chore: Support anonymously embedded fields for audit diffs (#5746)

- Anonymously embedded structs are expanded as top level fields.
- Unit tests for anonymously embedded structs

Co-authored-by: Steven Masley <stevenmasley@coder.com>

enterprise/audit/diff.go

@@ -6,6 +6,7 @@ import (
 	"reflect"
 
 	"github.com/google/uuid"
+	"golang.org/x/xerrors"
 
 	"github.com/coder/coder/coderd/audit"
 	"github.com/coder/coder/coderd/database"
@@ -18,11 +19,9 @@ func structName(t reflect.Type) string {
 func diffValues(left, right any, table Table) audit.Map {
 	var (
 		baseDiff = audit.Map{}
-
-		leftV = reflect.ValueOf(left)
-
-		rightV = reflect.ValueOf(right)
-		rightT = reflect.TypeOf(right)
+		rightT   = reflect.TypeOf(right)
+		leftV    = reflect.ValueOf(left)
+		rightV   = reflect.ValueOf(right)
 
 		diffKey = table[structName(rightT)]
 	)
@@ -31,19 +30,25 @@ func diffValues(left, right any, table Table) audit.Map {
 		panic(fmt.Sprintf("dev error: type %q (type %T) attempted audit but not auditable", rightT.Name(), right))
 	}
 
-	for i := 0; i < rightT.NumField(); i++ {
-		if !rightT.Field(i).IsExported() {
-			continue
-		}
+	// allFields contains all top level fields of the struct.
+	allFields, err := flattenStructFields(leftV, rightV)
+	if err != nil {
+		// This should never happen. Only structs should be flattened. If an
+		// error occurs, an unsupported or non-struct type was passed in.
+		panic(fmt.Sprintf("dev error: failed to flatten struct fields: %v", err))
+	}
 
+	for _, field := range allFields {
 		var (
-			leftF  = leftV.Field(i)
-			rightF = rightV.Field(i)
+			leftF  = field.LeftF
+			rightF = field.RightF
 
 			leftI  = leftF.Interface()
 			rightI = rightF.Interface()
+		)
 
-			diffName = rightT.Field(i).Tag.Get("json")
+		var (
+			diffName = field.FieldType.Tag.Get("json")
 		)
 
 		atype, ok := diffKey[diffName]
@@ -145,6 +150,64 @@ func convertDiffType(left, right any) (newLeft, newRight any, changed bool) {
 	}
 }
 
+// fieldDiff has all the required information to return an audit diff for a
+// given field.
+type fieldDiff struct {
+	FieldType reflect.StructField
+	LeftF     reflect.Value
+	RightF    reflect.Value
+}
+
+// flattenStructFields will return all top level fields for a given structure.
+// Only anonymously embedded structs will be recursively flattened such that their
+// fields are returned as top level fields. Named nested structs will be returned
+// as a single field.
+// Conflicting field names need to be handled by the caller.
+func flattenStructFields(leftV, rightV reflect.Value) ([]fieldDiff, error) {
+	// Dereference pointers if the field is a pointer field.
+	if leftV.Kind() == reflect.Ptr {
+		leftV = derefPointer(leftV)
+		rightV = derefPointer(rightV)
+	}
+
+	if leftV.Kind() != reflect.Struct {
+		return nil, xerrors.Errorf("%q is not a struct, kind=%s", leftV.String(), leftV.Kind())
+	}
+
+	var allFields []fieldDiff
+	rightT := rightV.Type()
+
+	// Loop through all top level fields of the struct.
+	for i := 0; i < rightT.NumField(); i++ {
+		if !rightT.Field(i).IsExported() {
+			continue
+		}
+
+		var (
+			leftF  = leftV.Field(i)
+			rightF = rightV.Field(i)
+		)
+
+		if rightT.Field(i).Anonymous {
+			// Anonymous fields are recursively flattened.
+			anonFields, err := flattenStructFields(leftF, rightF)
+			if err != nil {
+				return nil, xerrors.Errorf("flatten anonymous field %q: %w", rightT.Field(i).Name, err)
+			}
+			allFields = append(allFields, anonFields...)
+			continue
+		}
+
+		// Single fields append as is.
+		allFields = append(allFields, fieldDiff{
+			LeftF:     leftF,
+			RightF:    rightF,
+			FieldType: rightT.Field(i),
+		})
+	}
+	return allFields, nil
+}
+
 // derefPointer deferences a reflect.Value that is a pointer to its underlying
 // value. It dereferences recursively until it finds a non-pointer value. If the
 // pointer is nil, it will be coerced to the zero value of the underlying type.

enterprise/audit/diff_internal_test.go

@@ -66,7 +66,6 @@ func Test_diffValues(t *testing.T) {
 		})
 	})
 
-	//nolint:revive
 	t.Run("PointerField", func(t *testing.T) {
 		t.Parallel()
 
@@ -98,6 +97,83 @@ func Test_diffValues(t *testing.T) {
 		})
 	})
 
+	//nolint:revive
+	t.Run("EmbeddedStruct", func(t *testing.T) {
+		t.Parallel()
+
+		type Bar struct {
+			Baz  int    `json:"baz"`
+			Buzz string `json:"buzz"`
+		}
+
+		type PtrBar struct {
+			Qux string `json:"qux"`
+		}
+
+		type foo struct {
+			Bar
+			*PtrBar
+			TopLevel string `json:"top_level"`
+		}
+
+		table := auditMap(map[any]map[string]Action{
+			&foo{}: {
+				"baz":       ActionTrack,
+				"buzz":      ActionTrack,
+				"qux":       ActionTrack,
+				"top_level": ActionTrack,
+			},
+		})
+
+		runDiffValuesTests(t, table, []diffTest{
+			{
+				name:  "SingleFieldChange",
+				left:  foo{TopLevel: "top-before", Bar: Bar{Baz: 1, Buzz: "before"}, PtrBar: &PtrBar{Qux: "qux-before"}},
+				right: foo{TopLevel: "top-after", Bar: Bar{Baz: 0, Buzz: "after"}, PtrBar: &PtrBar{Qux: "qux-after"}},
+				exp: audit.Map{
+					"baz":       audit.OldNew{Old: 1, New: 0},
+					"buzz":      audit.OldNew{Old: "before", New: "after"},
+					"qux":       audit.OldNew{Old: "qux-before", New: "qux-after"},
+					"top_level": audit.OldNew{Old: "top-before", New: "top-after"},
+				},
+			},
+			{
+				name:  "Empty",
+				left:  foo{},
+				right: foo{},
+				exp:   audit.Map{},
+			},
+			{
+				name:  "NoChange",
+				left:  foo{TopLevel: "top-before", Bar: Bar{Baz: 1, Buzz: "before"}, PtrBar: &PtrBar{Qux: "qux-before"}},
+				right: foo{TopLevel: "top-before", Bar: Bar{Baz: 1, Buzz: "before"}, PtrBar: &PtrBar{Qux: "qux-before"}},
+				exp:   audit.Map{},
+			},
+			{
+				name:  "LeftEmpty",
+				left:  foo{},
+				right: foo{TopLevel: "top-after", Bar: Bar{Baz: 1, Buzz: "after"}, PtrBar: &PtrBar{Qux: "qux-after"}},
+				exp: audit.Map{
+					"baz":       audit.OldNew{Old: 0, New: 1},
+					"buzz":      audit.OldNew{Old: "", New: "after"},
+					"qux":       audit.OldNew{Old: "", New: "qux-after"},
+					"top_level": audit.OldNew{Old: "", New: "top-after"},
+				},
+			},
+			{
+				name:  "RightNil",
+				left:  foo{TopLevel: "top-before", Bar: Bar{Baz: 1, Buzz: "before"}, PtrBar: &PtrBar{Qux: "qux-before"}},
+				right: foo{},
+				exp: audit.Map{
+					"baz":       audit.OldNew{Old: 1, New: 0},
+					"buzz":      audit.OldNew{Old: "before", New: ""},
+					"qux":       audit.OldNew{Old: "qux-before", New: ""},
+					"top_level": audit.OldNew{Old: "top-before", New: ""},
+				},
+			},
+		})
+	})
+
 	// We currently don't support nested structs.
 	// t.Run("NestedStruct", func(t *testing.T) {
 	// 	t.Parallel()