feat: add option noDefaultsForOptionals (#1051)

Adds a new option - `noDefaultsForOptionals` that allows for
compatibility with [Square/Block's Wire Protobuf
implementation](https://square.github.io/wire/) with respect to
defaulting of optional fields.

Note: As per the documentation added to the readme, this option provides
non-standard protobuf behaviour so it would be understandable if this
isn't something you'd like in the library. I'm hoping with the
appropriate warning in the docs that you'll consider this as as option.

README.markdown

@@ -603,6 +603,11 @@ export interface User {
 }
 ```
 
+- With `--ts_proto_opt=noDefaultsForOptionals=true`, `undefined` primitive values will not be defaulted as per the protobuf spec. Additionally unlike the standard behavior, when a field is set to it's standard default value, it *will* be encoded allowing it to be sent over the wire and distinguished from undefined values. For example if a message does not set a boolean value, ordinarily this would be defaulted to `false` which is different to it being undefined. 
+
+This option allows the library to act in a compatible way with the [Wire implementation](https://square.github.io/wire/) maintained and used by Square/Block. Note: this option should only be used in combination with other client/server code generated using Wire or ts-proto with this option enabled.
+
+
 ### NestJS Support
 
 We have a great way of working together with [nestjs](https://docs.nestjs.com/microservices/grpc). `ts-proto` generates `interfaces` and `decorators` for you controller, client. For more information see the [nestjs readme](NESTJS.markdown).

integration/no-defaults-for-optionals-with-nulls/no-defaults-test.ts

@@ -0,0 +1,48 @@
+import { Proto2TestMessage } from './proto-2';
+
+describe('proto2', () => {
+  it('preserves null values on optional fields', () => {
+    const message = Proto2TestMessage.fromJSON({
+      intValue: null,
+      stringValue: null,
+      boolValue: null,
+      mapValue: {},
+    });
+
+    const data = Proto2TestMessage.encode(message).finish();
+    const result = Proto2TestMessage.decode(data);
+
+    expect(result).toEqual(message);
+  });
+
+  it('encodes/decodes non-null values on optional fields', () => {
+    const message = Proto2TestMessage.fromJSON({
+      intValue: 100,
+      stringValue: 'string',
+      boolValue: true,
+      mapValue: {
+        v1:'1',
+        v2:'2',
+      }
+    });
+
+    const data = Proto2TestMessage.encode(message).finish();
+    const result = Proto2TestMessage.decode(data);
+
+    expect(result).toEqual(message);
+  });
+
+  it('encodes/decodes non-null values set to standard protobuf defaults', () => {
+    const message = Proto2TestMessage.fromJSON({
+      intValue: 0,
+      stringValue: '',
+      boolValue: false,
+      mapValue: {},
+    });
+
+    const data = Proto2TestMessage.encode(message).finish();
+    const result = Proto2TestMessage.decode(data);
+
+    expect(result).toEqual(message);
+  });
+})

integration/no-defaults-for-optionals-with-nulls/parameters.txt

@@ -0,0 +1 @@
+noDefaultsForOptionals=true,useNullAsOptional=true

integration/no-defaults-for-optionals-with-nulls/proto-2.proto

@@ -0,0 +1,11 @@
+syntax = "proto2";
+
+package omit;
+
+message Proto2TestMessage {
+    optional bool boolValue = 1;
+    optional int32 intValue = 2;
+    optional string stringValue = 3;
+
+    map<string, string> mapValue = 4;
+}

integration/no-defaults-for-optionals-with-nulls/proto-3.proto

@@ -0,0 +1,15 @@
+syntax = "proto3";
+
+package omit;
+
+message Proto3TestMessage {
+    bool boolValue = 1;
+    int32 intValue = 2;
+    string stringValue = 3;
+
+    optional bool optionalBoolValue = 4;
+    optional int32 optionalIntValue = 5;
+    optional string optionalStringValue = 6;
+
+    map<string, string> mapValue = 7;
+}