Introduce "outputDir" property of "codegenConfig" (facebook#41782)

Summary:

This diff adds `outputDir` property to `codegenConfig`.
Now codegen output dir is resolved like this:
1. It is set to `outputDir` argument of `generate-codegen-artifacts.js` if it is present.
2. *[New]* It is set to `outputDir` property of `codegenConfig` if it is present.
3. It is set to the project root.

Changelog: [General][Added] - Introduce "outputDir" property of "codegenConfig"

Reviewed By: cipolleschi

Differential Revision: D51494009

packages/react-native/scripts/codegen/generate-artifacts-executor.js

@@ -175,11 +175,8 @@ function buildCodegenIfNeeded() {
   });
 }
 
-function computeIOSOutputDir(outputPath, projectRoot) {
-  return path.join(
-    outputPath ? outputPath : projectRoot,
-    'build/generated/ios',
-  );
+function computeIOSOutputDir(outputPath) {
+  return path.join(outputPath, 'build', 'generated', 'ios');
 }
 
 function generateSchemaInfo(library) {
@@ -264,8 +261,7 @@ function createComponentProvider(schemas) {
   console.log(`Generated provider in: ${outputDir}`);
 }
 
-function findCodegenEnabledLibraries(projectRoot) {
-  const pkgJson = readPkgJsonInDirectory(projectRoot);
+function findCodegenEnabledLibraries(pkgJson, projectRoot) {
   return [
     ...findExternalLibraries(pkgJson),
     ...findProjectRootLibraries(pkgJson, projectRoot),
@@ -321,17 +317,41 @@ function cleanupEmptyFilesAndFolders(filepath) {
  * @throws If it can't find a cli for the CodeGen.
  */
 function execute(projectRoot, outputPath) {
-  buildCodegenIfNeeded();
-
   try {
-    const libraries = findCodegenEnabledLibraries(projectRoot);
+    console.log(
+      `[Codegen] Analyzing ${path.join(projectRoot, 'package.json')}`,
+    );
+
+    const pkgJson = readPkgJsonInDirectory(projectRoot);
+    if (pkgJson.codegenConfig == null) {
+      console.log(
+        '[Codegen] The "codegenConfig" field is not defined in package.json. Not running codegen.',
+      );
+      return;
+    }
+
+    if (typeof pkgJson.codegenConfig !== 'object') {
+      throw '[Codegen] "codegenConfig" field must be an Object.';
+    }
+
+    buildCodegenIfNeeded();
+
+    const libraries = findCodegenEnabledLibraries(pkgJson, projectRoot);
 
     if (libraries.length === 0) {
       console.log('[Codegen] No codegen-enabled libraries found.');
       return;
     }
 
-    const iosOutputDir = computeIOSOutputDir(outputPath, projectRoot);
+    if (outputPath == null) {
+      const outputPathOverride = pkgJson.codegenConfig.outputDir;
+      if (outputPathOverride && typeof outputPathOverride === 'string') {
+        outputPath = outputPathOverride;
+      } else {
+        outputPath = projectRoot;
+      }
+    }
+    const iosOutputDir = computeIOSOutputDir(outputPath);
 
     const schemaInfos = generateSchemaInfos(libraries);
     generateNativeCode(iosOutputDir, schemaInfos);