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Merge pull request #32628 from overleaf/em-bg-history-bug

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Prevent incorrect merging of ops with different hpos offsets

GitOrigin-RevId: d171a93dcb29e952c7105afd81c3b29ca7e9788e
This commit is contained in:
Eric Mc Sween
2026-04-07 08:46:52 -04:00
committed by Copybot
parent 7e327ee548
commit 77952e5d21
2 changed files with 100 additions and 0 deletions
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10
services/project-history/app/js/UpdateCompressor.js
View File

@@ -394,6 +394,16 @@ function _concatTwoUpdates(firstUpdate, secondUpdate) {
firstOp.p <= secondOp.p && secondOp.p <= firstOp.p + firstSize
const combinedLengthUnderLimit = firstSize + secondSize < MAX_UPDATE_SIZE
// When ops come from a multi-component update, the history position offset
// (hpos - p) may differ between ops because each component's hpos is computed
// against a different tracked-change state. Merging ops with different
// offsets would produce incorrect history positions, so we bail out.
const firstHposOffset = (firstOp.hpos ?? firstOp.p) - firstOp.p
const secondHposOffset = (secondOp.hpos ?? secondOp.p) - secondOp.p
if (firstHposOffset !== secondHposOffset) {
return [firstUpdate, secondUpdate]
}
// Two inserts
if (
firstOp.i != null &&

90
services/project-history/test/unit/js/UpdateCompressor/UpdateCompressorTests.js
View File

@@ -877,6 +877,36 @@ describe('UpdateCompressor', function () {
])
})
it('should not merge inserts with different hpos offsets (multi-component update)', function () {
// hpos offsets: first op has offset 10 (13-3),
// second op has offset 12 (18-6)
expect(
this.UpdateCompressor.compressUpdates([
{
op: { p: 3, i: 'foo', hpos: 13 },
meta: { ts: this.ts1, user_id: this.user_id },
v: 42,
},
{
op: { p: 6, i: 'bar', hpos: 18 },
meta: { ts: this.ts2, user_id: this.user_id },
v: 43,
},
])
).to.deep.equal([
{
op: { p: 3, i: 'foo', hpos: 13 },
meta: { ts: this.ts1, user_id: this.user_id },
v: 42,
},
{
op: { p: 6, i: 'bar', hpos: 18 },
meta: { ts: this.ts2, user_id: this.user_id },
v: 43,
},
])
})
it('should not merge updates from different users', function () {
expect(
this.UpdateCompressor.compressUpdates([
@@ -1091,6 +1121,36 @@ describe('UpdateCompressor', function () {
])
})
it('should not merge deletes with different hpos offsets (multi-component update)', function () {
// hpos offsets: first op has offset 10 (13-3),
// second op has offset 12 (15-3)
expect(
this.UpdateCompressor.compressUpdates([
{
op: { p: 3, d: 'foo', hpos: 13 },
meta: { ts: this.ts1, user_id: this.user_id },
v: 42,
},
{
op: { p: 3, d: 'bar', hpos: 15 },
meta: { ts: this.ts2, user_id: this.user_id },
v: 43,
},
])
).to.deep.equal([
{
op: { p: 3, d: 'foo', hpos: 13 },
meta: { ts: this.ts1, user_id: this.user_id },
v: 42,
},
{
op: { p: 3, d: 'bar', hpos: 15 },
meta: { ts: this.ts2, user_id: this.user_id },
v: 43,
},
])
})
it('should not merge when the deletes are tracked', function () {
// TODO: We should be able to lift that constraint, but it would
// require recalculating the hpos on the second op.
@@ -1264,6 +1324,36 @@ describe('UpdateCompressor', function () {
},
])
})
it('should not merge insert and delete with different hpos offsets (multi-component update)', function () {
// hpos offsets: first op has offset 10 (13-3),
// second op has offset 12 (17-5)
expect(
this.UpdateCompressor.compressUpdates([
{
op: { p: 3, i: 'foo', hpos: 13 },
meta: { ts: this.ts1, user_id: this.user_id },
v: 42,
},
{
op: { p: 5, d: 'o', hpos: 17 },
meta: { ts: this.ts2, user_id: this.user_id },
v: 43,
},
])
).to.deep.equal([
{
op: { p: 3, i: 'foo', hpos: 13 },
meta: { ts: this.ts1, user_id: this.user_id },
v: 42,
},
{
op: { p: 5, d: 'o', hpos: 17 },
meta: { ts: this.ts2, user_id: this.user_id },
v: 43,
},
])
})
})
describe('delete - insert', function () {