Moved no-receiver size_hint method to a separate trait

askama/src/lib.rs

@@ -492,7 +492,7 @@ pub use askama_escape::{Html, Text};
 pub trait Template {
     /// Helper method which allocates a new `String` and renders into it
     fn render(&self) -> Result<String> {
-        let mut buf = String::with_capacity(Self::size_hint());
+        let mut buf = String::with_capacity(self.dyn_size_hint());
         self.render_into(&mut buf)?;
         Ok(buf)
     }
@@ -502,6 +502,10 @@ pub trait Template {
     fn extension() -> Option<&'static str>
     where
         Self: Sized;
+    fn dyn_size_hint(&self) -> usize;
+}
+
+pub trait TemplateSizeHint {
     /// Provides an conservative estimate of the expanded length of the rendered template
     fn size_hint() -> usize;
 }

askama_derive/src/generator.rs

@@ -143,6 +143,14 @@ impl<'a> Generator<'a> {
         ));
         buf.writeln("}");
 
+        buf.writeln("fn dyn_size_hint(&self) -> usize {");
+        buf.writeln(&format!("{}", size_hint));
+        buf.writeln("}");
+
+        buf.writeln("}");
+
+        self.write_header(buf, "::askama::TemplateSizeHint", None);
+
         buf.writeln("fn size_hint() -> usize {");
         buf.writeln(&format!("{}", size_hint));
         buf.writeln("}");