app-static-to-dynamic-error with generateMetadata using getI18n on page not found

[AvaN0x]

Describe the bug A clear and concise description of what the bug is.

Hello, I get a app-static-to-dynamic-error error when I go in a route that is not matched by the middleware.

To Reproduce Steps to reproduce the behavior:

1. Clone this repro repo : https://github.com/AvaN0x/repro-next-international-generate-metadata

2. npm i
   npm run build
   npm run start

3. Click on the link in the page
4. See the following error:

   ⨯ Page changed from static to dynamic at runtime /a.a, reason: headers
   see more here https://nextjs.org/docs/messages/app-static-to-dynamic-error

   

I also see that, when the path do not match the middleware, it'll still use the first part as the locale, this can be seein with the log locale not found a.a in the console.

Expected behavior I'd expect the not-found page to show, instead I get a 500 error. The error disappear when you remove the use of getI18n in the generateMetadata function in [locale]/layout.ts. The error does not occur in npm run dev.

About (please complete the following information):

• next-international version : 1.1.4
• Next.js version: 14.0.3

Infos about the repro

• it was created using npx create-next-app@latest
• it contains a full next-international config
• it has a button to change locale, even if it's not needed for the repro, it might still be useful
• it also has a check in [locale]/layout.ts RootLayout to know if the locale params is indeed a locale or something else

I can provide more infos if needed

[AvaN0x]

I found a fix to the issue (the repro has been updated accordingly) with a call to setStaticParamsLocale in the generateMetadata function. This is related to this part of the code that'll check the headers if no staticParams were found: https://github.com/QuiiBz/next-international/blob/e4acd2fdf3c6ec181e218df82477f05df90c7311/packages/next-international/src/app/server/get-locale-cache.tsx#L19-L31

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But I still get locale not found a.a logs in the layout by clicking the link in the repro. It would be nice if the params.locale value was always a valid locale.

Because of that, I have to add a check before passing the value to setStaticParamsLocale or redirect myself to the not found page.

https://github.com/AvaN0x/repro-next-international-generate-metadata/blob/80920471993de4b470e076d99254025e3abdff14/src/app/%5Blocale%5D/layout.tsx#L16-L18

https://github.com/AvaN0x/repro-next-international-generate-metadata/blob/80920471993de4b470e076d99254025e3abdff14/src/app/%5Blocale%5D/layout.tsx#L42-L46

locales and fallbackLocale are coming from my locales/shared.ts file.

[QuiiBz]

It would be nice if the params.locale value was always a valid locale.

Agree, that's why we use generateStaticParams to make sure the dynamic params are valid. This again seems like a bug with Next.js, I'll have to dig more.