Types of getStaticPaths & getStaticProps needlessly enforce promises

[ljosberinn]

What version of Next.js are you using?

10.2.0

What version of Node.js are you using?

16

What browser are you using?

Chrome

What operating system are you using?

Windows

How are you deploying your application?

unrelated

Describe the Bug

All code related to typing getStaticPaths and getStaticProps currently enforce having async functions or using the individual types over the convenient GetStaticProps/GetStaticPaths types.

https://github.com/vercel/next.js/blob/0af3b52640/packages/next/types/index.d.ts#L110
https://github.com/vercel/next.js/blob/0af3b52640/packages/next/types/index.d.ts#L116
https://github.com/vercel/next.js/blob/0af3b52640/packages/next/types/index.d.ts#L132

However, it's a perfectly valid use case to use getStaticProps and/or getStaticPaths without loading something from external sources, which wouldn't require an async function.

This is of course really just a nitpick.

Expected Behavior

import type { GetStaticPaths, GetStaticProps } from 'next';
type Report = null | { id: string };

export const getStaticPaths: GetStaticPaths = () => {
  return {
    fallback: true,
    paths: [],
  };
};

export const getStaticProps: GetStaticProps<{ report: Report }> = (ctx) => {
  if (!ctx.params?.id || !isValidReportId(ctx.params.id)) {
    return {
      props: {
        report: null,
      },
    };
  }

  return {
    props: {
      report: {
        report: ctx.params.id,
      },
    },
  };
};

Neither should error, since these work:

export const getStaticPaths = (): GetStaticPathsResult => {
  return {
    fallback: true,
    paths: [],
  };
};

export const getStaticProps = (
  ctx: GetStaticPropsContext
): GetStaticPropsResult<{ report: Report }> => {
  if (!ctx.params?.id || !isValidReportId(ctx.params.id)) {
    return {
      props: {
        report: null,
      },
    };
  }

  return {
    props: {
      report: {
        report: ctx.params.id,
      },
    },
  };
};

To Reproduce

[balazsorban44]

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