feat: add intersection schema

[alonidiom]

Fixes #113 (including the specific case mentioned)

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[fabian-hiller]

Thank you for your contribution! The next few days I have to focus on my bachelor thesis. As soon as I find time, I'll get back to you.

[fabian-hiller]

If there is still interest in this PR, please check this comment beforehand and give me feedback on it.

[Karakatiza666]

In my case validation errors from intersected objects didn't bubble up, and I had to do this:

return !issues && output
        ? {
           ...
          }
        : issues?.length
            ? { issues }
            : getIssues(info, 'type', 'intersection', error || 'Invalid type', input, issues)

Please check this, and if valid this applies to intersectionAsync, too

[Karakatiza666]

In my case validation errors from intersected objects didn't bubble up, and I had to do this:

        if (result.issues) {
          issues = result.issues
          while (issues?.length) {
            issues = (issues => issues.length ? issues as Issues : undefined)(issues.flatMap(i => i.issues ?? []))
              ?? issues
            break
          }
          break
        } else ...

Please check this, and if valid this applies to intersectionAsync, too

[fabian-hiller]

I will probably review this PR in the next few days.

[Karakatiza666]

@alonidiom Please check out my fork of your PR! Karakatiza666@fd1830f
I believe it improves type inference, and behaviour when handling parsing errors

[fabian-hiller]

I am currently working on this PR. I'll check your code in a moment.

[fabian-hiller]

union is a logical OR. For this reason, the issues are added as subissues, as they usually contradict each other. intersection is a logical AND, so in my opinion this procedure is not necessary here. I have also investigated the implementation of Zod in this regard.

I'm not done yet, but I welcome feedback or questions now before I finalize it.

[fabian-hiller]

Apart from that, I also revised the code that merges two or more outputs so that it should now work with every schema.

[Karakatiza666]

Will check if I encounter issues with new code tomorrow, wasn't able to try earlier

[fabian-hiller]

I have finalized the implementation. Feel free to test out the changes and let me know if anything can be improved.

[fabian-hiller]

I plan to merge this PR today or tomorrow.