print the diff between right result and wrong result

[hawkingrei]

When your result set changes significantly, it's not easy to directly discern the differences from the logs. I've modified the log format so that it can print the diff.

before

after the improvement

[YangKeao]

LGTM

[lance6716]

what's the effect of checklines = false?

[hawkingrei]

Actually, I gave it a try, but I couldn't see any difference.

[lance6716]

Copilot:

In sergi/go-diff, the checklines parameter controls whether the diff algorithm first does a fast, line‑level diff before falling back to a more precise, character‑level diff.

Specifically:

• DiffMain(text1, text2, checklines bool) passes checklines down to diffCompute:

  func (dmp *DiffMatchPatch) diffCompute(text1, text2 []rune, checklines bool, deadline time.Time) []Diff {
      …
      } else if checklines && len(text1) > 100 && len(text2) > 100 {
          return dmp.diffLineMode(text1, text2, deadline)
      }
      return dmp.diffBisect(text1, text2, deadline)
  }

• When checklines == true and both texts are longer than 100 runes, it uses diffLineMode, which:
  • Does a quick diff at line granularity (treating each line as a token), then
  • “Rediffs” the changed line blocks at character level for better accuracy.

Effects in practice

• checklines = false

  • Always uses diffBisect (a Myers-style character-level diff).
  • Slower on large inputs, but tends to give minimal/optimal character-level diffs.

• checklines = true

  • For long texts: runs the faster line-mode pre-pass, then refines.
  • This usually gives a significant speedup on big inputs, at the cost of possibly non-minimal diffs (more or differently grouped hunks than the theoretical minimum).

The tests (TestDiffMainWithCheckLines) confirm that:

• For most cases, results with and without checklines match exactly.
• It’s explicitly documented that the speedup “can produce non-minimal diffs” (comment on diffLineMode), and there’s a TODO about a failing test case, highlighting that behavior can differ.

[bb7133]

LGTM