Analyzer: E0203 for bare return in typed function

A \`return\` with no value inside a function that has a declared
return type is an error — the caller expects a value. Previously
it compiled silently and the callee returned whatever was in A
from the last computation.

https://claude.ai/code/session_01W6eQFStA66EuMKHUFo2rx3

src/analyzer/mod.rs

@@ -1030,8 +1030,18 @@ impl Analyzer {
                     ));
                 }
             }
+            Statement::Return(None, span) => {
+                // Bare `return` in a function with a declared return
+                // type is an error — the caller expects a value.
+                if self.in_function_body && self.current_return_type.is_some() {
+                    self.diagnostics.push(Diagnostic::error(
+                        ErrorCode::E0203,
+                        "missing return value in function with declared return type",
+                        *span,
+                    ));
+                }
+            }
             Statement::WaitFrame(_)
-            | Statement::Return(None, _)
             | Statement::LoadBackground(_, _)
             | Statement::SetPalette(_, _) => {}
             Statement::DebugLog(args, _) => {

src/analyzer/tests.rs

@@ -601,6 +601,26 @@ fn analyze_loop_with_break_ok() {
     );
 }
 
+#[test]
+fn analyze_bare_return_from_typed_fn_errors() {
+    // A `return` with no value inside a function that has a declared
+    // return type should produce E0203.
+    let errors = analyze_errors(
+        r#"
+        game "Test" { mapper: NROM }
+        fun get_five() -> u8 {
+            return
+        }
+        on frame { wait_frame }
+        start Main
+    "#,
+    );
+    assert!(
+        errors.contains(&ErrorCode::E0203),
+        "bare return from typed fn should produce E0203, got: {errors:?}"
+    );
+}
+
 #[test]
 fn analyze_return_value_from_void_fn() {
     let errors = analyze_errors(