Replace baseUrl with prefixUrl

[szmarczak]

Checklist

• I have read the documentation.
• I have included a pull request description of my changes.
• I have included some tests.
• If it's a new feature, I have included documentation updates.

Fixes #783
Fixes #814

[szmarczak]

Suggested change

	- No `baseUrl` option. Instead, there is `prefixUrl` which appends ending slash if not present.
	- No `baseUrl` option. Instead, there is `prefixUrl` which appends ending slash if not present. If `prefixUrl` is used, it will be always prepended to the `url` argument.

Actually should we do

if (options.prefixUrl && !urlArgument.startsWith('http:') && !urlArgument.startsWith('https:') && !urlArgument.startsWith('unix:')) {
    ...
}

or let this behavior be?

[szmarczak]

/cc @sholladay

[sholladay]

My opinion has always been that input should not be able to override the host of a prefixUrl, otherwise it's not really a prefix. If such an override is needed, and it very well may be for some use cases, then I feel that full URL resolution is the answer (I.e. baseUrl). I don't think we have any business keeping a list of "special" schemes like http: where absolute URLs can override the target host. That is the job of a URL resolver, and I'd prefer to either fully embrace URL resolution or not at all.

I'm personally fine with having both prefixUrl and baseUrl. But I know Sindre felt that would be confusing.

[szmarczak]

What if we pass a URL instance to input? I think we should ignore prefixUrl then (same for Ky).

[sholladay]

Why does a URL instance change the behavior as opposed to a string? I would expect them to behave the same.

[szmarczak]

The URL instance is an absolute URL. Is there any use case for joining two absolute URLs? The string does not need to be absolute. That's the difference.

[sholladay]

Oh, right. I forgot that URL instances are always absolute, because that's such a silly limitation in the URL class. So, yeah, if absolute URLs are allowed to override prefixUrl, then it makes sense. However, in terms of the code, I would probably not explicitly check for URL instances, if possible. After all, what if URL starts supporting relative URLs in the future? I think they could introduce support for that without breaking too many things. And I hope they do, personally.

[sindresorhus]

My opinion has always been that input should not be able to override the host of a prefixUrl

👍 (We can reconsider if we get a lot of complain about this)

[sindresorhus]

There are still some references to baseUrl:

readme.md
715:	baseUrl: 'https://example.com',
733:		baseUrl: 'httpbin.org',
1024:	baseUrl: 'https://<api-id>.execute-api.<api-region>.amazonaws.com/<stage>/',
1149:Use `got.extend()` to make it nicer to work with REST APIs. Especially if you use the `baseUrl` option.
1158:	baseUrl: 'example.com',

[sindresorhus]

There are still some references to baseUrl:

Fixed

[sindresorhus]

Nice work! :)