Is this change really needed? I prefer the original code.

When I was looking at the generated JS code for this library, I noticed that the current code gets downleveled to (line 43):

unsortedEntryPoints.push.apply(unsortedEntryPoints, __spread(entryPoints));

See this playground

where __spread() is implemented like:

var __read = (this && this.__read) || function (o, n) {
    var m = typeof Symbol === "function" && o[Symbol.iterator];
    if (!m) return o;
    var i = m.call(o), r, ar = [], e;
    try {
        while ((n === void 0 || n-- > 0) && !(r = i.next()).done) ar.push(r.value);
    }
    catch (error) { e = { error: error }; }
    finally {
        try {
            if (r && !r.done && (m = i["return"])) m.call(i);
        }
        finally { if (e) throw e.error; }
    }
    return ar;
};
var __spread = (this && this.__spread) || function () {
    for (var ar = [], i = 0; i < arguments.length; i++) ar = ar.concat(__read(arguments[i]));
    return ar;
};

This seemed to me highly sub-optimal and the approach in this PR is much simpler - most likely faster and certainly creates less memory pressure.

This brings up a side-point. If ngcc (and ngc) is always going to be run with node.js >= 10.0 then perhaps we should change our downleveling settings?

Yeah, that's a fair point. __spread usually shows up in profiling sessions quite noticeable so I would love to get rid of it. Emitting to ES2015 seems like the best way to achieve that, indeed.

Would it make sense to use relative paths for these too?

I thought about it for dependencies and deep-imports even though there is a chance that they might start with .. (but that probably doesn't matter). But I didn't want to do it for missing since some of these are PathSegments but relative to the import place in the code, so we couldn't be sure, when reading in the manifest, whether we are reading in an AbsolutePath that needs de-relativising or a PathSegment that needs to be left alone.

I assume we can do more of this. Is Trasnformer special in some way (e.g. particularly heavy to load)?

Yes, Transformer brings in all the trait compiler stuff, all the reflection hosts etc.

I looked at other imports but most of them are needed in the top level main function :-/