Store parent field type in TemplateInput

2 files changed, 19 insertions, 17 deletions

diff --git a/askama_derive/src/generator.rs b/askama_derive/src/generator.rs
index 5d16f2c..6c6e1e7 100644
--- a/askama_derive/src/generator.rs
+++ b/askama_derive/src/generator.rs
@@ -61,9 +61,10 @@ impl<'a> Generator<'a> {
             if ctx.extends.is_none() {
                 self.define_trait(ctx);
             } else {
-                let parent_type = get_parent_type(self.input.ast)
-                    .expect("expected field '_parent' in extending template struct");
-                self.deref_to_parent(parent_type);
+                match self.input.parent {
+                    Some(ty) => self.deref_to_parent(ty),
+                    None => panic!("expected field '_parent' in extending template struct"),
+                }
             }
 
             let trait_nodes = if ctx.extends.is_none() {
@@ -930,20 +931,6 @@ where
     }
 }
 
-fn get_parent_type(ast: &syn::DeriveInput) -> Option<&syn::Type> {
-    match ast.data {
-        syn::Data::Struct(syn::DataStruct {
-            fields: syn::Fields::Named(ref fields),
-            ..
-        }) => fields.named.iter().filter_map(|f| {
-            f.ident
-                .as_ref()
-                .and_then(|name| if name == "_parent" { Some(&f.ty) } else { None })
-        }),
-        _ => panic!("derive(Template) only works for struct items"),
-    }.next()
-}
-
 #[derive(Clone, PartialEq)]
 enum AstLevel {
     Top,
diff --git a/askama_derive/src/input.rs b/askama_derive/src/input.rs
index d835763..afa4226 100644
--- a/askama_derive/src/input.rs
+++ b/askama_derive/src/input.rs
@@ -10,6 +10,7 @@ pub struct TemplateInput<'a> {
     pub print: Print,
     pub escaping: EscapeMode,
     pub ext: Option<String>,
+    pub parent: Option<&'a syn::Type>,
     pub path: PathBuf,
 }
 
@@ -83,6 +84,7 @@ impl<'a> TemplateInput<'a> {
             }
             _ => {}
         }
+
         let escaping = match escaping {
             Some(m) => m,
             None => {
@@ -101,6 +103,18 @@ impl<'a> TemplateInput<'a> {
             }
         };
 
+        let parent = match ast.data {
+            syn::Data::Struct(syn::DataStruct {
+                fields: syn::Fields::Named(ref fields),
+                ..
+            }) => fields.named.iter().filter_map(|f| {
+                f.ident
+                    .as_ref()
+                    .and_then(|name| if name == "_parent" { Some(&f.ty) } else { None })
+            }),
+            _ => panic!("derive(Template) only works for struct items"),
+        }.next();
+
         let path = match source {
             Source::Source(_) => match ext {
                 Some(ref v) => PathBuf::from(format!("{}.{}", ast.ident, v)),
@@ -115,6 +129,7 @@ impl<'a> TemplateInput<'a> {
             print,
             escaping,
             ext,
+            parent,
             path,
         }
     }