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Bound minimal Myers input in the unified diff fuzz target - #3094
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<!-- agent --> The reported `unified_diff_printer` ClusterFuzz timeout decodes to 68,956 before tokens and 3,832 after tokens. Replaying it in the integration test spends 29.77 seconds computing `MyersMinimal`, before postprocessing or unified diff printing. Histogram and ordinary Myers finish in under 40 milliseconds each. Minimal Myers deliberately disables early-abort heuristics. Git's `xdiff/xdiffi.c` at `6de20f6092` likewise continues its search when `need_min` is set, and `gix-imara-diff` documents this potentially expensive behavior. Preserve that contract and apply the existing `comprehensive_diff` fuzz policy here: retain complete inputs for Histogram and Myers, then truncate each token sequence to 512 for minimal Myers. Assisted-by: GPT 6.1 Sol Co-authored-by: GPT 6.1 Sol <codex@openai.com>
Sebastian Thiel (Byron)
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Sebastian Thiel (Byron)
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The supplied ClusterFuzz testcase spends 29.77 seconds in
MyersMinimalbefore unified diff printing starts. This fuzz target now uses the existingcomprehensive_diffpolicy: Histogram and Myers process the complete input, while minimal Myers processes at most 512 tokens per side. The regression completes in about 70 ms in debug mode, and the AddressSanitizer fuzz harness executes the original file in 48 ms.The library's minimal-diff contract is preserved. Git's
xdiff/xdiffi.cat reference checkout commit6de20f6092also disables early-abort heuristics for minimal searches. The added fixture and integration test cover decoding, all three algorithms, postprocessing, printing, valid line prefixes, and a three-second budget.Reported issue
Here is a reproducer for a timeout to fix '/Users/byron/Downloads/clusterfuzz-testcase-minimized-gix-imara-diff-unified_diff_printer-5862399987744768'
Validation
GIX_TEST_IGNORE_ARCHIVES=1 cargo test -p gix-imara-diffcargo clippy -p gix-imara-diff --all-targets --all-features -- -D warningscargo fmt --all -- --checkcargo +nightly fuzz run --fuzz-dir gix-imara-diff/fuzz unified_diff_printer <reproducer> -- -runs=1 -timeout=3(AddressSanitizer)