Narrow the type of Params

[Pimm]

Fixes #5442.

/cc @tony-sull & @bholmesdev

Changes

#3087 changed the type of Params from Record<string, string | undefined> to Record<string, string | number | undefined> to formerly allow getStaticPaths to return numbers.

However, as the change was made to Params and not GetStaticPathsResult or GetStaticPathsItem, it also affects Astro.params.

This PR essentially moves the change made in #3087 from Params to GetStaticPathsItem, reverting the type of Astro.params while keeping the type of getStaticPaths.

Note that while looking into this, I found this comment by @bholmesdev:

• if you pass a number to params.year in your getStaticPaths, it should still be a number when destructuring Astro.params. If not, that's a bug.
• if you created an SSR dynamic route like [year].astro, year will always be a string (even if it could be parsed to a number). This is where string -> number conversion would be manual.

In my experience, Astro.params never contains numbers, not even in static mode. While reviewing, please consider that this PR changes the types to match the behaviour, although judging by this comment, we might want to change the behaviour to match the types instead.

Testing

This is testable like so:

const artist: string | undefined = Astro.params.artist;

I haven't found any type definition tests to which this one could be added.

Docs

From what I understand, this change is in line with the current docs:

params are encoded into the URL, so only strings are supported as values.

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[Pimm]

This is more concise and works for undefined, numbers, and strings, but does require support for the ?. operator. Since this support was added in Node.js 14.0.0, this should be OK.

[bholmesdev]

I param very impressed! Great change 👍

[sarah11918]

While our API reference page does in fact say that params must be strings, we have this in our new Error reference guide:

https://docs.astro.build/en/reference/error-reference/#invalid-value-for-getstaticpaths-route-parameter

So, no objections from docs if we're now all rallying behind Team String, but our error reference will have to change to match. (cc @Princesseuh @matthewp )

[Pimm]

Thanks @sarah11918.

The error reference looks correct to me as-is. getStaticPaths may still return numbers (although those numbers will reincarnate as strings in Astro.params).