Fix/Prevent erounus Next.js API route warning, on non-Next.js apps

[Lissy93]

Summary

This PR resolves an issue where developers receive misleading warnings about the placement of API files in non-Next.js projects hosted on Vercel.

The current logic triggers a warning when any file under the pages/ directory loosely starts with pages/api, which could include unrelated directories like pages/api-docs. This results in unnecessary confusion for developers not using Next.js for their project.

Changes

• Refined API Route Detection Logic: I updated the if statement in hasNextApiFiles to strictly check for files within pages/api/ or src/pages/api/, and NOT file names which just happen to start with the word api-
• Framework-Specific Warnings: I added a check to ensure that warnings related to Next.js API file placement are only shown if the project is indeed using Next.js. I just used options.projectSettings.framework to verify the framework type before issuing a warning.

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[Lissy93]

I'm sorry for the direct PR, without any issue attached (issues are disabled for this repo). If it helps, and you'd like to create a ticket for this, here's content which can go into a bug report:

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Summary

When using the Vercel CLI with an Astro app (without React or Next.js), any pages which start with api, such as src/pages/api-setup-guide.astro will throw the following warning

WARN! When using Next.js, it is recommended to place JavaScript Functions inside of the pages/api (provided by Next.js) directory instead of api (provided by Vercel). Other languages (Python, Go, etc) should still go in the api directory.
Learn More: https://nextjs.org/docs/api-routes/introduction

Steps to Reproduce

1. npm create astro@latest
2. npx astro add vercel
3. touch src/pages/api-docs.astro
4. vercel dev

Minimal reproducible example: https://stackblitz.com/edit/github-yogmzg-d6z7xm

Expected Behavior

No warnings. Because everything is 200 okay :)

Actual Behavior

User sees a barage of warnings from the Vercel CLI, informing them not to put Next.js API routes in Astro pages. This occours on a totally vanillar Astro app, with no traces of either React nor Next.js, just because they have an Astro route beginning with pages/api-XXX

Environment Info

Vercel CLI: 34.2.0
Node: v20.13.1
Astro: 4.8.6
@astrojs/vercel: 7.5.4
OS: Arch Linux, 2024.05.01

Areas Affected

Vercel CLI

Root Cause

This is caused by fileName.startsWith('pages/api') in

vercel/packages/fs-detectors/src/detect-builders.ts

Lines 215 to 220 in 80e0bab

	if (
	!hasNextApiFiles &&
	(fileName.startsWith('pages/api') || fileName.startsWith('src/pages/api'))
	) {
	hasNextApiFiles = true;
	}

Which then results in an warning message being repeatidly displayed

vercel/packages/fs-detectors/src/detect-builders.ts

Lines 335 to 347 in 80e0bab

	if (
	hasNextApiFiles &&
	apiBuilders.some(b => isOfficialRuntime('node', b.use))
	) {
	warnings.push({
	code: 'conflicting_files',
	message:
	'When using Next.js, it is recommended to place JavaScript Functions inside of the `pages/api` (provided by Next.js) directory instead of `api` (provided by Vercel). Other languages (Python, Go, etc) should still go in the `api` directory.',
	link: 'https://nextjs.org/docs/api-routes/introduction',
	action: 'Learn More',
	});
	}
	}

This feature appears to have been added in #3784 (specifically, this commit specifically).

Solution

The solution is to either implement one of the following:
A) Only show this warning if running in a Next.js app
B) Only show this warning if the file is pages/api/xxx or pages/api (but ignore routes which just start with the word api, like pages/api-xxx)
C) Provide a method for users to disable such warnings

---

Hope that helps 💖