Initial move to returning results from render calls.

src/renderer/errors.rs

@@ -1,9 +1,19 @@
+use crate::renderer::walkable::ContextElement;
 use std::error;
 use std::fmt;
 
-#[derive(Clone)]
-pub struct RenderError {
-    pub message: String,
+pub enum RenderError<'a> {
+    Generic(String),
+    /// For when walking is absolutely impossible
+    CantWalk {
+        segment: String,
+        elem: &'a dyn ContextElement,
+    },
+    /// For when walking fails (example, a missing key on a map)
+    WontWalk {
+        segment: String,
+        elem: &'a dyn ContextElement,
+    },
 }
 
 #[derive(Clone)]
@@ -11,19 +21,35 @@ pub struct CompileError {
     pub message: String,
 }
 
-impl fmt::Display for RenderError {
+impl fmt::Display for RenderError<'_> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "Error rendering: {}", self.message)
+        match self {
+            RenderError::Generic(msg) => write!(f, "{}", msg),
+            RenderError::CantWalk { segment, elem } => {
+                write!(f, "Tried to walk to {} from {:?}", segment, elem)
+            }
+            RenderError::WontWalk { segment, elem } => {
+                write!(f, "Failed to walk to {} from {:?}", segment, elem)
+            }
+        }
     }
 }
 
-impl fmt::Debug for RenderError {
+impl fmt::Debug for RenderError<'_> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "Error rendering: {}", self.message)
+        match self {
+            RenderError::Generic(msg) => write!(f, "{}", msg),
+            RenderError::CantWalk { segment, elem } => {
+                write!(f, "Tried to walk to {} from {:?}", segment, elem)
+            }
+            RenderError::WontWalk { segment, elem } => {
+                write!(f, "Failed to walk to {} from {:?}", segment, elem)
+            }
+        }
     }
 }
 
-impl error::Error for RenderError {
+impl error::Error for RenderError<'_> {
     fn source(&self) -> Option<&(dyn error::Error + 'static)> {
         None
     }