fix(watch): use maximum depth for duplicates #13434

skirtles-code · 2025-06-04T15:38:19Z

While recursing for deep watchers, we keep track of which objects have already been 'seen', to avoid duplicated effort and prevent cycles. But currently we don't take account of the depth.

If we encounter an object twice during the traversal, with different values for depth, we need to traverse it at the greater depth.

I think the fix for this is relatively simple, using a Map instead of a Set to store the seen objects. If we encounter an object again then we may need to traverse it again if the previous traversal wasn't deep enough.

While this may lead to wasted effort, traversing the same object multiple times, in practice it happens very rarely. It needs a pretty specific data structure and the value passed for deep needs to be an unusually large but finite number. The simplest broken example I could find uses deep: 3:

I did briefly test the performance impact, but I didn't see a noticeable difference.

#13433 would also fix this problem, because it processes the items in depth order. But I think that PR may prove difficult to merge.

Summary by CodeRabbit

Tests
- Added a new test to verify that watchers with different depth levels respond appropriately to changes in deeply nested reactive arrays.
Refactor
- Improved internal handling of deep watching by refining how nested values are tracked, enhancing the accuracy of change detection for different watcher depths.

coderabbitai · 2025-06-04T15:38:27Z

Walkthrough

The traverse function in the reactivity system was refactored to use a Map for tracking seen values and their traversal depths instead of a Set. Correspondingly, a new test was added to verify the behavior of watchers with varying deep levels, ensuring correct triggering based on nested mutations.

Changes

File(s)	Change Summary
packages/reactivity/src/watch.ts	Refactored `traverse` to use `Map<unknown, number>` for `seen` parameter; updated logic accordingly.
packages/runtime-core/tests/apiWatch.spec.ts	Added test for watching the same object at different depths with various `deep` options.

Sequence Diagram(s)

sequenceDiagram
    participant User
    participant Watcher
    participant ReactiveArray

    User->>Watcher: Set up watchers with deep: 1, 2, 3, 4
    User->>ReactiveArray: Mutate nested properties at various depths
    ReactiveArray-->>Watcher: Notify relevant watchers based on deep level
    Watcher-->>User: Trigger callbacks for matching deep levels

Poem

In the warren of code, a Map takes the stage,
Remembering depths as we traverse each page.
Watchers now listen with ears tuned just right,
Deep or shallow, they trigger on sight.
With each nested hop, our tests leap and bound—
Hooray for new depths that the rabbits have found! 🐇

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📥 Commits

Reviewing files that changed from the base of the PR and between e53a4ff and a004e23.

📒 Files selected for processing (2)

packages/reactivity/src/watch.ts (1 hunks)
packages/runtime-core/__tests__/apiWatch.spec.ts (1 hunks)

🧰 Additional context used

🧬 Code Graph Analysis (1)

packages/reactivity/src/watch.ts (3)

packages/shared/src/general.ts (1)

isObject (53-54)

packages/runtime-core/src/index.ts (1)

ReactiveFlags (210-210)

packages/reactivity/src/index.ts (1)

ReactiveFlags (82-82)

⏰ Context from checks skipped due to timeout of 90000ms (3)

GitHub Check: Redirect rules
GitHub Check: Header rules
GitHub Check: Pages changed

🔇 Additional comments (3)

packages/reactivity/src/watch.ts (2)

334-334: LGTM: Parameter type change enables depth tracking.

The type change from Set<unknown> to Map<unknown, number> correctly supports storing both the traversed object and its depth, which is essential for the fix.

340-344: LGTM: Depth-aware traversal logic correctly implemented.

The implementation properly handles depth tracking:

Map initialization is correct

The condition (seen.get(value) || 0) >= depth ensures objects are re-traversed when encountered at greater depths

Storing seen.set(value, depth) maintains the maximum depth for each object

This elegantly solves the issue where objects encountered multiple times at different depths might miss deeper nested changes.

packages/runtime-core/__tests__/apiWatch.spec.ts (1)

1692-1741: Excellent test coverage for the depth-aware watcher fix.

This test case comprehensively validates the fix by:

Creating a complex nested structure where the same object (arr3) appears at multiple depths

Setting up watchers with varying deep levels (1-4) on the same root array

Testing mutations at different nesting levels and verifying selective watcher triggering

Ensuring shallow watchers don't trigger on deep mutations while deeper watchers do

The test scenarios effectively demonstrate that the fix resolves the issue where objects encountered at different depths now properly trigger watchers based on their configured depth sensitivity.

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github-actions · 2025-06-04T15:39:24Z

Size Report

Bundles

File	Size	Gzip	Brotli
runtime-dom.global.prod.js	101 kB (+10 B)	38.3 kB (+8 B)	34.6 kB (+23 B)
vue.global.prod.js	159 kB (+10 B)	58.5 kB (+8 B)	52 kB (-74 B)

Usages

Name	Size	Gzip	Brotli
createApp (CAPI only)	46.6 kB	18.2 kB	16.6 kB
createApp	54.6 kB (+10 B)	21.2 kB (+8 B)	19.4 kB (+11 B)
createSSRApp	58.8 kB (+10 B)	23 kB (+6 B)	20.9 kB (+4 B)
defineCustomElement	59.5 kB (+10 B)	22.8 kB (+9 B)	20.8 kB (+1 B)
overall	68.7 kB (+10 B)	26.4 kB (+5 B)	24 kB (-68 B)

pkg-pr-new · 2025-06-04T15:39:34Z

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commit: a004e23

fix(watch): use maximum depth for duplicates

a004e23

edison1105 added ready to merge The PR is ready to be merged. scope: reactivity labels Jun 5, 2025

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skirtles-code commented Jun 4, 2025 •

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