Add new features to DiffReport and Diff (#48788)

* simplify String for Diff
* add IsAddOperation and IsDeleteOperation to Diff
* add method Paths to DiffReport

pkg/util/cmputil/reporter.go

@@ -78,6 +78,15 @@ func (r DiffReport) String() string {
 	return b.String()
 }
 
+// Paths returns the slice of paths of the current DiffReport
+func (r DiffReport) Paths() []string {
+	var result = make([]string, len(r))
+	for _, diff := range r {
+		result = append(result, diff.Path)
+	}
+	return result
+}
+
 type Diff struct {
 	// Path to the field that has difference separated by period. Array index and key are designated by square brackets.
 	// For example, Annotations[12345].Data.Fields[0].ID
@@ -87,15 +96,34 @@ type Diff struct {
 }
 
 func (d *Diff) String() string {
-	left := d.Left.String()
+	return fmt.Sprintf("%v:\n\t-: %+v\n\t+: %+v\n", d.Path, describeReflectValue(d.Left), describeReflectValue(d.Right))
+}
+
+func describeReflectValue(v reflect.Value) interface{} {
 	// invalid reflect.Value is produced when two collections (slices\maps) are compared and one misses value.
 	// This way go-cmp indicates that an element was added\removed from a list.
-	if !d.Left.IsValid() {
-		left = "<none>"
+	if !v.IsValid() {
+		return "<none>"
 	}
-	right := d.Right.String()
-	if !d.Right.IsValid() {
-		right = "<none>"
-	}
-	return fmt.Sprintf("%v:\n\t-: %+v\n\t+: %+v", d.Path, left, right)
+	return v
+}
+
+// IsAddOperation returns true when
+//  - Left does not have value and Right has
+//  - the kind of Left and Right is either reflect.Slice or reflect.Map and the length of Left is less than length of Right
+// In all other cases it returns false.
+// NOTE: this is applicable to diff of Maps and Slices only
+func (d *Diff) IsAddOperation() bool {
+	return !d.Left.IsValid() && d.Right.IsValid() || (d.Left.Kind() == d.Right.Kind() && // cmp reports adding first element to a nil slice as creation of one and therefore Left is valid and it is nil and right is a new slice
+		(d.Left.Kind() == reflect.Slice || d.Left.Kind() == reflect.Map) && d.Left.Len() < d.Right.Len())
+}
+
+// IsDeleteOperation returns true when
+//  - Right does not have value and Left has
+//  - the kind of Left and Right is either reflect.Slice or reflect.Map and the length of Right is less than length of Left
+// In all other cases it returns false.
+// NOTE: this is applicable to diff of Maps and Slices only
+func (d *Diff) IsDeleteOperation() bool {
+	return d.Left.IsValid() && !d.Right.IsValid() || (d.Left.Kind() == d.Right.Kind() &&
+		(d.Left.Kind() == reflect.Slice || d.Left.Kind() == reflect.Map) && d.Left.Len() > d.Right.Len())
 }

pkg/util/cmputil/reporter_test.go

@@ -0,0 +1,132 @@
+package cmputil
+
+import (
+	"math/rand"
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	ptr "github.com/xorcare/pointer"
+
+	"github.com/grafana/grafana/pkg/util"
+)
+
+type subStruct struct {
+	Data interface{}
+}
+
+type testStruct struct {
+	Number       float64
+	NumberPtr    *float64
+	Text         string
+	TextPtr      *string
+	Flag         bool
+	FlagPtr      *bool
+	Dict         map[float64]float64
+	Slice        []float64
+	SubStruct    subStruct
+	SubStructPtr *subStruct
+}
+
+func testStructDiff(left, right testStruct) DiffReport {
+	var reporter DiffReporter
+	ops := make([]cmp.Option, 0, 4)
+	ops = append(ops, cmp.Reporter(&reporter))
+	cmp.Equal(left, right, ops...)
+	return reporter.Diffs
+}
+
+func TestIsAddedDeleted_Collections(t *testing.T) {
+	testCases := []struct {
+		name  string
+		left  testStruct
+		right testStruct
+		field string
+	}{
+		{
+			name: "nil vs non-empty slice",
+			left: testStruct{
+				Slice: nil,
+			},
+			right: testStruct{
+				Slice: []float64{rand.Float64()},
+			},
+			field: "Slice",
+		},
+		{
+			name: "empty vs non-empty slice",
+			left: testStruct{
+				Slice: []float64{},
+			},
+			right: testStruct{
+				Slice: []float64{rand.Float64()},
+			},
+			field: "Slice",
+		},
+		{
+			name: "nil vs non-empty map",
+			left: testStruct{
+				Dict: nil,
+			},
+			right: testStruct{
+				Dict: map[float64]float64{rand.Float64(): rand.Float64()},
+			},
+			field: "Slice",
+		},
+		{
+			name: "empty vs non-empty map",
+			left: testStruct{
+				Dict: map[float64]float64{},
+			},
+			right: testStruct{
+				Dict: map[float64]float64{rand.Float64(): rand.Float64()},
+			},
+			field: "Slice",
+		},
+	}
+	for _, testCase := range testCases {
+		t.Run(testCase.name, func(t *testing.T) {
+			left := testCase.left
+			right := testCase.right
+			field := testCase.field
+			t.Run("IsAddOperation=true, IsDeleted=false", func(t *testing.T) {
+				diff := testStructDiff(left, right)
+				require.Lenf(t, diff, 1, "diff was expected to have only one field %s but got %v", field, diff.String())
+				d := diff[0]
+				require.Truef(t, d.IsAddOperation(), "diff %v should be treated as Add operation but it wasn't", d)
+				require.Falsef(t, d.IsDeleteOperation(), "diff %v should not be treated as Delete operation but it was", d)
+			})
+			t.Run("IsDeleted=true, IsAddOperation=false", func(t *testing.T) {
+				diff := testStructDiff(right, left)
+				require.Lenf(t, diff, 1, "diff was expected to have only one field %s but got %v", field, diff.String())
+				d := diff[0]
+				require.Truef(t, d.IsDeleteOperation(), "diff %v should be treated as Delete operation but it wasn't", d)
+				require.Falsef(t, d.IsAddOperation(), "diff %v should not be treated as Delete operation but it was", d)
+			})
+		})
+	}
+
+	t.Run("IsAddOperation=false, IsDeleted=false if changes in struct fields", func(t *testing.T) {
+		left := testStruct{}
+		right := testStruct{
+			Number:    rand.Float64(),
+			NumberPtr: ptr.Float64(rand.Float64()),
+			Text:      util.GenerateShortUID(),
+			TextPtr:   ptr.String(util.GenerateShortUID()),
+			Flag:      true,
+			FlagPtr:   ptr.Bool(true),
+			SubStruct: subStruct{
+				Data: rand.Float64(),
+			},
+			SubStructPtr: &subStruct{Data: rand.Float64()},
+		}
+
+		diff := testStructDiff(left, right)
+		require.Len(t, diff, 8)
+		for _, d := range diff {
+			assert.Falsef(t, d.IsAddOperation(), "diff %v was not supposed to be Add operation", d.String())
+			assert.Falsef(t, d.IsDeleteOperation(), "diff %v was not supposed to be Delete operation", d.String())
+		}
+	})
+}