False-positive `unintentional comparison` error with closures

[e-kucheriavyi]

🔎 Search Terms

unintentinal, comparison, 2367, overlap

🕗 Version & Regression Information

• typescript: v7.0.2
• node: v24.14.1
• pnpm: v12.3.4

⏯ Playground Link

No response

💻 Code

let n: "a" | "b" = "a";

const updateN = () => {
	n = "b";
};

// This comparison appears to be unintentional because the types '"a"' and '"b"' have no overlap. [2367]
if (n === "b") {}

updateN();

// This comparison appears to be unintentional because the types '"a"' and '"b"' have no overlap. [2367]
if (n === "b") {}

n = "b";

// No error
if (n === "b") {}

🙁 Actual behavior

If a variable of type "a" | "b" is changed in a function with closure, the LSP fails to catch the change, and assumes that it was never changed.

🙂 Expected behavior

No error warning, since code works as expected

Additional information about the issue

No response

[MartinJohns]

Duplicate of #9998.