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);

[CraigMacomber]

Cases like that where Combo is explicitly referring the types in the union work fine, even without this change. The problem that is being addressed and demoed in this file is "open "polymorphism where you need to somehow express "Combo" without referencing the actual members in it leaving the implicit union "open" for extension (in such a setup the implementation refer to what they are implementing, in this case "Combo", like if Combo and SyncCombo were interfaces things could implement, not a union of types).

[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!!

[CraigMacomber]

Still pending

[CraigMacomber]

Still pending

[CraigMacomber]

Still pending

[github-actions]

🔗 Found some broken links! 💔

Run a link check locally to find them. See
https://github.com/microsoft/FluidFramework/wiki/Checking-for-broken-links-in-the-documentation for more information.

linkcheck output

> [email protected] ci:check-links /home/runner/work/FluidFramework/FluidFramework/docs
> start-server-and-test "npm run serve -- --no-open" 3000 check-links

1: starting server using command "npm run serve -- --no-open"
and when url "[ 'http://127.0.0.1:3000' ]" is responding with HTTP status code 200
running tests using command "npm run check-links"


> [email protected] serve
> docusaurus serve --no-open

[SUCCESS] Serving "build" directory at: http://localhost:3000/

> [email protected] check-links
> linkcheck http://localhost:3000 --skip-file skipped-urls.txt

 ELIFECYCLE  Command failed with exit code 1.