First attempt at a section render function.

Running into an issue with generics vs dynamic references.

js/test_cases/sections/main.dust

@@ -1,5 +1,5 @@
 {#things}
 Thing: {.}
 {:else}
-No things
+No things {.}
 {/things}

src/parser/parser.rs

@@ -90,9 +90,9 @@ pub struct Span<'a> {
 
 #[derive(Clone, Debug, PartialEq)]
 pub struct Container<'a> {
-    path: Path<'a>,
+    pub path: Path<'a>,
-    contents: Option<Body<'a>>,
+    pub contents: Option<Body<'a>>,
-    else_contents: Option<Body<'a>>,
+    pub else_contents: Option<Body<'a>>,
 }
 
 #[derive(Clone, Debug, PartialEq)]

src/renderer/context_element.rs

@@ -22,7 +22,5 @@ pub trait Loopable {
     /// once with the context being the element at that path. Finally,
     /// if its an array-like value then it will render n-times, once
     /// for each element of the array.
-    ///
-    /// TODO: Should this return an iterator instead of a vec?
     fn get_loop_elements(&self) -> Result<Vec<&dyn ContextElement>, RenderError>;
 }

src/renderer/renderer.rs

@@ -91,6 +91,42 @@ impl<'a> DustRenderer<'a> {
                     return val?.render(&reference.filters);
                 }
             }
+            DustTag::DTSection(container) => {
+                let val = walk_path(context, &container.path.keys);
+                if let Err(RenderError::WontWalk { .. }) = val {
+                    // If reference does not exist in the context, it becomes an empty string
+                    return Ok("".to_owned());
+                } else {
+                    let loop_elements: Vec<&dyn ContextElement> = val?.get_loop_elements()?;
+                    if loop_elements.is_empty() {
+                        // Oddly enough if the value is falsey (like
+                        // an empty array or null), Dust uses the
+                        // original context before walking the path as
+                        // the context for rendering the else block
+                        //
+                        // TODO: do filters apply? I don't think so
+                        // but I should test
+                        return match &container.else_contents {
+                            Some(body) => self.render_body(&body, context),
+                            None => Ok("".to_owned()),
+                        };
+                    } else {
+                        match container.contents {
+                            None => Ok("".to_owned()),
+                            Some(body) => {
+                                let rendered_results: Result<Vec<String>, RenderError> =
+                                    loop_elements
+                                        .into_iter()
+                                        .map(|array_elem| self.render_body(&body, array_elem))
+                                        .collect();
+                                let rendered_slice: &[String] = &rendered_results?;
+                                return Ok(rendered_slice.join(""));
+                            }
+                        };
+                        return Ok("".to_owned());
+                    }
+                }
+            }
             _ => (), // TODO: Implement the rest
         }
         Ok("".to_owned())