Function cleanupSurroundingIdentical

cmp/report_slices.go:553–614

cleanupSurroundingIdentical scans through all unequal groups, and moves any leading sequence of equal elements to the preceding equal group and moves and trailing sequence of equal elements to the succeeding equal group. This is necessary since coalesceInterveningIdentical may coalesce edit groups

(groups []diffStats, eq func(i, j int) bool)

//		{NumIdentical: 64}, // incremented by 10
//	]
func cleanupSurroundingIdentical(groups []diffStats, eq func(i, j int) bool) []diffStats {
	var ix, iy int // indexes into sequence x and y
	for i, ds := range groups {
		// Handle equal group.
		if ds.NumDiff() == 0 {
			ix += ds.NumIdentical
			iy += ds.NumIdentical
			continue
		}

		// Handle unequal group.
		nx := ds.NumIdentical + ds.NumRemoved + ds.NumModified
		ny := ds.NumIdentical + ds.NumInserted + ds.NumModified
		var numLeadingIdentical, numTrailingIdentical int
		for j := 0; j < nx && j < ny && eq(ix+j, iy+j); j++ {
			numLeadingIdentical++
		}
		for j := 0; j < nx && j < ny && eq(ix+nx-1-j, iy+ny-1-j); j++ {
			numTrailingIdentical++
		}
		if numIdentical := numLeadingIdentical + numTrailingIdentical; numIdentical > 0 {
			if numLeadingIdentical > 0 {
				// Remove leading identical span from this group and
				// insert it into the preceding group.
				if i-1 >= 0 {
					groups[i-1].NumIdentical += numLeadingIdentical
				} else {
					// No preceding group exists, so prepend a new group,
					// but do so after we finish iterating over all groups.
					defer func() {
						groups = append([]diffStats{{Name: groups[0].Name, NumIdentical: numLeadingIdentical}}, groups...)
					}()
				}
				// Increment indexes since the preceding group would have handled this.
				ix += numLeadingIdentical
				iy += numLeadingIdentical
			}
			if numTrailingIdentical > 0 {
				// Remove trailing identical span from this group and
				// insert it into the succeeding group.
				if i+1 < len(groups) {
					groups[i+1].NumIdentical += numTrailingIdentical
				} else {
					// No succeeding group exists, so append a new group,
					// but do so after we finish iterating over all groups.
					defer func() {
						groups = append(groups, diffStats{Name: groups[len(groups)-1].Name, NumIdentical: numTrailingIdentical})
					}()
				}
				// Do not increment indexes since the succeeding group will handle this.
			}

			// Update this group since some identical elements were removed.
			nx -= numIdentical
			ny -= numIdentical
			groups[i] = diffStats{Name: ds.Name, NumRemoved: nx, NumInserted: ny}
		}
		ix += nx