Implement IntoContextElement for ParametersContext.

src/renderer/parameters_context.rs

@@ -16,6 +16,7 @@ use crate::renderer::Renderable;
 use crate::renderer::Truthiness;
 use crate::renderer::WalkError;
 use crate::renderer::Walkable;
+use std::borrow::Borrow;
 use std::cmp::Ordering;
 use std::collections::HashMap;
 use std::rc::Rc;
@@ -57,6 +58,7 @@ impl<'a> ParametersContext<'a> {
                 };
                 v.map(|some_v| (k, some_v))
             })
+            // TODO: Should a None value here be the same as a key not existing, or should we store the Nones?
             .filter_map(|pair| pair)
             .collect();
 
@@ -66,6 +68,29 @@ impl<'a> ParametersContext<'a> {
     }
 }
 
+impl<'a> IntoContextElement for ParametersContext<'a> {
+    fn into_context_element<'b>(
+        &'b self,
+        renderer: &DustRenderer,
+        breadcrumbs: Option<&'b BreadcrumbTree<'b>>,
+    ) -> Option<IceResult<'b>> {
+        panic!("into_context_element cannot be called on pseudo elements");
+    }
+}
+
+impl<'a> Walkable for ParametersContext<'a> {
+    fn walk(&self, segment: &str) -> Result<&dyn IntoContextElement, WalkError> {
+        self.params
+            .get(segment)
+            .map(|bte| bte.borrow())
+            .ok_or(WalkError::CantWalk)
+    }
+
+    fn is_pseudo_element(&self) -> bool {
+        true
+    }
+}
+
 impl<'a> IntoContextElement for RValue<'a> {
     fn into_context_element<'b>(
         &'b self,