Append edit distance operations from end to start

Gopkg.toml

@@ -0,0 +1,38 @@
+# Gopkg.toml example
+#
+# Refer to https://github.com/golang/dep/blob/master/docs/Gopkg.toml.md
+# for detailed Gopkg.toml documentation.
+#
+# required = ["github.com/user/thing/cmd/thing"]
+# ignored = ["github.com/user/project/pkgX", "bitbucket.org/user/project/pkgA/pkgY"]
+#
+# [[constraint]]
+#   name = "github.com/user/project"
+#   version = "1.0.0"
+#
+# [[constraint]]
+#   name = "github.com/user/project2"
+#   branch = "dev"
+#   source = "github.com/myfork/project2"
+#
+# [[override]]
+#   name = "github.com/x/y"
+#   version = "2.4.0"
+#
+# [prune]
+#   non-go = false
+#   go-tests = true
+#   unused-packages = true
+
+
+[[constraint]]
+  name = "github.com/evanphx/json-patch"
+  version = "3.0.0"
+
+[[constraint]]
+  name = "github.com/stretchr/testify"
+  version = "1.2.1"
+
+[prune]
+  go-tests = true
+  unused-packages = true

jsonpatch.go

@@ -83,12 +83,12 @@ func matchesValue(av, bv interface{}) bool {
 			return true
 		}
 	case float64:
-		bt, ok  := bv.(float64)
+		bt, ok := bv.(float64)
 		if ok && bt == at {
 			return true
 		}
 	case bool:
-		bt, ok  := bv.(bool)
+		bt, ok := bv.(bool)
 		if ok && bt == at {
 			return true
 		}
@@ -183,9 +183,18 @@ func diff(a, b map[string]interface{}, path string, patch []Operation) ([]Operat
 }
 
 func handleValues(av, bv interface{}, p string, patch []Operation) ([]Operation, error) {
-	// If types have changed, replace completely
-	if reflect.TypeOf(av) != reflect.TypeOf(bv) {
-		return append(patch, NewPatch("replace", p, bv)), nil
+	{
+		at := reflect.TypeOf(av)
+		bt := reflect.TypeOf(bv)
+		if at == nil && bt == nil {
+			// do nothing
+			return patch, nil
+		} else if at == nil && bt != nil {
+			return append(patch, NewPatch("add", p, bv)), nil
+		} else if at != bt {
+			// If types have changed, replace completely (preserves null in destination)
+			return append(patch, NewPatch("replace", p, bv)), nil
+		}
 	}
 
 	var err error
@@ -220,13 +229,6 @@ func handleValues(av, bv interface{}, p string, patch []Operation) ([]Operation,
 				}
 			}
 		}
-	case nil:
-		switch bv.(type) {
-		case nil:
-			// Both nil, fine.
-		default:
-			patch = append(patch, NewPatch("add", p, bv))
-		}
 	default:
 		panic(fmt.Sprintf("Unknown type:%T ", av))
 	}
@@ -309,18 +311,21 @@ func min(x int, y int) int {
 
 func backtrace(s, t []interface{}, p string, i int, j int, matrix [][]int) []Operation {
 	if i > 0 && matrix[i-1][j]+1 == matrix[i][j] {
-		return append(backtrace(s, t, p, i-1, j, matrix), NewPatch("remove", makePath(p, i-1), nil))
+		op := NewPatch("remove", makePath(p, i-1), nil)
+		return append([]Operation{op}, backtrace(s, t, p, i-1, j, matrix)...)
 	}
 	if j > 0 && matrix[i][j-1]+1 == matrix[i][j] {
-		return append(backtrace(s, t, p, i, j-1, matrix), NewPatch("add", makePath(p, i), t[j-1]))
+		op := NewPatch("add", makePath(p, i), t[j-1])
+		return append([]Operation{op}, backtrace(s, t, p, i, j-1, matrix)...)
 	}
 	if i > 0 && j > 0 && matrix[i-1][j-1]+1 == matrix[i][j] {
 		if isBasicType(s[0]) {
-			return append(backtrace(s, t, p, i-1, j-1, matrix), NewPatch("replace", makePath(p, i-1), t[j-1]))
+			op := NewPatch("replace", makePath(p, i-1), t[j-1])
+			return append([]Operation{op}, backtrace(s, t, p, i-1, j-1, matrix)...)
 		}
 
 		p2, _ := handleValues(s[j-1], t[j-1], makePath(p, i-1), []Operation{})
-		return append(backtrace(s, t, p, i-1, j-1, matrix), p2...)
+		return append(p2, backtrace(s, t, p, i-1, j-1, matrix)...)
 	}
 	if i > 0 && j > 0 && matrix[i-1][j-1] == matrix[i][j] {
 		return backtrace(s, t, p, i-1, j-1, matrix)