fix: unicode is handled properly in strdist

internal/strdist/strdist.go

@@ -28,20 +28,28 @@ func StandardCost(ar, br rune) Cost {
 	return Cost{SwapAB: 1, DeleteA: 1, InsertB: 1}
 }
 
+// Distance returns the edit distance between two strings. The cost per edit is
+// given by the costFunc argument.
+//
+// There is an optional cut argument that when set will finish the computation
+// as early as possible once the final cost is certain to be >= cut. There is
+// no guarantee about the exact cost returned when this is the case other than
+// being >= cut. In particular, when cut is used, the function is not symmetric
+// on a and b.
 func Distance(a, b string, f CostFunc, cut int64) int64 {
 	if a == b {
 		return 0
 	}
 	lst := make([]CostInt, len(b)+1)
 	bl := 0
-	for bi, br := range b {
-		bl++
+	for _, br := range b {
 		cost := f(-1, br)
-		if cost.InsertB == Inhibit || lst[bi] == Inhibit {
-			lst[bi+1] = Inhibit
+		if cost.InsertB == Inhibit || lst[bl] == Inhibit {
+			lst[bl+1] = Inhibit
 		} else {
-			lst[bi+1] = lst[bi] + cost.InsertB
+			lst[bl+1] = lst[bl] + cost.InsertB
 		}
+		bl++
 	}
 	lst = lst[:bl+1]
 	// Not required, but caching means preventing the fast path
@@ -59,6 +67,9 @@ func Distance(a, b string, f CostFunc, cut int64) int64 {
 			lst[0] = last + cost.DeleteA
 		}
 		stop := true
+		if lst[0] < CostInt(cut) {
+			stop = false
+		}
 		i := 0
 		for _, br := range b {
 			i++
@@ -87,7 +98,6 @@ func Distance(a, b string, f CostFunc, cut int64) int64 {
 		if debug {
 			debugf("... %v", lst)
 		}
-		_ = stop
 		if cut != 0 && stop {
 			break
 		}

internal/strdist/strdist_test.go

@@ -36,6 +36,7 @@ var distanceTests = []distanceTest{
 	{f: uniqueCost, r: 6, a: "abc", b: "b"},
 	{f: uniqueCost, r: 6, a: "abc", b: "c"},
 	{f: uniqueCost, r: 9, a: "abc", b: ""},
+	{f: uniqueCost, r: 6, cut: 6, a: "abc", b: ""},
 	{f: uniqueCost, r: 5, a: "abc", b: "abcd"},
 	{f: uniqueCost, r: 5, a: "abc", b: "dabc"},
 	{f: uniqueCost, r: 10, a: "abc", b: "adbdc"},
@@ -58,7 +59,13 @@ var distanceTests = []distanceTest{
 	{f: strdist.GlobCost, r: 1, a: "a**f/hij", b: "abc/def/hik"},
 	{f: strdist.GlobCost, r: 2, a: "a**fg", b: "abc/def/hik"},
 	{f: strdist.GlobCost, r: 0, a: "a**f/hij/klm", b: "abc/d**m"},
+	{f: strdist.GlobCost, r: 1, a: "**a", b: ""},
 	{f: strdist.GlobCost, r: 0, a: "/*a/", b: "/a/"},
+	{f: strdist.GlobCost, r: 3, a: "abc", b: ""},
+	{f: strdist.GlobCost, r: 1, cut: 1, a: "abc", b: ""},
+	// Not symmetric.
+	{f: strdist.GlobCost, r: 2, cut: 3, a: "ab", b: ""},
+	{f: strdist.GlobCost, r: 2, cut: 1, a: "", b: "ab"},
 }
 
 func (s *S) TestDistance(c *C) {