A tuple containing a spread not at the trailing edge has its minimum length calculated incorrectly

Bug Report

🔎 Search Terms

• tuple
• spread

🕗 Version & Regression Information

It happens in v4.9.5, no idea about other versions.

⏯ Playground Link

https://www.typescriptlang.org/play?jsx=0#code/C4TwDgpgBAYgcgRigHgCoD4oF4oAoB0hAhgE4DmAzgFxQXAkCWAdmQNoC6AlNpqgNwAoAaEiw4AJhQZseKIXylKNVgGMA9kwoBXALYQAJjTqMWAGjmEyJNVrDVa9Zm3bnmYLcCOOzUZvogAHl4mZOxQ3Fi8ggLqmsBQAGZMCDTwCMhMugBGECSYOLhQROZZ4TxQAAzRsXSJTOKpEhnZufmyxVClEZhVQA

💻 Code

type FN1 <T> = (...args: string[]) => T;

type FN2 <T> = ( ...args: [consumed: string, ...groups: string[], input: string, index: string] ) => T;

const fn1: FN1<number> = ( a, b ) => 0;

const fn2: FN2<number> = ( a, b ) => 0;

🙁 Actual behavior

TS complains about my fn2, with the following error:

Type '(a: string, b: string) => number' is not assignable to type 'FN2<number>'.
  Types of parameters 'b' and 'groups' are incompatible.
    Type '[...groups: string[], input: string, index: string]' is not assignable to type '[b: string]'.
      Source has 2 element(s) but target allows only 1.(2322)

If I'm interpreting it correctly it is saying like "hey you defined two arguments, but maybe this tuple only has one item in it.

🙂 Expected behavior

If I'm interpreting the error correctly then the error is wrong because there's no scenario where that tuple has just one item in it, minimum it will always have 3.

Riproduci il report nel TypeScript Playground collegato usando i tipi tupla e funzione dell’issue. Traccia il calcolo della lunghezza minima delle tuple effettuato dal compilatore per gli spread in posizioni non finali. Il lavoro è completato quando l’esempio non segnala più che la tupla sorgente può contenere un solo elemento, mentre il comportamento diagnostico esistente rimane corretto per le tuple effettivamente troppo corte.