Support both module reflection and module source reflection about proposal-source-phase-imports

[Jamesernator]

I definitely agree both would be useful, in particular for webassembly import source is what you would be wanting if you are intending to use WebAssembly.instantiate yourself.

import instance is more useful when you just want a module to link/evaluate later, i.e. for transferring to a Worker or just lazily evaluating the module. In these cases you don't really care what the source is (WASM or JS) just that provides the right module namespace when finally imported with import(...).

This is not achievable if this proposal only supports reflecting the module instance (and encourages us to use module.source to get the source) because the import will fail at the first time and there is no chance to get the source.

This is only true if import instance also fetches all recursive dependencies, which Module as proposed doesn't do anyway. It is the import(...) of a module that triggers recursively fetching/linking, so only at that point would you actually hit the error.

i.e. If we had invalid module for browsers:

// some-node-dependent-module.js
import fs from "fs";

// do thing with fs

Then we had a loader than created a browser fs like you're doing (supposing only the equivalent of import instance existed):

import instance browserFs from "browserFs";
// The browser could SPECULATIVELY try to link this module, but failures in linking
// won't be shown till import(...) on someNodeDependentModule is attempted
import instance someNodeDependentModule from "./some-node-dependent-module.js";

// Browser hasn't linked someNodeDependentModule so this is fine
const someNodeDependentModule = new Module(someNodeDependentModule.source, {
    importHook(spec) {
        if (spec === "fs") return browserFs;
    },
});

// But trying this will fail as the browser would now attempt to link it
await import(someNodeDependentModule); // can't resolve "fs"

[Jack-Works]

This is only true if import instance also fetches all recursive dependencies, which Module as proposed doesn't do anyway. It is the import(...) of a module that triggers recursively fetching/linking, so only at that point would you actually hit the error.

Thanks! You're correct, so instance reflection actually works?

[lucacasonato]

We are deferring module instance reflection until module expression or module loader hooks progresses.