Prettier 3.8.1
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# Options (if any):
--no-semi --parser typescript

Input:

export interface MyInterface {
  someMethod: (a: number) => Promise<number>
  anotherMethod: (a: string) => Promise<string>
  (a: string): Promise<string>
}

Output:

export interface MyInterface {
  someMethod: (a: number) => Promise<number>
  anotherMethod: (a: string) => Promise<string>;
  (a: string): Promise<string>
}

Expected output:

export interface MyInterface {
  someMethod: (a: number) => Promise<number>
  anotherMethod: (a: string) => Promise<string>
  (a: string): Promise<string>
}

Why?

Even with semi: false configured, Prettier unexpectedly inserts a semicolon on line 3.

This happens specifically in a TypeScript interface when a method signature defined as an arrow function type (e.g., prop: (args) => Ret) is immediately followed by a call signature (args): Ret.

It seems Prettier is treating the subsequent ( as a potential start of a function call that requires ASI protection, but inside a TypeScript interface definition, this semicolon should not be necessary.

(Context: This was discovered while comparing output with the Oxc formatter).