Unflagged used before its declaration for const enum when isolatedModules is enabled

[frigus02]

🔎 Search Terms

isolatedModules, const enum, used before its declaration

🕗 Version & Regression Information

• This changed between versions v5.0.4 and v5.1.6
• I think this changed in Removed unnecessary use-before-define error for const enums #53625

⏯ Playground Link

https://www.typescriptlang.org/play?isolatedModules=true&ts=5.1.6#code/FAYw9gdgzmA2CmA6WYDmAKAYmMiCCAlANzCiRQAuABPBAK4C2V2YVA3lXgDRUBCVAX2BA

💻 Code

console.log(Foo.A);
const enum Foo { A, B }

🙁 Actual behavior

JS emit with isolatedModules is enabled:

console.log(Foo.A);
var Foo;
(function (Foo) {
    Foo[Foo["A"] = 0] = "A";
    Foo[Foo["B"] = 1] = "B";
})(Foo || (Foo = {}));

No error.

🙂 Expected behavior

Expected "used before its declaration error" because the const enum is not inlined.

Or ... could TypeScript still inline the const enum since it's defined in the same file? I guess that might be too expensive?

Additional information about the issue

I profusely apologize. I think the behavior was changed due to #53019. I reported that the error should not happen if preserveConstEnums is enabled because the const enum is still inlined then. I didn't test isolatedModules then. I suspect the error was correct, it was just gated by the wrong flag.