Add AllowUnsupportedFields to ignore interface/etc fields and not panic

fuzz.go

@@ -35,15 +35,16 @@ type fuzzFuncMap map[reflect.Type]reflect.Value
 
 // Fuzzer knows how to fill any object with random fields.
 type Fuzzer struct {
-	fuzzFuncs             fuzzFuncMap
-	defaultFuzzFuncs      fuzzFuncMap
-	r                     *rand.Rand
-	nilChance             float64
-	minElements           int
-	maxElements           int
-	maxDepth              int
-	allowUnexportedFields bool
-	skipFieldPatterns     []*regexp.Regexp
+	fuzzFuncs              fuzzFuncMap
+	defaultFuzzFuncs       fuzzFuncMap
+	r                      *rand.Rand
+	nilChance              float64
+	minElements            int
+	maxElements            int
+	maxDepth               int
+	allowUnexportedFields  bool
+	allowUnsupportedFields bool
+	skipFieldPatterns      []*regexp.Regexp
 
 	fuzzLock sync.Mutex
 }
@@ -60,13 +61,14 @@ func NewWithSeed(seed int64) *Fuzzer {
 			reflect.TypeOf(&time.Time{}): reflect.ValueOf(fuzzTime),
 		},
 
-		fuzzFuncs:             fuzzFuncMap{},
-		r:                     rand.New(rand.NewSource(seed)),
-		nilChance:             .2,
-		minElements:           1,
-		maxElements:           10,
-		maxDepth:              100,
-		allowUnexportedFields: false,
+		fuzzFuncs:              fuzzFuncMap{},
+		r:                      rand.New(rand.NewSource(seed)),
+		nilChance:              .2,
+		minElements:            1,
+		maxElements:            10,
+		maxDepth:               100,
+		allowUnexportedFields:  false,
+		allowUnsupportedFields: false,
 	}
 	return f
 }
@@ -198,6 +200,13 @@ func (f *Fuzzer) AllowUnexportedFields(flag bool) *Fuzzer {
 	return f
 }
 
+// AllowUnsupportedFields decides whether to ignore fields that we don't support fuzzing on,
+// like interfaces and channels, by default this is not allowed and the fuzzer will panic on an unsupported field.
+func (f *Fuzzer) AllowUnsupportedFields(flag bool) *Fuzzer {
+	f.allowUnsupportedFields = flag
+	return f
+}
+
 // SkipFieldsWithPattern Skip fields which match the supplied pattern. Call this multiple times if needed
 // This is useful to skip XXX_ fields generated by protobuf
 func (f *Fuzzer) SkipFieldsWithPattern(pattern *regexp.Regexp) *Fuzzer {
@@ -358,7 +367,9 @@ func (fc *fuzzerContext) doFuzz(v reflect.Value, flags uint64) {
 	case reflect.Interface:
 		fallthrough
 	default:
-		panic(fmt.Sprintf("Can't handle type %v with value %#v", v.Type(), v.Interface()))
+		if !fc.fuzzer.allowUnsupportedFields {
+			panic(fmt.Sprintf("Can't handle type %v with value %#v", v.Type(), v.Interface()))
+		}
 	}
 }
 

fuzz_test.go

@@ -511,6 +511,44 @@ func TestFuzzer_AllowUnexportedFields(t *testing.T) {
 	}
 }
 
+func TestFuzzer_AllowUnsupportedFields(t *testing.T) {
+	type S struct {
+		InterfaceField interface{}
+	}
+
+	f := New().NilChance(0)
+	obj := S{}
+
+	failingFuzz := func(obj *S) {
+		defer func() {
+			if r := recover(); r != nil {
+				t.Log("Panicked as expected")
+			}
+		}()
+		f.Fuzz(obj)
+		t.Errorf("Expected to panic")
+	}
+
+	failingFuzz(&obj)
+	if obj.InterfaceField != nil {
+		t.Errorf("Expected obj.InterfaceField to be empty")
+	}
+
+	f.AllowUnsupportedFields(true)
+	obj = S{}
+	f.Fuzz(&obj)
+	if obj.InterfaceField != nil {
+		t.Errorf("Expected obj.InterfaceField to be empty")
+	}
+
+	f.AllowUnsupportedFields(false)
+	obj = S{}
+	failingFuzz(&obj)
+	if obj.InterfaceField != nil {
+		t.Errorf("Expected obj.InterfaceField to be empty")
+	}
+}
+
 func TestFuzz_SkipPattern(t *testing.T) {
 	obj := &struct {
 		S1    string