Starlight is incompatible with the Astro build.format preserve option

[lschierer]

What version of starlight are you using?

0.21.5

What version of astro are you using?

4.6.3

What package manager are you using?

pnpm

What operating system are you using?

Mac

What browser are you using?

Chrome

Describe the Bug

when I add the options

    trailingSlash: 'always',
    build: {
      format: 'preserve',
    },

to an existing otherwise working starlight project, it stops working with the error

13:16:42 [ERROR] Cannot read properties of undefined (reading 'addBase')
  Stack trace:
    at formatPath (/home/projects/withastro-starlight-7ibewh/node_modules/@astrojs/starlight/utils/createPathFormatter.ts:25:25)
    [...] See full stack trace in the browser, or rerun with --verbose.

Link to Minimal Reproducible Example

https://stackblitz.com/edit/withastro-starlight-7ibewh?file=astro.config.mjs

Participation

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

[delucis]

Thank you for the bug report @lschierer! I think this is probably related to the 'preserve' setting — that was added to Astro after our logic for paths was added, so we’re likely not accounting for it in the createPathFormatter utility where that error is being logged.

Our formatting strategies account for the 'file' and 'directory' configurations, but not the newer 'preserve':

https://github.com/withastro/starlight/blob/be258c64d398173d061d5411ea4c9294860a74e7/packages/starlight/utils/createPathFormatter.ts#L15-L24