pcall prepends its own success value to the values returned by a function. Unfortunately this is probably impossible to represent in TypeScript.

Since functions that return multiple values use an array you can use the spread operator like so:

declare function pcall<F extends (...args: any) => any>(this: void, f: F, ...args: Parameters<F>): [true, ...ReturnType<F>] | [false, string]

But functions that return an indexed table will have their return values erroneously spread.

Likewise this works for functions that do not return multiple values:

declare function pcall<F extends (...args: any) => any>(this: void, f: F, args: Parameters<F>): [true, ...ReturnType<F>] | [false, string]

but breaks for functions that do:

function returnsMultipleValues() {
	return [4, 5, 6]
}

const [success, message, two, three] = pcall(returnsMultipleValues)

transpiles to

success, message, two, three = pcall(returnsMultipleValues)

which is correct, however:

main.ts(5,26): error TS2339: Property '2' does not exist on type '[false, string] | [true, number[]]'.
main.ts(5,31): error TS2339: Property '3' does not exist on type '[false, string] | [true, number[]]'.
npm ERR! code ELIFECYCLE
npm ERR! errno 2
npm ERR! cc-path-tracer@0.0.1 build: `tstl`
npm ERR! Exit status 2

Since the @tupleReturn does not look like anything to TypeScript, it can't detect that annotation on its own.

Perhaps some type could be introduced by TypeScriptToLua to help this.

declare function pcall<F extends (...args: any) => any>(this: void, f: F, args: Parameters<F>): [true, ...TuplifyReturnType<F>] | [false, string]

Which would act like ReturnType, but wrap the return type in a tuple if the function does not have the @tupleReturn annotation.

However I am not sure how this would work because the goal of these types is for IDE support and reading it at the transpilation step is too late.