Fix ViewModel issue where all lines were hidden#296709
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Pull request overview
This PR fixes an edge case in the editor ViewModel’s constant-time prefix sum implementation where getIndexOf could return an invalid index (e.g. when all values are zero), which can result in all lines being treated as hidden.
Changes:
- Fix
ConstantTimePrefixSumComputer.getIndexOfto handle sums that are not present in_indexBySum(notably when total sum is 0). - Fix
_ensureValidtrimming logic to avoid invalid_indexBySum.lengthwhen the values array is empty. - Expand the prefix sum test suite to run the same behavioral assertions against both
PrefixSumComputerandConstantTimePrefixSumComputer.
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.
| File | Description |
|---|---|
| src/vs/editor/test/common/viewModel/prefixSumComputer.test.ts | Refactors/expands tests to validate both prefix-sum implementations across many scenarios (zeroes, inserts/removes, mutations). |
| src/vs/editor/common/model/prefixSumComputer.ts | Adds a safety fallback in ConstantTimePrefixSumComputer.getIndexOf and fixes _indexBySum.length trimming for empty inputs. |
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
… areas When an edit (delete/undo) removes or merges the only visible line(s) into hidden lines, the view model could end up with zero visible lines, causing downstream crashes (e.g. 'Not supported' from HiddenModelLineProjection). The safety check in acceptVersionId only caught the case where exactly 1 hidden line remained. Generalize it to detect when getViewLineCount() === 0 and minimally restore visibility by making just the first line visible, preserving the caller's intended hidden areas as much as possible.
…ible lines) is now fixed at the source
When hidden area decorations drift via AlwaysGrowsWhenTypingAtEdges stickiness, _constructLines(resetHiddenAreas=false) — triggered by tab size or wrapping changes — can rebuild projections with all lines hidden. Extract _ensureAtLeastOneVisibleLine() shared by both _constructLines and acceptVersionId.
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
rebornix
approved these changes
Feb 21, 2026
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Fixes #293365
ConstantTimePrefixSumComputerto better handle the case where all values are zeroes.