fix(diff): bound the Myers n+m sum so it can't overflow (CodeQL)#3773
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CodeQL go/allocation-size-overflow (high) flagged `n + m` flowing into `make([]int, 2*maxD+1)`: a pathological line count could overflow the addition before the downstream clamp. The result was already safe (the clamp caught a wrapped-negative maxD), but the addition itself still tripped the query. Restructure to maxD = min(n+m, maxDiffEdits) with the sum taken only when n and m are within the cap — no overflow at the operation, identical bound.
| // maxD = min(n+m, maxDiffEdits); take the sum only when it can't overflow int. | ||
| maxD := maxDiffEdits // bound the trace's O(D²) footprint | ||
| if n <= maxDiffEdits && m <= maxDiffEdits-n { | ||
| maxD = n + m |
esengine
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…tion (#3775) Follow-up to #3773: that cleared the n+m addition alert, but CodeQL still flagged the 2*maxD allocation (go/allocation-size-overflow) because it doesn't propagate maxD's bound through the guarded sum. Clamp each line count to maxDiffEdits before summing, so the sum and the 2*maxD allocation both have constant-bounded operands. maxD stays min(n+m, maxDiffEdits). Co-authored-by: reasonix <reasonix@deepseek.com>
SuMuxi66
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Jun 10, 2026
…sengine#3773) CodeQL go/allocation-size-overflow (high) flagged `n + m` flowing into `make([]int, 2*maxD+1)`: a pathological line count could overflow the addition before the downstream clamp. The result was already safe (the clamp caught a wrapped-negative maxD), but the addition itself still tripped the query. Restructure to maxD = min(n+m, maxDiffEdits) with the sum taken only when n and m are within the cap — no overflow at the operation, identical bound. Co-authored-by: reasonix <reasonix@deepseek.com>
SuMuxi66
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Jun 10, 2026
…tion (esengine#3775) Follow-up to esengine#3773: that cleared the n+m addition alert, but CodeQL still flagged the 2*maxD allocation (go/allocation-size-overflow) because it doesn't propagate maxD's bound through the guarded sum. Clamp each line count to maxDiffEdits before summing, so the sum and the 2*maxD allocation both have constant-bounded operands. maxD stays min(n+m, maxDiffEdits). Co-authored-by: reasonix <reasonix@deepseek.com>
dorokuma
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Jun 10, 2026
…sengine#3773) CodeQL go/allocation-size-overflow (high) flagged `n + m` flowing into `make([]int, 2*maxD+1)`: a pathological line count could overflow the addition before the downstream clamp. The result was already safe (the clamp caught a wrapped-negative maxD), but the addition itself still tripped the query. Restructure to maxD = min(n+m, maxDiffEdits) with the sum taken only when n and m are within the cap — no overflow at the operation, identical bound. Co-authored-by: reasonix <reasonix@deepseek.com>
dorokuma
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Jun 10, 2026
…tion (esengine#3775) Follow-up to esengine#3773: that cleared the n+m addition alert, but CodeQL still flagged the 2*maxD allocation (go/allocation-size-overflow) because it doesn't propagate maxD's bound through the guarded sum. Clamp each line count to maxDiffEdits before summing, so the sum and the 2*maxD allocation both have constant-bounded operands. maxD stays min(n+m, maxDiffEdits). Co-authored-by: reasonix <reasonix@deepseek.com>
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Resolves the two open CodeQL
go/allocation-size-overflow(high) alerts ininternal/diff/diff.go(the Myers line-diff).maxD := n + mflows intomake([]int, 2*maxD+1). The value was already safe at the allocation —maxDis clamped tomaxDiffEdits(2000), and a prior fix added amaxD < 0guard for a wrapped sum — but CodeQL flags the addition itself as a potential overflow, which the post-hoc clamp doesn't clear.This restructures to
maxD = min(n+m, maxDiffEdits), taking the sum only whenn <= maxDiffEdits && m <= maxDiffEdits-n, son + mis evaluated only when provably within the cap. Identical bound, no overflow at the operation.In practice the inputs are file line counts, so the sum could never overflow a real
intanyway (you'd OOM building the slices first) — but this clears the alert cleanly rather than dismissing it.go build+go test ./internal/diff/pass locally.