Implement the data model for web renderers v0.9 #606

jacobsimionato · 2026-02-09T01:42:42Z

Refactor: Enhance DataModel robustness and type safety in web_core v0.9

This change refactors the DataModel in @a2ui/web_core/v0_9 to improve its robustness, type safety, and adherence to the A2UI protocol specification, particularly concerning data manipulation and path resolution.

Key changes include:

Improved DataModel.set path handling:
- Modified the set method to throw an error if an intermediate segment of a path points to a primitive value when attempting to set a nested property, preventing unexpected data corruption.
- Added a check to enforce numeric indices for array segments in paths, throwing an error for non-numeric access on arrays to maintain data model integrity.
- Updated documentation for the set method to explicitly describe the behavior when setting values to undefined for both objects (key removal) and arrays (index nullification).
Enhanced Type Safety:
- Updated the Subscription<T> interface to correctly type value and onChange callback parameters as T | undefined, reflecting potential undefined states in the data model and improving consumer type safety.
Test Coverage & Fixes:
- Added new test cases in data-model.test.ts to validate the error conditions for primitive path traversal and non-numeric array segment access.
- Resolved TypeScript compilation errors in web_core and lit by ensuring @types/node is correctly installed and by updating web_core/package.json to explicitly export v0_9 modules.
- Corrected implicit any type errors in test callbacks.
- Fixed a JSON syntax error in specification/v0_9/json/standard_catalog.json.
Documentation Updates:
- Updated specification/v0_9/docs/a2ui_protocol.md to reflect the refined data model behavior for undefined values and array index rules.

gemini-code-assist

Code Review

This pull request introduces a DataModel class for managing client-side state, complete with a comprehensive test suite. The implementation is robust, providing a reactive data store with path-based access and subscriptions. My review focuses on improving type safety, code clarity, and consistency. I've identified a significant type-safety issue in the Subscription interface that could lead to runtime errors, and I've provided a suggestion to fix it. I also found a minor redundancy in the notification logic and an inconsistency in handling undefined values that should be addressed or at least documented. Lastly, please note that the repository's contribution guidelines require the PR description to include the Pre-Review Checklist, which is currently missing.

renderers/web_core/src/v0_9/state/data-model.ts

jacobsimionato · 2026-02-09T02:26:42Z

I have addressed the feedback. Please take another look.

jacobsimionato · 2026-02-09T02:26:53Z

/gemini review

gemini-code-assist

Code Review

This pull request introduces the v0.9 data model for web renderers, including the DataModel class implementation and a comprehensive test suite. The implementation is well-structured and the tests cover many cases.

I've found a critical issue in the set method's path traversal logic that could lead to incorrect behavior when a path contains a primitive value. I've provided a fix for this. I've also suggested an additional test case to cover this scenario and ensure the model behaves as expected.

The rest of the changes, including package updates and documentation, look good and are consistent with the new data model implementation.

renderers/web_core/src/v0_9/state/data-model.ts

gemini-code-assist · 2026-02-09T02:28:03Z

renderers/web_core/src/v0_9/state/data-model.test.ts

+    model.set('/foo', 'bar');
+    assert.strictEqual(count, 0);
+  });
+});


This is a great set of tests! To make it even more robust, I recommend adding a test case to verify the behavior of set when a path segment contains a primitive value. This will ensure the fix for the issue I mentioned in data-model.ts is covered and prevent regressions.

Here's a suggested test case:

Suggested change

});

it('overwrites primitive values in path when setting nested properties', () => {

model.set('/user/name', 'not an object');

assert.strictEqual(model.get('/user/name'), 'not an object');

// Now, try to set a nested property. This should overwrite the primitive.

model.set('/user/name/first', 'Alice');

assert.deepStrictEqual(model.get('/user/name'), { first: 'Alice' });

assert.strictEqual(model.get('/user/name/first'), 'Alice');

});

});

References

The style guide requires that code changes should have tests. While tests are present, this comment suggests adding a test for a critical edge case that was missed, improving test coverage and robustness. ^(link)

Please add a test case for this, but verify failure as explained above.

jacobsimionato · 2026-02-09T02:39:19Z

I have addressed the feedback. Please take another look.

jacobsimionato · 2026-02-09T02:39:31Z

/gemini review

gemini-code-assist

Code Review

This pull request introduces the DataModel class for v0.9 of the web renderer, which provides a reactive data store with a subscription mechanism. The implementation is well-tested and includes comprehensive notification logic for subscribers. I've provided a couple of suggestions for improvement: one to prevent corrupting array data structures and another for enhancing performance in scenarios with many subscriptions. Overall, this is a solid implementation of a core feature.

renderers/web_core/src/v0_9/state/data-model.ts

jacobsimionato · 2026-02-09T02:54:00Z

I have addressed the feedback. Please take another look.

jacobsimionato · 2026-02-09T02:54:11Z

/gemini review

gemini-code-assist

Code Review

This pull request introduces the DataModel for v0.9 of the web renderers, which is a core component for managing client-side state. The implementation is well-structured and comes with a comprehensive test suite, which is great to see. The related documentation and dependency updates are also included.

My review has identified a couple of areas for improvement. The most significant is that the path parsing logic in DataModel is not fully compliant with the JSON Pointer (RFC 6901) specification, which could lead to issues with certain property keys. I've also noted a potential performance optimization in the subscriber notification logic. Lastly, please remember to fill out the Pre-Review Checklist in the pull request description as per the repository's contribution guidelines.

renderers/web_core/src/v0_9/state/data-model.ts

gspencergoog · 2026-02-09T16:49:39Z

specification/v0_9/docs/a2ui_protocol.md

 - **Scope instantiation:** For every item in the array, the client instantiates the template component.
 - **Relative resolution:** Inside these instantiated components, any path that **does not** start with a forward slash `/` is treated as a **Relative Path**.
  - A relative path `firstName` inside a template iterating over `/users` resolves to `/users/0/firstName` for the first item, `/users/1/firstName` for the second, etc.
+  - It is an error to use a non-numeric index on a path segment that refers to an array.


This is a good addition.

gspencergoog · 2026-02-09T16:50:20Z

specification/v0_9/docs/a2ui_protocol.md

 - If the path exists, the value is updated.
 - If the path does not exist, the value is created.
- If the value is `null`, the key at that path is removed.
+- If the value is omitted (or set to `undefined`), the key is removed. For arrays, the index is set to `undefined`, preserving length.


It's the value at the index that is set to undefined, right? Not the index itself.

ditman

Small question about the creation of Subscription objects!

ditman · 2026-02-09T18:39:02Z

renderers/web_core/src/v0_9/state/data-model.ts

+    Object.defineProperty(subscription, 'value', {
+      get: () => this.get(normalizedPath),
+      enumerable: true
+    });


This defineProperty maybe hints at the code wanting Subscription<T> to be a proper class, rather than an interface that we coerce a plain JS object to? That way we can make sure the exposed value is a proper getter? Why do we prefer this creating a new Subscription?

jacobsimionato added 2 commits January 30, 2026 08:28

Add gemignore

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Add data model

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github-project-automation bot moved this to Todo in A2UI Feb 9, 2026

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jacobsimionato added 3 commits February 9, 2026 12:15

Merge branch 'main' into implement-data-model

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Try to fix CI

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fix: Address PR feedback

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jacobsimionato added 2 commits February 9, 2026 13:01

Revert standard catalog change

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fix: Address PR feedback

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Fix standard catalog def

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jacobsimionato requested review from ditman and gspencergoog February 9, 2026 04:46

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-});
+  it('overwrites primitive values in path when setting nested properties', () => {
+    model.set('/user/name', 'not an object');
+    assert.strictEqual(model.get('/user/name'), 'not an object');
+    // Now, try to set a nested property. This should overwrite the primitive.
+    model.set('/user/name/first', 'Alice');
+    assert.deepStrictEqual(model.get('/user/name'), { first: 'Alice' });
+    assert.strictEqual(model.get('/user/name/first'), 'Alice');
+  });
+});

Implement the data model for web renderers v0.9 #606

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