Codegen

On the React Native official website, Codegen is usually used to generate glue code when Turbo Native Module and Fabric Native Component are created.

A OpenHarmony-based Codegen is also created in RNOH, which is described below.

Environment Setup

RNOH Codegen has been supported since version 0.72.13 and remains available on the 0.84.x line. To use Codegen, install @react-native-oh/react-native-harmony and @react-native-oh/react-native-harmony-cli. For versions, see Release Notes Overview.

The following two demo projects describe how to use the Codegen:

Usage

Creating Turbo Native Modules and Fabric Native Components Using Codegen

For Android and iOS, the procedure of using Codegen to create Turbo Native Module and Fabric Native Component is as follows:

(Optional) Create a frontend third-party library.
Declare JavaScript APIs.
Configure the Codegen.
Execute the Codegen.
Compile native code to implement the functions of TurboModule or the Fabric component.
Call TurboModule and the Fabric component on the JavaScript side.

For details, see the following documents:

Codegen Configuration

Codegen configuration involves the following scenarios:

1. codegenConfig

For Android and iOS, Codegen generates code based on codegenConfig in the package.json file of the third-party library or frontend project. Note that the codegenConfig field in RNOH must be nested in harmony. For example: Guides：https://reactnative.dev/docs/0.82/the-new-architecture/using-codegen

 ...
 "harmony": {
   "alias": "<Module name>",
   "codegenConfig": [
     {
       "version": 1,
       // Use this value if you only need to generate code for Turbo native modules.
+         "type": "modules",
       "specPaths": [
         "./src/specs/v1"
       ]
     },
     {
       "version": 2,
       // Use this value if you only need to generate code for Turbo native modules.
+         "type": "modules",
       "specPaths": [
         "./src/specs/v2"
       ]
     }
   ]
 }
 ...

where:

version: indicates the version, which only differs from application scenarios. "version": 1: applies to the scenario where TurboModule or ArkTS component is created. "version": 2: applies to the scenario where the CAPI component is created.
specPaths: path of the declaration file.

2. Configuring codegen-harmony

codegen-harmony is a command used to generate code. Generally, it is configured in the scripts of the frontend project package.json and executed using npm run xxx. For example:

"scripts": {
      ...
  "codegen": "react-native codegen-harmony --cpp-output-path ./entry/src/main/cpp/generated --rnoh-module-path ./entry/oh_modules/@rnoh/react-native-openharmony"
}

codegen-harmony is followed by some parameters of the command. The parameters are described as follows:

--rnoh-module-path <path>: specifies the relative path (for example, --rnoh-module-path ./entry/oh_modules/@rnoh/react-native-openharmony) of the RNOH OHOS module. The ArkTS type declaration file is generated in this directory.
--cpp-output-path <path>: specifies the relative path of the C++ file output directory. The default value is ./harmony/entry/src/main/cpp/generated.
--no-safety-check [boolean]: By default, Codegen cannot perform file operations outside the working directory. You can skip this check by configuring --no-safety-check. If the OpenHarmony project is not in the frontend project directory, this parameter needs to be transferred.

Codegen File Generation and Structure

After the Codegen command is executed, the structure of the generated file is as follows:

  └─entry
     └─src
     |  └─main
     |    └─cpp
     |      └─generated
     |          ├─GeneratedSampleViewArkTSComponentDescriptor.h
     |          ├─GeneratedSampleViewArkTSJSIBinder.h
     |          ├─RNOHGeneratedPackage.h
     |          └─react_native_harmony_sample
     |              ├─RNOH
     |              |   └─generated
     |              |       ├─BaseReactNativeHarmonySamplePackage.h
     |              |       ├─components
     |              |       |   ├─BaseGeneratedSampleViewComponentInstance.h
     |              |       |   └─GeneratedSampleViewJSIBinder.h
     |              |       └─turbo_modules
     |              |           ├─GeneratedSampleTurboModule.cpp
     |              |           └─GeneratedSampleTurboModule.h
     |              └─react
     |                  └─renderer
     |                      └─components
     |                          └─react_native_harmony_sample
     |                              ├─ComponentDescriptors.h
     |                              ├─EventEmitters.cpp
     |                              ├─EventEmitters.h
     |                              ├─Props.cpp
     |                              ├─Props.h
     |                              ├─ShadowNodes.cpp
     |                              ├─ShadowNodes.h
     |                              ├─States.cpp
     |                              └─States.h
     └─oh_modules
         └─@rnoh
             └─react-native-harmony
                 └─generated
                     ├─index.ets
                     ├─ts.ts
                     ├─components
                     │  ├─GeneratedSampleViewArkTS.ts
                     │  └─ts.ts
                     └─turboModules
                         ├─GeneratedSampleTurboModule.ts
                         └─ts.ts

The preceding file structure is for reference only. The actual file structure depends on the declaration file and Codegen configuration.

Codegen-lib-harmony

codegen-harmony traverses the Codegen configurations of all third-party libraries in the node_module directory and generates all glue code. If you want to write glue code for a specific third-party component due to various reasons (for example, the glue code is stored in different locations in different third-party libraries), run the codegen-lib-harmony command. codegen-lib-harmony is a new capability provided by react-native-harmony-cli@0.0.27. Check the dependency before using it.

Similar to codegen-harmony, codegen-lib-harmony is used in the following steps:

Create a frontend third-party library.
Declare JavaScript APIs.
Configure the Codegen.
Execute the Codegen.
Compile native code to implement the functions of TurboModule or the Fabric component.
Call TurboModule and the Fabric component on the JavaScript side.

Codegen Configuration

This step is performed in the third-party library. Different from codegen-harmony, the codegenConfig field is not required in the package.json file of the third-party library, and JavaScript declaration files that require separate glue code generation should not be contained in the harmony::codegenConfig::specPaths file.

However, these JavaScript declaration files need to be passed to codegen-lib-harmony through parameters. For example:

"scripts": {
  "codegen-lib": "react-native codegen-lib-harmony --no-safety-check --npm-package-name codegen-lib --cpp-output-path ../harmony/codegen-lib/src/main/cpp/generated --ets-output-path ../harmony/codegen-lib/src/main/ets/generated --turbo-modules-spec-paths ./src --arkts-components-spec-paths ./src/SelectBox.ts --cpp-components-spec-paths ./src/CppSampleNativeComponent.ts"
}
...

Generally, the preceding command is used to configure the package.json file of the third-party library. After the configuration is complete, run the npm run codegen-lib command in the path of the third-party library to generate the glue code.

The codegen-lib-harmony command supports the following parameters:

--npm-package-name <string>: bundle name of the third-party library. When the C++ code is generated, a directory with the same name as the bundle name is created and then the C++ file is stored in the directory.
--turbo-modules-spec-paths [path...]: path of the TurboModule declaration file, which can be a directory or a relative path of the declaration file. Multiple paths can be passed and separated by spaces.
--arkts-components-spec-paths [path...]: declaration file path of the ArkTS component, which can be a directory or a relative path of the declaration file. Multiple paths can be passed and separated by spaces.
--cpp-components-spec-paths [path...]: declaration file path of the CAPI component. It can be a directory or a relative path of the declaration file. Multiple paths can be passed and separated by spaces.
--cpp-output-path <path>: specifies the relative path of the C++ file output directory.
--ets-output-path <path>: specifies the output directory of the ArkTS type declaration file.
--no-safety-check [boolean]: indicates whether to skip file safety check. The operation is similar to that of codegen-harmony.

codegen-lib-harmony supports all the preceding parameters. The implementation logic of the native TurboModule and custom components is similar to that of codegen-harmony.