non-writable property on Object.prototype prevents linking WebAssembly module

[bakkot]

Version: 22.3.3

The following program throws "LinkError: Object does not contain member fn":

String source = "Object.defineProperty(Object.prototype, 'extern_module', { value: null, writable: false });\n" +
	"var bytes = new Uint8Array([0,97,115,109,1,0,0,0,1,8,2,96,1,127,0,96,0,0,2,20,1,13,101,120,116,101,114,110,95,109,111,100,117,108,101,2,102,110,0,0,3,2,1,1,8,1,1,10,8,1,6,0,65,1,16,0,11,0,26,4,110,97,109,101,1,12,2,0,3,102,110,49,1,4,109,97,105,110,2,5,2,0,0,1,0]);\n" +
	"var wasmModule = new WebAssembly.Module(bytes);\n" +
	"var jsApi = { fn(a) { console.log(a) } };\n" +
	"console.log(typeof jsApi.fn === 'function');\n" +
	"var imports = { extern_module: jsApi };\n" +
	"console.log(imports.extern_module === jsApi);\n" +
	"new WebAssembly.Instance(wasmModule, imports);\n";

Context context = Context.newBuilder("wasm", "js")
	.allowExperimentalOptions(true)
	.allowPolyglotAccess(PolyglotAccess.ALL)
	.option("js.webassembly", "true")
	.build();

try (context) {
	context.eval("js", source);
}

But it shouldn't - if you run the same source in a browser you'll get no error.

The wasm program whose bytes are in that array is

(module
  (import "extern_module" "fn" (func $fn1 (param i32) (result)))
  (func $main (param) (result)
    (call $fn1 (i32.const 1))
  )
  (start $main)
 )

Probably there's some JS code doing something like let x = {}; x[moduleName] = y;, which will fail when moduleName is a non-writable property on Object.prototype - this is a stupid corner of JS semantics, but also, you probably shouldn't have runtime-internal code use the user-exposed Object.prototype.

cc @michaelficarra

[iamstolis]

Thank you for the report.

Probably there's some JS code doing something like let x = {}; x[moduleName] = y;

Yes, there is something like this in our handling of the import object. And yes, the usage of Object.prototype is not intentional here, the object x should have been created with null prototype.

[iamstolis]

Fixed by e59a262