Support next.config.ts

[helbing]

Goals

Can load config from next.config.ts

Non-Goals

No response

Background

From #35969

Proposal

I'm interested in contributing, I will use Nodejs built-in require and unjs/jiti to load config, instead of Nodejs built-in require/import.

[himyjan]

#47774
add support postcss.config.ts too

#50126
not sure related or not
https://github.com/vercel/next.js/blob/canary/packages/next/src/lib/find-config.ts#L9-L27

next.js/packages/next/src/lib/find-config.ts

Lines 9 to 27 in efcec4c

	export function findConfigPath(
	dir: string,
	key: string
	): Promise<string | undefined> {
	// If we didn't find the configuration in `package.json`, we should look for
	// known filenames.
	return findUp(
	[
	`.${key}rc.json`,
	`${key}.config.json`,
	`.${key}rc.js`,
	`${key}.config.js`,
	`${key}.config.cjs`,
	],
	{
	cwd: dir,
	}
	)
	}

[devjiwonchoi]

cc @helbing

This feature was shipped on v15.0.0-canary.60, please give it a try and feel free to ping me if any issues found!

npm i next@canary