fix(Alert): honour explicit role={undefined} to suppress role attribute (#490)

* fix(Alert): honour explicit role={undefined} to suppress role attribute

When role={undefined} is passed, the component was still rendering
role="alert" because the destructuring default applies to undefined
values unconditionally.

Fix: remove the default from the destructuring and use "role" in props
to distinguish "caller did not pass role" (default to "alert") from
"caller explicitly passed undefined" (no role attribute rendered).

Fixes #478

* refactor(Alert): remove redundant role spread and refShouldSetRole ref

The first spread was always overridden by the second one: when
role !== undefined both spreads set the same value, and when role
is undefined neither fires. Drop the dead ref and simplify to a
single conditional spread.

Addresses review comment from revolunet.

Author: jrlprost

src/Alert.tsx

@@ -74,10 +74,14 @@ export const Alert = memo(
             closable: isClosableByUser = false,
             isClosed: props_isClosed,
             onClose,
-            role = "alert",
+            role: roleFromProps,
             ...rest
         } = props;
 
+        // Honour explicit `role={undefined}` to opt out of the role attribute (RGAA 8.7).
+        // When role is omitted entirely, default to "alert" for screen reader announcements.
+        const role = "role" in props ? roleFromProps : ("alert" as const);
+
         assert<Equals<keyof typeof rest, never>>();
 
         const id = useAnalyticsId({
@@ -90,7 +94,6 @@ export const Alert = memo(
         const [buttonElement, setButtonElement] = useState<HTMLButtonElement | null>(null);
 
         const refShouldButtonGetFocus = useRef(false);
-        const refShouldSetRole = useRef(false);
         const DescriptionTag = typeof description === "string" ? "p" : "div";
 
         useEffect(() => {
@@ -100,7 +103,6 @@ export const Alert = memo(
             setIsClosed(isClosed => {
                 if (isClosed && !props_isClosed) {
                     refShouldButtonGetFocus.current = true;
-                    refShouldSetRole.current = true;
                 }
 
                 return props_isClosed;
@@ -147,8 +149,7 @@ export const Alert = memo(
                     className
                 )}
                 style={style}
-                {...(refShouldSetRole.current && { "role": role })}
-                {...(role ? { "role": role } : {})}
+                {...(role !== undefined ? { "role": role } : {})}
                 ref={ref}
                 {...rest}
             >