feat: proto3 optional support (#1584)

Co-authored-by: Benjamin E. Coe <bencoe@google.com>

cli/targets/static.js

@@ -394,7 +394,8 @@ function buildType(ref, type) {
         if (config.comments) {
             push("");
             var jsType = toJsType(field);
-            if (field.optional && !field.map && !field.repeated && field.resolvedType instanceof Type)
+            if (field.optional && !field.map && !field.repeated && field.resolvedType instanceof Type ||
+                    field.options && field.options.proto3_optional)
                 jsType = jsType + "|null|undefined";
             pushComment([
                 field.comment || type.name + " " + field.name + ".",
@@ -410,6 +411,9 @@ function buildType(ref, type) {
             push(escapeName(type.name) + ".prototype" + prop + " = $util.emptyArray;"); // overwritten in constructor
         else if (field.map)
             push(escapeName(type.name) + ".prototype" + prop + " = $util.emptyObject;"); // overwritten in constructor
+        else if (field.options && field.options.proto3_optional) {
+            push(escapeName(type.name) + ".prototype" + prop + " = null;"); // do not set default value for proto3 optional fields
+        }
         else if (field.long)
             push(escapeName(type.name) + ".prototype" + prop + " = $util.Long ? $util.Long.fromBits("
                     + JSON.stringify(field.typeDefault.low) + ","

src/field.js

@@ -82,6 +82,9 @@ function Field(name, id, type, rule, extend, options, comment) {
      * Field rule, if any.
      * @type {string|undefined}
      */
+    if (rule === "proto3_optional") {
+        rule = "optional";
+    }
     this.rule = rule && rule !== "optional" ? rule : undefined; // toJSON
 
     /**

src/parse.js

@@ -316,11 +316,19 @@ function parse(source, root, options) {
                     break;
 
                 case "required":
-                case "optional":
                 case "repeated":
                     parseField(type, token);
                     break;
 
+                case "optional":
+                    /* istanbul ignore if */
+                    if (isProto3) {
+                        parseField(type, "proto3_optional");
+                    } else {
+                        parseField(type, "optional");
+                    }
+                    break;
+
                 case "oneof":
                     parseOneOf(type, token);
                     break;
@@ -379,7 +387,16 @@ function parse(source, root, options) {
         }, function parseField_line() {
             parseInlineOptions(field);
         });
-        parent.add(field);
+
+        if (rule === "proto3_optional") {
+            // for proto3 optional fields, we create a single-member Oneof to mimic "optional" behavior
+            var oneof = new OneOf("_" + name);
+            field.setOption("proto3_optional", true);
+            oneof.add(field);
+            parent.add(oneof);
+        } else {
+            parent.add(field);
+        }
 
         // JSON defaults to packed=true if not set so we have to set packed=false explicity when
         // parsing proto2 descriptors without the option, where applicable. This must be done for
@@ -413,11 +430,19 @@ function parse(source, root, options) {
                     break;
 
                 case "required":
-                case "optional":
                 case "repeated":
                     parseField(type, token);
                     break;
 
+                case "optional":
+                    /* istanbul ignore if */
+                    if (isProto3) {
+                        parseField(type, "proto3_optional");
+                    } else {
+                        parseField(type, "optional");
+                    }
+                    break;
+
                 /* istanbul ignore next */
                 default:
                     throw illegal(token); // there are no groups with proto3 semantics
@@ -699,10 +724,18 @@ function parse(source, root, options) {
 
                 case "required":
                 case "repeated":
-                case "optional":
                     parseField(parent, token, reference);
                     break;
 
+                case "optional":
+                    /* istanbul ignore if */
+                    if (isProto3) {
+                        parseField(parent, "proto3_optional", reference);
+                    } else {
+                        parseField(parent, "optional", reference);
+                    }
+                    break;
+
                 default:
                     /* istanbul ignore if */
                     if (!isProto3 || !typeRefRe.test(token))

tests/comp_optional.js

@@ -0,0 +1,26 @@
+var tape = require("tape");
+
+var protobuf = require("..");
+
+var proto = "syntax = \"proto3\";\
+\
+message Message {\
+    int32 regular_int32 = 1;\
+    optional int32 optional_int32 = 2;\
+    oneof _oneof_int32 {\
+        int32 oneof_int32 = 3;\
+    }\
+}\
+";
+
+tape.test("proto3 optional", function(test) {
+    var root = protobuf.parse(proto).root;
+
+    var Message = root.lookup("Message");
+    test.equal(Message.fields.optionalInt32.optional, true);
+    test.equal(Message.fields.optionalInt32.options.proto3_optional, true);
+    test.equal(Message.oneofs._optionalInt32.name, '_optionalInt32');
+    test.deepEqual(Message.oneofs._optionalInt32.oneof, ['optionalInt32']);
+
+    test.end();
+});