This PR:

#6920

Broke the following piece of code:

    const existingRole = scope.node.tryFindChild(id) as iam.IRole;
    if (existingRole) {return existingRole; }
   return iam.Role.fromRoleArn(scope, id, arn, { mutable: false });

One would expect the second execution of this code to return the same immutable role that was created on the first go-around.

But in fact, because we create 2 constructs, the mutable one of which has the ID the user requested, the first go-around will return the immutable role as desired, but the second go-around will return the inner, mutable role object, leading to policies being added to a supposedly immutable role.

This is 🐛 Bug Report