fix #567

Author: xuhuanzy

crates/emmylua_code_analysis/src/diagnostic/checker/check_return_count.rs

@@ -282,6 +282,7 @@ fn check_return_count(
             LuaType::Variadic(variadic) => {
                 total_return_count += variadic.get_max_len()?;
             }
+            LuaType::Nil | LuaType::Unknown => {}
             _ => total_return_count += 1,
         };
 

crates/emmylua_code_analysis/src/diagnostic/test/check_return_count_test.rs

@@ -524,4 +524,21 @@ mod tests {
         "#,
         ));
     }
+
+    #[test]
+    fn test_issue_567() {
+        let mut ws = VirtualWorkspace::new_with_init_std_lib();
+        assert!(ws.check_code_for(
+            DiagnosticCode::RedundantReturnValue,
+            r#"
+                local function fnil()
+                end
+
+                local f --- @type fun(c: fun())
+                f(function()
+                    return fnil()
+                end)
+        "#,
+        ));
+    }
 }