react-native code-gen > C++ TurboModules struct support (#35265)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/35265

This adds a templating layer for C++ TurboModules to automatically generate struct templates from TurboModule specs.

You have to define concrete types for those templates to use them in your C++ TurboModule.

E.g. for the JS flow type:
```
export type ObjectStruct = {|
  a: number,
  b: string,
  c?: ?string,
|};
```
code-gen will now generate the following template code:
```
#pragma mark - NativeCxxModuleExampleCxxBaseObjectStruct

template <typename P0, typename P1, typename P2>
struct NativeCxxModuleExampleCxxBaseObjectStruct {
  P0 a;
  P1 b;
  P2 c;
  bool operator==(const NativeCxxModuleExampleCxxBaseObjectStruct &other) const {
    return a == other.a && b == other.b && c == other.c;
  }
};

template <typename P0, typename P1, typename P2>
struct NativeCxxModuleExampleCxxBaseObjectStructBridging {
  static NativeCxxModuleExampleCxxBaseObjectStruct<P0, P1, P2> fromJs(
      jsi::Runtime &rt,
      const jsi::Object &value,
      const std::shared_ptr<CallInvoker> &jsInvoker) {
    NativeCxxModuleExampleCxxBaseObjectStruct<P0, P1, P2> result{
      bridging::fromJs<P0>(rt, value.getProperty(rt, "a"), jsInvoker),
      bridging::fromJs<P1>(rt, value.getProperty(rt, "b"), jsInvoker),
      bridging::fromJs<P2>(rt, value.getProperty(rt, "c"), jsInvoker)};
    return result;
  }

  static jsi::Object toJs(
      jsi::Runtime &rt,
      const NativeCxxModuleExampleCxxBaseObjectStruct<P0, P1, P2> &value) {
    auto result = facebook::jsi::Object(rt);
    result.setProperty(rt, "a", bridging::toJs(rt, value.a));
    result.setProperty(rt, "b", bridging::toJs(rt, value.b));
    if (value.c) {
      result.setProperty(rt, "c", bridging::toJs(rt, value.c.value()));
    }
    return result;
  }
};
```
and you can use it in our C++ TurboModule for example as:
```
using ObjectStruct = NativeCxxModuleExampleCxxBaseObjectStruct<
    int32_t,
    std::string,
    std::optional<std::string>>;

template <>
struct Bridging<ObjectStruct>
    : NativeCxxModuleExampleCxxBaseObjectStructBridging<
          int32_t,
          std::string,
          std::optional<std::string>> {};
```
or as
```
using ObjectStruct = NativeCxxModuleExampleCxxBaseObjectStruct<
    float,
    folly::StringPiece,
    std::optional<std::string>>;

template <>
struct Bridging<ObjectStruct>
    : NativeCxxModuleExampleCxxBaseObjectStructBridging<
          float,
          folly::StringPiece,
          std::optional<std::string>> {};
```
Or as
...

Changelog: [Internal]

Reviewed By: rshest

Differential Revision: D41133761

fbshipit-source-id: fdf36e51073cb46c5234f6121842c79a884899c7

packages/react-native-codegen/src/generators/modules/GenerateModuleH.js

@@ -16,6 +16,7 @@ import type {
   NativeModuleTypeAnnotation,
   NativeModuleFunctionTypeAnnotation,
   NativeModulePropertyShape,
+  NativeModuleAliasMap,
 } from '../../CodegenSchema';
 
 import type {AliasResolver} from './Utils';
@@ -28,8 +29,13 @@ type FilesOutput = Map<string, string>;
 const ModuleClassDeclarationTemplate = ({
   hasteModuleName,
   moduleProperties,
-}: $ReadOnly<{hasteModuleName: string, moduleProperties: string[]}>) => {
-  return `class JSI_EXPORT ${hasteModuleName}CxxSpecJSI : public TurboModule {
+  structs,
+}: $ReadOnly<{
+  hasteModuleName: string,
+  moduleProperties: string[],
+  structs: string,
+}>) => {
+  return `${structs}class JSI_EXPORT ${hasteModuleName}CxxSpecJSI : public TurboModule {
 protected:
   ${hasteModuleName}CxxSpecJSI(std::shared_ptr<CallInvoker> jsInvoker);
 
@@ -186,6 +192,76 @@ function translatePrimitiveJSTypeToCpp(
   }
 }
 
+function createStructs(
+  moduleName: string,
+  aliasMap: NativeModuleAliasMap,
+  resolveAlias: AliasResolver,
+): string {
+  return Object.keys(aliasMap)
+    .map(alias => {
+      const value = aliasMap[alias];
+      if (value.properties.length === 0) {
+        return '';
+      }
+      const structName = `${moduleName}Base${alias}`;
+      const templateParameterWithTypename = value.properties
+        .map((v, i) => 'typename P' + i)
+        .join(', ');
+      const templateParameter = value.properties
+        .map((v, i) => 'P' + i)
+        .join(', ');
+      return `#pragma mark - ${structName}
+
+template <${templateParameterWithTypename}>
+struct ${structName} {
+${value.properties.map((v, i) => '  P' + i + ' ' + v.name).join(';\n')};
+  bool operator==(const ${structName} &other) const {
+    return ${value.properties
+      .map(v => `${v.name} == other.${v.name}`)
+      .join(' && ')};
+  }
+};
+
+template <${templateParameterWithTypename}>
+struct ${structName}Bridging {
+  static ${structName}<${templateParameter}> fromJs(
+      jsi::Runtime &rt,
+      const jsi::Object &value,
+      const std::shared_ptr<CallInvoker> &jsInvoker) {
+    ${structName}<${templateParameter}> result{
+${value.properties
+  .map(
+    (v, i) =>
+      `      bridging::fromJs<P${i}>(rt, value.getProperty(rt, "${v.name}"), jsInvoker)`,
+  )
+  .join(',\n')}};
+    return result;
+  }
+
+  static jsi::Object toJs(
+      jsi::Runtime &rt,
+      const ${structName}<${templateParameter}> &value) {
+    auto result = facebook::jsi::Object(rt);
+${value.properties
+  .map((v, i) => {
+    if (v.optional) {
+      return `    if (value.${v.name}) {
+      result.setProperty(rt, "${v.name}", bridging::toJs(rt, value.${v.name}.value()));
+    }`;
+    } else {
+      return `    result.setProperty(rt, "${v.name}", bridging::toJs(rt, value.${v.name}));`;
+    }
+  })
+  .join('\n')}
+    return result;
+  }
+};
+
+`;
+    })
+    .join('\n');
+}
+
 function translatePropertyToCpp(
   prop: NativeModulePropertyShape,
   resolveAlias: AliasResolver,
@@ -251,6 +327,7 @@ module.exports = {
         moduleNames: [moduleName],
       } = nativeModules[hasteModuleName];
       const resolveAlias = createAliasResolver(aliases);
+      const structs = createStructs(moduleName, aliases, resolveAlias);
 
       return [
         ModuleClassDeclarationTemplate({
@@ -258,6 +335,7 @@ module.exports = {
           moduleProperties: properties.map(prop =>
             translatePropertyToCpp(prop, resolveAlias, true),
           ),
+          structs,
         }),
         ModuleSpecClassDeclarationTemplate({
           hasteModuleName,