perf(layout): avoid quadratic shift() in resolveBookmarks

[exoego]

Summary

resolveBookmarks walks the whole document tree on every render to find bookmark props. It does this even when the document has no bookmarks.

The walk takes items from a single queue with listToExplore.shift(). The queue holds a whole level of the tree, so it gets large on big documents. Each shift() on a large array moves every remaining item, so the walk is quadratic in the number of elements.

This PR reads the queue by index instead. The visit order is the same breadth-first order as before. Bookmark refs and parent links do not change.

Measurements

Rendering rows of 9 cells with no bookmarks. Apple M4 Pro, Node 24.21.0, median of 3 runs.

Rows	Render before	Render after	resolveBookmarks before	resolveBookmarks after
2,000	1.36 s	1.26 s	97 ms	3 ms
4,000	2.79 s	2.35 s	425 ms	9 ms
8,000	6.62 s	4.90 s	1,721 ms	17 ms

At 8,000 rows the whole render is 26% faster. Before this change, doubling the rows made resolveBookmarks about 4 times slower. After it, the time doubles.

The step runs before pagination, so both pagination engines are affected. In our 270-page report with large tables, it took 4.5 s of a 26 s render.

How to reproduce

Render many rows with no bookmarks. Profile with node --cpu-prof and look at the self time of resolveBookmarks.

const doc = (rows) => (
  <Document>
    <Page size="A4" experimentalPagination>
      {Array.from({ length: rows }, (_, r) => (
        <View key={r} style={{ flexDirection: 'row' }}>
          {Array.from({ length: 9 }, (_, c) => (
            <View key={c} style={{ flex: 1 }}>
              <Text>{`${r}-${c}`}</Text>
            </View>
          ))}
        </View>
      ))}
    </Page>
  </Document>
);

await renderToBuffer(doc(8000));

Tests

No new tests. The existing "should resolve bookmark hierarchy" test already checks the breadth-first ref order and parent links. A timing test would be flaky in CI. All layout tests pass.

Notes

fetchAssets and buildXLinksIndex use the same shift() pattern. Their queues stay small, so they are not slow in practice. I left them out to keep this PR focused.

[changeset-bot]

🦋 Changeset detected

Latest commit: ab2035a

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 6 packages

Name	Type
@react-pdf/layout	Patch
@react-pdf/renderer	Patch
@react-pdf/examples	Patch
@react-pdf/math	Patch
@react-pdf/mermaid	Patch
@react-pdf/ui	Patch

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