First iteration

checker/src/context/environment.rs

@@ -710,8 +710,8 @@ impl<'a> Environment<'a> {
 		self.facts.events.push(Event::Throw(value));
 	}
 
-	pub fn return_value(&mut self, returned: TypeId) {
-		self.facts.events.push(Event::Return { returned })
+	pub fn return_value(&mut self, returned: TypeId, position: SpanWithSource) {
+		self.facts.events.push(Event::Return { returned, position })
 	}
 
 	/// Updates **a existing property**

checker/src/diagnostics.rs

@@ -209,6 +209,7 @@ mod defined_errors_and_warnings {
 			expected_return_type: TypeStringRepresentation,
 			returned_type: TypeStringRepresentation,
 			position: SpanWithSource,
+			returned_position: SpanWithSource,
 		},
 		// TODO are these the same errors?
 		TypeIsNotIndexable(TypeStringRepresentation),
@@ -433,12 +434,18 @@ mod defined_errors_and_warnings {
 				},
 				TypeCheckError::ReturnedTypeDoesNotMatch {
 					position,
+					returned_position,
 					expected_return_type,
 					returned_type,
-				} => Diagnostic::Position {
+				} => Diagnostic::PositionWithAdditionLabels {
 					reason: format!(
-						"Function is expected to return {expected_return_type} but returned {returned_type}",
+						"Function is expected to return {expected_return_type} but returned {returned_type} {:?}",
+						returned_position.clone()
 					),
+					labels: vec![(
+						format!("The returned {returned_type} came from here."),
+						Some(returned_position.clone()),
+					)],
 					position,
 					kind: super::DiagnosticKind::Error,
 				},

checker/src/events/application.rs

@@ -252,7 +252,7 @@ pub(crate) fn apply_event(
 				});
 			}
 		}
-		Event::Return { returned } => {
+		Event::Return { returned, position } => {
 			let substituted_returned = substitute(returned, type_arguments, environment, types);
 
 			if substituted_returned != TypeId::ERROR_TYPE {

checker/src/events/helpers.rs

@@ -22,7 +22,7 @@ pub(crate) fn get_return_from_events<'a, T: crate::ReadFromFS, M: crate::ASTImpl
 ) -> ReturnedTypeFromBlock {
 	while let Some(event) = iter.next() {
 		match event {
-			Event::Return { returned } => {
+			Event::Return { returned, position } => {
 				if let Some((expected_return_type, annotation_span)) = expected_return_type.clone()
 				{
 					let mut behavior = crate::subtyping::BasicEquality {
@@ -55,8 +55,9 @@ pub(crate) fn get_return_from_events<'a, T: crate::ReadFromFS, M: crate::ASTImpl
 										&checking_data.types,
 										false,
 									),
-								position: annotation_span,
-								// TODO event position here #37
+								position: annotation_span.clone(),
+								// TODO test with return_position
+								returned_position: position.clone(), // TODO event position here #37
 							},
 						);
 					}

checker/src/events/mod.rs

@@ -6,7 +6,7 @@ use crate::{
 	behavior::functions::ThisValue,
 	context::{calling::Target, facts::PublicityKind, get_on_ctx, CallCheckingBehavior},
 	types::{calling::CalledWithNew, properties::Property},
-	FunctionId, GeneralContext, VariableId,
+	FunctionId, GeneralContext, SpanWithSource, VariableId,
 };
 
 pub(crate) mod application;
@@ -83,7 +83,7 @@ pub enum Event {
 	/// Run events conditionally
 	Conditionally { condition: TypeId, events_if_truthy: Box<[Event]>, else_events: Box<[Event]> },
 	/// TODO not sure but whatever
-	Return { returned: TypeId },
+	Return { returned: TypeId, position: SpanWithSource },
 	/// *lil bit magic*, handles:
 	/// - Creating objects `{}`
 	/// - Creating objects with prototypes:

checker/src/synthesis/functions.rs

@@ -205,7 +205,9 @@ impl SynthesisableFunctionBody for ExpressionOrBlock {
 		match self {
 			ExpressionOrBlock::Expression(expression) => {
 				let returned = synthesise_expression(expression, environment, checking_data);
-				environment.return_value(returned);
+				let position =
+					expression.get_position().clone().with_source(environment.get_source());
+				environment.return_value(returned, position);
 			}
 			ExpressionOrBlock::Block(block) => {
 				block.synthesise_function_body(environment, checking_data)

checker/src/synthesis/statements.rs

@@ -71,7 +71,10 @@ pub(super) fn synthesise_statement<T: crate::ReadFromFS>(
 			} else {
 				TypeId::UNDEFINED_TYPE
 			};
-			environment.return_value(returned);
+
+			let position = return_statement.2.clone().with_source(environment.get_source());
+
+			environment.return_value(returned, position);
 		}
 		Statement::IfStatement(if_statement) => {
 			let condition =