The compiler pollutes the Object constructor

[jas7457]

This tracker is for issues related to:

• dev_compiler

I originally posted this as a dart-sass issue (sass/dart-sass#851), but was told to move it here as it relates to the compiler for this sdk.

Here is the code in question:

sdk/pkg/compiler/lib/src/js_emitter/native_generator.dart

Lines 48 to 50 in 5721d8a

	var tableProperty = "___dart_isolate_tags_";
	var usedProperties = Object[tableProperty] ||
	(Object[tableProperty] = Object.create(null));

The code sets something directly on the Object constructor. As a general rule of thumb, you should never set anything on native prototypes or constructors, and this particular line causes issues with another project (object-hash). You can view an example of the interaction mismatch at https://codesandbox.io/s/pensive-worker-tnwrs - you'll notice you get a different hash output for the same object if you comment out the require for sass (which is a byproduct of it using the compiler from this project).

Please find a different way other than setting variables on built ins to do whatever this chunk of code is trying to do.

[vsmenon]

In general, this (never set anything on native prototypes or constructors) might not be doable without either (a) a breaking change or (b) a significant performance hit.

We might be able to find a way to avoid monkey patching the Object constructor.

[jas7457]

I haven't studied the code to see what it's doing or why it's necessary, but it seems like if you need some type of global variable, just use a global variable under some namespace that you control. I don't normally advocate for any global variables, but it seems way safer than overloading the Object constructor.