Improve docs on function

minijinja/src/functions.rs

@@ -99,6 +99,13 @@ pub(crate) struct BoxedFunction(Arc<FuncFunc>, #[cfg(feature = "debug")] &'stati
 ///
 /// For a list of built-in functions see [`functions`](crate::functions).
 ///
+/// **Note:** this trait cannot be implemented and only exists drive the
+/// functionality of [`add_function`](crate::Environment::add_function)
+/// and [`from_function`](crate::value::Value::from_function).  If you want
+/// to implement a custom callable, you can directly implement
+/// [`Object::call`](crate::value::Object::call) which is what the engine
+/// actually uses internally.
+///
 /// # Basic Example
 ///
 /// ```rust

minijinja/src/lib.rs

@@ -258,7 +258,7 @@ pub mod machinery {
 
     use crate::Output;
 
-    /// Returns a reference to a [`CompiledTemplate`] from a [`Template`].
+    /// Returns a reference to a [`CompiledTemplate`] from a [`Template`](crate::Template).
     pub fn get_compiled_template<'x, 'env>(
         tmpl: &'x crate::Template<'env, 'env>,
     ) -> &'x CompiledTemplate<'env> {

minijinja/src/value/object.rs

@@ -153,7 +153,7 @@ impl dyn Object {
 
     /// Checks if the object is of a specific type.
     ///
-    /// For details of this operation see [`downcast_ref`](Self::downcast_ref).
+    /// For details of this operation see [`downcast_ref`](#method.downcast_ref).
     pub fn is<T: 'static>(&self) -> bool {
         let type_id = (*self).type_id();
         type_id == TypeId::of::<T>()