Implement walking for a single segment,

src/renderer/renderer.rs

@@ -178,18 +178,41 @@ impl<'a> DustRenderer<'a> {
     }
 }
 
-fn new_walk_path<'a>(
+enum WalkResult<'a> {
+    NoWalk,
+    PartialWalk,
+    FullyWalked(&'a dyn ContextElement),
+}
+
+fn walk_path_from_single_level<'a>(
     context: &'a dyn ContextElement,
     path: &Vec<&str>,
-    breadcrumbs: Vec<&'a dyn ContextElement>,
-) -> Result<&'a dyn ContextElement, RenderError<'a>> {
-    let mut output = context;
-
-    for elem in path.iter() {
-        output = output.walk(elem)?;
+) -> Result<WalkResult<'a>, RenderError<'a>> {
+    if path.is_empty() {
+        return Ok(WalkResult::FullyWalked(context));
     }
 
-    Ok(output)
+    let mut walk_failure = WalkResult::NoWalk;
+    let mut output = context;
+    for elem in path.iter() {
+        let new_val = output.walk(elem);
+        if let Err(RenderError::WontWalk { .. }) = new_val {
+            return Ok(walk_failure);
+        } else if let Err(RenderError::CantWalk { .. }) = new_val {
+            return Ok(walk_failure);
+        }
+        walk_failure = WalkResult::PartialWalk;
+        output = new_val?;
+    }
+
+    Ok(WalkResult::FullyWalked(context))
+}
+
+fn new_walk_path<'a>(
+    breadcrumbs: Vec<&'a dyn ContextElement>,
+    path: &Vec<&str>,
+) -> Result<&'a dyn ContextElement, RenderError<'a>> {
+    Err(RenderError::Generic("temp".to_owned()))
 }
 
 // TODO: rename walk_path_from_single_level