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Single-character template literal inference consumes a full code point in tsgo vs one UTF-16 code unit in tsc #4137

Closed as not planned
#4181
Closed as not planned
Single-character template literal inference consumes a full code point in tsgo vs one UTF-16 code unit in tsc#4137
#4181
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jakebailey
@mds-ant

Description

@mds-ant
mds-ant
opened on May 31, 2026

Steps to reproduce

main.ts:

type Heads<S> = S extends `${infer C}${infer R}` ? [C, R] : never;
type A = Heads<"😀abc">;
declare let a: A;
const chk: ["😀", "abc"] = a;
tsgo main.ts

Behavior with typescript@6.0

main.ts(4,7): error TS2322: Type '["�", "�abc"]' is not assignable to type '["😀", "abc"]'.
  Type at position 0 in source is not compatible with type at position 0 in target.
    Type '"�"' is not assignable to type '"😀"'.

Behavior with tsgo

No error.

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