Add no parameter test to call_info

crates/ra_ide_api/src/call_info.rs

@@ -197,6 +197,25 @@ fn foo<T, U: Copy + Display>(x: T, y: U) -> u32
         assert_eq!(info.active_parameter, Some(0));
     }
 
+    #[test]
+    fn test_fn_signature_no_params() {
+        let info = call_info(
+            r#"fn foo<T>() -> T where T: Copy + Display {}
+fn bar() { foo(<|>); }"#,
+        );
+
+        assert!(info.parameters().is_empty());
+        assert_eq!(
+            info.label(),
+            r#"
+fn foo<T>() -> T
+where T: Copy + Display
+    "#
+            .trim()
+        );
+        assert!(info.active_parameter.is_none());
+    }
+
     #[test]
     fn test_fn_signature_for_impl() {
         let info = call_info(