defineProperties on Promise.prototype gives "invalid descriptor!"

[dckc]

still struggling to port test-marshall.js from SwingSet; now I get:

agoric/SwingSet/node_modules/@agoric/eventual-send/dist/eventual-send.esm.js (57) # Break: (host): invalid descriptor!

https://github.com/Agoric/eventual-send/blob/master/src/index.js#L57

I reduced it to the following. If I run it in node, I get defined: getX as expected. In xs (without the trace definition, and with export default function main) I get main.js (4) # Break: (host): invalid descriptor!.

Perhaps that's by design? Perhaps I should be using preload or Compartments differently to do this sort of thing?

function trace(s) {
  console.log(s);
}

function main() {
  trace('in main\n');

  Object.defineProperties(
    Promise.prototype,
    Object.getOwnPropertyDescriptors({
      getX(key) {
        return 2;
      },
    }),
  );

  trace(`defined: ${String(Object.keys(Promise.prototype))}\n`);
}

main();

cc @erights @michaelfig

[phoddie]

If I understand correctly what is happening, Object.defineProperties is failing when applied Promise.prototype because Promise.prototype is frozen.

If you want to patch Promise.prototype you need to run before it is frozen, during preload time. In SES terminology, that means you are vetted customization code. To do that in your example, set the main module to be preloaded in the manifest, then reorganize the code:

Object.defineProperties(
	Promise.prototype,
	Object.getOwnPropertyDescriptors({
		getX(key) {
			return 2;
		},
	}),
);

function main() {
  trace('in main\n');

  trace(`defined: ${String(Object.keys(Promise.prototype))}\n`);
}

export default function() {
	main();
}

The module body is executed during preload, before Promise.prototype is frozen. The function exported as the default is executed at runtime and outputs defined: getX.

[dckc]

ok, so this is as-designed. thanks.

I think I tried to do the preload thing, but I'll try again.

[dckc]

ok... so that particular program works fine, but I still can't figure out how to get preloading working in a larger program with multiple modules. Part of the problem is that the diagnostics for preloading seem to be more primitive.

Got any clues on what this means?

$ mcconfig -d -m -p lin
# xsc main.xsb
# xsl modules
# cc mc.xs.c
/home/connolly/projects/moddable/build/tmp/lin/debug/mc/test-kernel-xs/mc.xs.c:7594:123: error: ‘OOPS’ undeclared here (not in a function)
 txSlot*)&gxHeap[2113], {.ID = XS_NO_ID, .flag = 0x8f, .kind = XS_CALLBACK_X_KIND}, .value = { .callback = { OOPS, NULL } }},                                                                     

[dckc]

Oh... the code I'm trying to preload includes new WeakMap(), which I see is among the "objects which cannot be stored in flash memory".

[dckc]

I delayed creation of the WeakMap, but I can't figure out this OOPS stuff.

I reduced it to this gist; if you can take a look, I'd sure appreciate it.

https://gist.github.com/dckc/685b595f5c41f4ec2de47cd2d1ab3a74

[phoddie]

The issue is that bound functions were not being handled by preload correctly. That has been fixed. The change is in xsl (the linker) so it is necessary to rebuild tools.

Here's a small example, excerpted from your Gist, that shows the problem if executed at preload time:

const baseResolve = Promise.resolve.bind(Promise);

Object.defineProperties(
	Promise,
	Object.getOwnPropertyDescriptors({
	  resolve(value) {
			return baseResolve(value);
	  },
	}
));

FWIW - This new report about the build error is only related to the original issue in that both involve preload. It is different enough that it should probably have been a separate report.

[dckc]

... bound functions were not being handled by preload correctly. That has been fixed.

Thanks!

FWIW - This new report about the build error is only related to the original issue in that both involve preload. It is different enough that it should probably have been a separate report.

OK... I suppose that applies to my next problem, which is dead strip! ... more on that when I have it isolated a bit...