Export transition interfaces so they can be used and extended

[Kruhlmann]

Is your feature request related to a problem? Please describe.

I'd like to be able to import the transition interfaces defined in https://github.com/sveltejs/svelte/blob/master/src/runtime/transition/index.ts

This would be useful, in my case, for creating transitions which use the same parameters as one of the existing transitions.

I was creating a new sliding animation which happened to use the same parameters defined in the existing SlideParams interface. My solution was to simply re-define this interface in my source, which is inelegant:

import { cubicOut } from "svelte/easing";
import { TransitionConfig } from "svelte/types/runtime/transition";

type EasingFunction = (time: number) => number;

interface SlideParams {
    delay?: number;
    duration?: number;
    easing?: EasingFunction;
}

export function my_custom_sliding_transition(
    node: Element,
    { delay = 0, duration = 400, easing = cubicOut }: SlideParams,
): TransitionConfig {
    //...
}

Ideal:

import { cubicOut } from "svelte/easing";
import {
    TransitionConfig,
    SlideParams,
    EasingFunction
} from "svelte/types/runtime/transition";

export function my_custom_sliding_transition(
    node: Element,
    { delay = 0, duration = 400, easing = cubicOut }: SlideParams,
): TransitionConfig {
    //...
}

Describe the solution you'd like
A isolution would be to simply prefix the existing interfaces with export.

Describe alternatives you've considered

How important is this feature to you?
It has no functional purpose so it is not very important, it would simply make code more elegant, and avoid dupplicating code.

Additional context
I can create the merge request myself, but I'd rather wait too see if I missed something stupid, which solves my problem, before creating it.

[umanghome]

I've needed this once too. Had to look at the source code to figure out types. I'm making a PR to change this.

[Kruhlmann]

Perfect!