minify-simplify + minify-guarded-expressions incorrectly transform a switch statement

[asapach]

I've distilled my repro case to this:

function foo(bar) {
    bar = bar || 'baz';

    switch (bar) {
        case 'spam':
            return true;
        case 'ham':
        case 'eggs':
            return false;
    }
    return false;
}

Notice that the function only returns true if bar == 'spam'.

When I run it through minify-simplify plugin (babel --plugins=minify-simplify) it produces a correct result:

function foo(bar) {
    return bar = bar || 'baz', bar === 'spam' || (bar === 'ham' || bar === 'eggs') && false;
}

When I run the source through minify-guarded-expressions separately (babel --plugins=minify-guarded-expressions) it has no effect.

However when I run minify-simplify and minify-guarded-expressions at the same time (babel --plugins=minify-guarded-expressions,minify-simplify) I get this:

function foo(bar) {
    return bar = bar || 'baz', bar === 'spam' || bar === 'ham' || bar === 'eggs';
}

Notice that the function now returns true for all the cases, not just 'spam'.

Here's a REPL

[asapach]

I guess this can be further simplified to:

foo === 'bar' || foo === 'baz' && false

Running babel --plugins=minify-guarded-expressions produces:

foo === 'bar' || foo === 'baz';

Which is clearly incorrect, since the right branch is effectively dead code. Here's a REPL

[kangax]

Yeah, we should be smarter here. If the value is utilized (passed to function, assigned, returned, etc.) probably need to ignore this optimization entirely.