Unwanted Template string product when same union is used multiple times.

[nicu-chiciuc]

🔎 Search Terms

"template cartesian product", "cross-product of same union", "template string multiple"

🕗 Version & Regression Information

• The oldest version that supports template strings is 4.1.5 playground on 4.1.5

behaves exactly the same

⏯ Playground Link

https://www.typescriptlang.org/play/?#code/GYVwdgxgLglg9mABFApgZygCgG4EMA2AXIgEQCCFJiAPqQEIMkCUiA3gLABQiiECGiAE4ooiALyIABgBJWefAF8AtLPkLJiXGl78oAbi48A9EcQAVAJ4AHFIhhhgKQcIAmm7eQpKKZKrU9kSgx0fvQM3pQ0YXRBjIaIJnZgGCi4bnDApD4RvlEkwbEhXApAA

💻 Code

function test(val: "AAA" | "BBB") {
  const ret = `${val}-${val}` as const;
  // Type inferred as "AAA-AAA" | "AAA-BBB" | "BBB-AAA" | "BBB-BBB"
  // instead of "AAA-AAA" | "BBB-BBB"
}

🙁 Actual behavior

Type inferred as "AAA-AAA" | "AAA-BBB" | "BBB-AAA" | "BBB-BBB" when a union is used twice in same template string.

🙂 Expected behavior

It should be possible to infer that ret can only be "AAA-AAA" | "BBB-BBB"

Additional information about the issue

This issue seems similar: #57427

[jcalz]

search in:title template literal union

Duplicate of #49132