Add check for structs without any exported fields

Author: breml

errchkjson.go

@@ -110,12 +110,16 @@ func (e *errchkjson) handleJSONMarshal(pass *analysis.Pass, n ast.Node, fnName s
 		t = t.(*types.Pointer).Elem()
 	}
 
-	err := jsonSafe(t)
+	err := jsonSafe(t, 0)
 	if err != nil {
 		if _, ok := err.(unsupported); ok {
 			pass.Reportf(n.Pos(), "`%s` for %v", fnName, err)
 			return
 		}
+		if _, ok := err.(noexported); ok {
+			pass.Reportf(n.Pos(), "Error argument passed to `%s` does not contain any exported field", fnName)
+		}
+		// Only care about unsafe types if they are assigned to the blank identifier.
 		if blankIdentifier {
 			pass.Reportf(n.Pos(), "Error return value of `%s` is not checked: %v", fnName, err)
 		}
@@ -135,7 +139,7 @@ const (
 	unsupportedBasicTypes   = types.IsComplex
 )
 
-func jsonSafe(t types.Type) error {
+func jsonSafe(t types.Type, level int) error {
 	if types.Implements(t, textMarshalerInterface()) {
 		return fmt.Errorf("unsafe type `%s` found", t.String())
 	}
@@ -162,20 +166,21 @@ func jsonSafe(t types.Type) error {
 		}
 
 	case *types.Array:
-		err := jsonSafe(ut.Elem())
+		err := jsonSafe(ut.Elem(), level+1)
 		if err != nil {
 			return err
 		}
 		return nil
 
 	case *types.Slice:
-		err := jsonSafe(ut.Elem())
+		err := jsonSafe(ut.Elem(), level+1)
 		if err != nil {
 			return err
 		}
 		return nil
 
 	case *types.Struct:
+		exported := 0
 		for i := 0; i < ut.NumFields(); i++ {
 			if !ut.Field(i).Exported() {
 				// Unexported fields can be ignored
@@ -187,15 +192,19 @@ func jsonSafe(t types.Type) error {
 					continue
 				}
 			}
-			err := jsonSafe(ut.Field(i).Type())
+			err := jsonSafe(ut.Field(i).Type(), level+1)
 			if err != nil {
 				return err
 			}
+			exported++
+		}
+		if level == 0 && exported == 0 {
+			return newNoexportedError(fmt.Errorf("struct does not export any field"))
 		}
 		return nil
 
 	case *types.Pointer:
-		err := jsonSafe(ut.Elem())
+		err := jsonSafe(ut.Elem(), level+1)
 		if err != nil {
 			return err
 		}
@@ -206,7 +215,7 @@ func jsonSafe(t types.Type) error {
 		if err != nil {
 			return err
 		}
-		err = jsonSafe(ut.Elem())
+		err = jsonSafe(ut.Elem(), level+1)
 		if err != nil {
 			return err
 		}

errchkjson_test.go

@@ -25,3 +25,13 @@ func TestOmitSafeFlag(t *testing.T) {
 	testdata := analysistest.TestData()
 	analysistest.Run(t, testdata, errchkjson, "nosafe")
 }
+
+func TestNoExportedField(t *testing.T) {
+	errchkjson := errchkjson.NewAnalyzer()
+	err := errchkjson.Flags.Set("omit-safe", "true")
+	if err != nil {
+		t.Fatalf("error setting 'omit-safe' command line flag: %v", err)
+	}
+	testdata := analysistest.TestData()
+	analysistest.Run(t, testdata, errchkjson, "noexport")
+}

noexported_error.go

@@ -0,0 +1,23 @@
+package errchkjson
+
+type noexported interface {
+	noexported()
+}
+
+var _ noexported = noexportedError{}
+
+type noexportedError struct {
+	err error
+}
+
+func newNoexportedError(err error) error {
+	return noexportedError{
+		err: err,
+	}
+}
+
+func (u noexportedError) noexported() {}
+
+func (u noexportedError) Error() string {
+	return u.err.Error()
+}

testdata/src/noexport/a.go

@@ -0,0 +1,30 @@
+package example
+
+import (
+	"encoding/json"
+)
+
+// JSONMarshalStructWithoutExportedFields contains a struct without exported fields.
+func JSONMarshalStructWithoutExportedFields() {
+	var err error
+
+	var withoutExportedFields struct {
+		privateField            bool
+		ExportedButOmittedField bool `json:"-"`
+	}
+	_, err = json.Marshal(withoutExportedFields) // want "Error argument passed to `encoding/json.Marshal` does not contain any exported field"
+	_ = err
+}
+
+// JSONMarshalStructWithoutExportedFields contains a struct without exported fields.
+func JSONMarshalStructWithNestedStructWithoutExportedFields() {
+	var err error
+
+	var withNestedStructWithoutExportedFields struct {
+		ExportedStruct struct {
+			privatField bool
+		}
+	}
+	_, err = json.Marshal(withNestedStructWithoutExportedFields)
+	_ = err
+}