Custom 404 page injected using injectRoute not used

[delucis]

What version of astro are you using?

2.3.2

Are you using an SSR adapter? If so, which one?

None

What package manager are you using?

npm/pnpm

What operating system are you using?

macOS / Stackblitz

What browser are you using?

Firefox

Describe the Bug

When a project includes src/pages/404.astro, this route gets used as a custom 404 page, including in dev.

However, if an integration uses the injectRoute hook to inject a custom page at /404, Astro does not treat this the same way: the injected page is only available at /404, other 404 errors continue to show the standard Astro 404 screen during dev. (The injected route does get correctly built as 404.html though, so should work in production on static hosts that support that pattern like Netlify.)

I’d expect injecting a route to /404 to allow an integration to set the 404 users see during dev.

Link to Minimal Reproducible Example

https://stackblitz.com/edit/github-3u16qb?file=astro.config.mjs

Participation

• I am willing to submit a pull request for this issue.