Merge pull request #9 from InVisionApp/unexported

Handle Unexported Struct Fields

README.md

@@ -105,6 +105,16 @@ results in:
 }
 ```
 
+### Options
+**Overwrite** `bool`  
+If true, overwrite a target value with source value even if it already exists
+
+**ErrorOnUnexported** `bool`  
+Unexported fields on a struct can not be set. When a struct contains an unexported
+field, the default behavior is to treat the entire struct as a single entity and
+replace according to Overwrite settings.  
+If this is enabled, an error will be thrown instead.
+
 ### Custom Merge Functions
 #### Define a custom merge function for a type:
 ```go

merge.go

@@ -11,6 +11,15 @@ type Options struct {
 	// Overwrite a target value with source value even if it already exists
 	Overwrite bool
 
+	// Unexported fields on a struct can not be set. When a struct contains an unexported
+	// field, the default behavior is to treat the entire struct as a single entity and
+	// replace according to Overwrite settings. If this is enabled, an error will be thrown instead.
+	//
+	// Note: this is used by the default mergeStruct function, and may not apply if that is
+	// overwritten with a custom function. Custom struct merge functions should consider
+	// using this value as well.
+	ErrorOnUnexported bool
+
 	// A set of default and customizable functions that define how values are merged
 	MergeFuncs *funcSelector
 
@@ -35,7 +44,7 @@ func Merge(target, source interface{}, opt *Options) error {
 	}
 
 	if !reflect.Indirect(vT).IsValid() {
-		return errors.New("can not assign to zero value target. Use MergeCopy")
+		return errors.New("target can not be zero value")
 	}
 
 	// use defaults if none are provided

merge_test.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"errors"
 	"reflect"
+	"time"
 
 	. "github.com/onsi/ginkgo"
 	. "github.com/onsi/ginkgo/extensions/table"
@@ -276,6 +277,10 @@ var _ = Describe("Merge", func() {
 				true,
 				false,
 			),
+			Entry("time",
+				time.Now(),
+				time.Now().Add(time.Hour),
+			),
 		)
 
 		Context("merge map", func() {
@@ -354,7 +359,7 @@ var _ = Describe("Merge", func() {
 
 					err := Merge(target, &source, NewOptions())
 					Expect(err).To(HaveOccurred())
-					Expect(err.Error()).To(Equal("can not assign to zero value target. Use MergeCopy"))
+					Expect(err.Error()).To(Equal("target can not be zero value"))
 				})
 			})
 		})

mfunc.go

@@ -144,12 +144,18 @@ func mergeStruct(t, s reflect.Value, o *Options) (reflect.Value, error) {
 		fieldT := newT.Field(i)
 		logrus.Debug("merging struct field %s", fieldT)
 
-		//should never happen because its created above. Maybe remove?
-		if !fieldT.IsValid() || !fieldT.CanSet() {
-			return reflect.Value{}, fmt.Errorf("problem with field(%s) valid: %v; can set: %v",
-				newT.Type().Field(i).Name, fieldT.IsValid(), fieldT.CanSet())
+		// field is addressable because it's created above. So this means it is unexported.
+		if !fieldT.CanSet() {
+			if o.ErrorOnUnexported {
+				return reflect.Value{}, fmt.Errorf("struct of type %v has unexported field: %s",
+					t.Type().Name(), newT.Type().Field(i).Name)
+			}
+
+			// revert to using the default func instead to treat the struct as single entity
+			return defaultMergeFunc(t, s, o)
 		}
 
+		//fieldT should always be valid because it's created above
 		merged, err := merge(valT.Field(i), valS.Field(i), o)
 		if err != nil {
 			return reflect.Value{}, fmt.Errorf("failed to merge field `%s.%s`: %v",

mfunc_test.go

@@ -946,11 +946,42 @@ var _ = Describe("mergeStruct", func() {
 			sourceBazVal = reflect.ValueOf(sourceBaz)
 		})
 
-		It("errors", func() {
-			merged, err := mergeStruct(targetBazVal, sourceBazVal, NewOptions())
-			Expect(err).To(HaveOccurred())
-			Expect(err.Error()).To(ContainSubstring("problem with field(private) valid: true; can set: false"))
-			Expect(merged.IsValid()).ToNot(BeTrue())
+		Context("ErrOnUnexported is true", func() {
+			It("errors", func() {
+				opt := NewOptions()
+				opt.ErrorOnUnexported = true
+				merged, err := mergeStruct(targetBazVal, sourceBazVal, opt)
+				Expect(err).To(HaveOccurred())
+				Expect(err.Error()).To(ContainSubstring("struct of type Baz has unexported field: private"))
+				Expect(merged.IsValid()).ToNot(BeTrue())
+			})
+		})
+
+		Context("ErrOnUnexported is false", func() {
+			var opt *Options
+
+			BeforeEach(func() {
+				opt = NewOptions()
+				opt.ErrorOnUnexported = false
+			})
+
+			Context("overwrite is true", func() {
+				It("replaces the whole struct", func() {
+					opt.Overwrite = true
+					merged, err := mergeStruct(targetBazVal, sourceBazVal, opt)
+					Expect(err).ToNot(HaveOccurred())
+					Expect(merged).To(Equal(sourceBazVal))
+				})
+			})
+
+			Context("overwrite is true", func() {
+				It("replaces the whole struct", func() {
+					opt.Overwrite = false
+					merged, err := mergeStruct(targetBazVal, sourceBazVal, opt)
+					Expect(err).ToNot(HaveOccurred())
+					Expect(merged).To(Equal(targetBazVal))
+				})
+			})
 		})
 	})