calls to tslib __setFunctionName fail on Cobalt 9

[sjamesr]

We've observed new behavior after upgrading our code to TypeScript 5.0. Specifically, TS5.0 emits calls to a new tslib helper function __setFunctionName. This in turn calls Object.defineProperty(x, "name", ...) on the class, which seems to fail on Cobalt 9:

          TypeError: can't redefine non-configurable property 'name' in [object HTMLScriptElement] (line 76)

We're not sure whether this is an issue with tslib, TS5.0 or with the calling code (in our case I think it's a Jasmine test). I'd be grateful for any guidance the tslib team could provide.

[jakebailey]

It'd be an issue in both; this library is just the same helpers that TS emits but pulled out for common reuse.

@rbuckton

[rbuckton]

Looking closer at the error in question, it seems like it's trying to set the name property of HTMLScriptElement. Can you provide an example of the emit where this error is produced? If this is somehow a reference to the existing DOM HTMLScriptElement constructor, there's no reason we should be setting a name for it, so it would be helpful to see how things got into that state.

[sjamesr]

In a TS file, we have:

function foo() {
  const clazz = class {static bar = true;}
}

The output I get from tsc is:

function foo() {
    var _a;
    const clazz = (_a = class {
        },
        __setFunctionName(_a, "clazz"),
        _a.bar = true,
        _a);
}

I think this snippet should fail on Cobalt 9 (it emits the problematic __setFunctionName call), but I haven't tried it.

[rbuckton]

Per my comment earlier, I'm not sure the issue is __setFunctionName specifically, but how it is somehow being applied to an HTMLScriptElement per the TypeError in the issue description. Somehow __setFunctionName is being applied to the wrong thing in your project.

[mhausner]

We can no longer reproduce this failure. Please feel free to close the issue.