fixed bug in reverse overlap elimination - added pretty printing for diff sets in tests

Author: rwcarlsen

diff/dmp.go

@@ -917,9 +917,10 @@ func (dmp *DiffMatchPatch) DiffCleanupSemantic(diffs []Diff) []Diff {
 					float64(overlap_length2) >= float64(len(insertion))/2 {
 					// Reverse overlap found.
 					// Insert an equality and swap and trim the surrounding edits.
+					overlap := Diff{DiffEqual, insertion[overlap_length2:]}
 					diffs = append(
 						diffs[:pointer],
-						append([]Diff{Diff{DiffEqual, insertion[0:overlap_length2]}}, diffs[pointer:]...)...)
+						append([]Diff{overlap}, diffs[pointer:]...)...)
 					// diffs.splice(pointer, 0,
 					//     [DiffEqual, deletion[0 : overlap_length2)]]
 					diffs[pointer-1].Type = DiffInsert

diff/dmp_test.go

@@ -7,6 +7,7 @@ import (
 	"testing"
 	"time"
 	"runtime"
+	"bytes"
 
 	"github.com/bmizerany/assert"
 )
@@ -25,6 +26,25 @@ func caller() string {
 	return ""
 }
 
+func pretty(diffs []Diff) string {
+	var w bytes.Buffer
+	for i, diff := range diffs {
+		w.WriteString(fmt.Sprintf("%v. ",i))
+		switch diff.Type {
+		case DiffInsert:
+			w.WriteString("DiffIns")
+		case DiffDelete:
+			w.WriteString("DiffDel")
+		case DiffEqual:
+			w.WriteString("DiffEql")
+		default:
+			w.WriteString("Unknown")
+		}
+		w.WriteString(fmt.Sprintf(": %v\n", diff.Text))
+	}
+	return w.String()
+}
+
 func assertMapEqual(t *testing.T, seq1, seq2 interface{}) {
 	v1 := reflect.ValueOf(seq1)
 	k1 := v1.Kind()
@@ -63,6 +83,7 @@ func assertDiffEqual(t *testing.T, seq1, seq2 []Diff) {
 
 	for i := range seq1 {
 		if a, b := seq1[i], seq2[i]; a != b {
+			t.Errorf("%v\nseq1:\n%v\nseq2:\n%v", caller(), pretty(seq1), pretty(seq2))
 			t.Fatalf("%v %v != %v", caller(), a, b)
 		}
 	}