Fix Myers diff backtracking off-by-one (#112)#121
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josephburnett merged 1 commit intojosephburnett:masterfrom Feb 21, 2026
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Fix Myers diff backtracking off-by-one (#112)#121josephburnett merged 1 commit intojosephburnett:masterfrom
josephburnett merged 1 commit intojosephburnett:masterfrom
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buildMyersEdits used trace[D-1] for backtracking, but the trace is saved before each forward iteration updates V. trace[D] holds the V state after D-1 steps, not trace[D-1]. Wrong lookup produced garbled edit sequences for arrays with more than 10 elements. Includes regression test reproducing the exact scenario from #112.
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LGTM. The trace indexing fix is correct - trace[D] holds the V state after D-1 steps since it's saved before iteration D runs. Thanks for the fix and the regression test. We'll add broader correctness test coverage for the Myers path as a follow-up.
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Fixes #112.
buildMyersEditsusestrace[D-1]for backtracking, but the trace is saved before each forward iteration updates V. Sotrace[D]holds the V state after D-1 steps, nottrace[D-1]. Wrong lookup produces garbled edit sequences for arrays with more than 10 elements.Fix:
trace[D-1]->trace[D](v2/list.go:1033).Includes a regression test reproducing the exact scenario from #112.