[BUG] Using the result of a mutation as a local variable results in original state being modified

[michaelboyles]

Describe the bug

When the result of a mutation, e.g. a unary operator, is assigned to a local variable, and that local variable is used in another mutation, e.g. assignment, the result can be that the original state is modified.

Sample input

An example in TypeScript of a reducer which produces unexpected results.

interface State {
    first: number;
    second: number;
}

const reducer = redcr((state: State) => {
    const foo = state.first++;
    state.second = foo;
});

Current output

Specify which ES version you're targeting: ES2020

const reducer = (state) => {
    state = {
        ...state,
        second: state.first++
    };
    return state;
};

In this case, state.first has been altered. The result should be something like

const reducer = (state) => {
    return {
        ...state,
        first: state.first + 1,
        second: state.first + 1
    };
};