Improve error messages for multiple chidren in a widget and config loading errors

crates/eww/src/config/eww_config.rs

@@ -67,7 +67,13 @@ impl EwwConfig {
     }
 
     pub fn get_window(&self, name: &String) -> Result<&EwwWindowDefinition> {
-        self.windows.get(name).with_context(|| format!("No window named '{}' exists in config", name))
+        self.windows.get(name).with_context(|| {
+            format!(
+                "No window named '{}' exists in config.\nThis may also be caused by your config failing to load properly, \
+                 please check for any other errors in that case.",
+                name
+            )
+        })
     }
 
     pub fn get_script_var(&self, name: &VarName) -> Result<&ScriptVarDefinition> {

crates/yuck/src/config/widget_definition.rs

@@ -10,7 +10,7 @@ use crate::{
         from_ast::{FromAst, FromAstElementContent},
     },
 };
-use eww_shared_util::{AttrName, Span, VarName};
+use eww_shared_util::{AttrName, Span, Spanned, VarName};
 
 use super::widget_use::WidgetUse;
 #[derive(Debug, PartialEq, Eq, Clone, serde::Serialize)]
@@ -33,7 +33,7 @@ impl FromAstElementContent for WidgetDefinition {
             .note(EXPECTED_WIDGET_DEF_FORMAT)?;
         let expected_args = expected_args.into_iter().map(|x| x.as_symbol().map(AttrName)).collect::<AstResult<_>>()?;
         let widget = iter.expect_any().note(EXPECTED_WIDGET_DEF_FORMAT).and_then(WidgetUse::from_ast)?;
-        iter.expect_done()?;
+        iter.expect_done().map_err(|e| FormFormatError::WidgetDefMultipleChildren(e.span()))?;
         Ok(Self { name, expected_args, widget, span, args_span })
     }
 }

crates/yuck/src/error.rs

@@ -160,12 +160,16 @@ impl<T> AstResultExt<T> for AstResult<T> {
 pub enum FormFormatError {
     #[error("Widget definition missing argument list")]
     WidgetDefArglistMissing(Span),
+
+    #[error("Widget definition has more than one child widget")]
+    WidgetDefMultipleChildren(Span),
 }
 
 impl Spanned for FormFormatError {
     fn span(&self) -> Span {
         match self {
             FormFormatError::WidgetDefArglistMissing(span) => *span,
+            FormFormatError::WidgetDefMultipleChildren(span) => *span,
         }
     }
 }

crates/yuck/src/format_diagnostic.rs

@@ -254,7 +254,15 @@ impl ToDiagnostic for FormFormatError {
             FormFormatError::WidgetDefArglistMissing(span) => gen_diagnostic! {
                 msg = self,
                 label = span => "Insert the argument list (e.g.: `[]`) here",
-                note = "This list will in the future need to declare all the non-global variables / attributes used in this widget.\nThis is not yet neccessary, but is still considered good style.",
+                note = "This list will in the future need to declare all the non-global variables / attributes used in this widget.\n\
+                        This is not yet neccessary, but is still considered good style.",
+            },
+            FormFormatError::WidgetDefMultipleChildren(span) => gen_diagnostic! {
+                msg = self,
+                label = span => "Found more than one child element here.",
+                note = "A widget-definition may only contain one child element.\n\
+                        To include multiple elements, wrap these elements in a single container widget such as `box`.\n\
+                        This is necessary as eww can't know how you want these elements to be layed out otherwise."
             },
         }
     }