fix(comment): bound errored-project rendering to prevent comment-generation hang - #21
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…ration hang formatErroredProject built its output with `s += ...` while splitting the diagnostic message on ": " and applying a per-piece growing indent via strings.Repeat. A large critical diagnostic (e.g. a multi-MB Terraform HCL parse error, which also contains many ": " separators) turned this into an O(n^2) string build, spinning a single goroutine on-CPU indefinitely. This runs inside GenerateComment, before renderWithTruncation, so the 64KB comment cap never kicked in. Fixes: - formatErroredProject uses strings.Builder, caps each diagnostic message to 4KB before splitting, caps indent depth, and caps the number of critical diagnostics rendered per project (10) with a summarised remainder. - processProjectCostDetails caps the combined errored-projects section (32KB), since the whole section is built before truncation. Adds a regression test that hangs on the old implementation and completes instantly with the fix.
vdmgolub
approved these changes
Jul 2, 2026
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Problem
A production run hung indefinitely after logging
Total after diff: 182 project(s). A goroutine dump showed the single run goroutine[runnable](on-CPU, not blocked on I/O or locks) spinning in:formatErroredProjectbuilt its output withs += ...while splitting the diagnostic message on": "and applying a per-piece growing indent viastrings.Repeat. A large critical diagnostic — e.g. a multi-MB Terraform HCL parse error, which also contains many": "separators — turns this into an O(n²) string build (quadratic in both concatenation and cumulative indent). Because this runs insideGenerateComment, beforerenderWithTruncation, the 64 KB comment cap never gets a chance to kick in.Fix
pkg/vcs/comment/cost_details.go:formatErroredProject: usestrings.Builder; cap each diagnostic message to 4 KB (rune-safe, viaprefixWithin) before splitting; cap indent depth at 8; cap the number of critical diagnostics rendered per project at 10, with a… and N more error(s)summary.processProjectCostDetails: cap the combined errored-projects section at 32 KB (built before truncation), with a… and N more project(s) with errorsnote.Both quadratic terms are removed; total work is now linear and bounded regardless of diagnostic size or error count.
Test
Adds
errored_project_test.go:TestFormatErroredProject_Pathological— a ~6 MB diagnostic with ~2M": "separators. Verified it hangs (5s guard trips, ~4 cores pinned) on the old implementation and completes in ~0s with the fix, output bounded.TestFormatErroredProject_LimitsErrorCount— asserts the per-project error cap + summary.go build ./...,go vet, and the fullpkg/vcs/commentsuite pass.