[Generator] implement DisallowUnknownFields from go 1.10

bootstrap/bootstrap.go

@@ -22,10 +22,11 @@ type Generator struct {
 	PkgPath, PkgName string
 	Types            []string
 
-	NoStdMarshalers bool
-	SnakeCase       bool
-	LowerCamelCase  bool
-	OmitEmpty       bool
+	NoStdMarshalers       bool
+	SnakeCase             bool
+	LowerCamelCase        bool
+	OmitEmpty             bool
+	DisallowUnknownFields bool
 
 	OutName   string
 	BuildTags string
@@ -120,6 +121,9 @@ func (g *Generator) writeMain() (path string, err error) {
 	if g.NoStdMarshalers {
 		fmt.Fprintln(f, "  g.NoStdMarshalers()")
 	}
+	if g.DisallowUnknownFields {
+		fmt.Fprintln(f, "  g.DisallowUnknownFields()")
+	}
 
 	sort.Strings(g.Types)
 	for _, v := range g.Types {

easyjson/main.go

@@ -27,6 +27,7 @@ var stubs = flag.Bool("stubs", false, "only generate stubs for marshaler/unmarsh
 var noformat = flag.Bool("noformat", false, "do not run 'gofmt -w' on output file")
 var specifiedName = flag.String("output_filename", "", "specify the filename of the output")
 var processPkg = flag.Bool("pkg", false, "process the whole package instead of just the given file")
+var disallowUnknownFields = flag.Bool("disallow_unknown_fields", false, "return error if any unknown field in json found")
 
 func generate(fname string) (err error) {
 	fInfo, err := os.Stat(fname)
@@ -60,18 +61,19 @@ func generate(fname string) (err error) {
 	}
 
 	g := bootstrap.Generator{
-		BuildTags:       trimmedBuildTags,
-		PkgPath:         p.PkgPath,
-		PkgName:         p.PkgName,
-		Types:           p.StructNames,
-		SnakeCase:       *snakeCase,
-		LowerCamelCase:  *lowerCamelCase,
-		NoStdMarshalers: *noStdMarshalers,
-		OmitEmpty:       *omitEmpty,
-		LeaveTemps:      *leaveTemps,
-		OutName:         outName,
-		StubsOnly:       *stubs,
-		NoFormat:        *noformat,
+		BuildTags:             trimmedBuildTags,
+		PkgPath:               p.PkgPath,
+		PkgName:               p.PkgName,
+		Types:                 p.StructNames,
+		SnakeCase:             *snakeCase,
+		LowerCamelCase:        *lowerCamelCase,
+		NoStdMarshalers:       *noStdMarshalers,
+		DisallowUnknownFields: *disallowUnknownFields,
+		OmitEmpty:             *omitEmpty,
+		LeaveTemps:            *leaveTemps,
+		OutName:               outName,
+		StubsOnly:             *stubs,
+		NoFormat:              *noformat,
 	}
 
 	if err := g.Run(); err != nil {

gen/decoder.go

@@ -461,7 +461,15 @@ func (g *Generator) genStructDecoder(t reflect.Type) error {
 	}
 
 	fmt.Fprintln(g.out, "    default:")
-	fmt.Fprintln(g.out, "      in.SkipRecursive()")
+	if g.disallowUnknownFields {
+		fmt.Fprintln(g.out, `      in.AddError(&jlexer.LexerError{
+          Offset: in.GetPos(),
+          Reason: "unknown field",
+          Data: key,
+      })`)
+	} else {
+		fmt.Fprintln(g.out, "      in.SkipRecursive()")
+	}
 	fmt.Fprintln(g.out, "    }")
 	fmt.Fprintln(g.out, "    in.WantComma()")
 	fmt.Fprintln(g.out, "  }")

gen/generator.go

@@ -33,9 +33,10 @@ type Generator struct {
 
 	varCounter int
 
-	noStdMarshalers bool
-	omitEmpty       bool
-	fieldNamer      FieldNamer
+	noStdMarshalers       bool
+	omitEmpty             bool
+	disallowUnknownFields bool
+	fieldNamer            FieldNamer
 
 	// package path to local alias map for tracking imports
 	imports map[string]string
@@ -110,6 +111,11 @@ func (g *Generator) NoStdMarshalers() {
 	g.noStdMarshalers = true
 }
 
+// DisallowUnknownFields instructs not to skip unknown fields in json and return error.
+func (g *Generator) DisallowUnknownFields() {
+	g.disallowUnknownFields = true
+}
+
 // OmitEmpty triggers `json=",omitempty"` behaviour by default.
 func (g *Generator) OmitEmpty() {
 	g.omitEmpty = true