimpleEnum<'_, X> = SimpleEnum::C(12, 34);
+    assert_eq!(tmpl.render().unwrap(), "C(12, 34)");
+
+    let tmpl: SimpleEnum<'_, X> = SimpleEnum::D {};
+    assert_eq!(tmpl.render().unwrap(), "D {}");
+
+    let tmpl: SimpleEnum<'_, X> = SimpleEnum::E { a: "hello", b: X };
+    assert_eq!(tmpl.render().unwrap(), "E { a: hello, b: X }");
+
+    let tmpl: SimpleEnum<'_, X> = SimpleEnum::F;
+    assert_eq!(
+        tmpl.render().unwrap(),
+        "&enum::test_simple_enum::SimpleEnum<enum::X> | F",
+    );
+
+    let tmpl: SimpleEnum<'_, X> = SimpleEnum::G;
+    assert_eq!(
+        tmpl.render().unwrap(),
+        "&enum::test_simple_enum::_::__Rinja__SimpleEnum__G<enum::X> | \
+        __Rinja__SimpleEnum__G(\
+            PhantomData<&enum::test_simple_enum::SimpleEnum<enum::X>>\
+        )",
+    );
+}
+
+#[test]
+fn test_enum_blocks() {
+    #[derive(Template, Debug)]
+    #[template(
+        ext = "txt",
+        source = "\
+            {% block a -%} <a = {{ a }}> {%- endblock %}
+            {% block b -%} <b = {{ b }}> {%- endblock %}
+            {% block c -%} <c = {{ c }}> {%- endblock %}
+            {% block d -%} <d = {{ self::type_name_of_val(self) }}> {%- endblock %}
+        "
+    )]
+    enum BlockEnum<'a, C: Display> {
+        #[template(block = "a")]
+        A { a: u32 },
+        #[template(block = "b")]
+        B { b: &'a str },
+        #[template(block = "c")]
+        C { c: C },
+        #[template(block = "d")]
+        D,
+    }
+
+    let tmpl: BlockEnum<'_, X> = BlockEnum::A { a: 42 };
+    assert_eq!(tmpl.render().unwrap(), "<a = 42>");
+
+    let tmpl: BlockEnum<'_, X> = BlockEnum::B { b: "second letter" };
+    assert_eq!(tmpl.render().unwrap(), "<b = second letter>");
+
+    let tmpl: BlockEnum<'_, X> = BlockEnum::C { c: X };
+    assert_eq!(tmpl.render().unwrap(), "<c = X>");
+
+    assert_eq!(
+        BlockEnum::<'_, X>::D.render().unwrap(),
+        "<d = &enum::test_enum_blocks::_::__Rinja__BlockEnum__D<enum::X>>"
+    );
+}
+
+#[derive(Debug)]
+struct X;
+
+impl Display for X {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.write_str("X")
+    }
+}