feat: customizeSchemaTyping

[CraigMacomber]

Description

Add customizeSchemaTyping.

Status: Proof of concept / Proposal.

Before this could be mergeed it would need:

• Conceptual review and approval
• Cleanup of naming, docs and exports
• API review
• Attempt to update (and test) recursive type variants to use this pattern.
• More testing

Breaking Changes

TODO

Reviewer Guidance

The review process is outlined on this wiki page.

[CraigMacomber]

This PR builds upon #23053 . This changeset will probably need to be rewritten based on the major changes.

[CraigMacomber]

This shows customizeSchemaTyping being used to implement a previously requested feature of narrowing leaf types.

It can also be used for branding of lead types, which would be even safer from a soundness perspective.

[tyler-cai-microsoft]

This looks cool

[CraigMacomber]

This file shows several ways to do open polymorphism / schema child dependency injection. This one uses customizeSchemaTyping, and makes everything just work.

[tyler-cai-microsoft]

I would love to try something like this:

interface A {
  type: "a";
  foo: string;
}
interface B {
  type: "b";
  bar: number;
}
interface C {
  easy: number
}
type Combo = A | B;
interface Root {
  faz: Combo;
  c: C;
}

class SyncedRoot extends sf.object(...) implements Root {}
...

const a: A = { ... }
const root: Root = {...}
const syncedRoot = new SyncedRoot(root);
syncedRoot.faz = new SyncedA(a);

[github-actions]

🔗 No broken links found! ✅

Your attention to detail is admirable.

linkcheck output

> [email protected] ci:linkcheck /home/runner/work/FluidFramework/FluidFramework/docs
> start-server-and-test ci:start 1313 linkcheck:full

1: starting server using command "npm run ci:start"
and when url "[ 'http://127.0.0.1:1313' ]" is responding with HTTP status code 200
running tests using command "npm run linkcheck:full"


> [email protected] ci:start
> http-server ./public --port 1313 --silent


> [email protected] linkcheck:full
> npm run linkcheck:fast -- --external


> [email protected] linkcheck:fast
> linkcheck http://localhost:1313 --skip-file skipped-urls.txt --external

Crawling...

Stats:
  444350 links
    3418 destination URLs
       2 URLs ignored
       0 warnings
       0 errors

[msfluid-bot]

Code Coverage Summary

↓ packages.dds.tree.src.simple-tree.api:
Line Coverage Change: -0.05%    Branch Coverage Change: No change

Metric Name	Baseline coverage	PR coverage	Coverage Diff
Branch Coverage	88.76%	88.76%	→ No change
Line Coverage	82.35%	82.30%	↓ -0.05%

↑ packages.dds.tree.src.simple-tree:
Line Coverage Change: 0.15%    Branch Coverage Change: 0.02%

Metric Name	Baseline coverage	PR coverage	Coverage Diff
Branch Coverage	94.07%	94.09%	↑ 0.02%
Line Coverage	97.23%	97.38%	↑ 0.15%

---

Baseline commit: e603044
Baseline build: 307393
Happy Coding!!

Code coverage comparison check passed!!